Subject: [Isis-wg] IS-IS Restart Capability: receiving/processing "old" IIH packets?

From: "Miyagishima, Corwyn (Corwyn)" <[email-masked]>
Date: Mon, 8 Apr 2002 11:56:45 -0400

I guess it's time for me to delurk...

It seems as though there's a decently high (or at least non-zero)
probability that Restart Capability can fail under normal operating
circumstances, if I'm reading the draft properly.  Please forgive me if this
has been discussed before (I didn't see it in the archives) or if I'm
misunderstanding something...

Given that a restarting router ("A") is probably in an unstable state for
some length of time, it might not be immediately able to process the packets
it receives, so a periodic IIH might be sent by a neighbor ("B") before A
has signalled a restart, but not processed until after A has sent an IIH
with the RR bit set.  As such, A will then assume that B has failed a
restart and revert back to a start, rather than a restart.  Is this a
correct analysis?

If, indeed, this is a side-effect of the current design, would it be prudent
to allow A to "ignore" a certain number (1?  3?  42?) of IIHs without the RA
bit set immediately following a restart, or is there a better solution to
this?

Thanks!

Corwyn Y. Miyagishima
Senior Software Engineer
Lucent Technologies
978-952-7632 

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From: mike shand <[email-masked]>
Date: Mon, 08 Apr 2002 17:36:49 +0100

>restart and revert back to a start, rather than a restart.  Is this a

No. The text below from the draft describes the case where the IIH contains 
NO restart option.

Receipt of an IIH not containing the "re-start" option is also treated as 
an acknowledgement, since it indicates that the neighbor is not re-start 
capable. In this case the neighbor will have re-initialized the adjacency 
as normal, which in the case of a Point-to-Point link will guarantee that 
SRMflags have been set on its database, thus ensuring eventual LSPDB 
synchronization. In the case of a LAN interface, the usual operation of the 
update process will also ensure that synchronization is eventually 
achieved. However, since no CSNP is guaranteed to be received over this 
interface, T1 is cancelled immediately without waiting for a CSNP. 
Synchronization may therefore be deemed complete even though there are some 
LSPs which are held (only) by this neighbor (see section 4.3).

However, in the case you describe, the IIH will still contain the restart 
option (because the neighbor is re-start capable,) but it will NOT have the 
RA bit set. In this case it will simply be ignored and eventually the IIH 
with the RA bit set will be received (or if not, the RR will be retransmitted).

         Mike