VoIP Faxing

[itl3]

Hey guys,
I'm new to CSF, but I think it's amazing! I am running CSF v7.60 on CentOS 6.5 Final.
I am trying it on an asterisk PBX that is dedicated for VoIP faxing and am having some issues which I have been unable to diagnose. When the CSF is enabled, faxes fail. When I disable CSF and load a regular iptables script instead, they are flawless. I haven't been able to figure out why.

I've played with the following settings one at a time and nothing:

1) UDP IN and OUT: i've set ports 1:65535 open to see and that didn't change anything, which means it is not a port issue.
2) PACKET_FILTER: I suspected maybe it was dropping out of order packets, since UDP doesnt have any error correction. But no go!
3) PT_LIMIT: I disabled process tracking thinking maybe it was killing off a process that would cause the fax to fail. Nothing!
4) WHITELIST: I even whitelisted the IP sending the faxes. Still nothing.

I've also tried using the "low security" script available with CSF, but it also failed.

From what I understand about CSF, it is simply a great GUI for iptables, in addition to other features, such as using public blocklists from SPAMHAUSE etc... I think it is a great tool and would like to continue using it; so i'd like to figure out what is causing the faxes to fail. RTP seemingly works fine through it since I have made some voice test calls and have audio in both directions. Wireshark also shows T38 re-invites working for the faxes, yet they fail.

Not sure if this comment is silly or not, but I suspect it is caused by the forward chain somehow. I am not an expert on iptables and chains but I will do some research.

If anyone can suggest a setting I have overlooked, or point me in the right direction, I would be very grateful!

Thanks to all for any advice!

[itl3]

I was thinking about watching the logs while a fax is being sent. Can anyone tell me what log files to watch to see if packets are getting dropped?

Thanks for any help!