The Xbox is on that VLAN untagged via the switch config, my server and desktop (both Linux) has it tagged. This way I just turn it on and off in the network manager when testing things.
The rest of the network isn't on that VLAN at all, except the WiFi which has a separate SSID for the dual-stack network, again in case I want to test it on different clients.
Frustrating the Xbox now says IPv6 is working but moans uPNP is not available and the NAT is strict - so what the heck is the point of IPv6 there if its using IPv4 for gaming traffic? I thought the whole point was Microsoft was using Teredo for Xbox Live so it would work seamlessly when moving to IPv6.
I can tell you my experience.
I initially had it on ipv4 single stack as I didnt have ipv6 enabled on my guest VLAN, but the teredo just wouldnt work and hence had no multiplayer.
I then added a ipv6 subnet to the vlan and, it all came to life, multiplayer working fine. NAT reported as moderate, not sure why there is a NAT test on native ipv6.
I dont have issues with clients on guest VLAN been able to ping gateways on other VLANs for both stacks.
Firewall rules in pfsense doesnt allow guest vlan traffic to hit main vlan.
I assume your DHCP servers are isolated on appropriate VLANs and each VLAN has its own gateway ip?
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Testing ipv6 only connectivity now, console as usual forcing OS and controller firmware updates, waiting for these to complete.
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Same result as you, no single stack ipv6 support, thats really lame, looking at the view IP screen, the issue I think is DNS, it doesnt use any ipv6 DNS servers only v4.