ISIS show Commands

Router 8 is listed as an L1 and an L2 IS. The Router 8 loopback has the default circuit type of L1 and L2. Therefore, the IS is both an L1 and L2 IS.

Two entries for Router 8 are in the L2 link-state database. This is because Router 8 is the DIS for the Ethernet network. The entry, Router8.00-00, represents the actual IS, while the entry, Router8.01-00, represents the pseudonode that is created by the DIS for the multiaccess network.

The show isis topology command lists the metric to reach other ISs in the network. Example 8-24 shows the output of the command issued on Router 8.

Example 8-24 Router 8 IS-IS Topology Table

The metric to reach Router 10 is 20. The metric on the serial link between Router 9 and Router 10 was changed for L1 routes only; therefore, the default metric, 10, is still used for L2 routes for a total path cost from Router 8 to Router 10 of 20.

For Router 9, the show clns is-neighbors command shows the adjacent ISs, the IS type, priority, and state, as displayed in Example 8-25.

Example 8-25 IS Neighbor Display on Router 9

Router 9 is adjacent to two ISs, Router 10 and Router 8. Both L1 and L2 adjacencies have been formed on the link between Router 9 and Router 10. The link between Router 9 and Router 8 is L2 only. The Router 9 priority on the Ethernet interface is 64. The Circuit ID is a single-byte numerical identifier that uniquely identifies the IS-IS interface. The Circuit Id associated with Router 8 is Router8.01. This is the pseudonode identifier, which consists of the DIS system name concatenated with the Circuit Id.

For Router 9, the show ip route command shows all L1 and L2 routes for the network. The show ip protocols command displays the protocol configuration on Router 9. Example 8-26 displays the results of the commands show ip route, show ip protocols, show isis topology, and show isis database on Router 9.

Example 8-26 Router 9 Routing Table, Protocol Configuration, Topology, and Database

Router9#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route

Gateway of last resort is not set

S 10.0.0.0/8 is directly connected, Null0

192.16.100.0/24 is variably subnetted, 6 subnets, 3 masks C 192.16.100.240/30 is directly connected, Serial0

i L1 192.16.100.32/28 [115/50] via 192.16.100.242, Serial0 C 192.16.100.16/28 is directly connected, Ethernet0

i L2 192.16.100.1/32 [115/15] via 192.16.100.20, Ethernet0 C 192.16.100.2/32 is directly connected, Loopback0

i L1 192.16.100.3/32 [115/50] via 192.16.100.242, Serial0

Router9#show ip protocols Routing Protocol is "isis cisco"

Invalid after 0 seconds, hold down 0, flushed after 0

continues

Example 8-26 Router 9 Routing Table, Protocol Configuration, Topology, and Database (Continued)

Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Redistributing: static, isis Address Summarization: None

Routing for Networks: Loopback0 Serial0 Ethernet0 Routing Information Sources:

Gateway Distance Last Update

192.16.100.1 115 00:04:02

192.16.100.3 115 00:04:02

Distance: (default is 115)

Router9#show isis topology

IS-IS paths to level-1 routers

System Id Metric Next-Hop Interface SNPA

Router10 40 Router10 Se0 *HDLC*

Router9 --

IS-IS paths to level-2 routers

System Id Metric Next-Hop

Router10 10 Router10

Router9 --

Router8 10 Router8

Router9#

Interface Se0

SNPA *HDLC*

00e0.b064.6e49

Router9#show isis database

IS-IS Level-1 Link LSPID

Router10.00-00 Router9.00-00 IS-IS Level-2 Link LSPID

Router10.00-00 Router9.00-00 Router8.00-00 Router8.01-00

State Database:

LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL

0x000000D6 0x4E0C 820 0/0/0

* 0x000000DE 0xF943 1017 0/0/0 State Database:

LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL

0x00000004 0x2F63 1012 0/0/0

* 0x000000DE 0xDBD2 1014 0/0/0 0x000000D5 0xA508 1062 0/0/0 0x000000D3 0xA060 848 0/0/0

The routing table for Router 9 shows L1 routes learned from Router 10 and L2 routes learned from Router 8.

The output from the show ip protocols command displays information about the configured IS-IS protocol and its tag value, cisco. The process redistributes static routes and runs on interfaces Loopback 0, Ethernet 0, and Serial 0. The IS is learning routes from 192.16.100.1 (Router 8) and 192.16.100.3 (Router 10).

The topology table shows the L1 and L2 metrics to Router 10. The L1 metric is 40, as configured on the IS. The L2 metric is the default value of 10.

The IS-IS database shows that Router 9 and Router 10 are L1/L2 ISs.

The Router 10 IP routing table is displayed in Example 8-27.

Example 8-27 Router 10 IP Routing Table

The entry for the redistributed route 10.0.0.0 is redistributed as both L1 and L2. Router 8 displayed the route as an L2 route. Here, it is an L1 route even though Router 9 advertises both L1 routes and L2 routes. If multiple paths exist to the same destination, as with 10.0.0.0 (path 1 is L1, path 2 is L2), the L1 path is preferred over the L2 path.

Continue reading here: IBGP

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