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

[Christian Koch]

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