Here is a quick example of configuring ISIS between two cisco IOS-XR devices. The configuration is a little different than how we do on Cisco IOS or IOS-XE devices, however, theoretically, it is exactly the same so it doesn’t take much to understand and learn the configuration. So let’s quickly jump to the configuration.
Configuration Task:
Configure IOS-XR routers XR-1 and XR-3 for ISIS IPv4 and IPv6 point-point adjacencies.Topology is given below…

Configurations:
XR-1 Config : interface Loopback1 ipv4 address 5.5.5.5 255.255.255.255 ipv6 address 2222::7/128 ! interface GigabitEthernet0/0/0/1 ipv4 address 20.20.20.1 255.255.255.252 ipv6 address 2007::1/126 ! router isis CORE is-type level-1 net 49.0000.0000.0005.00 address-family ipv4 unicast ! address-family ipv6 unicast single-topology ! interface Loopback1 address-family ipv4 unicast ! address-family ipv6 unicast ! ! interface GigabitEthernet0/0/0/1 circuit-type level-1 point-to-point address-family ipv4 unicast ! address-family ipv6 unicast ! !
XR-3 Config: interface Loopback1 ipv4 address 6.6.6.6 255.255.255.252 ipv6 address 2222::8/128 ! interface GigabitEthernet0/0/0/0 ipv4 address 20.20.20.2 255.255.255.252 ipv6 address 2007::2/126 ipv6 enable ! router isis CORE net 49.0000.0000.0008.00 address-family ipv4 unicast ! address-family ipv6 unicast single-topology ! interface Loopback1 address-family ipv4 unicast ! address-family ipv6 unicast ! ! interface GigabitEthernet0/0/0/0 circuit-type level-1 point-to-point address-family ipv4 unicast ! address-family ipv6 unicast ! !
Verification:
XR-1: RP/0/0/CPU0:ios#sh isis neighbors Wed May 26 01:41:30.352 UTC IS-IS CORE neighbors: System Id Interface SNPA State Holdtime Type IETF-NSF R1 Gi0/0/0/0 *PtoP* Up 25 L1 Capable 0000.0000.0008 Gi0/0/0/1 *PtoP* Up 23 L1 Capable RP/0/0/CPU0:ios#sh route ipv4 isis Wed May 26 01:41:57.720 UTC i L1 1.1.1.1/32 [115/20] via 10.10.10.5, 00:50:21, GigabitEthernet0/0/0/0 i L1 6.6.6.4/30 [115/20] via 20.20.20.2, 00:50:20, GigabitEthernet0/0/0/1 i L1 10.10.10.0/30 [115/20] via 10.10.10.5, 00:50:21, GigabitEthernet0/0/0/0 i L1 20.20.20.4/30 [115/20] via 20.20.20.2, 00:50:20, GigabitEthernet0/0/0/1 RP/0/0/CPU0:ios#sh route ipv6 isis Wed May 26 01:42:02.670 UTC i L1 2001::/126 [115/20] via fe80::e83:95ff:fe99:1f01, 00:50:26, GigabitEthernet0/0/0/0 i L1 2008::/126 [115/20] via fe80::e83:95ff:fe35:a501, 00:50:25, GigabitEthernet0/0/0/1 i L1 2222::1/128 [115/20] via fe80::e83:95ff:fe99:1f01, 00:50:26, GigabitEthernet0/0/0/0 i L1 2222::8/128 [115/20] via fe80::e83:95ff:fe35:a501, 00:50:24, GigabitEthernet0/0/0/1 RP/0/0/CPU0:ios# XR-2: RP/0/0/CPU0:ios#sh isis neighbors Wed May 26 01:49:22.680 UTC IS-IS CORE neighbors: System Id Interface SNPA State Holdtime Type IETF-NSF 0000.0000.0005 Gi0/0/0/0 *PtoP* Up 29 L1 Capable Total neighbor count: 1 RP/0/0/CPU0:ios#sh route ipv4 isis Wed May 26 01:50:15.776 UTC i L1 1.1.1.1/32 [115/30] via 20.20.20.1, 00:58:36, GigabitEthernet0/0/0/0 i L1 5.5.5.5/32 [115/20] via 20.20.20.1, 00:58:37, GigabitEthernet0/0/0/0 i L1 10.10.10.0/30 [115/30] via 20.20.20.1, 00:58:36, GigabitEthernet0/0/0/0 i L1 10.10.10.4/30 [115/20] via 20.20.20.1, 00:58:37, GigabitEthernet0/0/0/0 RP/0/0/CPU0:ios#sh route ipv6 isis Wed May 26 01:50:19.936 UTC i L1 2001::/126 [115/30] via fe80::e83:95ff:fe05:b102, 00:58:40, GigabitEthernet0/0/0/0 i L1 2002::/126 [115/20] via fe80::e83:95ff:fe05:b102, 00:58:41, GigabitEthernet0/0/0/0 i L1 2222::1/128 [115/30] via fe80::e83:95ff:fe05:b102, 00:58:40, GigabitEthernet0/0/0/0 i L1 2222::7/128 [115/20] via fe80::e83:95ff:fe05:b102, 00:58:41, GigabitEthernet0/0/0/0 RP/0/0/CPU0:ios#
Conclusion:
Above is the small snippet of isis config on the ios-xr devices, I am going to expand this to frr and lfa etc in my future blog posts. The overall config is very simple and seamless. Thanks for reading. Happy learning.
Also I have a youtube video created on this blog, please visit if you want to see the live configuration.