How to protect BGP session from interface flapping?

[boldbayarj]

Hello, How to keep BGP connection? It only takes 50ms (carrier switches its path) when physical interface up->down->up. At that moment BGP connection is not turned into down. After 3 secs physical link was failed, the BGP session changed into down. At both sides, keepalive and hold timers are configured 30, 90 secs and min acceptable hold time is 3. Also, bgp fast-external-fallover is disabled. And I set carrier-delay on the interface. But it was the same. I think the hold time is not working. And there were no messages received "hold time expired" from the remote side.  Below is the log. Please help me.

LC/0/0/CPU0:Oct 22 22:03:47.001 UTC: ifmgr[208]: %PKT_INFRA-LINK-3-UPDOWN : Interface TenGigE0/0/0/1, changed state to Down
LC/0/0/CPU0:Oct 22 22:03:47.001 UTC: ifmgr[208]: %PKT_INFRA-LINEPROTO-5-UPDOWN : Line protocol on Interface TenGigE0/0/0/1, changed state to Down
LC/0/0/CPU0:Oct 22 22:03:47.045 UTC: vic_0[366]: %PLATFORM-VIC-4-SIGNAL : Interface TenGigE0/0/0/1, Detected Signal failure
LC/0/0/CPU0:Oct 22 22:03:47.057 UTC: ifmgr[208]: %PKT_INFRA-LINK-3-UPDOWN : Interface TenGigE0/0/0/1, changed state to Up
LC/0/0/CPU0:Oct 22 22:03:47.058 UTC: ifmgr[208]: %PKT_INFRA-LINEPROTO-5-UPDOWN : Line protocol on Interface TenGigE0/0/0/1, changed state to Up
RP/0/RSP0/CPU0:Oct 22 22:03:50.178 UTC: bgp[1060]: %ROUTING-BGP-5-ADJCHANGE : neighbor XXX.XXX.XXX.XXX Down - Peer closing down the session (VRF: default) (AS: XXXXX)
RP/0/RSP0/CPU0:Oct 22 22:04:25.137 UTC: bgp[1060]: %ROUTING-BGP-5-ADJCHANGE : neighbor XXX.XXX.XXX.XXX Up (VRF: default) (AS: XXXXX)

[ADP_89]

Hello,

This flap doesn't depend on your router and his configuration. From the logs you can read that the bpg peer torned down the session. You might need to get in touch with the BGP administrator who manages the other end and ask him to disable the ebgp fast-external-fallover.

HTH,

ADP

[Alex Pfeil]

Please check out this info from Cisco BGP command reference:

bgp fast-external-fallover

To configure a Border Gateway Protocol (BGP) routing process to immediately reset external BGP peering sessions if the link used to reach these peers goes down, use the bgp fast-external-fallover command in router configuration mode.

To disable BGP fast external fallover, use the no form of this command.

bgp fast-external-fallover

no bgp fast-external-fallover

Full link below.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/command/iproute_bgp-xe-3se-3850-cr-book/iproute_bgp-xe-3se-3850-cr-book_chapter_00.html#wp1719224769

I would check to see if this is enabled.

Please rate helpful posts.