11-20-2016 06:38 AM - edited 03-08-2019 08:13 AM
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.
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11-20-2016 07:40 AM
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.
11-20-2016 07:40 AM
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.
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