BGP between Cisco and Alcatel Router

[Magesh Kumar]

Hi All,

One of our MPLS Circuit Continuously Fluctuating. Our Environment like PE (Alcatel) to CE (Cisco) Router. This fluctuation will Reset the BGP Session with following logs (BGP state went down and after some seconds automatically become up)

Sep 27 02:39:44.638: %BGP-3-NOTIFICATION: received from neighbor 10.XX.XX.XX 4/0 (hold time expired) 0 bytes
Sep 27 02:39:44.638: %BGP-5-NBR_RESET: Neighbor 10.XX.XX.XX reset (BGP Notification received)
Sep 27 02:39:44.642: %BGP-5-ADJCHANGE: neighbor 10.XX.XX.XX Down BGP Notification received
Sep 27 02:39:44.642: %BGP_SESSION-5-ADJCHANGE: neighbor 10.XX.XX.XX IPv4 Unicast topology base removed from session BGP Notification received
Sep 27 02:39:44.698: %BGP-5-ADJCHANGE: neighbor 10.XX.XX.XX Up

With Regards,

Magesh Kumar G

[paul driver]

Hello

Have you checked with your isp regards the physical connectivity between your CE and their PE rtr

Bgp peerings are mainly directly connected and for a bgp peering session to time out  suggests client/server connectivity between these rtrs is failing due a possible an underlying physical problem.

[Magesh Kumar]

Hi paul,
We have already spoken to ISP regarding Physical connectivity. Its like Alcatel Router (PE) ---> Layer 2 Switch ---> Cisco Router (CE).
Other Info:
MTU Size of Alcatel Router Egress Interface = 9164
MTU Size of Cisco Router Egress interface = 1500
Path MTU discovery enabled in both Routers.

Regards,
Magesh Kumar G

[paul driver]

Hello

TBH having a bgp neighbor that was stable and now is flapping suggests intermittently your l2\l3 is fine also is tcp connectivity and your bgp config.

So has any changes been made recently that could have any bearing on your issue?

Are these peers directly connected, if not it is possible the underlying route between these peers is falling?

[Georg Pauwen]

Hello,

can you post both the Alcatel and the Cisco configurations ?

[Magesh Kumar]

Hi Georg,

Since Alcatel router was maintained by ISP, I can't provide that router configurations. As analyzed our CE router configuration, I found that no ip unreachables configured under PE facing interface.

BGP Logs:

 %BGP-3-NOTIFICATION: sent to neighbor XX.XX.XX.XX 4/0 (hold time expired) 0 bytes
%BGP-5-NBR_RESET: Neighbor XX.XX.XX.XX reset (BGP Notification sent)
%BGP-5-ADJCHANGE: neighbor XX.XX.XX.XX Down BGP Notification sent
 %BGP_SESSION-5-ADJCHANGE: neighbor XX.XX.XX.XX IPv4 Unicast topology base removed from session BGP Notification sent
%BGP-5-ADJCHANGE: neighbor XX.XX.XX.XX Up

Is above BGP logs related to no ip unreachables?

With Regards,

Magesh Kumar G