NATed UA RTP Packets go to LAN IP

[tekknow]

We have NAT ed Cisco 7960 phones that have been used with other IPPBX systems and VOIP providers directly with 100% success. We have battled with registering to 3CX on a Public IP. THe phone is behind a NAT and not the PBX.

IN the case if the CIsco Phone , and this did not happen with Snoms, an ethereal capture from the 3cx machine revealed it was sending all RTP packets to the LAN IP of the phone, and NOT the public IP . Those packets originating from a Public IP are clearly destined for 192.168.1.X , a non routable LAN IP. OF course on the Snom we had to enable STUN , which is not an option for the Cisco. I think STUN resolves the public IP


I might point out that the phone registers, however I suspect that the source for the RTP IP is derived differently than the IP for SIP packets.

I originally did the Capture from the 3cx machine to look to see the destination ports, and much to my surprise I found them destined for the LAN IP, not the publicly routable IP

Any ideas?

 

[Philco]

I find it strange that the LAN IP address of the remote phone is actually sent to the server. Is this normal, i.e is the LAN IP address of the remote phone behind NAT normally encapsulated in the message to the 3cx server?

I guess its something peculiar with cisco phones and 3cx server in this instance, however I know of one of the members of the forums on here that had a system working then all of a sudden, his system then started responding to the LAN address and not the public address to a remote phone which was a Grandstream device, which I think had actually gone faulty.

Would be interesting to see what is said about this.

Phil

 

[tekknow]

I posted a related thread of a working Cisco 7960 Config, http://www.3cx.com/forums/finally-cisco-7960-success-7398.html#p37443
At least in my case. I do not believe my configuration of 3cx is typical, but IS typical of other IP PBX systems we integrate.

The difference is that our 3cx system is on a Public IP, No LAN


The phones connect though a NAT and separate public IP

IN this case the phone had been successfully configured from the menus to go from One type of IP PBX to another and to Various SIP Proxies. Only with 3cx DId we see the issue of the LAN IP

FYI it is typical that in the SIP Message on a phone behind a NAT that both the Public and LAN IPs are present. This is sometimes called "NAT Mapping" such as In Linksys/Sipura terminology

In the case of the Cisco Config "nat_enable: "1"" and ONLY IN THE CASE OF 3CX another NAT option " nat_received_processing: "1"" was necessary, which we have never had to enable before.

 

[Philco]

Ah yes, Nat MAping I investigated further, makes a mock of NAT security to some extent IMHO.

I have 3cx test set up here that is on public IP no LAN, well yes it is a LAN but all devices have their own public IP addresse and where remote phones are behind a NAT with or without public IP they work fine to the 3cx server.

Not used the Cisco, only Grandstreams and Snoms (only one) and not had any issues.

So have you manged to get it working.

Phil