ISIS Configuration
Overview
Intermediate System to Intermediate System (IS-IS) is an interior routing protocol operating within a single administrative domain.It is a link-state routing protocol, operating by reliably flooding link state information throughout a network of routers. Each IS-IS router independently builds a database of the network's topology, aggregating the flooded network information. IS-IS uses Dijkstra's algorithm for computing the best path through the network. Packets (datagrams) are then forwarded, based on the computed ideal path, through the network to the destination.
Topology
ISIS Topology for VRF
Configuration IPv4 VRF
R1
#configure terminal | Enter configuration mode. |
(config)#ip vrf vrf1 | Create vrf1 |
(config-vrf)#exit | Exit VRF mode |
(config)#router isis 1 vrf1 | Associate the ISIS process to vrf1 |
(config-router)#net 49.0001.0000.0000.0001.00 | Establish a network entity title for this instance, specifying the area address and the system ID. |
(config-router)#is-type level-1 | Configure instance 1 as level-1 routing |
(config-router)#exit | Exit router mode |
(config)#interface eth1 | Enter interface mode |
(config-if)#ip vrf forwarding vrf1 | Associate the interface to vrf1 |
(config-if)#ip address 2.2.2.1/24 | Configure the IP address 2.2.2.1 to eth1 |
(config-if)#ip router isis 1 | Enable ISIS routing on an instance for area 49 |
(config-if)#isis circuit-type level-1 | Configure interface as level-1 |
(config-if)#commit | Commit the candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode |
(config)#exit | Exit config mode |
R2
#con t | Enter configuration mode. |
(config)#ip vrf vrf1 | Create vrf1 |
(config-vrf)#exit | Exit VRF mode |
(config)#router isis 1 vrf1 | Associate the ISIS process to vrf1 |
(config-router)#net 49.0001.0000.0000.0002.00 | Establish a network entity title for this instance, specifying the area address and the system ID. |
(config-router)#is-type level-1 | Configure instance 1 as level-1 routing |
(config-router)#exit | Exit router mode |
(config)#interface eth1 | Enter interface mode |
(config-if)#ip vrf forwarding vrf1 | Associate the interface to vrf1 |
(config-if)#ip address 2.2.2.2/24 | Configure the IP address 2.2.2.1 to eth1 |
(config-if)#ip router isis 1 | Enable ISIS routing on an instance for area 49 |
(config-if)#isis circuit-type level-1 | Configure interface as level-1 |
(config-if)#commit | Commit the candidate configuration to the running configuration |
(config-if)#exit | Exit interface mode |
(config)#exit | Exit config mode |
Validation
R1
#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 0
Total number of adjacencies: 1
Tag 1: VRF : vrf1
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth1 5254.0047.dc01 Up 24 L1 IS-IS
R2
#show clns neighbors
Total number of L1 adjacencies: 1
Total number of L2 adjacencies: 0
Total number of adjacencies: 1
Tag 1: VRF : vrf1
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0001 eth1 5254.0060.d535 Up 5 L1 IS-IS
R1
#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** invalid
Tag 1: VRF : vrf1
Destination Metric Next-Hop Interface Tag
C 2.2.2.0/24 10 – eth1 0
R2
#show ip isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
** invalid
Tag 1: VRF : vrf1
Destination Metric Next-Hop Interface Tag
C 2.2.2.0/24 10 – eth1 0