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

[Justin Shore]

I hadn't tried that.  I'm curious as to why this would be started all of 
a sudden.  It worked fine until that night on a number of other routers. 
  There's another router sitting next to the edge router that 
experienced the problem.  It's configured almost identically.  Together 
they provide redundancy to the devices behind the pair of routers.  It 
didn't exhibit the problem at all.  A debug of IS-IS adjacency packets 
on the 7600s only showed the high MTU on that one link.  Perplexing.

I'll give that a try.  Unfortunately at this point it looks like we're 
going to have to switch back to OSPF for the short-term; we can't hold 
up our projects do to poor IS-IS support.  We've had numerous IS-IS 
problems that as of yet have not been resolved.  TAC has been unable to 
assist us with IS-IS issues as well.  OSPF doesn't fit our network 
design or IGP needs but at least it works.

Thanks
  Justin




Alex wrote:
> Justin,
> Have you tried "clns mtu" under interface?
> Rgds
> Alex
> 
> ----- Original Message ----- From: "Justin Shore" <justin at justinshore.com>
> To: "'Cisco-nsp'" <cisco-nsp at puck.nether.net>
> Sent: Tuesday, May 08, 2007 3:10 PM
> Subject: [c-nsp] IS-IS hello packet size issues
> 
> 
>> 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
>>
>>
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>