How to Configure Integrated IS-IS

Cisco Integrated IS-IS is part of a link-state Interior Gateway protocol and supports CLNP, IPv4, and IPv6.  To verify your platform support, please see my article covering the Cisco IOS Feature Navigator. An Intermediate-System-to-Intermediate System (IS) operates at Level 1 or Level 2 routing, or both.

Following is a sample configuration showing a router using IS-IS as the IP protocol.

routerB(config)# router isis
routerB(config-router)# net 49.0001.0000.0000.000a.00
routerB(config-router)# interface ethernet1/1
routerB(config-if)# ip address 10.1.1.1 255.255.255.0
routerB(config-if)# ip router isis
routerB(config-if)# interface serial 2/0
routerB(config-if)# ip router isis
routerB(config-if)# ip address 192.168.1.2 255.255.255.0

Additionally, do the show ip route command to verify your configuration. Notice the “i” routes. These are your IS-IS Routes:

RouterB# show ip route
Codes: C – connected, S – static, 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
i – IS-IS, su – IS-IS summary, 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
C 172.21.1.0 is directly connected, Serial5/0
172.22.0.0/24 is subnetted, 1 subnets
i L1 172.22.1.0 [115/20] via 172.21.1.2, Serial5/0
10.0.0.0/24 is subnetted, 1 subnets
i L1 10.1.1.0 [115/20] via 192.168.1.2, Serial2/0

For more information, please see the Cisco documentation on Cisco IOS IP Routing Protocols and Cisco’s Configuring IS-IS for IP on Cisco Routers.