BGP flapping

[Dayesh Shetty]

Hi Experts,

We have scenario where we have a point to point BGP configured between them.

Router A >> Tunnel 10 >> 10.50.0.1  255.255.254.0 (Subnet mask /20)

Router B >> Tunnel 10 >> 10.50.0.11 255.255.240.0 (Subnet mask /23)

The BGP connection is flapping every couple of hours/days etc.

Do you see any issue by any chance if the connection is flapping due to mismatch in the subnet mask?

Regards,

Dayesh

[paul driver]

Hello

Do you have any L2/L3 issues that can be causing connectivity loss between source/destination of the bgp tunnels?
Can you post the configuration for the tunnels and bgp stanza

sh run int tun x
sh run | sec router
sh ip route static
sh ip interface  br

sh ip bgp sum
sh ip bgp neighbors x.x.xx | in state

[balaji.bandi]

The BGP connection is flapping every couple of hours/days etc.

what is the logs you see on the device ? any interface up and down?

what % of usage that time on the interface?

what % CPU that time when it flaps?

what kind of links between this device to establish BGP?

is the BGP running over the tunnel, is the tunnel interface is the stable?

[Harold Ritter]

Hi @Dayesh Shetty ,

A very common cause for BGP session flapping is a mismatch path MTU between the two neighbors. Please refer to the following document to find out how to troubleshoot it.

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/116377-troubleshoot-bgp-mtu.html

Regards,

[Yunus Emre DEV]

hi,

for the problem you need to get debug, you need to get interface and bgp debug !

the problem may be mtu or L1 level, cable signal or gbic sfp problem