-ES:Non routing host or node (end system), End System (ES) - Host machines (PCs)
-IS:Router (Intermediate System).
-CLNS:ConnectionLess Network Service uses CLNP Connectionless Network Protocol.
-CMNS:Connection Mode Network Service uses CONP Connection Oriented Network Protocol.
-Area:Logical entity (Set of contiguous routers, hosts, and links)
-Domain: Collection of connected areas, equivalent to an autonomous system
-ES-IS routing protocols Handle level-0 routing
-OSPF:There are a couple of things to keep in mind about this. An individual interface can be in only a single OSPF process at a time. In OSPF the network statement includes a netmask so that you can identify specific unique interfaces and assign it in whichever OSPF process you want it to be. when you have multiple OSPF processes, the routes will all appear in the local routing table with no indication of which process they came from. But an OSPF process will not advertise to its neighbors information learned by another OSPF process unless you redistribute between the processes.
-LSA: Both LSA type 3 and 4 are generated by the ABR(s). It is not only sent to the other ABRs but to all the routers in the area it is flooded in. The type 3 is generated from both type 1 and 2 LSAs from one area to another. A type 4 is generated for the each ASBR into an area to another.
From RFC2328: The B bit has to be set when the router is an area border router (B is for border).
-IS-IS and OSPF both require hirachical topology
-EIGRP
EIGRP is a Cisco proprietary routing protocol and will not run on another vendor's equipment. OSPF is vendor independent.
-Auto Summarization
occurs for Ripv1, Ripv2, IGRP, EIGRP, BGP
-Ripv1 does not support Authentication, Ripv2 support Authentication in clear and md5 to accept routhing update
-EIGRP, is-is, Ripv2, OSPF : support VLSM
-ClassLess:EIGRP, RIPV2, OPSF, is-is and BGP
-IGRP and EIGRP: are cisco proprieory routing protocols
-Class
leading bit 0 , class B leading bit 10 class c leading bit 110
-class c
124 8 0 254
125 7 128 127
126 6 192 62
127 5 224 30
128 4 240 14
129 3 248 7
130 2 252 2
131 1 254 0
-Ripv2, EIGRP are VLSM compatible
-172.16.100.0/24 + 172.16.106.0/24 = 172.16.96.0/20
-route summarization used with contiguos network
-" no auto-summary " disables the automatic summarization of routes
-you cannt ping an unnumbered interface
-calculate network address 172.16.0.10/29
29=24+5
10=00001010
network = 00001000
-on a serial link we need only 2 ip addresses one for each side of the link, subnet mask of 255.255.255.252
-broadcast addresss for the 172.16.1.10/25=172.16.1.27 set last 7 bits to 1
-SNMP are not supported in NAT
-the NAT router used about 160 bytes pretranslation, this means that about 1000 translation will use about 1.53 MB of RAM
-the OSPF process ID is not contained in the OSPF Hello packet
-An eBGP router will not set the NEXT_HOP attrib to itself when a route is orginated by an iBGF router in the same AS and on the same subnet as itself and the remote eBGP router
-126.52.80.0/24, 99.255.0.0/24, 72.95.85.1/24 = 64.0.0.0/2
-if the k-values and the as no. do not match, EIGRP devices will not form a neighbor relationship
-the debug is-is adj-packets command will display information about the is-is Hello PDLL's a router is sending and recieving
- a volume of 0 in the unfeasible routes length filed means that the with draw routes fild means that the with raw routes filed is not present in the UPDATE MESSAGE
- Routing table exchange is not a category of the OSPF operation. the exchange of Routing table information occurs during the LSA flooding category of OSPF operation
- the OSPF process ID is locally significant to the router it is configured on. you can have multiple istances of OSPF running on router and the process ID used to distinguish between them.
- IP address,Interface, Metric all can be used with match statement for route map
- the ge-value and le-value for prefix lists are used to specify the network range.
- Route Reflectors and can confiderations can be used in conjunction or alone to overcome the scalability limitation of iBGP.
- in the Broadcast network, the only device that will send a CSNP is the DIS.
- during the init state of the OSPF, the router has recived a Hello packet from it's neighbor, but the router has not see it's own router ID in theHello packet. once the router sees its own router ID the Heelo packet from the naighbor, the OSPF state will transition to 2 way.
- non broadcast OSPF network require you manually configure neibors.
- broadcast, P2P,P2M, will automatically form neighbors.
- route maps are used to manipulate routes being redistributed from one IGP to another IGP. Distribute lists are used to filter routes contained in an iGP filter lists and prefix lists are used to filter BGP routes, distributed lists don't exist.
- a level 2 router will form adjacencies with all other level 2 routers and all level1/2 routers.
- is-is the default is-is network of P2P interface is p2P. 2xrouters,one with physical interface, in the same is-is area,could form an is-is adjacency.
- when configuring a device to participate in a memeber - as you must specify the memeber - as no., confederation ID and the confederation peers.
- Ripv2, IGRP are both distance vector
- when advertising routes to another memeber- as the eBGP router will check to see is the as-path has an As. CONFED-SEQUENCE included, if it does not, the router will add the As-CONFED-SEQUENCE with its memeber as included. if the As-path does have an as-CONFED-SEQUENCE the router will add its memberto the seguence.
- confederations are made up of memeber-As
- if the route reflector recieves an UPDATE message containing routes from a route reflector with the same cluster ID as itself the route reflector will discard the routes.
- the command " a real stub " would be needed on all non-ABR routers for the area the command " area 1 stub no-summary " would be needed on a router tahtwas an ABR for the area.
- virtual links are used to connect areas to area 0 that are not directly connected to area 0
- EIGRP can configured to support up to six routes per destination.
- a level1/2 router would have link-state database for the level 1 LSP's and would leave one link-state database for the level 2 LSP's for the total of the two link-state database.
- ORIGIN and NEXT-HOP man datory attrib community is optional tranitive MED is optional , non transitive.
- distance vector routing protocols are based on the Bellman-ford algorithm, send thier on entire routing table in updates and are less scalable thyan link-state routing protocol.
- the OSPF network type broadcast prefers a full mesh, doesnt require neighbor statements, and elects a DR.
- OSPF, LSA type 3 is generated by an ABR and is summary to the networks in an area.
- non client BGP device types must be fully meshed with each other, clients dont need to be fully meshed because they are connected to a route reflector. a BGP speaker is not a BGP device typre.
- the show IP policy command will list all interfaces that have route maps configuredon them and what routemap they are using.
-TSA will not accept LSA type 3,4 or 5
-IPv4 = 32bits , IPv6 = 128 bits
-NAT works only with IP addresses
-neighbour in OSPF is another route with the same network address.
-DR resposible for making adjacencies with allroutes on a multiaccess link and maintaining thos adjacancies.
-OSPF router with priority set equal 0, cannt be DR or BDR
-inteface in init states, it means taht a router comming online is waiting for a Hello from neighbour.
-LSDB = topology map LSA=link state advertisement LSR =link state request LSU=link state update
-cost is the metric of OSPF
-priority,a cisco tool by which the DR can be manually elected or converted from taking part in DR,BDR election.
-cisco has defined a max of "6" paths taht can be used simultaneusly.
-OSPF can be used on "6" different WAN technology ( BMA, P2P, P2M, NBMA, VirtLink)
-BMA network can be ethernet TR FDDI
-P2p network can be direct connet ( no DRI, BDR )
-P2M network can be FR ( no DR, BDR )
-NBMA network can be FR, ATM
-VirtLink virtual connectiong to remote area
-"show IP policy" displays the route maps used for policy-based routing on the routes interface
-"show route-map" used to show the configured route maps
-route maps can be used for NAT, BGP, Redistrib
- method enable you to control routing info sent between routers during distribution ( pass inteface, static route, default route, null inteface, distribute list, route map )
-control routing is usefull for ( to hide certain network from the rest, to prevent routing loops, to control overload on the wire ,simple security reason )
-place subnet 172.16.20.128 in areal, and all other in area 0
network 172.16.20.128 0.0.0.255 area1
network 172.16.0.0 0.0.255.255 area2
-config OSPF # router OSPF procc-no
-a triggered update is when a routing update is sent a synchronously in response to change in the networktopology if there is a charge in the metric, the update is sent immediatly without waiing for the update timer to expire
-BGP sends incremental updates that can contain only the network change
-Dijkstra algorithm : this is a routing algorithm that iterates on the length of path to determine a shortest path first tree ( SPF tree ) it is commonly used in link-state routing protocols to determine which route to use. this is used in OSPF
-show IP OSPF neighbour will show the DR and BDR
-show IP OSPF, show IP OSPF database and show IP OSPF intefatce all show the OSPF process ID on the router
-an ABR must be resident in area 0, as well as in the area that is connecting to the nach bone area, it has two topological database, one for each area in which it is resident , so tha tit knows how to forward traffic.
-stub area, cannt accept ext. LSA and a virtual link cannt caontain a stub area.
-cisco suggests that a router should be a DR or a BDR for only one LAN
-Dis sends out " hello" every 3.3 sec.
-a L1/2 router has 2x link-state database, one for the L1 routers and other for the L2 router, a separate SPF algorithm is run for each database
-using the " set " command modifies matching routes
-RFC compliant NBMA, P2M
-cisco specific P2M non broadcat, broadcast, P2P
-full mesh:every router is conncted to every other router.
-partial meah:some router are directly connceted other are through another router.
-star(hub&spoke):one router acts as the connection to every other router.
-P2P non-broadcast hello = 30 sec dead 120
-P2P hello =10 sec dead in 40
-broadcast hello = 10 sec dead 40
-NBMA hello = 30 sec dead = 120
-S packets on OSPF used to build routing table hello protocol, database descripter,linkstate request linkstate. linkstate ack.
-if multiple routers have the same priority the router with routerwith the highest RID will be selected as the DR
-OSPF router ID ( RID ) is the highest IP address or the highest loop back address if one exist
-full mesh n(n-1)/2
- DR/BDR 2n-2
- if a router determines a CSNP mentioned an LSP it doesnthave , the router will multicast a P2NP reqesting the LSP
- R ( config ) # router BGP 100
- R ( config-router ) # no synch
- R ( config-router ) # no auto-summary
-since the remote as No. is different than the As No. specified when BGP was enabled,this will be an eBGP neighbour
- the command neighbour 1.1.1.1 distrib-list 10 out would an outband distribute list tothe BGP session with the router tah thas address 1.1.1.1
- you can add toprefixd list without having to delete it and reenter it like an access list
- Egress filtering is performed on a route when the route is moved from Loc-RiB to the Adj-RiB's out
-During the exchange state of OSPF routes are exchanging DD and LSR packets
-During the 2way OSPF state, a router has seen its own router ID in the hello packet ofneighbor
-the IP unnumbered command will allow a serial interface to borrow an IP address from another interface
-trace route uses the time-to-live field of an IP pachet to determine the hop-by-hop path of a packet
-for cisco devices,a DIS will by defualt multicast CSNP every 10 sec on broadcast networks
-if the router detects it has an LSP that is missing from the CSNP it will multicast that LSP to all ofthe neighbours
-stub areas do not accept type 4 or type 5 LSA's.a stub area will instead accept a type 3 LSA with a default route
-EIGRP uses theprotocol No. 88
-in the open confirm state, the router is waiting to recieve a KEEPALIVE message from its peer. once it recieve theKEEPALIVE message, the state will transition to ectablished
-the COMMUNITY attribute is an optional transitive attribute
-NSSA will allow an ASBR in the area to generate 7 LSA's for external routes the type 7 LSA's will then propagate across the area. the ABR will translate the type 7 LSA to a type 5 LSA and advertise it out of the area
-Policy-Based routing can be used for QoS through the use of the precendence ToSbits ???? and it can be used tocreate asynchronous routing
-OSPF DR's use well known multicast address 224.0.0.6
-P2P and P2M OSPF network type will not elect a DR or BDR
-OSPF and IS-IS both require a hirarichal network design
-periodic SPF calculations occur every 15 min
-L1/2 routers are similar to OSPF ABR's
-the ! symbol represents a successfull ping
-NGP uses TCP port 179 to establish TCP connection
-OSPF, LSA type 4 will adertise infoabout an ASBR into an area
-Topology table: The topology table holds a map of every link in the area. Every topology table in the area is the same. This is sometimes referred to as the link-state database.
-The ip ospf priority number command is used to determine the DR manually. The higher the
priority, the greater the likelihood is of success.
-OSPF configuration over a point-to-point:It is necessary to have one subnet per connection. Thus, if there are four point-to-point links,four subnets are required.
-Five packets are used to build the routing table for the first time:
The hello packet —This is used to find neighbors and to determine the designated and BDR. The continued propagation of the hello packet maintains the transmitting router in the topology database of those that hear the message.
The database descriptor —This is used to send summary information to neighbors to synchronize topology databases.
- The LSR —This is a request for more detailed information, which is sent when the router receives a database descriptor that contains new information.
The LSU —This is the LSA packet issued in response to the request for database information in the LSR packet.
The link-state acknowledgement —This acknowledges the LSU.
-The exstart state is a stage in the forming of an adjacency between neighbors. This stage is the stage when the DR and the BDR have been elected. The master/slave relationship has been
established, as has the initial sequence number of the DDP packets.
-Referred to as DBDs or database descriptor packets (DDPs), these are packets exchanged between neighbors during the exchange state. The DDPs contain summary information taken from the LSAs, which describe the links of every router in the neighbor’s topology table.
-A link-state advertisement (LSA) is a packet describing a router’s links and the state of those
links. There are different types of LSAs to describe the different types of links. An LSR is a link-state request, which is used when the router receives a DDP complete with summary information taken from the LSA. It compares the LSA against the topological database. If either the LSA entry is not present or the entry is older than the DDP, it will request further information via an LSR.
-The hello packet is used to maintain the neighbor table. Whenever a hello is heard, the source
address in the hello packet is used to reset the hello interval timer. This shows that the neighbor
is still active.
-OSPF defines cost as the OSPF metric, but does not define what cost represents. Thus, any determinant could be used and defined manually as cost. Cisco has set a default metric to be the inverse of bandwidth, making the fastest link the most preferred link. This default can be overridden by manual configuration.
-BDR stands for backup designated router. This router acts as the backup to the DR in case the
DR fails. The BDR performs none of the DR functions while the DR is operating correctly.
-When election dynamically, the DR is elected arbitrarily. The election is made on the basis of the highest router ID or IP address present on the network segment. It is wise to be aware that the highest IP address is the numerically highest number, not the class ranking of the addresses.
Therefore, a remote, small router with a Class C address might end up as a DR.
-When a new router connects to a network, it will find a neighbor using the Hello protocol and
will exchange routing information.
-The receiving router will send a copy of the LSA it holds in its database to the source of the old LSA and then discard the old LSA it received.
-Remember that the DDPs are simply a summary of the routes about which the neighbor knows. If there is a discrepancy between the information in the received DDPs and the router’s topology database, then the router requests more detailed information from its neighbor on those routes of which it was unaware. The different stages or states that the router goes through gathering routing information to update the topology database from a neighbor are shown in the following list:
The loading state —If the receiving router, the 2500, requires more information, it
will request that particular link in more detail using the LSR packet.
The LSR will prompt the master router to send the LSU packet. This is the same as an LSA
used to flood the network with routing information. While the 2500 is awaiting the LSUs
from its neighbor, it is in the loading state.
The full state —When these LSRs are received and the databases are updated and
synchronized, the neighbors are fully adjacent.
-The RFC 2328 that defines OSPF does not state the number of equal-cost paths that can be
entered into the routing table. Cisco has defined this to be four paths by default, which can be configured to contain up to six equal-cost paths.
-The LSA is flooded out of all the interfaces, excepting the interface through which it was
received. The LSA is copied into the topology database, replacing the original LSA if it existed.
The received LSA is acknowledged. The SPF algorithm is run to update the routing table.
-The configuration options proprietary to Cisco for NBMA are:
Point-to-multipoint nonbroadcast/Broadcast/Point-to-point
-In a point-to-point network, the concept of broadcast is not relevant because the communication
is direct to another router. There is very little network overhead. An IP subnet is required for
each point-to point link. In point-to-multipoint connections, OSPF simulates a broadcast, the network traffic is replicated and sent down each physical link and uses multicast addressing.
-The default network type for serial interfaces with HDLC encapsulation is point-to-point and
the hello packet is sent out every 10 seconds.
-The BDR listens to all the OSPF network traffic, which is addressed to both the designated and BDRs. All the routers on the medium have an adjacency with both DRs. The difference is that the BDR listens but does not respond. If the DR fails, the BDR becomes the DR.
-The priority command is used to determine manually the DR. The higher the priority, the
greater the likelihood is of success. Remember that the default=1 and p=0 means that the router
cannot win.
-The bandwidth parameter configured on an interface of a route in OSPF on a Cisco router is used to determine the default cost or the value of the path with the lowest cost.
-The router command creates the OSPF process with an ID number to identify it. To create another process on the same router, issue the same command again with a different ID number.It is possible to have more than one process, although it is rarely configured. The process ID in the command router ospf process-id not only starts the process, but also identifies the process; repeating the command with another ID number will create another process. One possible scenario for this configuration is a service provider that wants to separate its OSPF domain from its customer.
-The “ip ospf network non-broadcast” command is the RFC-compliant mode for NBMA. It is the default mode for interfaces and point-to-multipoint subinterfaces. It is used in a full or partial meshed network, and OSPF operates as if on a nonbroadcast network. It is necessary to define manually the DR to be a hub router that is connected to all the other routers. Neighbors must be defined manually.
-It is necessary to manually configure the neighbors in the industry-standard NBMA mode and
in the Cisco point-to-multipoint nonbroadcast mode.
You need to define the neighbors to the router because the router believes that it is a
nonbroadcast medium, so it cannot send out the multicast traffic to ascertain the neighbors.
-The industry-standard NBMA configuration can be chosen in a fully meshed environment. It
requires an additional manual configuration of the neighbors, but the network will elect the DR
and the BDR. There might be some design concerns about running this mode in an unstable
network, which could burden the CPU and the WAN links.
It is possible to use point-to-point subinterfaces without worrying about the OSPF network type
because they will become neighbors.
The other alternative is the Cisco broadcast mode, which does not require the manual
configuration of neighbors.
-The Cisco solution point-to-point does not require the election of either a DR or a BDR because
there are only two nodes on the network. They form an adjacency immediately.
-There are several ways to configure the process to include the interface. The command network
network-number wildcard-mask area area-number would be a subcommand to the global
command router ospf process-id . The network command is used in both possible solutions;
the difference is in the wildcard mask.
— network 192.100.56.10 0.0.0.0 area 2 —This will match every bit in the interface
address.
— network 192.100.56.10 0.0.7.255 area 2 —This will also match the interface because
it will resolve to the subnet assigned to the wire connected to the interface. This bit
allocation was chosen merely to demonstrate the technique. The allocation assumed is
the subnet mask of 255.255.248.0. Note that the wildcard mask is the inverse of the
subnet mask, ensuring that the individual subnet is selected for the interface.
-Underneath the appropriate interface, issue the command ip ospf cost . The value for cost is an unsigned integer value expressed as the link-state metric. It can be a value in the range 1 to 65,535.
-If the command ip ospf network non-broadcast is used, the additional statement that is required is the neighbor statement. Because the network is a nonbroadcast network that cannot
see its neighbors, the neighbors are to be manually configured.
-The show ip ospf neighbor command will show the DR and the backup router. Another command that will show the DRs is the show ip ospf interface command.
-The command show ip ospf database shows the contents of the topology database and gives a
status on the LSAs that have been sent and received, including how long it has been since the
last LSA was received.
-The command “show ip ospf interface” shows the adjacencies that exist with neighbors.
-The command “debug ip packet” shows OSPF packets being sent and received in real time.
-The commands “show ip ospf” , “show ip ospf database” , and show ip ospf interface all show the OSPF process ID on the router.
-The debug command has the highest process priority and is therefore capable of consuming all the resources on the router, thus becoming the problem as opposed to helping to solve the problem.
-The sequence number is used to ensure the LSA that has been received contains the most recent
information about the network. This prevents any packets arriving out of sequence from resulting in a change in the network that is incorrect.
-The SPF schedule delay is the time between OSPF receiving a topology change and starting an
SPF calculation. The delay can be an integer from 0 to 65,535. The default time is 5 seconds.
If the value is set to 0, this means that the SPF calculation is started as soon as a valid LSA is received. There is a balance between responding to a topology change quickly and the use of CPU processing.
-The show ip ospf interface command shows how the interface has been configured for OSPF.
This allows for the immediate identification of typing errors that result in a mismatch between
neighbors.
-The command "debug ip rip" is used to provide real-time info about the Ripv1 and Ripv2
-is-is and OSPF both require hirachical topology.
-Automatic summarization occurs for Ripv1, Ripv2,IGRP,EIGRP,BGP
-load balance on unequal cost paths supported by IGRP, EIGRP
-Ripv1 does not support Authentication
-Ripv2 support Authentication in clear and md5 to accept routhing update
-classless : EIGRP, RIPV2, OPSF, is-is and BGP
-IGRP and EIGRP are cisco proprieory routing protocols
-class A leading bit 0 , class B leading bit 10, class c leading bit 110
- class c
/24 8 0 254
/25 7 128 127
/26 6 192 62
/27 5 224 30
/28 4 240 14
/29 3 248 7
/30 2 252 2
/31 1 254 0
-Ripv2, EIGRP are VLSM compatible
-172.16.100.0/24 + 172.16.106.0/24 = 172.16.96.0/20
-Route summarization used with contiguos network
-"no auto-summary" disables the automatic summarization of routes
-you cannt ping an unnumbered interface
- calculate network address 172.16.0.10/29
29=24+5
10=00001010
network = 00001000
- on a serial link we need only 2 ip addresses one for each side of the link, subnet mask of 255.255.255.252
-Broadcast addresss for the 172.16.1.10/25=172.16.1.27 set last 7 bits to 1
-SNMP are not supported in NAT
-The NAT router used about 160 bytes pretranslation, this means that about 1000 translation will use about 1.53 MB of RAM
-The OSPF process ID is not contained in the OSPF Hello packet
-An eBGP router will not set the NEXT_HOP attrib to itself when a route is orginated by an iBGF router in the same AS and on the same subnet as itself and the remote eBGP router
-126.52.80.0/24 + 99.255.0.0/24+ 72.95.85.1/24=64.0.0.0/2
-if the k-values and the AS no. do not match, EIGRP devices will not form a neighbor relationship
-the debug is-is adj-packets command will display information about the is-is Hello PDLL's a router is sending and recieving
-PSNP can be used to request LSP info
-a volume of 0 in the unfeasible routes length filed means that the with draw routes fild means that the with raw routes filed is not present in the UPDATE MESSAGE
-Routing table exchange is not a category of the OSPF operation. the exchange of Routing table information occurs during the LSA flooding category of OSPF operation
-the OSPF process ID is locally significant to the router it is configured on. you can have multiple istances of OSPF running on router and the process ID used to distinguish between them.
-IP address,Interface, Metric all can be used with match statement for route map
-ge-value and le-value for prefix lists are used to specify the network range.
-Route Reflectors and confiderations can be used in conjunction or alone to overcome the scalability limitation of iBGP.
-Broadcast network, the only device that will send a CSNP is the DIS.
-During the init state of the OSPF, the router has recived a Hello packet from it's neighbor, but the router has not see it's own router ID in theHello packet. once the router sees its own router ID the Heelo packet from the naighbor, the OSPF state will transition to 2 way.
-Nonbroadcast OSPF network require you manually configure neighbors.
-Route maps are used to manipulate routes being redistributed from one IGP to another IGP. Distribute lists are used to filter routes contained in an iGP filter lists and prefix lists are used to filter BGP routes, distributed lists don't exist.
-L2 router will form adjacencies with all other level 2 routers and all level1/2 routers.
-Default is-is network of P2P interface is p2P. 2xrouters,one with physical interface, in the same is-is area,could form an is-is adjacency.
-when configuring a device to participate in a memeber - as you must specify the memeber - as no., confederation ID and the confederation peers.
-Ripv2,IGRP are both distance vector.
-when advertising routes to another memeber- as the eBGP router will check to see is the as-path has an As. CONFED-SEQUENCE included, if it does not, the router will add the As-CONFED-SEQUENCE with its memeber as included. if the As-path does have an as-CONFED-SEQUENCE the router will add its memberto the seguence.
-confederations are made up of memeber-As
-if the route reflector recieves an UPDATE message containing routes from a route reflector with the same cluster ID as itself the route reflector will discard the routes.
-command" a real stub " would be needed on all non-ABR routers for the area the command " area 1 stub no-summary " would be needed on a router tahtwas an ABR for the area.
-virtual links are used to connect areas to area 0 that are not directly connected to area 0
-EIGRP can configured to support up to six routes per destination.
-level1/2 router would have link-state database for the level 1 LSP's and would leave one link-state database for the level 2 LSP's for the total of the two link-state database.
-ORIGIN and NEXT-HOP mandatory attrib community is optional tranitive MED is optional , non transitive.
-Distance vector routing protocols are based on the Bellman-ford algorithm,send thier on trrie routing table in updates and are less
-IS-IS routing protocols - Handle level-1, level-2, and level-3 routing
-Ripv2, IS-IS and BGP are classless, IGRP is classfull.
-To summarize an area in ospf ,you must use the "area area# range addr mask" command on the ABR for an area.
-BGP uses port 179 to open as session with a remote BGP speaker.
-When dealing with routers that have low mem and cpu, it best to set the area up as totally stub area TSA.
-TSA will not allow lsa to be passed into it.
-Class D is IP multicast addr.
-Hold Timer expired errors do not have an error sub-code.
-The show ip policy will list all interfaces that have route maps configured on them and which route map they are using.
-IS-IS rides on CLNS.
-type lsa 3 and 4 consiered to be summary link advs. while totally stubby areas do not receive summary link advs, stub areas do
-In order for a route to be come a FS, the route adv distance must be less than the successor routes FD.
-Negotion and disconnect are not valid BGP states. connect and active are valid BGP states.
-"Summary-address address mask" can be used only when summarizing routes that are being redistributed into ospf.
- By default, cisco devices are L1/2 IS-IS routers.
- From the global configuration mode, "R1#route-map name {permit|deny} sequence" is used to configure route maps.
-AD of Stat ic route pointing to next hop address is 1.
-OSPF and IS-IS are bothlink state routing protocol and use the Dijkstra algorithm.
-When redistributing into IS-IS, by default allroutes are marked as internal L2 routes.
-if you have to elect between (EIGRP/OSPF/IS-IS/EX.BGP) then a AD of 20 for external BGP would be preferred route
-OSPf will use the highst loopback address on a router as the Router ID, if loopback is not configured on the router, ospf will use the highst configured
IP addr on the router
-A bgb UPDATE message can contain only one new route. it can, however contain multiple routes to withdraw.
-An eBGP router will not sent the NEXT_HOP attrb to itself when a route is orginated by an iBGP router in the same AS and on the same subnet as itself and the remote eBGP router.
-ORGIN, NEXT_HOP and AS_PATH are well known mandatory attrb
-LOCAL_PREF is well-known discretionary attribute.
-ARIN assign public AS numbers
-Route reflectors and confederation can be used to overcome the scalability limitations of iBGP.
-IS-IS will preempt for the designated router; ospf will not,
-A multi-homed AS has more than one exit point.
-ACK and HELLO packets do not require an acknowledgement to be sent.
-a TSA will not allow any LSA to be propagated into it.
-The COMMUNITY attrib is an optional transitive attribt.
-if no topology changes occur, ospf will still send out an lsa evry 30min.
-if a disconnect message is received from TCP, the BGP session will transition back to idle.
-summarize 172.16.32.0/24 172.16.36.0/24 172.16.64.0/24 = 172.16.0.0/17
-88 for EIGRP, 89 for OSPF, 6 for TCP and 17 for UDP.
-P2P,P2M,Broadcast,Nonbroadcast all are valid OSPF network type.
-AS_SEQ is not an AS_PATH type.
-A default cost of 10 is a ssigned to all IS-IS interface.
-The only time a CSNP is sent on P2P link is during the start up process.
-The cod D represents routes learned by EIGRP in routing table.
-EIGRP and IGRP are both cisco propriety routing protocols
-Client, non-client, and route reflector are all valid BGP device types.
-The D class 244.0.0.5 is used for OSPF on P2P connection.
-Default route
0.0.0.0 0.0.0.0 is the combination required for defining a default route.
-AS
The private AS number are 64512 through 65535, the public AS no. are 1 through 64511
-Hello Timer
The default Dead timer is 3x the value of the Hello timer.
-the NSAP selector bit represents the services available by a host, this value must be always be 00.
-OSPF
By default, the OSPF Dead timer is 4x greater than the Hello timer.
OSPF will assign a metric of 20, if one has not been specified, to all routers redistributed into it. In order for ospf to accept classless routes. the subnets keyword needs to be a append to the redistribution time.
-IS
is a device that is capable of routing.
-Ipv6
Uni/mlti/Any-cast are all IPv6 address.
-NAT
NAT translates only IP address and can use the TCP and UDP ports to create unique IP address.
NAT can support approx 64000 hosts by one IP address.
NAT seperate between the inside and outside network whare NAT PAT should be configured.
-Layer
Local VLAN and High port density are used on Access layer.
In the core Layer is designed to be optimized transport and Packet switching.
The Distribution layer is the only layer where layer 3 should be terminated.
-VLSM
supported by OSPF and when incorparated can make better use of the IP address space.
-OSPF
During the Exstart state of ospf, the master/slave relation is formed in order to form an adjacency by exchanging DD packets
-EIGRP
Eigrp uses the 224.0.0.10.
When configuring EIGRP summary address, you must configure the summary address on the interface where the summarization will occur.
-NSSA's support the transport of ospf lsa type7
-Traceroute gives you a hop by hop account of the path packet uses.
-An origin code of incomplete is represented in the BGP routing table with the "?" symbole
-IS-IS summarization L1 routes can be summarized into L2 area.
-The Loc-RIB is used to populate the BGP routing table.
-if a router detect LSP missing from CSNP, it will multicast that LSP to all of its neighbors
-if a router determines a CSNP mentions an LSP that it does not have, the router will multicast a PSNP requesting the LSP.
-OSPF LSA type 2, also known as network link adv, is generated by DR and sent to only those routers that are on the network of the DR in the same Area.
-Broadcast and point-to-point ospf network types have Hello intervall of 10 sec and Dead interval of 40 sec.
-Non-Broadcast and P2M ospf network types have a hello interval of 30 sec and a Dead interval of 120 sec.
-ip nat {inside | outside}
-ip nat pool
-ip nat inside source {list
-ip nat inside source list
-ip nat outside source {list
-show ip nat translations verbose
-clear ip nat translation {* |
-The show ip route command will not display the BGP table. You must use the show ip bgp command to display the entries in the BGP routing table.
-The highest ip address on an active interface is normally used as the OSPF router ID. This can be overridden by 224.0.0.6 is the address of all OSPF DRs and BDRs. configuring an IP address on a loopback address on a loopback interface.
-Ipv6
IPv6 Address Type: Unicast - An IPv6 unicast address is an identifier for a single interface, on a single node. A packet that is sent to a unicast address is delivered to the interface identified by that address.
IPv6 Address Type: Anycast - An anycast address is an address that is assigned to a set of interfaces that typically belong to different nodes. A packet sent to an anycast address is delivered to the closest interface as defined by the routing protocols in use—identified by the anycast address.
IPv6 Address Type: Multicast - An IPv6 multicast address is an IPv6 address that has a prefix of FF00::/8
An IPv6 multicast address is an identifier for a set of interfaces that typically belong to different nodes.
-OSPF
224.0.0.6 is the address of all OSPF DRs and BDRs.
-Sending route summaries– routing information advertised out an interface is automatically summarized at major (classful) network address boundaries by RIP, IGRP, and EIGRP.
-IS-IS：：A two-level hierarchy is used to support large routing domains. A large domain may be administratively divided into areas. Each system resides in exactly one area.
-L
L1: Routing within an area.
L2: Routing between areas is referred to as Level 2 routing. A Level 2 Intermediate System (IS) keeps track of the paths to destination areas.
L1: keeps track of the routing within its own area. For a packet destined for another area, a Level 1 IS sends the packet to the nearest Level 2 IS in its own area, regardless of what the destination area is. Then the packet travels via Level 2 routing to the destination area, where it may travel via Level 1 routing to the destination. It should be noted that selecting an exit
from an area based on Level 1 routing to the closest Level 2 IS might result in suboptimal routing
-Class D
Class D addresses are not as widely used.
Class D addresses are multicast addresses; some Class D multicast addresses used by routing protocols are as follows:OSPF – 224.0.0.5 and 224.0.0.6/ RIPSv2 – 224.0.0.9/EIGRP – 224.0.0.10
-Area
Stub Areas: These areas do not accept routes belonging to external autonomous systems (AS);
however, these areas have inter-area and intra-area routes. In order to reach the outside networks, the routers in the stub area use a default route which is injected into the area by the Area Border Router(ABR).
Normal Areas: These areas can either be standard areas or transit (backbone) areas. Standard areas are defined as areas that can accept intra-area, inter-area and external routes.
Backbone area is the central area to which all other areas in OSPF connect.
Totally Stub Areas: These areas do not allow routes other than intra-area and the default routes to be propagated within the area. The ABR injects a default route into the area and all the routers belonging to this area use the default route to send any traffic outside the area.
NSSA: This type of area allows the flexibility of importing a few external routes into the area while still trying to retain the stub characteristic. Assume that one of the routers in the stub area is connected to an external AS running a different routing protocol, it now becomes the ASBR, and hence the area can no more be called a stub area. However, if the area is configured as a NSSA, then the ASBR generates a NSSA external link-state advertisement (LSA) (Type-7) which can be flooded throughout the NSSA area. These Type-7 LSAs are converted into Type-5 LSAs at the NSSA ABR and flooded throughout the OSPF domain
-EIRGP summary: ip summary-address eigrp 109 192.1.0.0 255.255.0.0
-BGP summary: aggregate-address address mask [as-set] [summary-only]
-OSPF ABR summary: area (area-id) range (address mask)
-OSPF ASBR summary: summary-address ip-address mask
-NSSA:area area-id nssa
-Type-7 LSA: External routing information is imported into an NSSA in Type-7 LSAs.Type-7 LSAs are similar to Type-5 AS-external LSAs, except that they can only be flooded into the NSSA. In order to further propagate the NSSA external information, the Type-7 LSA must be translated to a Type-5 AS-external-LSA by the NSSA ABR
-Define an NSSA Totally Stub Area: area
-OSPF
The command that configures an OSPF area as stub is: area
-Totally stubby areas is: area
-Normal Area <-> None
-Stub Area <-> No Type 5 AS-external LSA allowed
-Totally Stub <-> No Type 3, 4 or 5 LSAs allowed except the default summary route
-NSSA<->No Type5 AS-external LSAs allowed,but Type 7 LSAs that convert to Type 5 at the NSSA ABR
-NSSA Totally Stub <-> No Type 3, 4 or 5 LSAs except the default summary route, but Type 7 LSAs that convert to Type 5 at the NSSA ABR are allowed
-Configure OSPF on an on-demand circuit using the following interface command:
interface bri 0
ip ospf demand-circuit
-Two routers will not become neighbors unless they agree on the following--
Area-id
Authentication
Hello and Dead Intervals
Stub area flag
-ASRB already has default route --- default-information originate
-ASBR doesn't have a default route --- default-information originate always
-Redistributing Routes into OSPF:
redistribute protocol [process-id] [metric value] [metric-type] 1/2 subnets
redistribute rip metric 10 subnets
type 2 - external cost
type 1 - external and internal cost. A type 1 route is always preferred over a type 2 route
-External routes fall under two categories, external type 1 and external type 2. The difference between the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 routes always the external cost, irrespective of the interior cost to reach that route. A type 1 cost is the addition of the external cost and the internal cost used to reach that route. A type 1 route is always preferred over a type 2 route for the same destination
-Injecting Defaults into OSPF:
router ospf 10
redistribute rip metric 10 subnets
network 203.250.15.0 0.0.0.255 area 0
default-information originate metric 10
-OSPF Virtual links :area (area-id) virtual-link (router-id)
RTA#
router ospf 10
area 2 virtual-link 2.2.2.2
RTB#
router ospf 10
area 2 virtual-link 1.1.1.1
-Selecting Interface Network Types, the command used to set the network type of an OSPF interface is:ip ospf network {broadcast | non-broadcast | point-to-multipoint}
-Setting a broadcast interface : ip ospf network broadcast
-If your autonomous system will be passing traffic through it from another autonomous system to a third autonomous system, it is very important that your autonomous system be consistent about these routes that it advertises. For example, if your BGP were to advertise a route before all routers in your network had learned about the route through your IGP, your autonomous system could receive traffic that some routers cannot yet route. To prevent this from happening, BGP must wait until the IGP has propagated routing information across your autonomous system. This causes BGP to be synchronized with the IGP. Synchronization is enabled by default. Only if all routers in the transit path in the AS are running BGP it is safe to turn synchronization off.
-The private NSAP addresses have AFI beginning with 39, 45 and 47. AESA Network Service Access Point (NSAP) ATM Addresses
-command sh ip ospf, view SPF recalculated times, out-of-data routes removed time
-The ip default-network command is used as a method of distributing route information to other routers.
-There are 5 methods to prevent loops, change metric/change AD/use default route(not static route)/passive-interface/distribute-list)
-EIGRP：
Neighbor table - lists adjacent routers
Topology Table - route entries for all destinations.
Routing table - best routes to a destination
-Successor - primary route used to reach a destination
-Feasible successor - backup route to the destination.
-EIGRP by default assumes the bandwidth is a T1 (1.544 Mbps) if not specified (including subinterfaces). Because the question ask for "what is the bandwidth of each frame Relay connection..." the answer is 1.544 Mbps/24 = 64.3 kbps.
-When configuring routers in a NBMA topology, subinterfaces are typically used. A physical interface can be split into multiple logical interfaces, called subinterfaces, with each subinterface being defined as point-tomultipoint interface. Subinterfaces originally were created to better handle issues caused by spilt horizon over NBMA and distance vector-based routing protocols.
-The ip bandwidth-percent eigrp command is used to configure the percentage of bandwidth that may be used by Enhanced IGRP (EIGRP) on an interface.
-There are four types of IS-IS packets: IS-IS Hello Packets, Link State Packets (LSPs), Complete Sequence Number Packets (CSNPs), and Partial Sequence Number Packets (PSNPs). PSNPs function as ACKs. Loss of a PSNP may result in an unnecessary retransmission of an LSP, but does not prevent correct operation of the routing protocol.
-We examine the following command: distance 140 0.0.0.0 255.255.255.255 9
140 defines the administrative distance that specified routes will be assigned.
0.0.0.0 255.255.255.255 defines the source address of the router supplying the routing information, in this case any router.
-defines the access-list to be used to filter incoming routing updates to determine which will have their administrative distance changed.
-The default metric used on Cisco IOS for IS-IS is the default (cost) metric and not delay.
-In EIGRP, the reliable packets are reply, query and update.
-If no alternate path is specified and the next hop router fails, policy based routing will default to dynamic routing decisions.
-A router running BGP have A BGP topology table and A BGP attribute table.
-To configure an IS-IS routing process for IP on an interface, use the ip router isis interface configuration command.
-Note: To enable IS-IS, perform the following tasks starting in global configuration mode:
Step 1: router isis - Enable IS-IS routing and specify an IS-IS process for IP, which places you in router configuration mode.
Step 2: net network-entity-title - Configure NETs for the routing process; you can specify a name for a NET as well as an address.
Step 3: interface type number-Enter interface configuration mode.
Step 4: ip router isis [tag]-Specify the interfaces that should be actively routing IS-IS.
- Perform the following steps to configure EIGRP for IP:
Step 1 Enable EIGRP and define the autonomous system.
routerTK(config)#router eigrp autonomous-system-number
Step 2 Indicate which networks are part of the EIGRP autonomous system.
routerTK(config-router)#network network-number
Step 3 Define bandwidth of a link for the purposes of sending routing update traffic on the link.
routerTK(config-if)#bandwidth kilobits
-（OSPF）The no-summary extension of the area stub command is used only for ABRs connected to totally stubby areas. It prevents an ABR from sending summary link advertisements into the stub area. This option is used for creating a totally stubby area.
-By default, EIGRP will limit itself to using no more than 50% of the available bandwidth.
-Using the show ip ospf neighbor command, you can observe the neighbor data structure. This command displays OSPF-related neighbor information. The Interface field shows the interface on which the OSPF neighbor has formed adjacency.Sample:
RouterTK2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
192.168.45.1 1 FULL/DR 00:00:36 10.0.0.1 Ethernet0
-The show ip ospf interface command displays area ID and adjacency information
-Redistribution of static routes configured to the null 0 interface into BGP is done to a
dvertise aggregate routes rather than specific routes from the IP table. However, Cisco recommends the use of the aggregate-address-command instead.
-There are many similarities between the IS-IS and the OSPF routing protocols:
link-state database
Shortest Path First (SPF) algorithm
Update, Decision, and Flooding Process
Hello protocol to establish and maintain adjacencies
-The BGP next-hop attribute is a well-known mandatory attribute that indicates the next hop IP address that is to be used to reach a destination. For EBGP, the next hop is the IP address of the neighbor specified who sent the update, Router TK2 in this scenario. However, since Router TK2 learned this route through IBGP with the next-hop of 40.1.1.2, this value will be used instead. This avoids an unnecessary hop.
-The aggregate route, 200.52.1.0 255.255.255.0, and the more specific route, 200.52.1.192
255.255.255.224, will both be advertised. To only advertise the aggregate route the summaryonly
option of the aggregate-address command must be used.
-The original IS-IS specification defines four different types of metrics: cost, delay, expense, and error. The Cisco implementation uses cost only. All links use the metric of 10 by default.
-The Cisco IOS software can handle simultaneous operation of up to 30 dynamic IP routing
processes. The combination of routing processes on a router or access server consists of the following protocols (with the limits noted):
Up to 30 IGRP routing processes
Up to 30 OSPF routing processes
One RIP routing process
One IS-IS process
One BGP routing process
Up to 30 EGP routing processes
-The default EIGRP link speed is 1.544 Mbps for serial media.
-Note: The enhanced code uses the "bandwidth" subcommand on interfaces and subinterfaces in order to determine the rate at which to generate EIGRP packets. This parameter is automatically set on fixed-bandwidth interfaces (such as LANs), but defaults to T1 (1544 Kbps) for all serial media.
-(OSPF)The area area-id range address mask command consolidates IA (intra-area) routes on an ABR. The command instruct the ABR to summarize routes for a specific area before injecting them into a different area.
-The distribute-list 5 out static command filters routes learned from static entries by using access list 3, before those routes are passed to the ospf process.
-One-way redistribution would help avoiding the routing loops problem.
-The distance eigrp command is used to allow the use of two administrative distances---in
ternal and external that could be a better route to a node.
Syntax: distance eigrp internal-distance external-distance
-Route maps are complex access lists: A collection of route-map statements that have the same route-map name are considered one route-map.
Step 1: RouterTestKing(config)# route-map map-tag [permit | deny] [ sequence-number]
First we define the conditions for policy routing.
Step2: RouterTestKing(config-route-map)#match { conditions}
Then we define the conditions to match
Step 3: RouterTestKing(config-route-map)# set { actions}
Finally we define the action to be taken on a match.
-Using this command for OSPF causes an OSPF autonomous system boundary router (ASBR) to advertise one external route as an aggregate for all redistributed routes that are covered by the address. For OSPF, this command summarizes only routes from other routing protocols that are being redistributed into OSPF.
-Multiple autonomous systems or routing domains can share route information through the redistribution process. Proper implementation of redistribution requires route filters to prevent feedback loops from forming. It is strongly recommended that redistribution between multiple ASs or multiple routing protocols be accompanied by route filters.
-IGBP routes are propagated to all IBGP peers and only the IBGP peers.
-The show ip ospf border-routers command displays the internal OSPF routing table entries to an area border router (ABR) and autonomous system boundary router (ASBR). The SPF No in the output is thei nternal number of SPF calculation that installs this route.
-EIGRP sends hello packets every 5 seconds on high bandwidth links and every 60 seconds on low bandwidth multipoint links. The hold time is typically three times the hello interval. In this scenario, on slow NBMA media, hold time will be 180 seconds.
-EIGRP by default assumes the bandwidth is a T1 (1.544 Mbps) if not specified (including subinterfaces)
-The show ip bgp summary command displays the status of all BGP connections. Neighbors with corresponding AS value will be listed, both interior and external.
-IGRP and EIGRP support unequal cost path load balancing, which is known as variance. OSPF,RIPv1 and RIPv2 do not support this.
-If you want router to advertise a static-route in a routing protocol,you ll need to redistributeit.
-If you define a static route to an interface that is not one of the networks defined in a network command, no dynamic routing protocols will advertise the route unless a redistribute static command is specified for these protocols.
-The bandwidth can be configured separately on each subinterface. Since this is NBMA we can assume that Frame Relay is used. For Frame Relay on point-to-point the bandwidth should be set it to the CIR of the PVC.
-Note: NBMA (Non-broadcast Multi-access) supports many (more than two) routers,but have no broadcast capability. Frame Relay and X.25 are example of NBMA.
-Note: The CIR (Committed Information Rate) is the committed rate (in bits per second) at which the ingress access interface trunk interfaces, and egress access interface of a Frame Relay network transfer information to the destination Frame Relay end system under normal conditions.
-OSPF, IS-IS and EIGRP support manual route summarization.
-The show ip prefix-list command is used to display information about a prefix list or prefix list entries.
-In OSPF, all areas must be connected to a backbone area, area 0.
-The ip summary-address eigrp command is used to configure a summary aggregate address for a specified interface. Syntax: ip summary-address eigrp autonomous-system-number address mask
-All routers within an area will have the same view of the area – they will all have the same topology table. All of them will know when another router joins the area.
-The ip helper-address command is used to have the Cisco IOS software forward User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface. DHCP protocol information is carried
inside of BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the router interface closest to the client. The helper address should specify the address of the DHCP server.
-Note: A DHCP server can be considered to be a BOOTP server, even though a DHCP server is more advanced.
-When configuring multipoint interfaces, especially for Frame Relay, remember that all neighbors share the bandwidth equally.
- This autonomous system designator is a 16-bit number, with a range of 1 to 65535. RFC 1930 provides guidelines for the use of AS numbers. A range of AS number, 64512 through 65535, is reserved for private use, much like the private Internet Protocol (IP) addresses.
-The ip default-network command is used as a method of distributing default route informat
ion to other routers. When running RIP, you can create the default route by using the ip defaultnetwork command. If the router has a directly connected interface onto the network specified in the ip default-network command, RIP will generate (or source) a default route to its RIP neighbor routers.
-The attributes defined by BGP include:
Well-known mandatory attributes: AS-path, Next-hop, Origin
Well-known discretionary attributes: Local preference, Atomic aggregate
Optional transitive attributes: Aggregator, Communities
Optional non-transitive attribute: Multi-Exit-Discriminator (MED)
-Class A:10.1.1.1 to 10.254.254.254
-Class B:172.16.1.1 to 172.31.254.254
-Class C:192.168.1.1 to 192.168.254.254
-There are 3 steps in routing packets:
Determine if the protocol is supported - IP, IPX, Appletalk, DECNET, etc;
Check for the destination address in the routing table;
Determine exit interface and then route packet.
-Static route example - "conf t", "ip route 192.168.2.0 255.255.255.0 192.168.1.10".
-Default route example - "conf t", "ip route 0.0.0.0 0.0.0.0 192.168.1.1".
-Static routes are to be used in small networks (10 routers or less).
-An Autonomous System (AS) is a collection of routing domains under the same administrative control.
-IGP (Interior Gateway Protocols) - route within the same AS.
-IGP can be broken down by: class- distance-vector and link-state, category- classful and classless.
-EGP (Exterior Gateway Protocols) - route between different AS's.
-Distance-vector routing protocols - they route "by rumor". Examples are RIP, IGRP, EIGRP.
-EIGRP is a hybrid protocol, Cisco considers it a distance-vector protocol.
-Distance-vector extended specifications:
-Periodic updates - 30 seconds for RIP, 90 seconds for IGRP.
-Neighbors - another router on the same logical (or data link) connection.
-Broadcast updates - when a router becomes active, it will send out a broadcast.
-Full routing table updates - the entire routing table is sent out with each update.
-Routing by rumor - a router sends its routing table to all neighbors.
-Invalid timer if a route is not updated for a while, it is marked invalid usually 3 to 6 times the update timer.
-Count to infinity - a maximum hop count is enforced (16 for RIPv1/RIPv2,255 for IGRP).Not used by EIGRP.
-Split Horizon - a route cannot be advertised through the interface it was learned on.
-Hold-down timer - information about a route is put "on hold". Useful when a device flaps. Not used by EIGRP.
-Triggered updates - an update will be sent out as soon as a significant event occurs. This will speed up convergence.
-Load balancing with equal paths - supported by RIPv1/RIPv2, IGRP, EIGRP.
-Load balancing with unequal paths - supported by IGRP and EIGRP. NOT supported by RIPv1 and RIPv2.
-VLSM support (Variable-Length Subnet Mask) - supported by RIPv2 and EIGRP. NOT supported by RIPv1 and IGRP.
-Metric - hops (RIPv1 and RIPv2), composite (IGRP and EIGRP).
-RIP (Routing Information Protocol) - version 1 and version 2.
-Common characteristics of RIPv1 and RIPv2:
Both are distance-vector routing protocols.
Both use the Bellman-Ford algorithm.
The metric is hop count - 1 to 15. 16 means unreachable.
Periodic updates are sent every 30 seconds.
Invalid timer is 90 seconds.
Route flush timer is 240 seconds (this timer starts after a route is marked invalid).
-Differences between RIPv1 and RIPv2:
RIPv1 is classful, and RIPv2 is classless.
RIPv2 supports authentication of routing updates.
RIPv2 supports multicast route updates.
RIPv2 carries next hop addresses with each route entry.
RIPv2 has automatic route summarization.
-Link-state routing - each router knows the exact topology of the network.
-Link-state protocols:
OSPF (Open Shortest Path First);
IS-IS (Intermediate System to Intermediate System);
EIGRP (hybrid, as mentioned earlier).
-Link-state advertisements = LSA
-LSA are generated for each link. Only updates are sent, and NOT the entire routing table.
-How Link-state routing protocols work:
A router forms adjacencies with directly connected neighbors.
The router then sends LSAs to each neighbor.
All routers store the LSAs in their own database.
Each router will use the Dijkstra algorithm to compute a best route to a destination.
-EIGRP uses the DUAL algorithm instead.
-Link-state extended specifications (OSPF ISIS EIGRP):
Hierarchical topology - needed by OSPF and IS-IS, NOT needed by EIGRP.
All three protocols retain knowledge of all possible routes.
All three protocols support manual route summarization.
Only EIGRP supports automatic route summarization.
All three protocols support event-triggered announcements.
All three protocols support load balancing with equal paths.
Only EIGRP supports load balancing with unequal paths.
All three protocols support VLSM.
OSPF and IS-IS use cost as a metric, EIGRP uses a composite metric.
Hop count limit is 200 for OSPF, 1024 for IS-IS, and a default 100 for EIGRP (max is 255).
IS-IS is suitable for the largest networks.
Classful routing - no netmask is sent with updates. Examples - RIPv1, IGRP.
Classless Interdomain Routing (CIDR) - A VLSM is sent with updates. Examples - RIPv2, EIGRP, OSPF, IS-IS.
Routes are chosen by administrative distance (lower is better), and by metric.
-Default administrative distances:
0 - directly connected /1 - static route /5 - EIGRP summary /20 - External BGP /90 - EIGRP
100 - IGRP /110 - OSPF/115 - IS-IS/120 - RIP/140 - EGP /170 - External EIGRP /200 - Internal BGP
255 - Unknown
-If there are two or more routes with the same AD, the one with the lowest metric (hop count, etc) is chosen.
-Convergence - the time it takes for all routers to agree on the network topology after a change.
-Two different reasons for a link to be considered down:
Physical - when an interface on a router does not receive three consecutive keepalives.
Logical - when a routing protocol fails to receive three consecutive Hello messages.
-Link-state protocols do not use hold-down timers, and therefore speed up convergence.
-Distance-vector convergence is generally slow (can be 240-490 seconds), with the exception of EIGRP (hybrid).
- Show the routing table - "sh ip route".
-Clear and recreate the routing table - "clear ip route *".
-Important troubleshooting tools - "ping" and "traceroute". "ping
-OSPF floods network with LSAs to prevent loops. IS-IS does NOT!
-RIPv1/RIPv2 use hop count as a metric.
-IS-IS and OSPF use bandwidth.
-IGRP and EIGRP use a composite metric.
-RIPv1, RIPv2, IGRP, and EIGRP support automatic route summarization.
-IS-IS and OSPF only support manual route summarization.
-Benefits of link-state over distance-vector protocols:
Link-state protocols use Hello messages to establish adjacencies;
When a network change occurs, link-state protocols send only the necessary info about the change, not the entire routing table.
-With classful routing, all devices on the network must have the same mask.
-The default metric for static routes can be:
0 - when the static route points to an interface;
1 - when the static route points to a next hop.
-IP addressing in decimal, binary, and hex - 172.16.30.56 = 10101100.00010000.00011110.00111000
-"host address" = "node address" - the host part of an IP address.
-Class A - leading bit "0", address range "1.0.0.0 - 126.255.255.255". Netmask 255.0.0.0
-Class B - leading bit "10", address range "128.0.0.0 - 191.255.255.255". Netmask 255.255.0.0
-Class C - leading bit "110", address range "192.0.0.0 - 223.255.255.255". Netmask 255.255.255.0
-Network address of all zeros (means "this network").
-Network address of all ones (means "all networks").
-Network 127 - loopback.
-Node address of all zeros (means "this network").
-Node address of all ones (means "all nodes").
-Entire IP address of all zeros (used to designate the default route).
-Entire IP address of all ones (broadcast).
-Number of subnets = 2^n - 2, where n = number of subnet bits.
-Number of hosts = 2^n - 2, where n = number of host bits.
-You can use the all zeros and all ones subnets (but NOT on the exam). The command is: "conf t", "ip subnet-zero".
-VLSM - for a network of only 2 hosts, the subnet mask is 255.255.255.252. Anything < 252 is a waste of IP space.
-A mask of 255.255.255.0 (/24) gives us 254 hosts. 255.255.255.128 (/25) = 126 hosts. 255.255.254.0 (/23)= 510 hosts.
- Old IOS - when you enter "8 bits for subnetting", the IOS shows mask /16 (for class A IP), as it adds the bits to the default mask.
- New IOS - when you enter "255.255.0.0" = 16 bits, the IOS shows mask /16 (no longer class-dependent).
-Practical VLSM example - 4 subnets needed - 2, 4, 200, and 300 hosts respectively. Available network is 172.16.0.0/16. A good rule is to start from the smallest subnet and move up.
subnet1 (2 hosts) - network 172.16.0.4, mask 255.255.255.252 (/30), hosts 172.16.0.5-172.16.0.6, broadcast 172.16.0.7.
subnet2 (4 hosts) - network 172.16.0.8, mask 255.255.255.248 (/29), hosts 172.16.0.9-172.16.0.14, broadcast 172.16.0.15.
subnet3 (200 hosts) - network 172.16.1.0, mask 255.255.255.0 (/24), hosts 172.16.1.1-172.16.1.254, broadcast 172.16.1.255.
subnet4 (300 hosts) - network 172.16.2.0, mask 255.255.254.0 (/23), hosts 172.16.2.1-172.16.3.254, broadcast 172.16.3.255.
It is not a good idea to separate subnets with another network. Example:
172.16.1.0/24 <--> 10.1.1.1 <--> 10.1.1.2 <--> 172.16.2.0/24. This is a BAD idea, although route summarization can fix it.
- CIDR notation - "/24" - network part has 24 bits. The first CIDR value is /8 (class A), and the last is /30 (2 hosts in a subnet).
-Note: With the release of RFC 3021, vendors will start supporting a /31 mask for point-to-point connections.
-Route summarization = route aggregation. Simple example - 172.16.1.0/24 + 172.16.2.0/24 + 172.16.3.0/24 = 172.16.0.0/16.
-Route summarization steps:
Convert all network numbers to binary.
Count the common bits between all of them, starting from the beginning. This is your mask.
Example:
We will summarize 172.16.18.0/24 and 172.16.30.0/24. I will separate the common part, for tidiness.
172.16.18.0 = 10101100.0001000.0001 0010.00000000
172.16.30.0 = 10101100.0001000.0001 1110.00000000
The common part is 172.16.16.0 (the rest of the 3rd octet is disregarded).
The mask is 255.255.240.0 (/20).
Our summarized answer is 172.16.16.0/20
Tip: When you have a list of networks, take the first and the last one, and then summarize.
-Only classless routing protocols support route summarization. Therefore, RIPv1 and IGRP are not suitable in this case.
-Route summarization is most effective with hierarchical addressing - the shortest subnet masks are on top of a tree (/16 for example), and below are longer subnet masks (/24), then down below even lower ones (/30).
- Discontiguous networks are one that are not hierarchical. There is no fixed order of subnetting.
-If you find yourself in a situation with a discontiguous network, you must disable automatic route summarization:
-RIPv2 - "router rip", "version 2", "network 10.0.0.0", "network 172.16.0.0", "no auto-summary".
-EIGRP - "router eigrp 100", "network 10.0.0.0", "network 172.16.0.0", "no auto-summary".
-IP unnumbered - another way to allow discontiguous networks to interconnect over a serial link.
-The serial interface "borrows" an IP from another interface –
"conf t", "int serial 0", "ip unnumbered ethernet 0".
-IP unnumbered is not supported on X.25 or SMDS (Switched Multi-Megabit Data Service) networks.
-Because an unnumbered serial interface does not have an IP, you will not be able to ping it (but you can poll it with SNMP).
-IP security options are not supported on an IP unnumbered interface.
- IP helper address - needed when UDP broadcasts are needed - DHCP or DNS packets.
-Example: "conf t", "int serial 0", "ip helper-address 172.16.1.10" - serial 0 will forward UDP packets to 172.16.1.10.
-You can have multiple IP helper addresses on an interface.
-The first two bits of a class B network are "10".
-Route summarization is primarily used in contiguous networks.
-IP unnumbered does not work over X.25. You cannot ping an unnumbered interface.
-If a host is 172.16.0.10/29, then the network is 172.16.0.8/29.
-In a discontiguous network: use IP unnumbered, disable route summarization.
-An IP address is most commonly represented in dotter-decimal or binary form.
-Although OSPF is not proprietary, Cisco has modified it by adding more features to it.
-OSPF uses Dijkstra's Shortest Path First (SPF) algorithm.
-MPLS (Multi-Protocol Label Switching) supports only OSPF and IS-IS, which makes OSPF even more popular.
-OSPFv1 (RFC 1131) never made it. OSPFv2 (RFC 2328) is what's used today.
-Within OSPF, links = interfaces.
-Advantages of OSPF:
Support of hierarchical network design through the use of areas
The use of link-state databases reduces the chance of routing loops
Full support of VLSM
-Route summarization
decreases routing table size; Routing updates are sent only when needed;Use of multicast instead of broadcast,reduces BW and CPU utilization for devices not running OSPF;Support for authentication.
-OSPF neighbor-another router with an interface in the same OSPF area. Neighbors are discovered via Hello packets.
-DR == Designated router
-(DR),arouter sending LSA's to adjacent routers (in a broadcast, multi-access area).
-Backup designated router (BDR) - a hot standby of the DR. The BDR does not flood with LSA's while being a backup.
-Internal router - has all of its interfaces in a single OSPF area.
-Area border router (ABR)
-ABR has multiple area assignments. An interface may belong to only one area.
-Autonomous system boundary router (ASBR)
-ASBR has an interface in an EIGRP (or other) AS. An ASBR can inject routes into OSPF.
-Non-broadcast multi-access (NBMA) networks - Frame Relay, X.25, ATM.
-Broadcast (multi-access) networks - Ethernet. Each broadcast network needs a DR and a BDR.
-Point-to-point networks - Frame Relay or ATM. No DR/BDR is needed.
-Router ID - the highest loopback address. If no loopbacks are present, the highest IP address.
-OSPF operation phases:
Neighbor and adjacency initialization;
LSA flooding;
SPF tree calculation.
-Neighbor and adjacency initialization - done via Hello packets. Hello packets are sent every 10 seconds.
-A Hello packet uses a common OSPF header and contains: Router ID, Area ID, Authentication information (and other parameters).
-Neighbor states:
Down - no Hello packets have been received from the neighbor;
Attempt (configured manually) - no updates have been received (in an NBMA network);
Init - Hello packets are coming in, but the router has not seen itself in them - no bi-directional communication yet;
2Way - The router has seen itself in the Hello packets - bi-directional communication has been established;
ExStart - master/slave relationship via DD (database description) packets. The router with the highest ID is the master;
Exchange - Routing information is exchanged using DD and LSR (link-state request) packets;
Loading - LSR packets are sent to neighbors to request new LSA's;
Full - All LSA information has been synchronized.
-Requirements for establishing an adjacency with a neighboring router:
Two-way communication, established via the Hello protocol;
Database synchronization - via DD, LSR, and LSU (Link-State Update) packets.
-Each non-designated OSPF router on a multi-access network forms 2 adjacencies - one with the DR and one with the BDR.
-DR/BDR election procedure - there is a Cisco priority ID (default 1). Set it to 0 and you will exclude that router from election.
-The router with the highest priority is elected to be a DR or BDR (or with the highest Router ID, if priorities are equal).
- OSPF will not preempt for the DR - if a router with a higher priority/ID joins the network at a later time, it will not become a DR.
-LSA Flooding - OSPF sends LSA's to one of these multicasts:
224.0.0.5 (AllSPFRouters);
224.0.0.6 (AllDR).
-What happens when a router on the network detects a change:
The router multicasts LSA's to AllDR (224.0.0.6);
The DR router receives the LSA's, and then floods them to AllSPFRouters (224.0.0.5) out all interfaces;
-Each SPF router acknowledges that the LSA's have been received.
-There are two types of acknowledgements:
Explicit (type 5 OSPF packet) - the recipient sends an LSA packet back to the DR;
Implicit - the recipient sends the original LSA back to the DR. 2 ways to create an implicit
-Acknowledgement:
Direct method - immediate send (if a duplicate LSA has been received, or LSA = MaxAge = 1 hour);
Delayed method - the acknowledgement is sent later together with other LSA's.
-SPF Tree Calculation - done by each router. Two destination types are recognized - network, router (ABR/ASBR).
-OSPF Metrics - cost. Cisco calculates cost via 10^8/bandwidth (a number between 1 and 65,535).
-Cost can be manipulated by the command "ip ospf cost".
- Non-Broadcast Multi-Access (NBMA) Environments - It is difficult to run OSPF on NBMA environments because there is no broadcast.
-In NBMA environments, with extended configuration, OSPF can be made to simulate one of the following:
Broadcast - Hello = 10 sec, Dead Interval = 40 sec, DR/BDR are elected;
Configure broadcast - "conf t", "int serial 0", "ip ospf network broadcast".
Non-broadcast (default) - Hello = 30 sec, Dead Interval = 120 sec, DR/BDR are elected;
Configure non-broadcast - "conf t", "int serial 0", "ip ospf network non-broadcast", "neighbor
-Point-to-point (via subinterfaces) - Hello = 10 sec, Dead Interval = 40 sec, DR/BDR are NOT elected;
Configure point-to-point - "conf t", "int serial 0", "ip ospf network point-to-point".
-Point-to-multipoint - Hello = 30 sec, Dead Interval = 120 sec, DR/BDR are NOT elected;
Configure point-to-multipoint - "conf t", "int serial 0", "ip ospf network point-to-multipoint".
-Simple OSPF configuration:
"conf t";
"router ospf 1"-"1" is a unique process ID.
It allows for more than 1 OSPF process to run on the same router.
"network 172.16.10.5 0.0.0.0 area 0" –
the interface (link) with an IP of 172.16.10.5 is assigned to area0.
"network 172.16.20.0 0.0.0.255 area 0" –
the network 172.16.20.0/24 is assigned to area 0.
-In a single OSPF area, there are no ABR's or ASBR's.
-If there is an interface in another OSPF area, there will be an ABR.
-If routes are being injected from EIGRP (or other protocols), there will be an ASBR.
-sh ip ospf -OSPF summary,including processes,router ID,area assignments, authentication, and SPF statistics.
-sh ip ospf 1 - summary for process ID 1.
-sh ip ospf border-routers - displays ABR and ASBR information.
-sh ip ospf database- displays the link-state database (link count, router ID).
-sh ip ospf interface- displays OSPF parameters at the interface level.
-sh ip ospf neighbor- displays neighbor and adjacency status.
-A router ID is chosen based on the highest IP address from any loopback interface (or regular interface, if there are no loopbacks).
-ip ospf cost -sets the default cost on an OSPF interface. Cost varies between 1 and 65535.
-According to Cisco, cost = 10^8 / bandwidth.
-Broadcast networks have a DR/BDR assigned. Point-to-point networks don't.
-224.0.0.5 is AllSPFRouters, 224.0.0.6 is AllDR.
-All OSPF networks with more than one area must contain area 0.
-Please note that the examples are NOT related. That is why "router ospf 1" was used in each case.
-Configuring OSPF for NBMA Environment: Broadcast (full mesh required):
"conf t"
"int serial 0"
"ip ospf network broadcast"
"encapsulation frame-relay"
"frame-relay map ip 172.16.11.2 102 broadcast"
"frame-relay map ip 172.16.11.3 103 broadcast"
"frame-relay map ip 172.16.11.4 104 broadcast"
"exit"
"router ospf 1"
"network 172.16.11.0 0.0.0.255 area 0"
-Configuring OSPF for NBMA Environment: Non-broadcast (all neighbors must be statically configured):
"conf t"
"interface serial 1"
"ip ospf network non-broadcast"
"encapsulation frame-relay"
"ip frame-relay map 172.16.25.10 210 broadcast"
"ip frame-relay map 172.16.25.11 211 broadcast"
"ip frame-relay map 172.16.25.12 212 broadcast"
"exit"
"router ospf 1"
"neighbor 172.16.25.10 priority 1"
"neighbor 172.16.25.11 priority 1"
"neighbor 172.16.25.12 priority 1"
"network 172.16.25.0 0.0.0.255 area 0"
-Configuring OSPF for NBMA Environment: Point-to-multipoint (a spin-off from point-to-point):
"conf t"
"interface serial 2"
"ip ospf network point-to-multipoint non-broadcast"
"encapsulation frame-relay ietf"
"frame-relay local dlci 300"
"frame-relay map ip 172.16.26.12 312 broadcast"
"frame-relay map ip 172.16.26.13 313 broadcast"
"exit"
"router ospf 1"
"neighbor 172.16.26.12 priority 1"
"neighbor 172.16.26.13 priority 1"
"network 172.16.25.0 0.0.0.255 area 0"
-Although IGRP and EIGRP are proprietary, Cisco has licensed IGRP to be used on Compaq and Nokia equipment.
-Distance-vector protocol scalability issues - convergence time, router overhead (CPU and memory), bandwidth utilization.
-Link-state protocols - they scale better. They peer via Hello packets (every 10 seconds or so), and only use incremental updates.
-If there are no network changes, link-state updates are sent every 30 minutes to 2 hours - "paranoid updates".
-IGRP was created in the mid-80s to replace RIPv1. IGRP uses a composite metric - bandwidth, delay, reliability,load.
-Default maximum hop count for IGRP is 100, but that can be incremented to 255.
-Common IGRP problems - Cisco proprietary, classful (does not scale well).
-IGRP recognizes three types of routes:
Interior - networks directly connected to a router interface
System - routes advertised by other IGRP neighbors within the same AS
Exterior - routes learned via IGRP from a different IGRP AS
-Some IGRP features - configurable metrics, triggered updates, hold-down updates, unequal-cost load balancing.
-IGRP timers:
update timer = 90 seconds. IGRP uses a random factor of 20%, so the actual update timer is between 72 and 90 seconds.
invalid timer = 3 x update timer = 270 seconds.
flush timer = 7 x update timer = 630 seconds.
hold-down timer = 3 x update timer + 10 = 280 seconds. Hold-down timers can be disabled in a loop-free environment.
-Set various timers
conf t
router igrp 50
timers basic
Example: "conf t", "router igrp 50", "timers basic 50 150 160 350".
-Disable hold-down timers in a loop-free environment:
conf t
router igrp 50
no metric holddown.
-IGRP uses the Hellman-Ford algorithm. With IGRP: metric = bandwidth + delay.
-IGRP weight values and corresponding metrics- K1(bandwidth),K2(delay),K3(reliability),K4(load), K5(MTU).
-Change default K values - "conf t", "router igrp 50", "metric weights 0
-Change the default IGRP administrative distance (100) - "conf t", "router igrp 50", "distance <1-255>".
-Setting a default metric - "conf t", "router igrp 50", "default-metric
-Set the number of maximum paths for IGRP load balancing - "conf t", "router igrp 50", "maximum-paths 5". Default is 4. Max is 6.
-Set the variance - "conf t", "router igrp 50", "variance 2". Default is 1.
-Feasible successor - a route with metric < lowest metric * variance.
-Route redistribution - routes known to one protocol are shared with another protocol. Redistribution can be one-way or mutual.
Example: Router1 (IGRP 100) <--> Router2 (IGRP 100, EIGRP 150) <--> Router3 (EIGRP 150). Redistribution is done on Router2.
Redistribution will automatically occur between IGRP and EIGRP with the same AS number.
-Configuring IGRP - "conf t", "router igrp 20", "network 192.168.1.0".
-Send unicast updates to a particular neighbor - "neighbor 192.168.1.10".
-Prevent an interface (usually WAN) from broadcasting IGRP - "passive-interface serial 0".
-Tip: Do not adjust IGRP (or any other) timers, unless you have a good reason to do it.
-Verify IGRP route information - "sh ip route", "sh ip route 192.168.1.0". Learned IGRP routes show as "I".
-A good way to display routing protocol information - "sh ip protocols" (execute from enable mode).
- Show MTU, bandwidth, reliability, load, etc - "show interface serial 0".
- Debug IGRP on two different levels - "debug ip igrp events" (brief), "debug ip igrp transactions" (detailed).
- To see debug output, you need to have logging enabled - "conf t", "logging console" (or "logging on" for all destinations).
-Disable debugging - "undebug all".
-EIGRP has many improvements over IGRP. EIGRP uses a different algorithm - DUAL (Diffusing Update Algorithm).
-EIGRP is a hybrid protocol.It converges rapidly, and only sends incremental updates.
-IGRP AD = 90.
-Main EIGRP components:
Support for IP, IPX, and Appletalk at the same time, via PDMs (protocol-dependent modules).
Reliable Transport Protocol (RTP).
Neighbor Discovery/Recovery.
Diffusing Update Algorithm (DUAL).
-Route tagging - you can have multiple AS numbers on a single router. They function like separate routing domains.
-Route redistribution -when routes are redistributed from AS to AS,they are tagged as ext. EIGRP
-Ext. EIGRP routes (AD = 170).
-EIGRP uses Hello packets to establish neighbor relationships with other routers (link-state quality).
-The only time when EIGRP advertises its entire routing table is when two neighbors start to communicate.
-EIGRP sends multicast Hello packets (instead of broadcast) every 5 seconds. The target is 224.0.0.10.
-X.25, frame relay,and ATM (if equal or slower to a T1),a Hello packet will be unicast every 60sec.
-IGRP uses 24-bit updates, and EIGRP uses 32-bit updates.
-EIGRP supports up to 6 redundant paths. The path with the lowest metric is the successor and is added to the routing table.
-Any route that has an AD lower than the successor's feasible distance,will become a feasible successor route.
-EIGRP uses the same metrics as IGRP-bandwidth,delay,reliability,load.By default,only bandwidth and delay are used.
-EIGRP has a protocol type of 88.
-EIGRP implements "pacing" to prevent routing updates from consuming too much bandwidth.Default is 50% of the interface bandwidth.
-Adjust pacing -"conf t", "interface serial 0", "ip bandwidth-percent eigrp 20" (decrease to 20%).
-DUAL speeds up convergence by recalculating routes only when it needs to.
-Three reasons for DUAL to start recalculating (if a feasible successor is not found after a change).
An alternate route is not found.
The new best route still goes through the original successor.
The new best route doesn't go through a feasible successor.
-SIA (Stuck in Active)
-If after a change no alternative route is found within 3 min,the current route ll be marked SIA
-The following databases exist for each type of EIGRP (IP-EIGRP, IPX-EIGRP, AT-EIGRP):
route database;
topology database;
neighbor table.
-EIGRP weight values and metrics (same as IGRP)
K1 (bandwidth), K2 (delay), K3 (reliability), K4 (load), K5 (MTU).
-EIGRP tuning (same as IGRP) - "metric weights ...", "distance ...", "default-metric ..."
-Set the Hello timer per interface for 20sec
"conf t", "int serial 0", "ip hello-interval eigrp 100 20" (for 20 seconds).
-Set the hold-timer per interface for 50sec
"conf t", "int serial 0", "ip hold-time eigrp 100 50" (for 50 seconds).
-Default EIGRP hold timer = 3 x Hello timer. So, it is 180 seconds for slow networks and 15 seconds for all others.
-When you redistribute EIGRP (with VLSM) into IGRP, you need to summarize routes at the classful IP boundaries.
-Configure EIGRP – "conf t", "router eigrp 100", "network 192.168.1.0".
-Disable automatic route summarization at classful boundaries - "no auto-summary".
-Define manually a summary address on an interface –
"conf t", "int serial 0", "ip summary-address eigrp 100
-Example: We have 172.20.128.0/24 and 172.20.192.0/24 –
"ip summary-address eigrp 100 172.20.128.0 255.255.128.0".
-EIGRP supports authentication, while IGRP does not.
-Verify EIGRP route information - "sh ip route", "sh ip route eigrp", "sh ip route 20.0.0.0". Learned EIGRP routes show as "D".
-Routing protocol info:"sh ip eigrp topology","sh ip eigrp topology 192.168.1.0","sh ip protocols","sh ip eigrp interfaces".
-Neighbor info-"sh ip eigrp neighbor","sh ip eigrp neighbor detail".
-Log any changes that happen to a neighbor-
"conf t", "router eigrp 100", "eigrp log-neighbor-changes".
-Debugging EIGRP –
"debug eigrp neighbors", "debug ip eigrp" (protocol info), "debug eigrp packets" (detailed).
-Monitor EIGRP -sh ip eigrp traffic (summary), sh ip eigrp events (full log).
-The neighbor table uses the following timers:
SRTT (smooth round-trip timer), RTO (retransmission timer), and hold-down.
-If there are no feasible successors and only one link to a destination, that link will always be in PASSIVE mode.
-Link-state protocols do NOT use a composite metric (except EIGRP, which is a hybrid and considered distance-vector by Cisco).
-"passive-interface" is used to stop an interface from sending or receiving routing updates.
-Route redistribution may cause ALL of the following problems:
non-optimal route choices;
slow convergence;
routing loops.
-Bydefault,IGRP can use up to 4 links to load-balance.This setting can be manually increased to6.
-NAT Sim
Router#config t
Router(config)#access-list 5 permit 10.30.50.0 0.0.0.255
Router(config)# ip nat inside source list 5 interface s0 overload
Router(config)#ip nat inside source static 10.30.50.5192.168.212.5
Router(config)#int s0
Router(config-if)#ip nat outside
Router(config-if)#exit
Router(config)#int e0
Router(config-if)#ip nat inside
Router(config-if)#
Router#copy running start
Router#show ip nat statistics
Total active translations: 3 (2 static, 1 dynamic; 1 extended)
Outside interfaces:
Ethernet0/0
Inside interfaces:
FastEthernet0/0, FastEthernet0/1
Hits: 2628 Misses: 44
Expired translations: 37
Dynamic mappings:
-- Inside Source
access-list 15 pool NATPOOL refcount 1
pool NATPOOL: netmask 255.255.255.0
start 172.16.1.100 end 172.16.1.150
type generic, total addresses 2, allocated 1 (50%), misses 9
Router#show ip nat translation verbose
Pro Inside global Inside local Outside local Outside global
icmp 172.16.1.100:21776 192.168.1.10:21776 172.18.3.2:21776 172.18.3.2:21776
192.168.3.2:4235
create 00:00:36, use 00:00:36, left 00:00:23, flags: extended
tcp 172.16.1.100:1029 192.168.1.10:1029 172.18.3.2:23 172.18.3.2:23
create 00:00:15, use 00:00:13, left 00:00:46, flags: extended, timing-out
--- 172.16.1.10 192.168.1.15 --- ---
create 1d00h, use 00:23:08, flags: static
--- 172.16.1.11 192.168.1.16 --- ---
create 1d00h, use 00:15:28, flags: static
Router#
-Cisco routers include a simple but useful debug facility for NAT. The basic form of the command is debug ip nat:
Router#debug ip nat
-You can also add the detailed keyword to this command to get more information on each NAT event:
Router#debug ip nat detailed
-Subnetting
Got this off another site but it's useful here also: To remember the subnetting tables all you have to do is start with "4" and double it until you get to "16384" Write them downward on a sheet of paper and when you are done just subtract 2 from each number.
ie: 4 = 2 , 8 = 6 , 16 = 14 , 32 = 30 , 64 = 62
once you have done that all you need to do is reverse the order of all the numbers going back up the sheet (subnets hosts) :(2 62) (6 30) (14 14) (30 6) (62 2) See how the numbers flip flop between each column? My example is for class C but it works for class B just the same. Once you have the subnet/host numbers written out, just remember the following numbers .192, .224, .240, .248, .252
class C:
sub hosts
.192 /26 2 62
.224 /27 6 30
.240 /28 14 14
.248 /29 30 6
.252 /30 62 2
The numbers with a slash (ie /26) are just short hand ways of writing out subnets. They can be really confusing if you are trying to learn subnetting for the first time. Just rember that ip addresses are made up of 32 bit addresses, or /32. These 32 bit addresses are broken down into class A,B, and C. class B are from /18 to /30 and class C go from /26 to /30. The reason the numbers don't go up to /32 are because it goes against the rules of subnetting (according to Cisco), I don't have any other reason why. You need to memorize this stuff!!! When I went to work I jotted notes all over my desk and tool boxes just so I would see it all the time.
Here is the class B example:
(1). start with 4 and double it till 16384: 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384.
(2). subtract 2 from each number: 2, 6, 14, 30, 62, 126, 254, 510, 1022, 2046, 4094, 8190, 16382.
(3). write them downward on a sheet of paper and then write them back up in reverse order:
2 16384
6 8190
14 4094
30 2046
62 1022
126 510
254 254
510 126
1022 62
2046 30
4094 14
8190 6
16382 2
(4) Finally you just have to add the net number to your list... Rember these numbers: .192.0 (/1) .224.0 (/19) .240.0 (/20) .248.0 (/21) .252.0 (/22) .254.0(/23) .255.0 (/24) .255.128 (/25) .255.192 (/26) .255.224 (/27) .255.240 (/28) .255.248 (/29) .255.252. (/30)
-ES-IS Discovery protocol == ip arp like.
-Level0 routing between ES’s and Iss in the same subnet.
-Level1 routing happens between Ises in same area.
-Level2 routing happens between different areas within same domain.
-ISH=Intermediate System Hello.
-ISIS = Dynamic Link State Protocol for the OSI protocol stack, for routingCLNP data for the ISO CLNS environment.
-Integrated ISIS == Implementation of the ISIS protocol for routing multiple N/W protocols.
-Area Border OR Boundary between areas is in the Link instead of routers as in OSPF.
-Lans have DIS: designated intermediate system.
-OSI Addressing : OSI Addresses are called Network Service Access Points (NSAP).
LSP, Hello PDU’s and other routing PDU’s are in OSI format hence every ISIS router requires OSI addresses.
-OSI-Adr:
AFI = Authority and Format Id = I Byte
IDI = Interdomain Id = Upto 10 bytes
IDP = Interdomain Part
When NSEL = 0 NSAP= NET (Network Entitiy Title).
DSP = Domain Specific Part.
Total Length of ISIS address = 8~20 Bytes.
AFI = 49 = Private Addresses.
AFI = 39 = ISO Data Country Code
AFI = 47 = ISO international Code designator.
Customary Length of Area Ids = 3 for Cisco.
OSI Address is assigned to a Device and not an interface.
Cisco IOS fixes system ID as 6 bytes preceding the 1 byte NSAP Selector.
-SNPA = Subnetwork point of attachment = MAC for Lans, VC for X.25 and ATM, the DLCI for Frame and HDLC for HDLC.
-Circuit ID = Interface are uniquely identified by Ckt Id, the Rtr assigns a one octet Ckt.Id to each I/F as follows:in the case lf a Lan I/F the ckt id is tagged to the end of the sys id.
-There are 4 general types of ISIS packets for routing maintenance:
LSP – Used to distr. LS info,
Hello PDU (ESH, ISH, IIH) for maintaining adjacencies,
PSNP used to acknowledge and request LS info,
CSNP Complete sequence number PDU used to distribute complete LS Database. Every 10seconds, elected due to highest priority on interface and then highest Mac addr.
-LSP lifetime counts down from 1200s to 0. LSP Refresh interval = 15 minutes.
-LSP fields = LSPId, PDU Type, Neighbor, Auth, IP Subnets.
-ISIS Metric = Cost = 1~63 Default = 10.
-Hello PDUs= Every 10s. Neighbor Down in 30s.
-OSI Forwarding DB == CLNS routing table.
-PRC= Partial Route Calculation.
-DIS election : On Lan Level1 and Level2 PDUs are used to establish adjacencies.
-On PointToPoint there is a common IIH format PDU and the same one is used for Level1 and Level2. The routers’ interface priority determines the DIS, and if all are equal highest Mac address-ed node is chosen as the DIS.
-Admin Distance for ISIS IP = 115
-ISIS Troubleshooting Commands:
router(config)#clns host
-show isis topology [
list of the least cost paths to all connected routers == system id, metric to destination, next-hop router, interface through which next hop is reached and the SNPA of the next hop.
-show clns route [
-show isis route == shows level 1 route to isis neighbors == system id, next-hop, interface, snpa, metric state
-show clns protocol == ISIS process tag, System ID, Level types, area id, Interfaces using ISIS for routing IP/CLNS, redistribution, CLNS Administrative Distance.
-show clns interface == Routing protocol, circuit-type, Metric,…
-show clns neighbors == system-id, Interface, SNPA, State, Holdtime, Level Type, protocol
-show clns is-neighbors
-show isis database
-which-route
-ISIS Config:
router(config)# router isis [tag]
router(config-router)# net
Give a network entity title to the router
router (config-interface)# ip router isis ==
enables interface for level1 and level2 routing unless the global is-type command was used earlier.
router(config-router)# is-type {level-1 | level-1-2 | level-2-only} ==
enables router for a certain level of routing.
router (config-interface)# isis circuit-type {level-1 | level-1-2 | level-2-only} ==
on an interface force a certain level only behavior.
router (config-interface)# isis metric
default value is 10 and can be 0~63 (defines cost of the link).
router(config-router)# summary-address
router (config-interface)# isis priority
default = 64, range 0~127 (for DIS election)
-BGP Uses TCP port 179
-(BGP)Private AS range = 64512 --> 65535 (RFC 1930)(1024 AS-es)
-BGP Attributes =
WO MD TN == to remember Wyoming, Maryland ,Tennessee (except Wyoming in WY(ignore that for now)) === WellKnown/Optional,Mandatory/Discretionary,Transitive/Non-Transitive
WM=WellKnown Mandatory Required and Recognized by all BGP implementations.
WD = WellKnown Discretionary == Not present in all BGP update messages, if present all routers will act on the information contained.
OT = Optional Transitive == A Rtr might not recognize this attr., so if it does not it marks it as partial and passes it on.
ON = Optional NonTransitive == These are NOT transmitted to BGP Peers. If a router does not recognize them it ignores them.
WM == As-Path, Next-Hop, Origin
WD ==LocalPref, AtomicAggregate
OT == Can be partial; Aggregator, Community
ON == MED, OriginatorID
Cisco Defined = Weight
As-path = a,b,c (a is first hop next as to go to, b is next and so on)
Origin = WM, Lower Preferred == IGP
LocalPref = WD, Higher preferred, def = 100. Local to AS and not sent to EBGP peers.
Community = OT, ability to tag routes that have something in common.
Weight = Cisco Only = 32768 = def for locally originated, others=0, higher preferred. Used for local to this router routing policy only.
Route Selection preference ==> highest Weight, highest Local pref, shortest as-path, lowest origin code, lowest med.
Atomic Aggregate Attribute: WD, indicates to neighbor AS that originator has aggregated routes.
Aggregator = OT = BGP Router ID and AS # of router that performed the route aggregation.
-BGP Rules:
(Learn these 3 rules, the test has these mingled and to understand the fine differences will be great advantage)
Synchronization Rule: A BGP router should not use or advertise to an external (EBGP) neighbor a router learned by IBGP, unless that route is local or is learnt from IGP. Only if all routers in the transit path in the AS are running BGP is it safe to turn synchronization off. Use no synchronization (router config) command to turn synch off, this command will aloow a rtr to use and advert to ebgp neighbor routes learnt by ibgp before learning them from IGP.
Split Horizon Rule: Causes the need for RouteReflectors: Routes Learnt from ibgp WILL not be advertised to ibgp peers.
Next Hop Rule : For IBGP: next hop advertised by EBGP should be carried into IBGP. For EBGP, the next hop is the ip address of the neighbor that sent the update.
-BGP RouterID == same as OSPF RouterID, highest I/F address OR Loopback Address is used.
-BGP Operation:
BGP Message Types == Open, Keepalive, Update, Notification (for errors/special conditions, closes connection immediately).
BGP Peers will exchange full BGP routing tables. Then incremental.
Open Message == Version, my AS, hold time, BGP Id, Optional Params (Authentication).
Update message has info on one path only == Withdrawn Routes, Path Attributes, NLRI (Network Layer Reachability Info) list of prefixes reachable via this path.
BGP Neighbor states == Idle, Connect, Active, OpenSent, OpenConfirm, Established.
In Established === update, keepalive, and notification messages are sent.
Keepalive == 19 bytes/60 seconds, Other messages == 19~4096 bytes. Def Hold time = 180 s.
-Route Selection :
Do not consider unsynched internal paths.
next hop not reachable – do not use.
highest weight
highest localpref
Orig by local router
shortest as-path
lowest origin code IGP < EGP < incomplete
Lowest MED
EBGP over IBGP.
if only internal paths remain, prefer lowest cost next hop.
Else Ebgp select oldest route
Lowest neighbor bgpid.
lowest neighbor ip address.
BGP only chooses a single path per destination.
-BGP Commands:
router(config)# router bgp
router(config-router)# neighbor {
router(config-router)# neighbor {
router(config-router)# no neighbor {
router (config-router)#neighbor
in the above we are indicating that update source on this router is the loopback
router (config-router)#neighbor {
(use the above command in case the ebgp peers are not directly connected) (ttl in above defaults to 255)
router (config-router)#network
the list of network commands must include all networks in your AS that you want to advertise. Note the above network/mask must match exactly an entry in the routing table.
router (config-router)#neighbor {
allows an ibgp peer to receive EBGP paths with next hop set to the IBGP peer.
router (config-router)#no synchronization
disables synchronization.
-BGP route summarization:
router (config-router)#aggregate-address
the networks being aggregated must be in the BGP table.
-Resetting bgp:
Clear ip bgp {* |
-Route Reflectors: BGP split horizon: routes learnt via IBGP are never propagated to other IBGP peers.
-RRs : modify BGP SH by allowing RRs to propagate to IBGP clients routes learned by IBGP, except those learned from the client itself.
-RR Operation:
Update from Client Peer: send update to all non-client peers and to client peers (except originator).
Update from Non-Client IBGP Peer: send update to all client peers.
Update from EBGP peer: send update to all non-client peers and to client peers.
router (config-router)#neighbor
-prefix lists:
better than ACLs as they allow incremental changes and deletion of individual lines.
Router(config)#ip prefix-list
router (config-router)#neighbor {
-To set weight attribute:
router (config-router)#neighbor {
-To set default local preference value to something other than 100
router (config-router)#bgp default local-preference
-BGP and route-maps:
Router bgp 65500
Neighbor 1.1.1.1 route-map toright in
Ip prefix-list customer permit 172.16.0.0/16
Route-map toright permit 10
Match ip address prefix-list customer
Set localpreference 800
-Troubleshooting BGP:
Show ip bgp ===BGP Table Version,local router ID, Network, Next Hop, Metric, LocPrf, Weight, Path
Show ip bgp
Show ip bgp summary === BGP table version, main routing table version, # of network entries, # of paths, Neighbor, version, AS, messages received, messages sent, Table version, input Q, output Q, Up/Down for, State/Prefixes received.
Show ip bgp neighbors === neighbor ip, remote-as, type of link, bgp version, neighbor router id, BGP state, table version, up for, hold time, keepalive interval, received message count, number of notifications, number queued, sent messages, sent notification count, sent queue depth, # of prefixes advertised, last reset and reason for reset.
The above command is also used to show RR clients.
Show ip prefix-list [detail | summary]
-Admin distance table:
Connected And Static to an interface = 0
Static Next hop = 1/Eigrp summary = 5/Ext bgp = 20/Int eigrp = 90/Igrp = 100/Ospf = 110/Is-Is =115/Rip = 120/Egp = 140/Ext eigrp =170/Int bgp = 200/Unknown = 255
-To change the administrative distance of a routing protocol:
Router(config-router)#distance
For a static route we can use:
Router(config)#ip route
-Remember core and edge protocols in reference to redistribution.
If 2 way distribution is unavoidable, use the following techniques to prevent loops and sub-optimal path selection:
Metric modification, admin dist modify, distribution lists.
Methods to control routing information:
Passive I/F, static routes, default routes, null interface, distribute lists, route maps.
Passive I/F: does not participate in routing: RIP & IGRP will listen but not send. OSPF and EIGRP does not listen or send.
Default Seed Metric: (2 ways: 1 default-metric command under routing process OR metric in redistribute command)
Rip,igrp,eigrp = infinity, isis=0, ospf=20(typeE2), but bgp routes are 1(typeE2).
-Redistribution syntax:
router(config-router)#redistribute
level-1, level-1-2 and level-2 in above are for isis routes being redistributed.
Metric in above should be used OR default metric declared for redirtibution.
metric-type value = 1 or and is relevant only when distributing into ospf.
match when redistributing ospf into other routing protocols, enables internal, e1 or e2 routes only into the protocol redistributed into.
weight is only relevant when redistributing into bgp.
Subnets for redistr into ospf used to bring subnets of classful networks in.
-Modifying Default Metric:
router(config-router)#default-metric
use above command to redistribute into all except eigrp and igrp.
router(config-router)#default-metric
bandwidth in kbps/
use the above for igrp and eigrp to set the default metric for redistribution.
-Modifying Administrative distance:
To change the administrative distance of a routing protocol:for eigrp:
router(config-router)#distance eigrp
-Modifying Administrative distance:
To change the administrative distance of a routing protocol:for others except eigrp and bgp:
router(config-router)#distance
-Modifying Administrative distance:
To change the administrative distance of a routing protocolfor bgp
router(config-router)#distance bgp
-Passive interface config ===
Router(config-router)#passive interface
-Default Route
Router(config)#ip route 0.0.0.0 0.0.0.0 s1
RIP will advertise the above automatically as a default route.
-Router(config)#ip default-network
-Filtering
router(config-router)#distribute-list {
router(config-router)#distribute-list {
-Route Maps:Used to control redistribution, implement policy based routing, control NAT and to implement BGP policy.Static routes forward packets based on destination n/w address. PBR routes based on source address or if using extended acls, both source and destination addr.
-router(config)#route-map
-router(config-route-map)#match ip address [
In the above if multiple acl’s are present then any one of them matching will result in a match.
-router(config-route-map)#match length
above matches length of ip packet
-router(config-route-map)#set default-interface
The above default interface is used only if there is no explicit route in the rting table.
-router(config-route-map)#set interface
The above forces the packet to take the first up interface in the list.
-router(config-route-map)#set ip default next-hop
The above default next-hop is used only if there is no explicit route in the rting table.
-router(config-route-map)#set ip next-hop
use the first available next hop in above command
-router(config-route-map)#set ip precedence
Set precedence bits in TOS field by above command
-router(config-route-map)#set ip tos
Set TOS value in TOS field by above command to use the route map
-router(config-if)#ip policy route-map
router(config-if)#ip local policy route-map
To use route-maps on packets generated locally
-Fast switching of PBR:
router(config-if)#ip route-cache policy
Using route-maps in redistribution commands:
router(config-route-map)#match interface (IP)::: distribute any routes that have their next hop out one of the I/F’s specified.
router(config-route-map)#match ip address [
router(config-route-map)#match ip next-hop
router(config-route-map)#match ip route-source
router(config-route-map)#match metric
router(config-route-map)#match route-type (IP)
router(config-route-map)#match tag
router(config-route-map)#set level {level-1 | level-2 |level-1-2 | stub-area | backbone}
router(config-route-map)#set metric
router(config-route-map)#set metric-type {internal | external | type-1 | type-2}
router(config-route-map)#set tag
router(config-router)#redistribute
-NAT
Interface determine which will be inside and outside, selection is similar to Firewalls.
router(config-interface)#ip nat {
-3types will be asked in exam:
Pool to Pool of addresses.
Static Nat.
All inside addresses converted to address of external interface of nat router.
-To nat inside addresses to a pool of addresses on the outside:
router(config)#ip nat pool
router(config)#ip nat inside source list
router(config)#access-list
example:
router(config)#ip nat pool test 172.16.131.2 172.16.131.10 netmask 255.255.255.0
router(config)#ip nat inside source list 7 pool test
router(config)#access-list 7 permit 10.10.10.0 0.0.0.31
-To static nat:
router(config)#ip nat inside source static
router(config)#ip nat inside source static 172.16.131.2 192.168.3.1
-To overload:
router(config)#ip nat inside source list
router(config)#ip nat inside source list 7 interface serial 0 overload
-Nat Terms:
Inside Local Ip Address: Valid ip address on inside.
Inside Global Ip Address: Inside ip address as it is known outside.
Outside Local Ip Address: Valid outside ip address as it is known inside.
Outside Global Ip Address: Valid outside ip address as it is known outside.
-Troubleshoot Nat commands:
Show ip nat translations
Show ip nat statistics
-Using route-maps in NAT:
Ip nat inside source route-map
-EIGRP Terminology:
Neighbor Table === List of adjacent routers is same as neighborship/adjacency database in ospf.
Topology table = all learned routes.
Routing table = best entries from topology table.
Successor = primary route to destination is put in the routing table, multiple equals are allowed or if allowed by the variance command (more on this later).
Feasible successor = backup route to destination, multiples are allowed. S FD > FS’sFD
-Topology table: Has all destinations advertised by neighboring routers. If a neighbor advertises a destination, it must be using that route, topology table also has a metric. The metric used locally is = sum of best metric from neighbor + metric to that neighbor.
-Route selection: eigrp selects primary and backup route and injects them into the topology table(upto 6 per dest), the primary routes are then moved into the routing table.
-Eigrp metric = igrp metric * 256 = 32 bits. Uses protocol number 88.
-Eigrp metrics:
B=Bandwidth,D=Delay,R=Reliability,L=Loading,M=MTU
bldrm == k1,k2,k3,k4,k5; usually k2=k4=k5=0; Then Eigrp metric = (bandwidth + delay)*256.
BW in above is smallest displayed bandwidth divided into 10**7 ( that is kbps value divided into 10 ** 7)Delay in above is 10’s of microseconds = displayed microseconds divided by 10.
-Use the metric weights command to change the k values, not recommended.
-If the tests asks for the actual calculation using k1->k5 walk out of the test.
-Eigrp equation is complex but remember it for the sake of BSCI as follows:
B=Bandwidth,D=Delay,R=Reliability,L=Loading,M=MTU
BLDRM (use this acronym to remember :Build Room), associate constants K1 through K5 to each alphabet sequentially. And usually only K1=K3=1 and all others are zero. So Only Bandwidth and Delay are considered and Metric = Bandwidth + Delay.
The actual equation is:
Metric = K1*B + [(K2*B)/(256-L)] + K3 * D
Use the above if K5=0
If K5 Not=0 Metric = Metric from above *[K5/(R+K4)]
-Eigrp packets:
Hello: used for neighbor discovery, multicasts, ack# in them is 0 means no need to acknowledge.
Update: update is sent to communicate routes that a router has used to converge. Sent as multicast and unicast, sent reliably.
Queries: if no feasible successor on a route that is under computation(active) queries are sent to neighbors as multicast reliably.
Replies: Response to a query, unicast, reliably sent.
ACK: for ack-ing queries, replies, updates.
-If a hello packet from a neighbor is not received, then a topology change is effected, neighbor adjacency is deleted, all topology table entries learnt from that neighbor are removed.
Route being PASSIVE is good, ACTIVE means recomputing route.
-Multicast address used is 224.0.0.10 for Update
-RTP= reliable transport protocol. Supports multicast and unicast.
-Hello interval = 5secs/60secs for multipoint serial and isdn bri.
-Holdtime=time in secs(3*hello) a router will wait to hear from a neighbor before declaring it down.neighborship ok with different values of hello and hold, but k values must be the same.
-Eigrp Routing:
AD = Advertised distance by neighbor.
FD = Feasible Distance = AD + Cost to neighbor.(Successor Route).
Next Hop Backup Path = Feasible Successor. To be a FS AD <= FD of Successor Route.
-Configuring Eigrp:
router(config)#router eigrp
router(config-router)# network
router(config-interface)#bandwidth
the above value is used in metric computation
router(config-interface)#ip eigrp hello-interval
router(config-interface)#ip eigrp hold-time
For summarization use:
router(config-router)#no auto-summary
router(config-interface)#ip summary-address eigrp
-EIGRP summary routes have an admin distance of 5.
-EIGRP and WAN: eigrp will use upto 50% of defined bandwidth on an I/F or a sub-I/F. This number can be adjusted as follows:
router(config-interface)#ip bandwidth-percent eigrp as-number percent on multipoint interfaces eigrp uses the bandwidth statement of the physical interface divided by the number of neighbors to get the bandwidth for each neighbor
-SIA ::: stuck in active is an eigrp phenomena when all outstanding queries are not replied for a route that went active.
router(config-router)#timers active-time [
router(config-router)#eigrp log-neighbor-changes
-router(config-router)#maximum-paths
if variance = x, then if x * current FD >= FD2 then FD2 is also used in load balancing, provided FD2 meets the AD < FD (through current FD)
router(config-rouer)#traffic-share {balanced | min}
-Troubleshooting eigrp:
Show ip eigrp neighbors : shows the ip neighbor table ::: H=handle,I/F=interface through which neighbor can be reached, hold uptime=max time to wait, uptime, SRTT (smooth round trip time=ms for return of ACK), RTO ms to wait before retransmitting,Queue out=packets waiting to be sent, seq num = seq# of last update.
-Show ip eigrp topology shows only successors and feasible successors=active/passive state of routes, # of successors, FD to dest.
-Show ip eigrp topology all-links =shows all routes in topology table.
-Show ip route eigrp = current eigrp entries in routing table.
-Show ip protocols = parameters and current state of routing protocols: eigrp as#, filtering and redistribution information, neighbor and distance information.
-Show ip eigrp traffic = eigrp packets sent and received, statistics of hello, update, queries, replies and ack.
-RIPV2 uses: 224.0.0.9)
-OSPF uses: 224.0.0.5 and 224.0.0.6.
-EIGRP = 224.0.0.10
-Fast Switching Vs Process switching.
-OSPF:Uses protocol number 89.
All ospf routers=224.0.0.5
All DR=224.0.0.6
-Time: Hello Dead
==== ====
Lan 10s 40s (4 times hello interval)
PTP 10s 40s
NBMA 30s 120s
-Hello Packet === RouterID, Hello Interval, Dead Interval, neighbors, AreaID, Router Priority, DR, BDR, Authentication Password, Stub Area Flag.
-Neighborship database===All neighbors with whom bi-directional communication has been established
-Links State DB === Topology DB = All routers in an area: a list of link-state entries of all routers in the area.
-OSPF Header:
Type = Hello, DBD, LS Req, LS Update, LS Ack.
Auth Type = 0 for No Authentication, 1 = Clear Text, 2 = MD5
-Adjacency = relationship between a router and DR, and a router and BDR, means the routers have synchronized Link State databases, meaningful only for routers sharing a common media segment.
-DBD= Describes content of the topological DB.
-Default OSPF priority = 1, 0 not eligible for DR/BDR, higher:more eligible for DR/BDR.
-Highest active IP Address OR Loopback Address = Router ID.
OSPF Startup:
Hello interval = 10s
Init === Router adds neighbor to neighbor list
2 Way === Router receives hello reply with its router id in neighbor’s reply.
EXSTART === DR BDR Election done. Exchange protocol begins.
Exchange state===DR/BDR communicate DBDs with each and every router in the segment.
Loading state===the process of the DR/BDR and router requesting LSA details and noting them in LS database.
FULL STATE=== DR/BDR have synchronized LS Database.
DBD === list of LSA Headers.
LSA header === LS Type, Address of advertising router, LSA Seq #.
LSA aging timer = 30 minutes.
Router reaction on receiving a LSU : if not present OR newer, store and ACK else if older send LSU to sender.
-Link State AdvertisementTypes:
LSA 1: Router Link Entry== Generated by each router for each area it belongs Entry to.
Describes the states of the router’s link into the (O = OSPF)area.(Router Link States)
LSA 2: N/W Link Entry=== Generated by DRs in MA networks. Describes the(O = OSPF)set of routers attached to a particular network(Net Link States)
LSA3 or 4: Summary Link Entry==Type3 LSAs describeroutes to networks (IA-OSPF InterArea)in local area sent to backbone area(Summary Net Link States Type4 LSAs describe reachability and Summary ASB Link to ASBR States)Not Flooded into TS areas.Originated by ABRs flooded into backbone
LSA 5:AS External Link Entry Orig by ASBR, describes routes to (E1=OSPF Ext Type1)destination external to the AS.(E2=OSPF Ext Type2) Not Flooded into Stubby, TS and NSSA (AS External Link State)
LSA 7: NSSA AS External Link Orig by ASBR in NSSA, similar to type 5.Except they are Flooded only within the(N1-OSPF NSSA Ext Type1)NSSA. At ABR’s selected type 7(N2-OSPF NSSA Ext Type2)LSAs are translated into Type5 and flooded into the backbone
-Cost of External routes: Type E1 = external cost + internal cost.
Type E2 = external cost only, is the default
Preference of OSPF routes: O, OIA, OE1, OE2.
-Configuring OSPF:
General OSPF commands:
router(config)#router ospf
router(config-router)#network
show ip ospf interface gives router-id.
router(config-interface)#ip ospf priority
router(config-interface)#ip ospf cost
(default cost of an interface is 10**8/BW in bits per second)
router(config-router)#auto-cost reference-bandwidth
router(config-router)#maximum-paths (changes from 4 to 6 maximum equal cost paths to balance load)
router(config-router)#timers spf
-OSPF in NBMA commands:
router(config-interface)#ip ospf network non-broadcast (default for Point To Multi Point subinterfaces)
router(config-interface)#ip ospf network point-to-multipoint
router(config-interface)#ip ospf network point-to-multipoint nonbroadcast
router(config-interface)#ip ospf network broadcast
router(config-interface)#ip ospf network point-to-point
router(config-router)#neighbor
-OSPF multi-area commands:
Virtual link command:
router(config-router)#area
router(config-router)#network
router(config-router)#area
COST of generated default route is 1 unless following is coded:
router(config-router)#area
router(config-router)#default-information originate [always] [metric
above generates type E2 (default) 0.0.0.0 route.
-Summarization in OSPF:
In the ABR: router(config-router)#area
in the ASBR:router(config-router)#summary-address
-summary route cost = cost of summary route + cost to abr advertising the route.
-External route cost = E1 = Cost of E1 route + cost to ASBR
-E2 = Cost of E2 route only.
-Troubleshooting OSPF:
Show ip ospf database === Router Link States: Link Id, Advertising Router, Age, Seq #, Checksum, Link Count, Network Link States, Summary Network Link States.
Show ip protocols === timers, filters, metrics, networks
Show ip route ospf === show only ospf routes
Show ip ospf interface === router id, timer-intervals, adjacencies, DR, BDR
Show ip ospf neighbor === neighbors, state(2/Way, drother, Full/DR, Full/BDR), DR
Show ip ospf === number of times spf algorithm has been executed
Show ip ospf border-routers = displays internal ospf routing table entries to ABR and ASBRs.
Show ip ospf virtual-links
Show ip ospf
-show ip ospf database ===Displays the OSPF topological database maintained by the router. This command also shows the router ID and OSPF process ID. Use additional keywords to view detailed information in each part of the database.
-show ip ospf interface === Displays details of the OSPF protocol on the interfaces, including the area, state, timers, neighbors, router ID, and network type.
-show ip protocols=== displays parameters about timers, filters, metrics, network, and other information for the entire router.
-show ip ospf neighbor=== is used to display OSPF-neighbor information on a per-interface basis.
-The area stub command is used to define an area as a stub area.Syntax: area area-id stub [no-summary]
The no-summary optional parameter prevents an ABR from sending summary link advertisements into the stub area.
-The summary-address router configuration command is used to create aggregate addresses for OSPF.
Simplified syntax: summary-address address mask
-show ip ospf border-routers=== displays the internal OSPF routing table entries to an area border router (ABR) and the autonomous system boundary router (ASBR). The SPF No in the output is the internal number of the SPF calculation that installs this route.
RouterTestKing# show ip ospf border-routers
OSPF Process 109 internal Routing Table
Destination Next Hop Cost Type Rte Type Area SPF No
160.89.97.53 144.144.1.53 10 ABR INTRA 0.0.0.3 3
160.89.103.51 160.89.96.51 10 ABR INTRA 0.0.0.3 3
160.89.103.52 160.89.96.51 20 ASBR INTER 0.0.0.3 3
160.89.103.52 144.144.1.53 22 ASBR INTER 0.0.0.3 3
-NBMA
There are three different scenarios for NBMA interfaces.
Pure Multipoint Configuration (No Subinterfaces)
Pure Point-to-Point Configuration (each VC on a separate subinterface)
Hybrid Configuration (point-to-point and multipoint subinterfaces)
-Mode:Adjency
NBMA:Manual Configuration DR/BDR elected
Broadcast:Automatic DR/BDR elected
-LSA types
Type 2 LSAs are generated by Designated Routers (DRs) in multiaccess networks. They describe the set of routers attached to a particular network and are flooded within the area that contains the network only.
Type-3 LSAs describe routes to networks within the local area and are sent to the backbone area.
-OSPF Areas
Normal Areas: These areas can either be standard areas or transit (backbone) areas. Standard areas are defined as areas that can accept intra-area, inter-area and external routes.
backbone area is the central area to which all other areas in OSPF connect.
Stub Areas: These areas do not accept routes belonging to external autonomous systems (AS); however, these areas have inter-area and intra-area routes. In order to reach the outside networks, the routers in the stub area use a default route which is injected into the area by the Area Border Router (ABR).
Totally Stub Areas: These areas do not allow routes other than intra-area and the default routes to be propagated within the area. The ABR injects a default route into the area and all the routers belonging to this area use the default route to send any traffic outside the area.
NSSA: This type of area allows the flexibility of importing a few external routes into the area while still trying to retain the stub characteristic. Assume that one of the routers in the stub area is connected to an external AS running a different routing protocol, it now becomes the ASBR, and hence the area can no more be called a stub area. However, if the area is configured as a NSSA, then the ASBR generates a NSSA external link-state advertisement (LSA) (Type-7) which can be flooded throughout the NSSA area. These Type-7 LSA’s are converted into Type-5 LSA’s at the NSSA ABR and flooded throughout the OSPF domain
-IS-IS:Partial sequence number PDUs (PSNPs) are used to request an LSP (or LSPs) and acknowledge receipt of an LSP (or LSPs).
-ConfigureIS-IS
To configure an IS-IS routing process for IP on an interface, use the ip router isis interface configuration command.
Note: To enable IS-IS, perform the following tasks starting in global configuration mode:
Step 1: router isis
Enable IS-IS routing and specify an IS-IS process for IP, which places you in router configuration mode.
Step 2: net network-entity-title
Configure NETs for the routing process; you can specify a name for a NET as well as an address.
Step 3: interface type number
Enter interface configuration mode.
Step 4: ip router isis [tag]
Specify the interfaces that should be actively routing IS-IS.
Reference: Cisco, Configuring Integrated IS-IS
show isis database (detail) command displays the contents of the IS-IS database.
-show isis routes Display the IS-IS Level 1 forwarding table for IS-IS learned routes.
-show clns route Display all of the destinations to which this router knows how to route packets.
-show isis database Display the IS-IS link state database.
-show clns neighbors command displays ES and IS neighbors. The output includes adjacency information.
NSAP: AESA Network Service Access Point (NSAP) ATM Addresses
-There are 3 types of private ATM addresses:
NSAP encoding format for E.164 addresses - The authority and format identifier (AFI) is 45. These addresses are used in establishing ISDN calls by public networks, and they are normally used in public telephony.
Data Country Code (DCC) AESA - The AFI is 39. These addresses are to be used in public networks. For example, the initial domain identifier (IDI) value 0x84.0f identifies the United States.
International Code Designator (ICD) AESA - The AFI is 47. These addresses are used in private organizations, and the ICD field indicates the code set or organization. Cisco uses by default ICD addresses.
-EIGRP: Peer relationships, adjacency, between routers will not be formed if the neighbor resides in a different autonomous system or if the metric-calculation mechanism (K values) is mis-aligned for that link.
-EIGRP: Uses composite metric base on Bandwidth, delay, reliability, load, and MTU.
-Each EIGRP router maintains a neighbor table that lists adjacent routers.
-Neighbor table – Each EIGRP router maintains a neighbor table that lists adjacent routers. This table is comparable to the neighborship (adjacency) database used by OSPF.
-Topology Table – An EIGRP router maintains a topology table for each network protocol configured: IP, IPX, and AppleTalk. All learned routes to a destination are maintained in the topology table.
-Routing table – EIGRP choose the best routes to a destination from the topology table and places these routes in the routing table. The router maintains one routing table for each network protocol.
-Successor – This is the primary route used to reach a destination. Successors are kept in the routing table.
-Feasible successor – This is a neighbor that is downstream with respect to the destination, but it is not the least-cost path and thus is not used for forwarding data. In other words, this is a backup route to the destination. These routes are selected at the same time as successors, but are kept in the topology table.
- Bandwidth Control
The enhanced implementation uses the configured interface bandwidth in order to determine how much EIGRP data to transmit in a given amount of time. By default, EIGRP will limit itself to using no more than 50% of the available bandwidth. The primary benefit of controlling EIGRP's bandwidth usage is to avoid losing EIGRP packets, which could occur when EIGRP generates data faster than the line can absorb it. This is of particular benefit on Frame Relay networks, where the access line bandwidth and the PVC capacity may be very different. A secondary benefit is to allow the network administrator to ensure that some bandwidth remains for passing user data, even when EIGRP is very busy.
- The ip summary-address eigrp command is used to configure a summary aggregate address for a specified interface. Syntax: ip summary-address eigrp autonomous-system-number address mask
- The show ip eigrp traffic command displays the number of Enhanced IGRP (EIGRP) packets sent and received. Also shows hello, updates, queries, replies, and acknowledgments.
-(BGP) The configuration of the multiple connections to the ISPs can be classified depending on the routes that are provided to the AS from the ISPs. Three common ways of the configuring the connections are:
All ISPs pass only default routes to the AS.
All ISPs pass default routes, and selected specific routes (for example, from customers with who the AS exchanges a lot of traffic) to the AS.
All ISPs pass all routes to the AS (A).
-show ip bgp displays the entries in the BGP routing table.
-BGP attributes:
Well-known mandatory attributes:AS-path/Next-hop/Origin
Well-known discretionary attributes:Local preference/Atomic aggregate/
Optional transitive attributes:Aggregator/Communities
Optional non-transitive attribute:Multi-Exit-Discriminator (MED)
-RIP, IGRP, and EIGRP automatically perform summarization at classful boundaries.
-IPv6 Address Type: Unicast - An IPv6 unicast address is an identifier for a single interface, on a single node. A packet that is sent to a unicast address is delivered to the interface identified by that address.
-IPv6 Address Type: Anycast - An anycast address is an address that is assigned to a set of interfaces that typically belong to different nodes. A packet sent to an anycast address is delivered to the closest interface—as defined by the routing protocols in use—identified by the anycast address.
-IPv6 Address Type: Multicast - An IPv6 multicast address is an IPv6 address that has a prefix of FF00::/8 (1111 1111). An IP
- The ip default-network command is used as a method of distributing default route information to other routers. When running RIP, you can create the default route by using the ip default-network command. If the router has a directly connected interface onto the network specified in the ip default-network command, RIP will generate (or source) a default route to its RIP neighbor routers.
-The combination of routing processes on a router or access server consists of the following protocols (with the limits noted):
Up to 30 IGRP routing processes
Up to 30 OSPF routing processes
One RIP routing process
One IS-IS process
One BGP routing process
Up to 30 EGP routing processes
-AS Numbers:
This autonomous system number is a 16-bit number, with a range of 1 to 65535, 64512 - 65535 are reserved for private use.
-Common (Port #) By default, the IP helper-address will forward the following UDP broadcasts:
DNS (port 53), time service (port 37)
Trivial File Transfer Protocol (TFTP) (port 69)
Terminal Access Control Access Control System (TACACS) service (port 49)
NetBIOS name server (port 137)
NetBIOS datagram server (port 138)
Boot Protocol (DHCP/BootP) client and server datagrams (ports 67 and 68)
IEN-116 name service (port 42)
-Administrative Distances:
Connect interface 0/Static Route out an interface 0/Static Route to a next hop 1/EIGRP summary route 5/External BGP 20/Internal EIGRP 90 /IGRP 100/OSPF 110/IS-IS 115/RIP(V1V2)120/ EGP140/External EIGRP 170/Internal BGP 200/Unknown 255
-Multicast Addresses:
224.0.0.5 OSPF hello packet
224.0.0.6 All OSPF DR’s and BDR’s
224.0.0.9 RIP version2
224.0.0.10 EIGRP
-Scalable networks: The key 5 characteristics of Scalable Internetworks are:
Reliable and available,Efficient,Responsive,Adaptable,Accessible and Secure
-The typical three-layer hierarchical:Core,Distribution,Access.
-Core layer: Core layer is responsible to provide an optimal and reliable transport structure. The core layer is the backbone network of the entire internetwork and may include LAN and WAN backbones. Core layer usually consists of fully redundant paths with technologies such as FDDI, Fast Ethernet, and/ or ATM.
-Distribution layer: Distribution layer is responsible to provide access to the internetwork as well as to the servers. Distribution layer sits between the Core layer and the Access layer. The policies such as ACLs are implemented at the distribution layer. Distribution layer is also known as workgroup layer.
-Access layer, provides the users, access to the resources on internetwork.
In real world, a single device may be functioning at both Access layer as well as distribution layer. This is true for even Core layer.
-Network segmentation: The primary purpose of segmentation is to reduce congestion in the network.
-Bridges and switches forwards all broadcasts, which puts extra load on the network. In other words, though bridges divide the network into different collision domains, the broadcast domain remain only one. This increases the overhead on the network.
-Access Control Lists: ACLs are used to permit or deny protocol update traffic, data traffic, and broadcast traffic. Cisco access lists are available for IP, IPX, and AppleTalk protocols.
-Snapshot routing: Snapshot routing can reduce WAN costs, by exchanging the routing table at predefined intervals. The routing tables for the distance vector protocols are kept frozen until the next update occurs. Snapshot routing is used only on distance vector protocols such as IP RIP. Snapshot routing is widely used on ISDN lines.
-Compression over WANs: Cisco IOS supports TCP/IP packet header, as well as data compression. Link compression is also supported, that compresses both header and data information in packets across point to point connections.
-DDR (Dial on Demand Routing): DDR are useful when the traffic flow is not continuous in nature. In DDR, channel is created only after intended traffic is detected by the router, by dialing the destination.
-Switched network access: Switched networks, such as Frame Relay, X.25 can share the bandwidth by establishing virtual circuits.
-Optimization of routing table size: Routing table entries consume bandwidth and processing power. These entries can be reduced by techniques such as route summarization, and incremental updates.
-Snapshot routing builds routing table based on a snapshot of a dynamic routing table available when the network is active. The snapshot routing table is used until another activity occurs on the network, at which time the routing table is rebuilt. No routing information is exchanged when the network is quiet. Snapshot routing can be applied to distance vector protocols such as IP RIP, IGRP, IPX RIP, and RTMP.
-Cisco IOS supports the following queuing methods:
Weighted fair-queuing: This is an automatic queuing method that provides fair bandwidth to all network traffic.
Priority queuing: Here, one particular type of traffic is given priority over all other types of traffic. Thus this particular traffic, for which priority is given, is assured of bandwidth. All other types of traffic do not have assured bandwidth.
Custom queuing: Here, each traffic type gets a pre-allocated bandwidth. Certain types of traffic can be allocated higher bandwidth depending on the requirement.
-RIP (and IGRP) always summarizes routing information by major network numbers. This is called classful routing.
-IP RIP based networks send the complete routing table during update. The default update interval is 30 seconds.
-RIP version 2 is a classless routing protocol, where as RIP version 1 (RIP 1) is a classful routing protocol. The disadvantage of classfull routing is that some address space may be wasted. In classless routing, routing protocols exchange the subnet mask information during periodic routing updates. This allows variable subnet masks to be used in the network, allowing better use of address space. For example, a WAN link may need only two IP addresses. If you use classless routing protocol with, say 6 bits for subnetting (62-2 subnets), only 2 subnet addresses are utilized and the remaining become wasted. On the other hand, if you use classless routing protocol, Variable Length Subnet Mask (VLSM) can be used within the network, giving only 2 valid addresses for the WAN link, thus saving valuable address space. (If you are using IP addresses, address space involves IP addresses).
-Metric limit for link-state protocols is 65,533.
-Convergence is the term used to describe the state at which all the internetworking devices, running specific routing protocol, are having the same information about the internetwork in their routing tables. The time it takes to arrive at common view of the internetwork is called Convergence Time.
-Distance vector protocol depends only on Hop count to determine the nearest next hop for forwarding a packet. One major disadvantage is that this may not always represent the best route. For example, if you have a destination connected through two hops via T1 lines, and if the same destination is also connected through a single hop through a 64KBPS line, RIP assumes that the link through 64KBPS is the best path!
-Distance Vector (Number of hops) - Distance vector routing determines the direction (vector) and distance to any link in the internetwork. Typically, the smaller the metric, the better the path. EX: Examples of distance vector protocols are RIP and IGRP. Distance vector routing is useful for smaller networks. The limitation is that any route which is greater than 15 hops is considered unreachable. One important thing that differentiates distance vector with Link state is that distance vector listens to second hand information to learn routing tables whereas, Link state builds its routing tables from first hand information. Distance vector algorithms call for each router to send its entire routing table to each of its adjacent neighbors.
-Link State Routing: Link State algorithms are also known as Shortest Path First (SPF) algorithms. SPF recreates the exact topology of the entire network for route computation by listening at the first hand information. Link State takes bandwidth into account using a cost metric. Link State protocols only send updates when a change occurs, which makes them more attractive for larger networks. Bandwidth and delay are the most heavily weighed parts of the metric when using Link-State protocols. EX: OSPF and NLSP.
-Benefits of Link State protocols:
Allows for a larger scalable network
Reduces convergence time
Allows “super netting”
-Balanced Hybrid - Balanced Hybrid combines some aspects of Link State and Distance Vector routing protocols. Balanced Hybrid uses distance vectors with more accurate metrics to determine the best paths to destination networks. EX: EIGRP.
-13. The default administrative distances are as below:
Directly connected 0/Static route 1/EIGRP Summary 5/External BGP 20/EIGRP 90/IGRP 100/OSPF 110/ISIS 115/RIP 120/Unreachable 255
-IGRP, EIGRP: IGRP and EIGRP are proprietary of Cisco. These two protocols use composite metric to determine the best path to a remote network.
-IGRP (as well as EIGRP) use the following components as metrics:
Delay: Calculated by adding up the delay along the path to the next router.
Reliability: This is representative of how many errors are occurring on the interface. The best reliability value is 255. A value of 128 represents only 50% reliability.
Load: Load metric also has a range from 1 to 255. If a serial link is being operated at 50% capacity, the load value is 255X0.5 or 12.5. Lower load value is better.
MTU: Stands for Maximum Transmit Unit size, in bytes. Ethernet and serial interface has a default MTU of 1500. Larger MTU size means that the link is more efficient.
Bandwidth: The bandwidth is specified in Kbps. Larger the bandwidth, better the link.
EIGRP (as well as IGRP) uses Bandwidth and Delay as default criteria to determine the best path.
“show ip route eigrp”: Displays the current EIGRP entries in the routing table.
“Show ip eigrp traffic”: This command can be used to learn the number of EIGRP packets sent and received.
-The neighbor table in EIGRP include the following fields:
Neighbor address: This is the network layer address of the neighbor router.
Queue: This represents the number of packets waiting in queue to be sent.
Smooth Round Trip Time (SRTT): This represents the average time it takes to send and receive packets from a neighbor. This timer is used to determine the retransmit interval (RTO).
-Hold Time: This is the period of time that a router will wait for a response from a neighbor. If there is no response at the end of this time period, the link is considered unavailable.
-Hello packets:
The types of router protocols that use "Hello" packets are EIGRP, IS-IS, and OSPF.
-Cisco IOS commands:
Show IP protocol: This command will show information on RIP timers including routing update timer (30sec default), hold-down timer (default 180sec). It also displays the number of seconds due for next update (this is fraction of update timer). This command also gives the network number for which IP RIP is enabled, Gateway, and the default metric.
Show IP route: This command will display the IP routing table entries. In addition, it displays the Gateway of last resort (if one is assigned). It also displays the codes used for various types of routes. Some of the important codes are:
C: directly connected/S: Statically connected/I : IGRP/R : RIP
-show IP interface: This command shows you interface-wise information such as IP address assigned to each interface, whether the interface is up, MTU etc.
-Debug IP RIP: Debug IP RIP will turn the RIP debugging ON. This will display a continuous list of routing updates as they are sent and received. This leads to lot of overhead, which is the reason that you use "undebug ip rip" to turn-off debugging as soon as you finish with debugging.
-The command "no router rip" is used for removing all rip entries from the router.
-The command “clear ip bgp *”:clears all the entries from the BGP routing table and reset BGP sessions. This command is used after every configuration change to ensure that the change is activated and that peer routers are informed.
-The command “clear ip bgp ” ex: clear ip bgp 172.31.0.0 removes the specified network from the BGP table.
-For IGRP routing, you need to provide the AS (Autonomous System) number in the command. Routers need AS number to exchange routing information. Routers belonging to same AS exchange routing information.
-IGRP:
IGRP update packet is sent every 90 seconds by default. This is 30 Sec for RIP.
By giving the command "show ip route igrp", we can see the routes found by IGRP. A route discovered by IGRP is denoted by letter "I" before start of the entry.
-The following three types of routes are recognized by IGRP:
Interior: Interior routes are those that are directly connected to a router interface.
System: Routes advertised by other IGRP neighbors within the same autonomous system (AS).
Exterior: These are the routes learned from a different Autonomous System number (ASN).
-Private Internet addresses:
The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space your use for private networks:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
-There are three ways a router learns how to forward a packet:
Static Routes - Configured by the administrator manually. The administrator must also update the table manually every time a change to the network takes place. Static routes are commonly used when routing from a network to a stub (a network with a single route) network.
The command is
ip route network mask address/interface [distance]
ex: ip route 165.44.34.0 255.255.255.0 165.44.56.5
Here, 165.44.34.0 is the destination network or subnet
255.255.255.0 is the subnet mask
165.44.56.5 is the default gateway.
Default Routes - The default route (gateway of last resort) is used when a route is not known or is infeasible. The command is
ip route 0.0.0.0 0.0.0.0 165.44.56.5
The default gateway is set to 165.44.56.5
Dynamic Routes - As soon as dynamic routing is enabled, the routing tables are automatically updated. Dynamic routing uses broadcasts and multicasts to communicate with other routers. Each route entry includes a subnet number, the interface out to that subnet, and the IP address of the next router that should receive the packet. The commands to enable rip are:
router rip network
-OSPF:
An OSPF area is a collection of networks and routers that has the same area identification.
-The following are the types of OSPF routers:
Internal router: An internal router has all the interfaces in the same area. All internal routers maintain same link state databases.
Backbone router: Backbone routers reside on the perimeter of Area 0, with at least one interface connected to backbone (Area 0).
Area Border Router (ABR): ABRs are routers that have interfaces attached to multiple areas. It may be noted that these routers maintain separate link-state databases for each area that they are connected. They are capable of routing traffic destined for or arriving from other areas.
Autonomous System Boundary Router (ASBR): This router has at least one interface to the external network (another autonomous system). This autonomous network can be non-OSPF. ASBRs are capable of route redistribution. Redistribution is the ability of a router to import routing information from non-OSPF networks, and distribute the same in OSPF network for which it is responsible and visa versa.
-LSA Types:
LSA Type 1: Router link entry, generated by all routers for each area to which it belongs. These are flooded within a particular area.
LSA Type 2: Network link entry, generated by designated router (DRs). Type 2 LSAs are advertised only to routers that are in the area containing the specific network.
LSA Type 3 and Type 4: Summary link entry, these LSAs are generated by area border routers (ABRs). These are sent to all routers within an area. These entries describe the links between the ABR and the internal routers of an area. These entries are flooded throughout the backbone area and to the other ABRs.
LSA Type 5: Autonomous System External Link Entry, these are originated by ASBR. These entries describe routes to destinations external to the autonomous system. These LSAs are flooded throughout the OSPF autonomous system except for stubby and totally stubby areas.
-The sequence of steps followed in OSPF operation are as below:
Establish router adjacencies
Elect DR and BDR
Discover Routes
Choose appropriate routes for use
Maintain routing information.
-The command "show ip ospf database" displays the contents of the topological database maintained by the router. This command also displays router id and the ospf process id.
-“show ip ospf interface” can be used to check whether the interfaces have been configured properly. The command also gives the timer intervals, including hello intervals, and neighbor adjacencies.
-OSPF keeps up to six equal-cost route entries in the routing table for load balancing.
-OSPF uses Dijkstra algorithm to calculate lowest cost route. The algorithm adds up the total costs between the local router and the each destination network. The lowest cost route is the preferred route when there are multiple paths to a given destination.
-OSPF has the following advantages over Distance Vector protocols such as RIP:
Faster convergence: OSPF network converges faster because routing changes are flooded immediately and computed in parallel.
Support for VLSM: OSPF supports VLSM. However, please note that RIP version2 also supports VLSM.
Network Reachability: RIP networks are limited to 15 hops. On the other hand, OSPF has practically no reachability limitation.
Metric: RIP uses only hop count for making routing decisions. This may lead to poor efficiency in some cases. For example, that a route is nearer but is very slow compared to another route with plenty of bandwidth available but few more hops away. OSPF uses "cost" metric to choose best path. Cisco uses "bandwidth" as metric to choose best route.
Efficiency: RIP uses routing updates every 30 seconds. OSPF multicasts link-state updates and sends the updates only when there is a change in the network status
-The path cost in OSPF network is calculated using bandwidth. The formula used is [10 <8> divided by Bandwidth]. For example, the cost of a 56kbps serial link is 1785. The default cost of a 10mbps Ethernet is 10.
-When a serial line is configured on a Cisco router, the default bandwidth is 1.544Mbps. If the line is slower speed, "bandwidth" command can be used to specify the real link speed. The cost of the link will then automatically correspond to the changed value.
-You must manually configure a static route to configure DDR (Dial on Demand Routing). DDR is widely used as a backup route, in case of failure of primary link.
-Route Summarization:
Route summarization is calculated as below:
Step 1:
Take the first IP: 172.24.54.0/24: 172.24. 0 0 1 1 0 1 1 0.0
Take the second IP: 172.24.53.0/24: 172.24. 0 0 1 1 0 1 0 1.0
Note that we are not really concerned about the octets that have equal decimal values. This is because they don’t come into play while calculating summarization route, in this case.
Step 2:
Count the number of bits in the third octet that are aligned (or lined up) with same values. In this case 6 bits are lined up in the third octet. The summarization route is calculated by adding this number (6) to the octets preceding the third (first and second octets).
Therefore, the number of bits in the summarized route is 8+8+6 = 22
Step 3:
Calculate the decimal equivalent for third octet with 6 bits as given in the matching binary. That is 0 0 1 1 0 1 x x. Note x is because it corresponds to non matching binary number. It is equal to 128*0 + 64*0 + 32*1 + 16*1 + 8*0 + 4*1 or 32+16+4 or 52.
Therefore, the summarized route is:172.24.52.0/22
-While evolving a network addressing scheme for an organization, you need to assign a different network number for each subnet. Also, you need to set aside one network number for each WAN connection.
-Representing a subnet mask with / notation:
Consider an IP subnet mask of 255.255.255.128. The same be represented as /25. This is arrived at, by taking the binary equivalent of 255.255.255.128 (= 11111111.11111111.11111111.10000000). Count the number of ones’, there are 25 of them. Therefore, the same can be written as /25.
-The following are link state routing protocols:IPX NLSP/IS-IS/IP-OSPF
-OSPF LSA, LSR, and LSUs:
LSA (Link State Advertisement): LSAs are included in the database description packets (DDPs or DBDs). LSA entries include link-state type, the address of the advertising router, the cost of the link, and the sequence number.
LSR ( Link State Request): When a slave router receives a DDP (Database Description Packet), it sends an LSAck packet. Then it compares the received information with its own information. If the DDP has more recent information, the slave router sends a link-state request (LSR) to the master router.
LSU ( Link State Update): LSU packet is sent in response to LSR (Link-State Request) packet that is sent from a slave router to a master router. LSU contains complete information about the requested entry.
-In an OSPF environment,
A DDP (Data Description Packet) is used during the exchange protocol and includes summary information about link-state entries.
A hello packet is used during the hello process and includes information that enables routers to establish neighbor relationship.
-An internal router is a router that resides within an area.
-Important features of stub area are:
A stub area reduces the size of the link-state database to be maintained in an area, which in turn result in less overhead in terms of memory capacity, computational power, and convergence time.
The routing in Stub and totally Stubby areas is based on default gateway. A default route (0.0.0.0) need to be configured to route traffic outside the area.
The stub areas suited for Hub-Spoke topology.
Area 0 is not configured as Stubby or totally Stubby. This is because stub areas are configured mainly to avoid carrying external routes, whereas Area 0 carries external routes.
-EIGRP:
Some of the important terms used in Enhanced IGRP are:
Successor: A route (or routes) selected as the primary route(s) used to transport packets to reach destination. Note that successor entries are kept in the routing table of the router.
Feasible successor: A route (or routes) selected as backup route(s) used to transport packets to reach destination. Note that feasible successor entries are kept in the topology table of a router. There can be up to 6 (six) feasible successors for IOS version 11.0 or later. The default is 4 feasible successors.
DUAL (Diffusing Update Algorithm): Enhanced IGRP uses DUAL algorithm to calculate the best route to a destination.
-Internet Assigned Numbers Authority (IANA) is responsible for assigning BGP autonomous system numbers.
-The assignable BGP autonomous system numbers are from 1 to 65,535 (I.e. 65,535 in total). Autonomous system numbers are of 16 bit length. There are 2 ^ 16 = 65536 -1 possible ASNs. ASN of all 0s is not assigned. Out of this, the Internet Assigned Numbers Authority (IANA) has reserved the following block of AS numbers for private use: 64512 through 65535.
-External BGP (eBGP) is used to establish session and exchange route information between two or more autonomous systems. Internal BGP (iBGP) is used by routers that belong to the same Autonomous System (AS).
-Routers running BGP in an AS use network Policy to choose the best path. Metrics are not used in BGP. Remember that Internet is made of autonomous systems (AS) that are connected together based on Policies specific to each AS. Also, AS numbers (ASN) are assigned by AINA and are unique over the Internet. In an internet (not big I) the ASNs can be assigned by the corporation itself that is implementing internet.
-The following are the four possible message types in a BGP header:
Type 1: OPEN message - This is the first message sent after TCP session is established.
Type 2: UPDATE message - An UPDATE message contains a new route or a route to be withdrawn or both. Note that only one new route can be advertised with one UPDATE message.
Type 3: NOTIFICATION message - this message is sent if an error occurs during a BGP session. This message can be used to troubleshoot the problem.
Type 4: KEEPALIVE message - KEEPALIVE message is used to confirm that the connection between the neighboring routers is still active.
-Command to set the router RouterA to autonomous system number 1340:
The correct syntax for the command is:
RouterA(config)#router bgp 1340
where 1340 is the AS number which can have a value between 1 and 65535 in an internetwork.
-Port number 179 is used to establish a session between two routers running BGP.
-Well-Known mandatory attributes must appear in all BGP update messages. The well-known mandatory messages are:
AS_PATH: BGP messages carry the sequence of AS numbers indicating the complete path a message has traversed.
NEXT_HOP: This attribute indicates the IP address of the next-hop destination router.
ORIGIN: This attribute tells the receiving BGP router, the BGP type of the original source of the NLRI information.
-Any two routers that have formed a TCP connection in order to exchange BGP routing information are called peers, or neighbors. BGP peers initially exchange their full BGP routing tables. After this exchange, routing table changes are sent as incremental updates. BGP keeps a version number of the BGP table, which should be the same for all of its BGP peers. The version number changes whenever BGP updates the table, likely due to routing information changes. Keep alive packets are sent to ensure that the connection is alive between the BGP peers.
-show ip bgp neighbors
This is a very useful command in troubleshooting BGP connections. When the connection is established, the peer/ neighbor router exchanges BGP information. If a TCP connection (BGP session) is not established, a BGP router can not exchange any BGP routing information with the adjacent router.
-Few recommended scenarios, where you use BGP are:
Connect two or more ISPs
The traffic flow out of your network need to be managed to suit the requirements of your organization.
The traffic need to be sent through one AS to get to another AS.
-The weight attribute in BGP has a range from 0 to 65535. This attribute can be set using "neighbor" command. The default value is 32,768.
-Various debug commands useful in troubleshooting bgp are:
Debug ip bgp events: Displays all bgp events as they occur.
Debug ip bgp dampening: Displays bgp dampening events as they occur.
Debug ip bgp keepalives: Displays all events related to bgp keepalive packets.
Debug ip bgp updates: Displays information on all bgp update packets.
-Prefix lists (filtering) are available only in Cisco IOS versions 12.0 and later.
-Characteristics of Prefix lists:
These are used for filtering BGP routing updates, so that certain path policy is applied.
Prefix lists put less load on the processor compared to Access lists.
Prefix lists are easier to configure and implement.
Prefix lists are read one line at a time.
There is an implicit deny all at the bottom of the Prefix list. However, if the prefix list is empty, there will be an implicit permit any.
The statement with the smallest sequence numbers is read first.
Sequence values are generated in increments of 5. The first sequence value generated in a prefix list would be 5, then 10, then 15, and so on.
-The following are a few examples of how a prefix list can be used (while configuring BGP policies to filter route updates):
To deny the default route 0.0.0.0/0:
ip prefix-list mylist1 deny 0.0.0.0/0
or
To permit the prefix 20.0.0.0/8:
ip prefix-list mylist1 permit 20.0.0.0/8
-A stub AS is a single-homed network with only one entry and exit point. This type of AS can be connected to the external world through the use of a statically configured route.
-Transit AS: Data from one AS need to reach a remote AS, then it has to travel through intermediate AS. The AS or Autonomous Systems which carry the data from one AS to another AS is (are) called Transit AS (es).
-eBGP: External BGP is used between two or more Autonomous Systems.
iBGP: Internal BGP is used within an AS.
-In BGP, to disable automatic summarization of subnet routes into network level routes use the command:”no auto-summary”
To enable automatic summarization of subnet routes into network level routes use the command:
“auto-summary”
Note that by default, auto-summary is enabled.
-BGP is an exterior routing protocol, whereas RIP, IGRP, and OSPF are all Interior routing protocols (IRP). Interior routing protocols run inside a company's network and can't run on the Internet. The Internet consists of numerous autonomous systems (AS) which are connected by Exterior Routing protocols like BGP.
-BGP commands:Suppose, RouterA and RouterB are running iBGP. The correct syntax for establishing neighbor relationship is:
router bgp 100
neighbor 175.23.1.2 remote-as 100
iBGP routers don't have to be directly connected, as long as there is some IGP running, that allows the two neighbors to reach one another. If two routers belong to the same AS, then they run iBGP, whereas, if they belong to different ASs, they need to run eBGP.
-The output is that of "show ip bgp summary". It contains the following among other details:
BGP router identifier: Router identifier specified by the bgp router-id command, loop back address, or lowest IP address.
BGP table version: Internal version number of BGP database.
Main routing table version: Last version of BGP database that was injected into main routing table.
Neighbor: IP address of a neighbor.
V: BGP version number spoken to that neighbor.
AS: Autonomous system.
-To specify the networks to be advertised by the Border Gateway Protocol (BGP) use the network command.
To remove an entry, use the no network form of this command.
“network network-number [mask network-mask]”
To remove,
“no network network-number [mask network-mask]”
-To distribute Border Gateway Protocol (BGP) neighbor information as specified in a prefix list, use the neighbor prefix-list command in address family or router configuration mode.
The following router configuration mode example applies the prefix list named mylist1 to outgoing advertisements from the neighbor 192.10.0.0:
!
router bgp 100
network 120.101.0.0
neighbor 192.10.0.0 prefix-list mylist1 out
-To distribute Border Gateway Protocol (BGP) neighbor information as specified in an access list, use the neighbor distribute-list command in address family or router configuration mode.
-Route maps are used with BGP to control and modify routing information and to define the conditions by which routes are redistributed between Autonomous Systems. The format of a route map is as follows:
“route-map map-name [[permit | deny] | [sequence-number]]”
The map-name is a name that identifies the route map, and the sequence number indicates the position that an instance of the route map is to have in relation to other instances of the same route map.
-Some of the terms used commonly with route reflectors in BGP are:
Route reflector: It is a router that is configured to advertise the routes that are learned from iBGP neighbors.
Client: A router that shares information with the router configured as route reflector.
Cluster: The set of all routers configured as route reflectors and clients.
Cluster ID: If there are one route reflector in a cluster, then, cluster ID is used to identify the route reflectors uniquely in the specified cluster.
-Do not apply both a neighbor distribute-list and a neighbor prefix-list command to a neighbor in any given direction (inbound or outbound) on a BGP router. These two commands are mutually exclusive, and only one command (neighbor prefix-list or neighbor distribute-list) can be applied to each inbound or outbound direction.
-BGP peer groups:
A BGP peer group significantly reduces the overhead of configuring policies on every individual BGP neighbor in an AS. When a peer group is created, policies are assigned to the name of the peer group itself and not to the individual neighbors.
Route maps, distribution lists, and filter lists usually set update policies.
Members of the peer group can be configured to override the configuration options for incoming updates, but not to the outgoing updates.
-The command (BGP)
neighbor
is used to add a neighbor to a peer-group.
The complete commands to add a neighbor are:
!
RouterA(config)#router bgp 100
RouterA(config-router)#neighbor mygroup peer-group
RouterA(config-router)#neighbor 1.1.1.1 peer-group mygroup
!
-When a route reflector in a BGP AS receives an update, it takes the following actions, depending on the type of peer that sent the update:
If the update is from a non-client peer : It sends the update to all clients in the cluster.
If the update is from a client peer: It sends the update to all nonclient peers and to all client peers.
If the update is from eBGP peer: It sends the update to all nonclient peers and to all client peers.
-The following are well known communities in BGP:
Internet: All routers belong to this community by default. Advertises the route to internet community.
No-export: This indicates not to advertise a route to eBGP
No-advertise: This indicates not to advertise a router to peers.
The community attribute in BGP can contain a value in the range 0 to 4294967200.
-The correct syntax to configure a router as a BGP route reflector is:
RouterA(config-router)#neighbor