Re: Question about IS-IS Restart Signaling

hi les,

some disagreement from my side - see comments inline;

Les Ginsberg (ginsberg) wrote:
> Hmmm...an interesting question.
> 
> I would have to say that the RFC is not explicit on this point.
> 
>>From an interoperability standpoint, I would be concerned that
> implementations might not parse past the initial restart TLV and
> therefore might not process a second restart TLV. This would not be
> fatal as the restarting router would eventually retransmit an IIH-RR
> (presumably by this time the other restarting router would have seen its
> RA) - but would be suboptimal as it would delay the reestablishment of
> the adjacency on the part of the restarting router. On the other hand,
> it would provide a means of decreasing the total number of IIH-RAs sent
> in response to the IIH-RRs in such a case.
> 
> This is, of course, a very unlikely case for two reasons:
> 
> 1)It is unlikely that two routers would restart "at the same time"

what about a buffer overrun during LSP parsing and a subsequent crash
in the isis module ? - since GR is engineered for control-plane failure
this *is* the case we are trying to address.

> 2)As the requirement on sending the IIH-RA is to send it "immediately"
> (with jitter on the LAN) the interval between receipt of IIH-RR from two
> different routers would need to be quite small.

the IIHs with the restart request could have been batched up,
until the adjacency mgmt module drains the IO queue making
them appear to have arrived simultaneous.

> In the conservative spirit of being "strict in what you send" I would be
> inclined to NOT include multiple restart TLVs in the same IIH. I would
> recommend sending two IIHs one immediately after the other. Note that
> such short bursts are already allowed in the case of LSP/CSNP
> transmissions.

i fail to see a violation of the "strict in what you send" by packing
multiple restart TLVs in a single IIH. what you are proposing actually
is a violation of "be liberal what you receive" principle by ruling
out a ligitimate way of encoding information in a single IIH.

an implementation note:
   most implementations have an internal representation of the data
   found in TLVs. it is highly recommended to store any data found
   in tree / list representation i.e. you may append information at any
   time. so ruling out "data may be spread over multiple TLVs" is like
   encouraging bad coding habits 

/hannes

>>-----Original Message-----
>>From: Kandula, Ramesh [mailto:Ramesh.Kandula <at> SpirentCom.COM]
>>Sent: Friday, March 24, 2006 11:07 PM
>>To: 'isis-wg <at> ietf.org'
>>Subject: [Isis-wg] Question about IS-IS Restart Signaling
>>
>>Hi all,
>>
>>According to RFC 3847, if multiple routers on a broadcast network
> 
> restart
> 
>>around the same time, is the helper (receiving) router supposed to
> 
> include
> 
>>multiple instances of Restart TLVs with RA bit set (one for each
>>restarting
>>router) in it's hellos?
>>
>>thanks
>>ramesh
>>
>>_______________________________________________
>>Isis-wg mailing list
>>Isis-wg <at> ietf.org
>>https://www1.ietf.org/mailman/listinfo/isis-wg
> 
> 
> _______________________________________________
> Isis-wg mailing list
> Isis-wg <at> ietf.org
> https://www1.ietf.org/mailman/listinfo/isis-wg