Subject: [OSPF] Query regarding draft-ietf-ospf-ospfv3-graceful-restart-04.txt

From: "satyapraveenkumar pasalapudi" <[email-masked]>
Date: Thu, 30 Nov 2006 14:25:47 +0800

Hi,

In section

*3.1  Preservation of LSA ID to Prefix Correspondence*

*    In OSPFv2 there is a direct correspondence between type 3 and type 5
    LSA IDs and the prefixes being advertised.  For OSPFv3, the LSA ID
    for inter-area prefix LSAs and external LSAs is simply an unsigned 32
    bit integer.  To avoid network churn during graceful restart, the
    restarting router SHOULD preserve the LSA ID to prefix correspondence
    across graceful restarts.*

**

My query is why is to maintain LS-ID prefix correspondence?

How it will cause network churn ?

Rgds,

Praveen.

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From: Acee Lindem <[email-masked]>
Date: Thu, 30 Nov 2006 06:25:54 -0500

Hi Praveen,

> My query is why is to maintain LS-ID prefix correspondence?
If we don't maintain the correspondence, it will cause churn since one 
or more
of the restarting router's self-originated LSAs containing prefixes will 
appear
to have changed. This, in turn, will result in unnecessary SPF 
calculations in
all the OSPFv3 routers  in the flooding domain of the changed LSAs.
Granted, this will be an incremental or partial SPF  for external, NSSA,
inter-area-prefix LSAs and inter-area-router LSAs. Furthermore,
if demand circuits (RFC 1793) or flooding reduction (RFC 4136) is deployed,
the changed LSAs will need to be flooded over these links.

Hope this helps,
Acee
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