Subject: [OSPF] ECMP from different areas of External Routes

From: Pranjal Chakravarty <[email-masked]>
Date: Thu, 12 Jun 2008 12:37:17 +0530 (IST)

I have a router with zebos implementation of ospf .
Is ECMP is allowed in the router if the routes are learned from two diffrernt non backbone areas(Same cost),Or only one route will be installed in the router .
The Route which is learnt from a higher area id will be installed in the router or both equal cost routes should be installed in the router.
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From: "Jishnu Banerjee" <[email-masked]>
Date: Thu, 12 Jun 2008 13:35:48 +0530

If nexthops to the same destination prefix, are of same cost, path-type
and same area, then ONLY ECMP comes into play else not. Now in case of
External Routes(Refer Section 16.4)  ecmp depends upon how you resolve
the nexthops w.r.t reachibility to ASBR(incase the forwarding address is
set to zero) else depends upon the nexthop through which the Forwarding
Address can be reached. However the criterion (cost,path-type,area)
still holds decide whether during SPF the same prefix should be
installed as ECMP(multiple nexthops).

Thanks,

Jishnu

Night after night 
Going round and round my brain 
His dream is driving me insane. 
In the corner of some foreign field 
The gunner sleeps tonight. 
What's done is done. 
We cannot just write off his final scene. 
Take heed of his dream. 
Take heed

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From: [email-masked] [mailto:[email-masked]] On Behalf Of
Pranjal Chakravarty
Sent: Thursday, June 12, 2008 12:37 PM
To: [email-masked]
Subject: [OSPF] ECMP from different areas of External Routes

Is ECMP is allowed in the router if the routes are learned from two
diffrernt non backbone areas(Same cost),Or only one route will be
installed in the router .

The Route which is learnt from a higher area id will be installed in the
router or both equal cost routes should be installed in the router.

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