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OSPF v ISIS ?

Hi,

With IS-IS, an L1/L2 router will hold a Level 1 LSD and a level 2 LSD and two separate SPF calculations are run for the L1 routes and the L2 routes.

With OSPF lets say that an ABR has two Areas connected e.g Area 0 and Area 1, then the router will hold separate LSA's for each of these Areas.

My question is: Will the SPF algorithm be run once or twice ?

2 REPLIES

Re: OSPF v ISIS ?

Hello,

I dont know the in depths of SPF calculation. But, I believe SPF is used to calculate the best route to a network and put this is the routing table. So , it would need all information (lsa) from all areas to do so.

So, I'd say its only 1 SPF calculation.

HTH,

if it does, please rate this post.

Vlad

Re: OSPF v ISIS ?

Hello again checking RFC 2328:

16.Calculatin of the routing table

"

(2) The intra-area routes are calculated by building the shortest-path tree for each area..."

"

HTH,

Vlad

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