[Serusers] Re: [Serdev] Better NAT support in registrar

[Jan Janak]

Yes, I am going to include this into the existing documentation.

  Jan.

On 01-03 11:07, Klaus Darilion wrote:
> Wow! A perfect description. Thanks Jan.
> 
> Wouldn't it be a good idea to put such detailed descriptions from the 
> mailinglist into the README files or any other repository, e.g. FAQomatic?
> 
> Sometimes there are really good descriptions on the mailinglist (e.g. 
> http://lists.iptel.org/pipermail/serdev/2005-February/003877.html) which 
> should also be put into the README files.
> 
> regards,
> klaus
> 
> 
> Jan Janak wrote:
> 
> >Hello,
> >
> >The development version of SER now includes enhanced NAT support in
> >registrar and user location database. A small example:
> >
> >Let's suppose that you have a single SER instance listening on two
> >ports -- 5060 and 5090. Using a different port seems to be often
> >necessary because of broken SIP ALGs (Application Level Gateways) that
> >are often built into DSL routers or other devices. Such ALGs would
> >mangle SIP requests and responses coming to and from port 5060 and the
> >only option how to avoid such mangling is using a different port number.
> >
> >Let's suppose that we have two UAs beind NAT, one of them is configured
> >to reach SER on port 5060, the other one is configured to use port 5090
> >(due to the reasons described above):
> >
> >                  +---------+
> >UA1 ---- NAT1 ----| 5060    |
> >                  |      SER|
> >UA2 ---- NAT2 ----| 5090    |
> >                  +---------+
> >
> >The previous version of registrar would store the public IP of NAT with
> >each registered contact, thus it would know how to reach both user
> >agents.
> >
> >But, it would not store the port number of SER the UAs used to register
> >themselves and later, when an INVITE comes, it would not know which
> >port number (5060 or 5090) it should use as the source port number of
> >the outgoing INVITE. The previous version would use the default one,
> >which would be the first one configured in the configuration file
> >(usually 5060).
> >
> >When an INVITE for UA1 comes, everything would work because UA1 used
> >port 5060 when registering and that is also the destination port in the
> >pinhole being kept open in NAT1:
> >
> >                                 SER
> >                 INVITE UA1  +--------+     INVITE UA1
> >UA1 ---- NAT1 <------------- |  5060  | <---------------- 
> >                             |        |
> >UA2 ---- NAT2                |  5090  |
> >                             +--------+
> >
> >When an INVITE for UA2 comes, SER would again use port 5060 as the
> >default outgoing source port number, but this time the message will be
> >dropped by NAT2, because the pinhole opened during the registration has
> >5060 as the destination port number:
> >
> >                                 SER
> >                 INVITE UA2  +--------+     INVITE UA2
> >UA1 ---- NAT1        +------ |  5060  | <--------------- 
> >                     |       |        | 
> >UA2 ---- NAT2 X <----+       |  5090  |
> >                             +--------+
> >
> >The new version of registrar would also store the destination IP and
> >port number used on SER side when performing registration and that
> >information would be used later by SER when forwarding INVITEs:
> >
> >                                 SER
> >                             +--------+     INVITE UA2
> >UA1 ---- NAT1                |  5060  | <---------------
> >                 INVITE UA2  |        |
> >UA2 ---- NAT2 <------------- |  5090  |
> >                             +--------+
> >
> >(Note that the X next to NAT2 has disappeared in this picture which
> > means that the message will be lucky enough to make it through :-).
> >
> >SER would encode this information into a SIP URI when saving contacts in
> >database and later, after restart of SER, this information will be
> >restored. The URI looks like:
> >
> >sip:1.2.3.4:5060;dstip=5.6.7.8;dstport=5090
> >
> >Where the hostname part is the public IP of the NAT, the port (5060) is
> >the port allocated by the NAT, "dstip" parameter is the IP used on SER
> >side and "dstport" parameter is the port number used on SER side during
> >registration. This information is later used to find the correct outgoing
> >socket in SER. If no such socket can be found (it can happen if you
> >reconfigure SER to use different ports or IPs), it will use the default 
> >IP/port again.
> >
> >Daredevils are encouraged to give it a try and send feedback to the list 
> >:-)
> >
> >   Jan.
> >
> >_______________________________________________
> >Serdev mailing list
> >serdev at lists.iptel.org
> >http://lists.iptel.org/mailman/listinfo/serdev
> >
> >
>