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Firefox Not Honoring Windows Tcpip6 Parameters on Dual-Stack Networks

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AndyPandy
AndyPandy

On a dual-stack network, with Windows tcpip6 ‘disabledcomponents’ parameter set to prefer IPv6, Firefox ignores this setting whenever an endpoint resolves both an IPv4 and a NAT64 address.

While monitoring traffic captured while connecting to sites in Firefox, if the initial DNS request for the site comes back with an IPv6 address only, the connection attempts from client’s IPv6 address to destination IPv6. If DNS answers come back with IPv4 and IPv6, the connection attempts IPv6 to IPv6. If DNS answers come back with IPv4 and a NAT64 address, Firefox doesn’t even attempt to connect to the NAT64 address, it immediately defaults to IPv4. I’ve tried disabling the IPv4 fallback setting which doesn’t change the behavior.

We’re running version 140.8.0esr. Is this behavior intended for Firefox? Is there a way to configure Firefox so it doesn’t ignore NAT64 addresses in dual-stack environments? The only way I found to force this was to completely disable the IPv4 stack on the client system’s NIC.

On a dual-stack network, with Windows tcpip6 ‘disabledcomponents’ parameter set to prefer IPv6, Firefox ignores this setting whenever an endpoint resolves both an IPv4 and a NAT64 address. While monitoring traffic captured while connecting to sites in Firefox, if the initial DNS request for the site comes back with an IPv6 address only, the connection attempts from client’s IPv6 address to destination IPv6. If DNS answers come back with IPv4 and IPv6, the connection attempts IPv6 to IPv6. If DNS answers come back with IPv4 and a NAT64 address, Firefox doesn’t even attempt to connect to the NAT64 address, it immediately defaults to IPv4. I’ve tried disabling the IPv4 fallback setting which doesn’t change the behavior. We’re running version 140.8.0esr. Is this behavior intended for Firefox? Is there a way to configure Firefox so it doesn’t ignore NAT64 addresses in dual-stack environments? The only way I found to force this was to completely disable the IPv4 stack on the client system’s NIC.

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