IS-IS Routing protocol configuration Step by Step [GNS3 Lab]

Before diving into configuration, you can refer to this article about IS-IS protocol basics:

IS-IS Routing Protocol Fundamental Explained


Lab Topology


ISIS Configurations

R1 configuration:

R1(config)#int e1/0
R1(config-if)#ip address 172.31.10.1 255.255.255.252
R1(config-if)#no sh
*Jun 13 15:39:18.723: %LINK-3-UPDOWN: Interface Ethernet1/0, changed state to up
*Jun 13 15:39:19.723: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet1/0, changed state to up
R1(config-if)#exit

R1(config)#router isis
R1(config-router)#is-type level-1
R1(config-router)#net 11.1111.1111.1111.1111.00
R1(config-router)#exit

R1(config)#int e1/0
R1(config-if)#ip router isis


R2 configuration:

R2(config)#int e1/0
R2(config-if)#ip address 172.31.10.2 255.255.255.252
R2(config-if)#no sh

R2(config)#int e1/1
R2(config-if)#ip address 172.31.0.1 255.255.255.252
R2(config-if)#no sh

R2(config)#router isis
R2(config-router)#net 11.1111.2222.2222.2222.00
R2(config-router)#is-type level-1-2
R2(config-router)#exit

R2(config)#int e1/0
R2(config-if)#ip router isis

R2(config)#int e1/1
R2(config-if)#ip router isis

R3 configuration:

R3(config)#int e1/0
R3(config-if)#ip address 172.31.0.2 255.255.255.252
R3(config-if)#no sh
R3(config-if)#ip router isis
R3(config-if)#end

R3(config-if)#ip add
R3(config-if)#ip address 172.31.20.1 255.255.255.252
R3(config-if)#no sh
R3(config-if)#ip router isis

R3(config)#router isis
R3(config-router)#is-type level-1-2
R3(config-router)#net 22.2222.3333.3333.3333.00
R3(config-router)#exit

R4 Configuration:

R4(config)#int e1/0
R4(config-if)#ip address 172.31.20.2 255.255.255.252
R4(config-if)#no sh
R4(config-if)#
*Jun 13 16:06:42.911: %LINK-3-UPDOWN: Interface Ethernet1/0, changed state to up
*Jun 13 16:06:43.911: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet1/0, changed state to up
R4(config-if)#exit


R4(config)#router isis
R4(config-router)#net 22.2222.4444.4444.4444.00
R4(config-router)#is-type level-1
R4(config-router)#exit

R4(config)#int e1/0
R4(config-if)#ip router isis

Verifications

* Verify ISIS neighbors on all devices:

R1#show isis neighbors

System Id      Type Interface   IP Address      State Holdtime Circuit Id
R2             L1   Et1/0       172.31.10.2     UP    8        R2.01  

----------------

R2#show isis neighbors

System Id      Type Interface   IP Address      State Holdtime Circuit Id
R1             L1   Et1/0       172.31.10.1     UP    22       R2.01           
R3             L2   Et1/1       172.31.0.2      UP    6        R3.01           

---------------

R3#show isis neighbors

System Id      Type Interface   IP Address      State Holdtime Circuit Id
R2             L2   Et1/0       172.31.0.1      UP    28       R3.01
R4             L1   Et1/1       172.31.20.2     UP    9        R4.01

---------------

R4#show isis neighbors

System Id      Type Interface   IP Address      State Holdtime Circuit Id
R3             L1   Et1/0       172.31.20.1     UP    22       R4.01


  • Verify ISIS CLNS neighbors:
R4#show clns neighbors
System Id      Interface   SNPA                State  Holdtime  Type Protocol
R3             Et1/0       ca03.4068.001d      Up     23        L1   IS-IS

  • Check routing tables:

R1:

R1#show ip route
Codes: L - local, 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, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 172.31.10.2 to network 0.0.0.0

i*L1  0.0.0.0/0 [115/10] via 172.31.10.2, 00:22:13, Ethernet1/0
      172.31.0.0/16 is variably subnetted, 3 subnets, 2 masks
i L1     172.31.0.0/30 [115/20] via 172.31.10.2, 00:22:21, Ethernet1/0
C        172.31.10.0/30 is directly connected, Ethernet1/0
L        172.31.10.1/32 is directly connected, Ethernet1/0


R2:

R2#show ip route
Codes: L - local, 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, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is not set

      172.31.0.0/16 is variably subnetted, 5 subnets, 2 masks
C        172.31.0.0/30 is directly connected, Ethernet1/1
L        172.31.0.1/32 is directly connected, Ethernet1/1
C        172.31.10.0/30 is directly connected, Ethernet1/0
L        172.31.10.2/32 is directly connected, Ethernet1/0
i L2     172.31.20.0/30 [115/20] via 172.31.0.2, 00:18:11, Ethernet1/1


R3:

R3#show ip route
Codes: L - local, 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, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is not set

      172.31.0.0/16 is variably subnetted, 5 subnets, 2 masks
C        172.31.0.0/30 is directly connected, Ethernet1/0
L        172.31.0.2/32 is directly connected, Ethernet1/0
i L2     172.31.10.0/30 [115/20] via 172.31.0.1, 00:24:18, Ethernet1/0
C        172.31.20.0/30 is directly connected, Ethernet1/1
L        172.31.20.1/32 is directly connected, Ethernet1/1


R4:

R4#show ip route
Codes: L - local, 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, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 172.31.20.1 to network 0.0.0.0

i*L1  0.0.0.0/0 [115/10] via 172.31.20.1, 00:18:56, Ethernet1/0
      172.31.0.0/16 is variably subnetted, 3 subnets, 2 masks
i L1     172.31.0.0/30 [115/20] via 172.31.20.1, 00:18:56, Ethernet1/0
C        172.31.20.0/30 is directly connected, Ethernet1/0
L        172.31.20.2/32 is directly connected, Ethernet1/0

Bilel-A

Enthusiastic Network Engineer specializing in Cisco ACI, passionate about solving challenges. A lifelong learner who loves gaining and sharing knowledge. Profile: https://www.linkedin.com/in/bilel-ameur-71116b2b5

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