The plan would be to set up a tunnel for serial communication over WAN using two TRB255 gateways. On server side a SIM card would be used that has a fixed IPv6 address assigned by the telecom provider.
Now it seems that the serial over ip implementation does not support IPv6 communication. Although the configuration of the Over IP client allows setting an IPv6 address as server, the ip filters for the server configuration only accept IPv4 addresses.
The Over IP server function also was tested using the LAN connection. Even without any active IP filters all connections to the configured port using IPv6 communication was blocked while access over IPv4 was fine. The tests were made with firmware 7.2 and the latest 7.4.2 (TRB2_R_00.07.04.2). Over LAN it seems that no firewall rule is blocking any communication by default. Also the web interface could be accessed via IPv6 so the network stack itself should be fine.
Is it true that the serial over IP feature does not support IPv6 communication? Or is there some other configuration that needs to be changed?