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--- RE: Cisco 7941G "Registering" and Symetric NAT (http://www1.pbxes.com/forum/threadid.php?threadid=1553)

Cisco 7941G "Registering" and Symetric NAT

We are have a lot of trouble gettign our ne wCisco 7941G phone to work we previously used Cisco 7940G & 7960G and these were easy to setup, but not the new version.

Our setup is this 4 phones plugged into a switch then a reouter doing NAT on a single static public IP. I have tried DMZ'ing one of the phoen to see if nat is the issue but no luck. All the phones are stuck in Registering I can see from the ssh interface they are trying to connect but for some reason they are having trouble. I beleive the problem is some thing to do with "symetric NAT"

taken from http://www.voip-info.org/wiki/view/Standalone+Cisco+7941%252F7961+without+a+local+PBX
Most consumer VOIP services, including providers that support Cisco 79x0 model phones, will not work with 79x1 phones without intervention on the provider side. Because the 79x1 phones send SIP messages from arbitrary high number UDP ports (e.g. 49000+) the symmetric NAT approach used by Asterisk (nat=yes) and most VOIP providers does not work with these phones. The 79x1 will transmit ICMP unreachable messages back to SIP proxies that attempt to respond to SIP registration using symmetric NAT (you will see inbound SIP messages from the proxy with a high number UDP port destination, assuming your router works with symmetric NAT).

The 79x1 behavior is RFC compliant, just incompatibly non-standard. Cisco support reports that this the use of random high number ports to send SIP messages is a "security enhancement" compared with Cisco's other/older products.
Any help with this matter would be great as we are looking to deploy a number of these phones in our company but we need to make sure they can work. Thanks for all your help.

RE: Cisco 7941G "Registering" and Symetric NAT

These phones cannot work behind NAT routers. On public IPs they don't work because of the way PBXes (and most other SIP servers) work.

Is there anyway that pbxes could disable nat for one of my extensions (as per RFC compliance nat should not be used anyway at the pbx end) so I can test.

From googling this seems to be a common problem with oter providers but each of theose where able to easily fix by turnign of nat for the extensions at the pbx end.

Apart from this problem we have been increadibly impressed with pbxes.com and would like to continue ing your service.

RE: Cisco 7941G "Registering" and Symetric NAT

Revisiting this discussion it seems there is not much demand for a change. Anyhow it would be technically possible. So we offer you to make these phones work on public IPs by paying 2.5 hours of paid support.

RE: Cisco 7941G "Registering" and Symetric NAT

Has any progress been made on this issue? I have a large number of Cisco 7960 phones with SIP firmware 8.12 (P0S3-8-12-00) which I would like to use with a premium PBXes account.

Has anyone made this work?

RE: Cisco 7941G "Registering" and Symetric NAT

I second this. This would be useful.

RE: Cisco 7941G "Registering" and Symetric NAT

uh, these are a pain. I'd suggest that cisco made them annoyingly deliberately to make you buy their software for a lan environment.

anyway, has anyone managed to get one to register with pbxes? I'm having all sorts of trouble.

RE: Cisco 7941G "Registering" and Symetric NAT

What is your hourly rate? I'd be interested in opting for the paid support option.