[Serusers] SER on masqueraded/NAT connection

[Kelvin Chua]

I would suggest a cisco router to act as a NAT. it can read the SIP
messages properly. Though I'm still undergoing some tests with it, so
far sa good :)

-----Original Message-----
From: serusers-admin at iptel.org [mailto:serusers-admin at lists.iptel.org] On
Behalf Of Jiri Kuthan
Sent: Tuesday, January 14, 2003 9:46 PM
To: Craig Graham; serusers at lists.iptel.org
Subject: Re: [Serusers] SER on masqueraded/NAT connection


Craigh,

the problem unfortunately lives deeper than in SER -- it is about SIP
interaction with NATs. SIP advertises IP addresses and port numbers in
its messages, a technique which does not work along with NATs. What
happens is that SIP messages from your private network get out to the
public Internet, still carry private IP addresses in it, and attempts of
other call parties to use these private IP addresses will fail.

A preview of the .11 documentation mentions these issues.
(I hope the correct link is www.iptel.org/ser/doc/, I'm offline
now.)

I'm unfortunately not aware of a method that would be able
to traverse Linux-NAT for Messengers. All of the methods 
I'm aware of take some kind of NAT-support in end-devices, SIP-support
in NATs or both. They include ALG (i.e., SIP awareness in NATs,for
example intertex NATs do that), STUN (phones' ability to "fool" NATs,
for example k-phone or snom do it), UPnP (must be supported by both
phone and NAT), manual configuration (one must have "tweakable" phones 
and NATs and the ability to actually tweak both), or
"symmetric phones" (like Cisco's ATA).

-Jiri

At 11:28 AM 1/14/2003, Craig Graham wrote:
>I have a Linux box at home acting as a masquerading/NAT gateway for a 
>few Windows PCs, and have installed SER on there in order to use MS 
>Messenger to talk to people outside.
>
>SER appears to be working in that I can get Messenger up on two PCs, 
>connect to SER and set up a voice connection between the two PCs. 
>However, I cannot connect to people offsite.
>
>Relevant IPChains entries are
>target     prot opt     source                destination
ports
>ACCEPT     udp  ----l-  anywhere             anywhere              any
->
>5060
>ACCEPT     udp  ------  anywhere             anywhere              any
->
>7070:7080
>
>I have made no changes to the default SIP configuration; it is working 
>as installed by the rpm package ser-0.8.10-1.i386.rpm. A browse through

>the mailing list archive and through the admin guide doesn't show 
>anything obvious. No errors are reported to /etc/messages or 
>/etc/syslog and serctl moni does not show anything that looks relevant.
>
>Does anyone have any suggestions?
>
>--
>Dr. Craig Graham, Software Engineer
>Advanced Analysis and Integration Limited, UK. http://www.aail.co.uk/
>
>
>
>_______________________________________________
>Serusers mailing list
>serusers at lists.iptel.org http://lists.iptel.org/mailman/listinfo/serusers

--
Jiri Kuthan            http://iptel.org/~jiri/ 

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