How to debug where BGP session is failing

Question

I've setup an Azure express route private peering session with on prem. Layer 2 connection is verified. I can ping from on prem to Azure. The ARP tables look good. The BGP peers are communicating but the BGP session is not established. How can I find out why BGP establishment is failing?The following is the router configuration:

router bgp 64512

 address-family ipv4 vrf azure

  neighbor 100.98.1.86 remote-as 12076

  neighbor 100.98.1.86 description Azure-Underlay

  neighbor 100.98.1.86 timers 3 10

  neighbor 100.98.1.86 fall-over bfd

   neighbor 100.98.1.86 activate

  neighbor 100.98.1.86 send-community both

  neighbor 100.98.1.86 advertisement-interval 15

  neighbor 100.98.1.86 soft-reconfiguration inbound

Answer 1

Hello @Thompson, Daryl

Welcome to Microsoft QnA!

I would check 2 things for starters

• The timers you've configured are 3 for keepalive and 10 for holdtime. Ensure that these values are within acceptable limits and match the expected configuration on the Azure side.
• If there's a mismatch in timers, the BGP session might not establish.

AND:

no ACLs or firewalls on your network or in Azure that are blocking TCP port 179, which is used by BGP for establishing sessions.

Can you run and if we can see the

show ip bgp summary

debug ip bgp

show bfd neighbors

Also please have a look :

https://learn.microsoft.com/en-us/azure/expressroute/expressroute-routing

https://learn.microsoft.com/en-us/azure/expressroute/expressroute-howto-circuit-arm

--

I hope this helps!

Kindly mark the answer as Accepted and Upvote in case it helped!

Regards