I noticed the log neighbor up/down very often on CE router. I check the PE found log
: Receiving unsupported capability 65
Is related to neighbor flapping issue?
BGP Capability code 65 is the support for 4 octect BGP AS number feature. I dont think this could be your root cause for the
BGP flapping... please check how stable your CE-PE link is..
you can setup a IP SLA to monitor the other end of your link and see whether you are getting a drops over a period of time
rate any helpful posts!
Thanks for reply.
You mean if CE use 2-byte ASN and PE use 4-byte ASN, the BGP session shoudn't be created if i didn't change some configure on CE. Am i correct?
The adjacent router is letting you know that that router is 4 octect capable router. In your case is the neighbor ever came up ? it is up and running and exchanging routes but sometimes you are seeing flaps ?
what is the exact behaviour
Right. From log, it look like the link or BGP peer issue.
10:35:57.635: %BGP-5-ADJCHANGE: neighbor 10.10.10.1 Up
10:46:15.195: %BGP-5-ADJCHANGE: neighbor 10.10.10.1 Down BGP Notification sent
10:46:15.203: %BGP-3-NOTIFICATION: sent to neighbor 10.10.10.1 4/0 (hold time expired) 0 bytes
10:46:15.539: %BGP_SESSION-5-ADJCHANGE: neighbor 10.10.10.1 IPv4 Unicast topology base removed from session BGP Notification sent
10:46:46.324: %BGP_SESSION-5-ADJCHANGE: neighbor 10.10.10.1 IPv4 Unicast topology base removed from session Peer closed the session
10:46:57.547: %BGP-5-ADJCHANGE: neighbor 10.10.10.1 Up
Please setp up a simple ip sla as follows to check the basic reachability
ip sla 20
ip sla schedule 20 life forever start-time now
verify as follows every time you get a flap and see any timeout for reachability
sh ip sla statistics 20
Hi Roger ,
You can use the following steps.
1. Please check if your BGP neigbor fallping every 3 minutes if yes then it could be related to MTU or MSS value mismatch.
2. Check on both the ends the interface health, do you see any errors, interface resets or and reliability of the link.
To check if capability negotiation is the reason for flap, try disabling capability negotiation
conf t router bgp [as] address-family ipv4 vrf xxxxx neighbor x.x.x.x dont-capability-negotiate