BGP route table not updating

Question

Hello,

We just provisioned an ExpressRoute and the private peering is functional, however the BGP routes are not updating. During our testing, we only included a small subset of routes to advertise. We have since included the full route table on our on-premise router, but Azure ExpressRoute is still showing the old routes. I have disabled the peering for about 5 minutes and re-enabled it. no difference. I also reset the Virtual Gateway. no difference.

We did accidently configure the BGP Community String in the Virtual Network, i am not sure if that created the issue?

BGP community string:12076:20001, 12076:50005

thanks for your help!

Brad

Answer 1

Verify BGP configuration: Double-check the BGP configuration on both the on-premises router and the Azure ExpressRoute virtual network gateway. Ensure that the BGP configuration parameters, such as the AS number, BGP community strings, and route filters, are correctly configured and match on both sides.

Check BGP session status: Verify the BGP session status between your on-premises router and the Azure ExpressRoute virtual network gateway. Ensure that the BGP session is established and that there are no errors or warnings related to the BGP session.

Validate route filtering: If you have configured any route filters, ensure that they are not inadvertently blocking the routes you expect to be advertised or received. Review your route filter configuration and verify that it aligns with your intended routing requirements.

Review BGP neighbor configurations: Ensure that the BGP neighbor configurations on both sides are correctly specified, including the IP addresses, AS numbers, authentication settings, and BGP timers. Any misconfiguration can prevent proper BGP route updates.

Check for BGP route propagation delay: BGP route updates can take some time to propagate between routers. Even after making changes on the on-premises router, it may take a few minutes for the updates to reach the Azure ExpressRoute virtual network gateway and vice versa. Monitor the BGP route table on both sides to see if the updates eventually propagate.

Regarding the BGP community string you mentioned, it typically does not cause issues with BGP route updates. However, it's worth reviewing your BGP route filters to ensure that the community string is not being used to filter or manipulate routes unintentionally.

If you have gone through these troubleshooting steps and the BGP routes are still not updating, it is recommended to reach out to Azure Support for further assistance. They can help investigate the issue in more detail and provide guidance specific to your Azure environment and ExpressRoute setup.

I hope this helps! Let me know if you have any further questions.