I am provisioning customers with IPv6 over PPPoE. I found out that there are MTU issues when customers connect to services that have a misconfigured firewall preventing PMTU discovery to work.
If I add mangle rules that adjust TCP MSS in SYN packets to 1432 when it’s bigger, the problem vanishes.
The PPP profile option “Change TCP MSS” adds mangle rules only on IPv4 PPPoE traffic. Is it possible to automatically add also IPv6 mangle rules to resize MSS on IPv6 PPPoE traffic?