ISIS Configuration
Configuration for IS-IS is relatively simple. An IS-IS process is created by using the router isis tag command. Only one IS-IS process performing L2 routing is allowed per IS, and that process can also perform L1 routing. However, multiple L1-only IS-IS routing processes can be configured (up to 29 additional L1-only processes). If the tag value is not specified, a null tag is assumed. If multiple L1 routing processes are configured, each is labeled with a tag to facilitate area identification. Multiple L1 routing processes can be configured if the L1/L2 IS is connected to multiple L1 areas. Multiarea functionality was added in IOS 12.0(5). Prior to that IOS level, only one area per IS was allowed. Then, the net network-entity-title command specifies area addresses for the IS-IS area. The NET address is not an IP address; instead, it is an OSI network layer address.
After the global configuration, the interfaces that participate in the IS-IS process are configured with the interface subcommand ip router isis tag. This command associates an interface with an IS-IS routing process and an area. The tag is the same value that was specified under the router isis command. If the tag is not specified in the router isis command, it must not be specified here.
The configurations for Routers 8, 9, and 10 in Figure 8-10 are displayed in this section. Router 8 is an L2 IS. Router 9 is an L1/L2 IS, which communicates L2 routes with Router 8, and L1 and L2 routes with Router 10. Router 9 redistributes an external static route to network 10.0.0.0/ 8 as an IS-IS external L1 and L2 route. Both Router 8 and Router 9 are configured with a link password of ciscopass. Router 9 is configured to originate a default-gateway route (0.0.0.0) with the default-information originate command. Router 8 is also configured with a DIS priority of 70 to make it the DIS for the Ethernet network.
Figure 8-10 Simple IS-IS Network
Router 9
NET: 49.0000.0001.C loopO: 192.16.100.2/ e0: 192.16.100.18/2i s0: 192.16.100.241/;
Static 10.0.0.0/24
Router 9
NET: 49.0000.0001.C loopO: 192.16.100.2/ e0: 192.16.100.18/2i s0: 192.16.100.241/;
Router 8
NET: 49.0000.0001.0003.00 loop0: 192.16.100.1/32 e0: 192.16.100.20/28 (Level 2)
Static 10.0.0.0/24
Router 8
NET: 49.0000.0001.0003.00 loop0: 192.16.100.1/32 e0: 192.16.100.20/28 (Level 2)
The configuration for Router 8 is shown in Example 8-19.
Example 8-19 IS-IS Configuration for Router 8
hostname Router8
interface Loopback0 ip address 192.16.100.1 255.255.255.255 ip router isis cisco isis metric 5 level-2
interface Ethernet0 ip address 192.16.100.20 255.255.255.240 ip router isis cisco isis circuit-type level-2-only isis password ciscopass level-2 isis priority 70 level-2
router isis cisco net 49.0000.0001.0003.00
ip classless
Use the tag value of cisco for both the router isis command and the ip router isis command. The Ethernet interface is configured to establish adjacencies only with other L2 ISs. Because Router 8 is an L2 IS, another way to make sure that only L2 adjacencies are formed with other ISs is to configure the command is-type level-2-only under the router isis process. The L2 password and priority are also configured on the Ethernet interface.
The configuration for Router 9 is shown in Example 8-20.
Example 8-20 IS-IS Configuration for Router 9
hostname Router9
interface Loopback0 ip address 192.16.100.2 255.255.255.255 ip router isis cisco isis circuit-type level-2-only isis metric 5 level-2
interface Ethernet0 ip address 192.16.100.18 255.255.255.240 ip router isis cisco isis circuit-type level-2-only isis password ciscopass level-2
interface Serial0 ip address 192.16.100.241 255.255.255.252 ip router isis cisco isis metric 40 level-1
continues
Example 8-20 IS-IS Configuration for Router 9 (Continued)
router isis cisco redistribute static ip metric 60 metric-type external level-1-2 default-information originate net 49.0000.0001.0002.00
ip classless ip route 10.0.0.0 255.0.0.0 Null0
Ethernet 0 has the same L2 password as the Router 8 Ethernet. These passwords must be the same for an adjacency to be formed. No priority is set on Ethernet 0, so the default value, 64, is used. Router 9 is an L1/L2 IS. It forms an L2 adjacency with Router 8. Because Serial 0 has no circuit-type defined, L1 and L2 adjacencies can be formed. If Router 10 is an L1-only IS, or if the serial interface on Router 10 is configured with the isis circuit-type level-1-only command, only L1 adjacencies are formed. Otherwise, both L1 and L2 adjacencies are formed. The isis metric command changes the default metric from 10 to 40 for L1 routes on Serial 0. The static IP address is redistributed into IS-IS as an L1 and an L2 external route with a metric of 60. A default route is originated by this IS and advertised to IS-IS L2 ISs.
The configuration for Router 10 is shown in Example 8-21.
Example 8-21 IS-IS Configuration for Router 10
hostname Router10
interface Loopback0 ip address 192.16.100.3 255.255.255.255 ip router isis cisco interface Ethernet0 ip address 192.16.100.33 255.255.255.240 ip router isis cisco isis circuit-type level-1
interface Serial0 ip address 192.16.100.242 255.255.255.252 ip router isis cisco no fair-queue isis metric 40 level-1
router isis cisco net 49.0000.0001.0001.00
ip classless
Router 10 is not defined as an L1-only IS, nor is Serial 0. L1 and L2 adjacencies are, therefore, established with Router 9.
Continue reading here: ISIS show Commands
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