Re: [hylafax-users] Hylafax Client - Server problem

[An Intrepid HylaFax User <hylafax@xxxxxxxxx>]

> According to previous discussion on fax client and server through FTP
> port 4559, no one can answer this firmly.
> 
> What I think is that this is a problem due to NAT. This situation occurs
> similarly in Voice Over IP (VOIP). For example, in SIP, NAT will only
> change the source IP address for LAYER 3 only, but those embedded in IP
> message at or above Layer 4 (TCP/UDP layer or above) will not be
> translated to the NAT address. A voice channel (UDP) cannot be
> established as internal IP address is un-routeable. This can be solved
> by installing STUN server or Tunneling techniques.

If you're using Linux as a router, you can configure your ip_nat_ftp module to
do protocol inspection for the hylafax ports as well as ftp.  Linux provides a
a rich set of flexible NAT and conntrack helpers which work with protocols
like FTP and IRC which pass around IP#s around as part of its session
conversations.

These topics are covered at length by various HOWTOs and FAQs.  The Hylafax
protocol looks almost identical to FTP's with respect to its file xfer
commands, so I suspect adding the hylafax ports to the nat/conntrack ftp
helpers will "make it all work" like magic.

=R=




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