Azure Virtual WAN Routing Scenario

Question

I've been having a problem with Azure Virtual WAN routing and was hoping somebody might have some insight. I also posted to Reddit communities but did not get any replies.

For testing, I have created a network described by the network diagram below. In my scenario, I am creating a traffic flow from VNet_1 to 10.200.0.10. BGP is used between the VPN Branches and the VirtualHubs.

• Initially, the traffic flow uses path 1. This is expected.
• If path 1 becomes unavailable then the traffic flow uses path 2. This is expected.
• If path 1 recovers then the traffic flow continues to use path 2. This is unexpected.

My expectations are based on the routing scenarios from https://learn.microsoft.com/en-us/azure/virtual-wan/about-virtual-hub-routing-preference . My understanding is that path 1 should always be preferred if it is available because the Virtual Hub will prefer a directly connected route over a route from a remote hub. I would at least expect the routing decision to be deterministic.

Answer 1

If anybody else runs into this, Microsoft support eventually shared the root cause

It was determined this is a code defect. The customer was informed they can mitigate by changing the local ASPATH to be length of 1 greater than the remote path.

Incident Information 352392269