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marunm
Visitor III
July 7, 2026
Solved

IPv6 problems with IPsec

  • July 7, 2026
  • 2 replies
  • 53 views

I’m having issues establishing a connection when IPv6 is enabled on the Windows client’s Wi‑Fi interface. As soon as I activate IPv6, the connection to the Fortigate fails. Has anyone experienced this or knows what might be causing it?

If you want it more technical or more detailed, I can refine it.

    Best answer by sjoshi

    Hi ​@marunm 

     

    When IPv6 is enabled on the client's network adapter, the FortiClient VPN connection may establish over IPv6 instead of IPv4, or the client may resolve FQDNs to both IPv4 and IPv6 addresses and then attempt to use IPv6. If the VPN tunnel is not configured for dual-stack (IPv4/IPv6).
    Instead of disabling ipv6,Configure Windows Registry to Prefer IPv4 over IPv6. another option is Enable block_ipv6 in FortiClient XML Configuration

    Refer:
    https://community.fortinet.com/fortigate-3/technical-tip-forticlient-windows-ipsec-dialup-tunnel-keep-disconnecting-due-to-windows-ipv6-settings-193700

    2 replies

    sjoshi
    Staff
    sjoshiAnswer
    Staff
    July 7, 2026

    Hi ​@marunm 

     

    When IPv6 is enabled on the client's network adapter, the FortiClient VPN connection may establish over IPv6 instead of IPv4, or the client may resolve FQDNs to both IPv4 and IPv6 addresses and then attempt to use IPv6. If the VPN tunnel is not configured for dual-stack (IPv4/IPv6).
    Instead of disabling ipv6,Configure Windows Registry to Prefer IPv4 over IPv6. another option is Enable block_ipv6 in FortiClient XML Configuration

    Refer:
    https://community.fortinet.com/fortigate-3/technical-tip-forticlient-windows-ipsec-dialup-tunnel-keep-disconnecting-due-to-windows-ipv6-settings-193700

    Thanks, Salon
      M
      marunmAuthor
      Visitor III
      July 13, 2026

      Thanks, that helped—I found the solution in that post.

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