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Rouse-DB's avatar
Rouse-DB
Copper Contributor
Apr 27, 2022

Site to Site VPN failed for no reason, cannot re-establish connection.

Hi all,

 

This is basically as simple as the title suggests. From last Friday, a site to site VPN connection ceased working for no visible reason. There have been no changes to Azure config, or local network. Using our local sonicwall, we can see traffic attempting the Ike negotiation, but then remote party timeout.

 

Azure says that the VPN gateway is not publicly visible, but it is, from various places I have tested, only Azure is at fault. I have deleted and recreated the local gateway and connection within our Azure tenancy, and updated the preshared ike passwhrase locally, in essence to try to recreate the connection from scratch, but this is not working.

1 Reply

  • Kidd_Ip's avatar
    Kidd_Ip
    MVP
    Oct 11, 2025

    Please check on this:

     

    1. Local Network Gateway IP

    • Double-check that the public IP of your SonicWall is correctly entered in Azure.
    • If your ISP changed your IP recently, Azure may still be trying to reach the old one.

    2. Firewall/NAT Rules

    • Ensure UDP 500 and 4500 are open and forwarded correctly.
    • SonicWall logs may show outbound attempts, but Azure might be silently dropping them.

    3. Azure Diagnostic Logs

    Enable and inspect:

    • IKEDiagnosticLog
    • TunnelDiagnosticLog
    • GatewayDiagnosticLog

    These can reveal if Azure is receiving IKE packets or rejecting them.

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