Clamping in IPv6
Oh my… Seems we might have a talent for weird problems.
ip6tables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
Now IPv6 works with end-to-end connections. I can do ssh from my laptop behind my router directly to the company’s server/gateway and then to my workstation.