Re: DROther/BDR graceful restart question

[Ashok Chandrashekar Holla <ashok_ch at HUAWEI.COM>]

Hi Nitin,
Although a modification was suggested in  
http://www.ietf.org/internet-drafts/draft-holla-ospf-update-graceful-restart-00.txt 
, after the discussions in this forum, I now feel that the existing 
mechanism need not be changed :).
Retaining BDR status is not necessary and provides little value addition 
(only the avoidance of the linear time bound election algorithm overhead).
- Ashok


Nitin Kakkar wrote:

> Ashok> For the second part:
> When a BDR undergoes GR, it will almost certainly lose its BDR status
> since BDR status is not maintained across GRs. So, when it comes up, it
> will run fresh election and the behavior is as per election algorithm
> (it may become a DROther).
>
>  
>
> > > Doesn't this defy the whole purpose of GR?
> > >      
> Nitin
>
>
> -----Original Message-----
> From: Mailing List [mailto:OSPF at PEACH.EASE.LSOFT.COM] On Behalf Of Ashok
> Chandrashekar Holla
> Sent: Friday, February 10, 2006 11:21 AM
> To: OSPF at PEACH.EASE.LSOFT.COM
> Subject: Re: DROther/BDR graceful restart question
>
> Hi Ramesh,
>
> For the first part:
> When a DROther comes up after restart, there is no need for it to 
> 'remember' that it was DROther before restart. The restarting router 
> learns the DR and BDR  using the usual hello mechanism. This behavior is
>
> no different from a non graceful restart.
> When it runs the election algorithm, it will determine that it is 
> currently DROther. Once this is done, it will complete forming 
> adjacencies with DR and BDR of the network and then exit GR.
>
> From the perspective of learning the pre-restart topology, there is no 
> need for a DROther to wait until it completes adj formation with both DR
>
> and BDR. However it is inevitable that this be done, since a helper 
> router (DR and BDR) in some scenarios, will declare a 'Peer down' in 
> their LSA if they see a flushed grace lsa before adjacency formation is 
> complete (basic protocol behavior).
>
> For the second part:
> When a BDR undergoes GR, it will almost certainly lose its BDR status 
> since BDR status is not maintained across GRs. So, when it comes up, it 
> will run fresh election and the behavior is as per election algorithm 
> (it may become a DROther).
>
> Hope it helps.
> - Ashok
>
>
> Ramesh Kandula wrote:
>
>  
>
> > Hi All,
> >
> > Suppose a DROther router restarts gracefully on a broadcast network. 
> > Before restart it has adjacencies with DR and BDR. According to clause
> >    
> in
>  
>
> > 2.2.1 (RFC 3623), it is supposed to wait till it forms adjacencies with
> >    
>
>  
>
> > BDR and DR before exiting restart mode.
> >
> > However there is no way for it to determine who the BDR was before
> >    
> restar
>  
>
> > t 
> > using the pre-restart router lsa (and/or pre-restart network lsa). Or
> >    
> am 
>  
>
> > I 
> > missing something? Actually why is it necessary to wait (i.e for
> >    
> exiting 
>  
>
> > restart mode) till it forms an adjaceny with BDR? Isn't it enough for
> >    
> it 
>  
>
> > wait till it forms an adjacency with DR?
> >
> > A similar issue arises with BDR restart as well. According to the same 
> >
> > clause it is supposed to wait till it forms adjacencies with all the 
> > routers on the network. However it has no way of determining that it
> >    
> was 
>  
>
> > the BDR using just the pre-restart lsas.
> >
> > Thanks,
> > Ramesh
> >
> >
> >
> >    
>
>