[Serusers] How to rewrite source IP -- SIP packet forwarding.

Ray Van Dolson rayvd at digitalpath.net
Tue Aug 2 00:37:38 CEST 2005

I'm using nathelper with SER.  Here's a quickie diagram of my

  [SIP ATA] <-------------> [SER] <------------------> [Asterisk]            eth1 -          eth0 - <public_ip1>
                       eth0 - <public_ip0>

I'm using the basic nathelper example configuration, except for one
modification.  I removed the call to t_relay and replaced it with:

t_relay_to("<public_ip1>", "5060");

Basically I want a SIP packet to come in to eth1 on SER server, get
rewritten as needed by nathelper, then get sent out to public_ip1 on my
Asterisk PBX.

This appears to be working except a tcpdump on eth0 on SER shows:

14:39:08.654908 IP > <public_ip1>.5060: UDP, length 629

Obviously the packets will never get back with that source IP address.  What
command should I be looking at to rewrite this IP so it shows up as
<public_ip0> automatically?

I'm trying to get SIP ATA's to REGISTER on my Asterisk box but proxy through
SER ... (and eventually make use of the rtp proxy).

Can post more info if requested, I am new to SER. :-)

Ray Van Dolson
Linux/Unix Systems Administrator
Digital Path, Inc.

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