Subject: A query in OSPF Graceful restart mechansim

From: Ashok <[email-masked]>
Date: Tue, 1 Nov 2005 16:44:26 +0800

Hi,

During graceful restart (as specified in RFC 3623), if an ABR completes
its adjacency formations in one area, BEFORE it discovers neighbors in
another area, it will exit GR using the router LSA checks. (I am
assuming that the pre-restart router and net lsas are not stored in
non-volatile memory across GR and are received from peers).

After GR exit, it will form adjacencies with the neighbors in the other
areas leading to network downtime since the forwarding table is updated
with the current route entries. This defeats the purpose of a GR. This
is in spite of using a sufficiently large grace period.

While implementations can overcome this problem with proprietary timers,
flags and other hacks, would it not be better if the Graceful restart
protocol specification itself could address this scenario?

Thanks,
Ashok

---

From: Padma Pillay-Esnault <[email-masked]>
Date: Tue, 1 Nov 2005 07:45:18 -0800

Ashok wrote:

> Hi,
>
>  
>
> During graceful restart (as specified in RFC 3623), if an ABR 
> completes its adjacency formations in one area, BEFORE it discovers 
> neighbors in another area, it will exit GR using the router LSA 
> checks. (I am assuming that the pre-restart router and net lsas are 
> not stored in non-volatile memory across GR and are received from peers).
>
This is incorrect. The GR should not exit GR until it has recovered all 
its database - which means *all* its areas
implicitly.

Router-lsa check allows you only to determine that a particular area is 
done.

Padma

> After GR exit, it will form adjacencies with the neighbors in the 
> other areas leading to network downtime since the forwarding table is 
> updated with the current route entries. This defeats the purpose of a 
> GR. This is in spite of using a sufficiently large grace period.
>
> While implementations can overcome this problem with proprietary 
> timers, flags and other hacks, would it not be better if the Graceful 
> restart protocol specification itself could address this scenario?
>
>  
>
> Thanks,
> Ashok
>
>  
>