migration from OSPF to IS-IS

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Jun 17th, 2008
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I am working for a client which is MPLS SP and having 200 numbers of PE in the core with 2 * RR. Current IGP is OSPF and now they are planning to migrate to IS-IS. Now my question is that how to start the migration with different process and zero dowtime.


regards

shivlu

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ashok_boin Wed, 06/18/2008 - 00:20
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The following link may help you to get some idea.


www.geant.net/upload/pdf/NEP-02-087.pdf


Usually, the migration procedure is like this.


1. Have the AD of new routing protocol greater than the existing routing protocol so that it will never be selected for normal routing of packets


2. Observe the behaviour from control plane perspective & migrate in parts one by one if the routes in IS-IS database reflecting exactly OSPF routes (don't compare the metric & routing protocol specific values).


Anyways, as the AD of IS-IS is greater than OSPF, you can try migrating a segment of your network from OSPF to IS-IS. First, please try in the lab first before migrating real network.


Regards...

-Ashok.



shivlu jain Wed, 06/18/2008 - 00:52
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hi ashok thaks for your reply; but actually my question is that lets if i start up with the isis on one router shd i have to redistribute the routes in the ospf


regards

shivlu

Giuseppe Larosa Wed, 06/18/2008 - 04:58
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Hello Shivlu,

as suggested in the previuos post you can start by running IS-IS in background on all routers because its AD 115 > OSPF's 110.

After that you have enabled IS-IS on all routers you can examine the IS-IS database and you can compare it with the ospf's DB.

If you do so you don't need to redistribute.


After that you have verified that all IP routes are in the IS-IS db you can start to change the AD distance for OSPF to a value bigger then 115 or you can remove the whole ospf router process.


If you remove all the ospf router processes in all routers you have completed the migration.


hope to help

Giuseppe

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