[c-nsp] IS-IS hello packet size issues

[Justin Shore]

I ran into another IS-IS problem this morning that stumped me.  I 
migrated an ATM router to our new core.  In the process I took the 
opportunity to try and get multi-area integrated IS-IS to work.  This 
basically consisted of removing the related net from the main IS-IS 
process (the current config is merging areas) and move that net to a new 
IS-IS process.  Then I tried to enable IS-IS with the named tag on that 
appropriate interface.  This prompted the following error:

%CLNS: Duplicate system ID configured in ip vrf <default> with router 
isis null

I haven't been able to work around that issue.

I removed the new IS-IS process and added the net back to the original 
process.  A few minutes later I received a page stating that a 
completely unrelated edge router just went down.  The router turned out 
to be up.  What happens was the IS-IS broke.  Through some debugging on 
the edge router I determined that it was sending massive IS-IS IIHs 
(9213 bytes).  The MTU on the physicals interfaces on both sides has 
been set 9216.  The MPLS MTU has also been set to 9216.  MPLS and LDP 
have both been enabled on the interfaces.  "No hello padding" was 
configured on both sides.  That didn't help.  I enabled and disabled 
hello padding on the edge router and they were all under 100 bytes.  I 
check the packet size on the 7600s in the core.  I shutdown the 
interfaces between the routers to kill IS-IS and then brought them back 
online.  No luck.  Finally I rebooted the edge router.  IS-IS still 
wasn't working the router came up.  This time however the IIHs were all 
under 100bytes.  Then I checked the 7600 again.  At that point the 7600s 
were sending 9213 bytes IIHs.  Rebooting them wasn't an option.

Has anyone seen this behavior before?

Thanks
  Justin