VPN stopped working

Hi @Chad Miller,

Thank you for reaching out on the Microsoft Q&A forum.

I understand your VPN tunnel is up, but traffic isn't passing through anymore. Let’s work through a few key questions to help narrow down the issue:

• Have any new subnets been added or removed on either side of the VPN recently?
• If you bypass the VPN Gateway and test connectivity directly (e.g., using a temporary public IP or alternate route), does traffic flow as expected?
• Are you using BGP for route exchange? If so, can you confirm that the correct prefixes are being advertised on both ends?
• Do you have User Defined Routes (UDRs) or Network Security Groups (NSGs) applied to the GatewaySubnet or connected VNets that could be blocking traffic?
• Have you tried performing a VPN Gateway reset in Azure and also resetting the tunnel on the on-premises device?

Additionally, could you let us know what basic troubleshooting steps you have already tried? This will help us focus on the next steps and avoid repeating any actions you've already taken.

If the VPN tunnel stays up but traffic stops passing through, here are some helpful next steps:

1. Check Configuration: Ensure that there haven’t been any recent changes to subnets on either side of the VPN.
2. Direct Connectivity Test: Bypass the VPN Gateway temporarily and test connectivity directly to identify if the issue is with the VPN connection or elsewhere.
3. BGP Checks: If using BGP, verify that the correct prefixes are being advertised on both ends.
4. Inspect Policies: Look at User Defined Routes (UDRs) and Network Security Groups (NSGs) to ensure no settings are inadvertently blocking traffic.
5. Perform a Gateway Reset: Sometimes resetting the Azure VPN gateway and the tunnel on your on-premises device can clear up connection problems.

Here are some resources that can help troubleshoot further if this issue arises again:

• Troubleshoot virtual network gateway and connections using the Azure portal
• Validate VPN throughput to a Virtual Network
• Troubleshoot Azure VPN Gateway

If the problem happens again, it can be useful to gather logs or look into the diagnostic tools Azure offers for deeper insights.

Kindly let us know if the above helps or you need further assistance on this issue.

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