I used a Mitel 5340 IP phone for work. Normally it works fine with the default configuration. However, when I make a network bridge to utilize the other ports on the firewall, it suddenly stops working, claiming "TFTP server unavailable" and getting stuck on "Contacting server".
This is odd because I look at the firewall log and there's no incoming traffic to the IP being blocked, and it still doesn't work even if I forward every TCP/UDP port to the phone's IP address (which still shouldn't be necessary as it works fine without the bridge). The only way to get it to work is to remove the network bridge by restoring the default configuration.
It is as follows: Mitel 5340 -> POE adapter -> Network Switch -> OPT0 (part of bridge)
Everything else works fine and the internet is accessible. I followed the network bridge guide to create it. The only thing that doesn't work is the TFTP client on the phone.
It seems to be the same problem as this person is having https://www.reddit.com/r/opnsense/comments/1dtzjmo/work_voip_phone_behind_opnsense_router_wont/
however there is no solution there either and the OP ends up giving up on the issue.
My modem is in bridge mode and all I can think to do is to just connect the phone directly to the ISP modem alongside the firewall, which does work. I'd prefer not having to do that however.