ISIS metric set to maximum value (16777214)

[Rahul Khude]

ISIS is running on all the three routers A, B and C. A is a downstream node. B and C are upstream and connected further to their upstream nodes in backbone.

ISIS metric set on link between A and B is 1000 making it preferable link for outgoing traffic from downstream. ISIS metric is set to maximum on link between A and C making it unusable.

My query is if link between A and B goes down, would the link between A and C take over the traffic or all downstream traffic will get impacted due to highest ISIS metric set on link between A and C.

[Jose Fonseca · Accepted solution]

Hi Rahul,

Even though you can use 2000 instead of the maximum, so you will make sure that the maximum won't cause further problem.

I just confirmed that the maximum metric will work for you. 

Please refer to the information below:

======================================================================

Router#sh ip route isis | b of
Gateway of last resort is not set

1.0.0.0/32 is subnetted, 1 subnets
i L1 1.1.1.1 [115/1000] via 10.1.1.1, 00:06:51, Ethernet0/0
3.0.0.0/32 is subnetted, 1 subnets
i L1 3.3.3.3 [115/16777214] via 10.2.2.3, 00:00:21, Ethernet0/1
13.0.0.0/24 is subnetted, 1 subnets
i L1 13.13.13.0 [115/1000] via 10.1.1.1, 00:00:21, Ethernet0/0

Router#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#inte e0/0
Router(config-if)#shut

Router#sh ip route isis | b of
Gateway of last resort is not set

3.0.0.0/32 is subnetted, 1 subnets
i L1 3.3.3.3 [115/16777214] via 10.2.2.3, 00:00:53, Ethernet0/1
13.0.0.0/24 is subnetted, 1 subnets
i L1 13.13.13.0 [115/16777214] via 10.2.2.3, 00:00:05, Ethernet0/1

======================================================================

As you can see as soon as I turned off the interface E0/0 going to your router B, the route recalculate the routes towards RouterC with no problem.

I hope this will help to your question, and let me know if you have further concern.