Site to Site VPN issues between Sonicwall and Zyxel

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James95
James95 Posts: 2 image  Freshman Member
in Security

We have successfully configured a Site-to-Site VPN between two locations using a pre-shared key. The VPN tunnel is up and running; however, we are experiencing connectivity issues between the two sites. We are unable to ping devices on either side or access network resources across the VPN.

We contacted SonicWall Support, and they confirmed that the configuration on the SonicWall TZ570 appears to be correct. They recommended checking the Zyxel firewall configuration.

Could you please help us identify the possible cause of this issue and advise what settings or firewall policies we should verify on the Zyxel side to enable communication between both networks?

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  • PeterUK
    PeterUK Posts: 4,796
    250 Answers 2500 Comments Friend Collector Ninth Anniversary
    image  Guru Member
    edited October 19
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    FLEX H ?

    Have you made routing rules for like LAN to WAN ? as I think there is a issue where traffic from the VPN makes it to the client but then follows the routeing rule out the WAN not down the VPN tunnel for the return traffic.

    so you need to make the routing rules for like LAN to WAN to exclude the Destination IP subnet return traffic like 192.168.50.0/24 IP range in a group with

    0.0.0.0 - 192.168.49.255

    192.168.51.0 - 255.255.255.254

    or make a top routeing rule with LAN to destination address 192.168.50.0/24 next hop IPSec VPN Tunnel

  • Zyxel_Tina
    Zyxel_Tina Posts: 1,047
    Zyxel Certified Network Administrator - Security Zyxel Certified Network Administrator - Switch 250 Answers 1000 Comments
    image  Zyxel Employee
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    Hi @James95,

    Welcome to the Zyxel Community!

    Since the tunnel is up but traffic cannot pass, this usually points to a routing or security policy issue. To narrow it down, please check the following:

    1. VPN type: route-based or policy-based?
      • If route-based, please check the routing rules. Make sure there is a route for the remote SonicWall subnet that points to the VPN tunnel interface. Without a matching route, the traffic will not be sent through the tunnel.
    2. VPN zone and security policy
      Please confirm whether the VPN tunnel is in the default VPN zone or a custom zone. If it is a custom zone, please ensure you have added the corresponding security policies in both directions, for example LAN → VPN zone and VPN zone → LAN, allowing the relevant source and destination subnets and services.

    If the issue persists after checking these, please share the exact model, firmware version, and a screenshot of your VPN, routing, and security policy configuration (via PM if it contains sensitive information). We will be happy to take a closer look.

    Zyxel Tina

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