[magicalhippo]

The cable modem is a dumb bridge, and the pfSense is doing the routing (AFAIK). I can't see any way to do relative rules though, which is what makes it difficult. Maybe I'm missing something though.

[fulafel]

The manual seems to talk about host and network aliases, which might be what you want. Hopefully there are magic aliases for the interface networkts.

edit: https://docs.netgate.com/pfsense/en/latest/firewall/firewall... also talks about "LAN net" and "WAN net" aliases.