[c-nsp] Can not establish MP-BGP sessions

[Andy Saykao]

Hi All,
 
We migrated a link between two pops onto a Switched Ethernet circuit and
since then we can't pass MPLS VPN traffic between those two pops from
PE1 to PE2 because PE1 and PE2 can not establish a MP-BGP session.
 
 ------------------------- 
BGP log on PE1:
-------------------------
Nov 16 14:26:48.693 AEDT: %BGP-5-ADJCHANGE: neighbor 172.16.99.4 Down
BGP Notification sent
Nov 16 14:26:48.693 AEDT: %BGP-3-NOTIFICATION: sent to neighbor
172.16.99.4 4/0 (hold time expired) 0 bytes

-------------------------
Topology:
-------------------------
POP1 [PE1 (lo99:172.16.99.13) --- Switched Ethernet --> P1 ] -->  POP2
[P2 --> PE2 (lo99:172.16.99.4)]
 
-------------------------
P1:
-------------------------
interface GigabitEthernet4/0/1
 description Connection to P2
 bandwidth 150000
 ip address 203.17.96.x 255.255.255.252
 load-interval 30
 negotiation auto
 mpls ip

-------------------------
P2:
-------------------------
interface GigabitEthernet0/2
 description Connection to P1
 bandwidth 150000
 ip address 203.17.96.x 255.255.255.252
 load-interval 30
 media-type gbic
 speed auto
 duplex auto
 negotiation auto
 mpls ip

Interesting thing to note is that if I remove "mpls ip" from P1's
interface, the MP-BGP sessions are formed between PE1 and PE2 and stay
up. When I put "mpls ip" back on the interface, the MP-BGP session times
out with the error messgage in the BGP log above.
 
The only thing that has changed is the introduction of the new Switched
Ethernet circuit. I was thinking that it might have something to do with
jumbo frames but our UpStream Providers tells me that they have
configured jumbo frames on either end of the link plus I can ping end
from P1 to P2 with  byte sizes larger than 8000 bytes.
 
Has anyone got any ideas as to why the MP-BGP sessions all of a sudden
can no longer stay up and what further debug/troubleshooting i can do?
 
Thanks.
 
Andy

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