[Abekkus]

Strange. This sounds like something Hurricane Electric specifically limited. There’s nothing in CGNAT that would naturally break such a tunnel

[pQd]

HE is using plain stateless IPv6 in IPv4 tunnel - it's neither TCP nor UDP, it's not NAT'able.

it's relatively simple for them to implement [ the stateless part ] but due to that puts some requirements on the party establishing the tunnel.

[TechDebtDevin]

I use tunnels all day like this with cgnat on multiple devices.