ISIS show Commands

After all ISs are configured, several show commands can verify connectivity when using IS-IS. These commands are as follows:

• show isis database

• show isis topology

• show clns is-neighbors

• show ip protocols

All the configurations in this section refer to Figure 8-10.

The output of these commands is displayed throughout this section. IS-IS routes are marked with an i. L1 and L2 mark L1 and L2 routes. IS-IS routes use 115 as an administrative distance in Cisco routers. Example 8-22 displays the routing table on Router 8.

Example 8-22 Router 8 Routing Table

Router8#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 192.16.100.18 to network 0.0.0.0

172.16.0.0/28 is subnetted, 1 subnets C 172.16.3.0 is directly connected, TokenRing0

i L2 10.0.0.0/8 [115/134] via 192.16.100.18, Ethernet0

192.16.100.0/24 is variably subnetted, 6 subnets, 3 masks i L2 192.16.100.240/30 [115/20] via 192.16.100.18, Ethernet0 i L2 192.16.100.32/28 [115/60] via 192.16.100.18, Ethernet0 C 192.16.100.16/28 is directly connected, Ethernet0

C 192.16.100.1/32 is directly connected, Loopback0

i L2 192.16.100.2/32 [115/15] via 192.16.100.18, Ethernet0 i L2 192.16.100.3/32 [115/60] via 192.16.100.18, Ethernet0 i*L2 0.0.0.0/0 [115/10] via 192.16.100.18, Ethernet0

Router 8's only connection to another IS is through an L2-only circuit, so only L2 routes are in the table. The redistributed route, 10.0.0.0, is shown as a L2 route, and the default route that was originated on Router 9 is also shown.

The show isis database command shows the L1 and L2 ISs listed in the database, as displayed in Example 8-23.

Example 8-23 Router 8IS-IS Database

Router8#show isis database

IS-IS Level-1 Link

State Database:

LSPID

LSP Seq Num

LSP Checksum

LSP Holdtime

ATT/P/OL

Router8.00-00

* 0x00000004

0x0DB6

1076

0/0/0

IS-IS Level-2 Link

State Database:

LSPID

LSP Seq Num

LSP Checksum

LSP Holdtime

ATT/P/OL

Router10.00-00

0x00000004

0x2F63

782

0/0/0

Router9.00-00

0x000000DE

0xDBD2

784

0/0/0

Router8.00-00

* 0x000000D5

0xA508

835

0/0/0

Router8.01-00

* 0x000000D3

0xA060

620

0/0/0

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

Router8#show isis topology

IS-IS paths

to

level-1

routers

System Id

Metric

Next-Hop

Interface

SNPA

Router8

IS-IS paths

to

level-2

routers

System Id

Metric

Next-Hop

Interface

SNPA

Router10

20

Router9

Et0

00e0.

b064

6e47

Router9

10

Router9

Et0

00e0.

b064

6e47

Router8

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

Router9>show

clns is-neighbors

System Id

Interface State

Type

Priority

Circuit

Id

Format

Router10

Se0 Up

L1L2

0 /0

00

Phase V

Router8

Et0 Up

L2

64

Router8

01

Phase V

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

Router10#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 192.16.100.

241 to network 0.0.0.0

i L1

10.0.0

.0/8 [115/164] via 192.16.

100.241, Serial0

192.16

.100.0/24 is variably subnetted, 6 subnets, 3 masks

C

192

.16.100.240/30 is directly

connected, Serial0

C

192

.16.100.32/28 is directly

connected, Ethernet0

i L2

192

.16.100.16/28 [115/20] via

192.16.100.241, Serial0

i L2

192

.16.100.1/32 [115/25] via

192.16.100.241, Serial0

i L2

192

.16.100.2/32 [115/15] via

192.16.100.241, Serial0

C

192

.16.100.3/32 is directly connected, Loopback0

i*L2

0.0.0.

0/0 [115/10] via 192.16.100.241, Serial0

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.

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  • martha
    How to show isis cost command?
    1 month ago

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