pfSense

In the config for igmpproxy, Network populates altnet and has to be in subnet format. Since the GUI has a drop-down for the CIDR/Prefix, that means Networks should validate an IP address only. As far as I can tell it can't use hostnames or aliases. The GUI code reassembles the value into subnet style before storing it in a space-separated list. So it should be tested before it gets that far.

"threshold" has no limits in the igmpproxy source or documentation but given that it is compared to a TTL, I'd say it should be limited to nearly the same range as a TTL, allowing for it to be set lower or higher than the possible values for a TTL.

Packets with a lower TTL than the threshol[d] value will be ignored. This setting is optional, and by default the threshold is 1.

Given that, perhaps -1-256 could be the allowed range. -1 would ignore nothing, 256 would ignore everything (which doesn't seem to make sense, but...)

Feel free to take a shot at the validation, Phil. If you don't have time right now then I can do it.

PR has been merged. Thanks!

works as expected on 2.5.0.a.20200220.1948