BGP flapping over S2S VPN tunnel - Troubleshooting Steps

Question

Hi
We are facing an issue where our BGP peering to our customers on-prem Gateway is flapping every couple of hours (stays down for few hours and also comes back up automatically). I need to know how we can troubleshoot this from Azure VPNGW - what are the logs that are available which could indicate the cause and other options available that we can leverage?
Note the on-prem device is customer owned and we do not have much visibility from that end too. Also, a point to note the S2S VPN tunnel stays up and no issues over the tunnel.

Thank You.
Shoeb

Answer 1

@Soeb Bohari
Thank you for reaching out to Microsoft Q&A. I understand that you are having issues with BGP Flapping over Azure S2S VPN and want to know how to go about troubleshooting the same.

I see that the S2S VPN itself stays stable. Can you confirm the following to further troubleshoot the issue?

1. Are you able to ping the Azure BGP Peer IP from the customer side Peer IP when the issue happens?
2. What state does BGP go to when this issue occurs? (You can get the BGP Status using this powershell command on Azure side) https://learn.microsoft.com/en-us/azure/vpn-gateway/bgp-diagnostics#powershell
3. Are you able to request any BGP/TCP logs from your customer side device?

On Azure side, you can check the BGP status using the Powershell command as mentioned above. You can also check the BGP Peers and their status on the Azure Portal as shown here.

Further, you can check the advertised routes and learned routes as seen from here. If you need more information regarding or in depth BGP logs, you will need to contact Azure Support for the same. Looking forward to your reply. Thank you!