[c-nsp] BGP Hold Time Expired, but why?

[Oliver Boehmer (oboehmer)]

No clue what's happening.. I've seen issues in the past with TCP PMTUD
when the path converges over a link with a different MTU (which is
happening in your case), but as BGP will not send packets larger than
4k, this shouldn't be an issue here.

How long did you take down the link before bringing it back up? I assume
longer than 3 minutes? Have you checked CEF and MPLS along the new path?
You have IP connectivity between the loopbacks aR1 and bR2? Does the
session come back up eventually, or will it stay down?

	oli

Christian Koch <> wrote on Saturday, July 19, 2008 8:38 AM:

> sorry forgot to specify
> 
> the bgp session from aR1 to bR2 is the session in question
> 
> ck
> 
> On Sat, Jul 19, 2008 at 2:21 AM, Christian Koch
> <christian at broknrobot.com> wrote:
> 
>> Hello -
>> 
>> I have the following topology in lab, testing different failure
>> scenarios. When i disconnect the link between aR1 and bR1, what
>> would appear to be normal happens - ospf and ldp neighbor go down.
>> 
>> When i re-connect the link between aR1 and bR1, the interface comes
>> back up, osfp/ldp neighbor is re-established.
>> 
>> 3minutes later, bgp holdtime expires , and all links are up..
>> 
>> aR1-----------------bR1
>>>                         |
>>>                         |
>>>                         |
>>>                         | aR2-----------------bR2
>> 
>> 
>> Some Notes
>> - All Links 10GE
>> - Full ibgp mesh
>> - Peering is to loopbacks
>> - OSPF as IGP
>> - Loopbacks in OSPF
>> - MPLS Enabled on Interfaces
>> 
>> 
>> OSPF cost between aR1 and aR2 is 1
>> OSPF cost between bR1 and bR2 is 1
>> OSPF cost between aR1 and bR1 is 250
>> OSPF cost betwen aR2 and bR2 is 500
>> 
>> MTU 9216 between aR1 and aR2, aR1 and bR1, aR2 AND BR2
>> MTU 9182 between bR1 and bR2
>> 
>> 
>> IOS on aR1 and aR2 is 12.2.33.SRB2 -  SUP720
>> IOS on bR1 and bR2 is 12.33.SRC - RSP720
>> 
>> 
>> i am stumped, any ideas would be helpful in trying to understand why
>> the bgp session is going down due to expired hold time, when all
>> links are up.. 
>> 
>> thanks!
>> 
>> ck
>> 
>> 
>> 
>> 
>> 
>> 
> 
> 
> --
> ^christian$
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