Register Cisco phone 7942 with external VoIP provider

[slimard001]

Hello,

I would need your help to solve registering a Cisco phone 7942 with external VoIP provider.

My phone is running firmawre SIP42.8-5-4S is used in home office behind an ADSL router.

I am attaching two log files (printscreens): Registration process from Cisco phone and response back from the VoIP provider. I have noticed that Cisco sent the SIP registration on UDP high port instead of 5060 and expect the answer back on UDP 5060. Unfortunately, the VoIP provider answers back on the high port. I learned this is called symmetric NAT.

Up to know, I cannot find a way to solve this and I appreciate if someone succeeded in this.

Thank you

Ben

[slimard001]

Hello,

No one? Is there some people with similar case? Is there any solution? If not, please let me know

Thanks

S.

[slimard001]

Hi all,

I would appreciate your feedback.

Many thanks

S.

[mkchandak]

The snapshot that you have shared, the higher number port is the source port and not the destination port. If you look at the destination port, that is 5060 which is the SIP port. I think you need to go back to your provider and show that the destination port is 5060 which is accurate based on the information provided above.

Hope this helps.,

[slimard001]

Hello,

Thanks for the answer. I have indeed contacted the provider before posting here.

Their answer is "We cannot respond to port 5060 if the register message originated from a different port."

[mkchandak]

Your SP needs the source port to be 5060 and the destination port to be 5060 as well ? I've not heard this before.

[slimard001]

It seems due to symmetric NAT. The problem exists only with model 7942 and higher. With Cisco 7940, it is working because source and destination port are 5060

[mkchandak]

7940/60 supported 3rd party SIP registrar and therefore there were known and supported options to make changed. With the new 79x1/2 phones, they are officially only supported with CUCM, therefore no configuratio file is available. Considering you are trying to register this, do you have a custom xml configuration file created which is being used ? If yes, you can update it to disable nat on it.

[slimard001]

Ok, thank you

[Leo Laohoo]

The snapshots you've posted are useless.  Can you attach (not post snapshots) of the 79X2's SEPmacaddress.cnf.xml file?  Just remove the username and password detail but leave everything else.

1.  Does your VSP support NAT?

2.  Does your VSP support ALG enabled?

3.  Can you ensure the outgoing and incoming proxy details are entered correctly?  Some VSP have different proxy details.

If you want a working SEPmacaddress.cnf.xml file, look at this. 

[slimard001]

Please find the file you requested.

1. They claim to support symmetric NAT

2. do not know

3. I received on proxy server from the provider

[Leo Laohoo]

I am attaching two log files (printscreens): Registration process from Cisco phone and response back from the VoIP provider. I have noticed that Cisco sent the SIP registration on UDP high port instead of 5060 and expect the answer back on UDP 5060. Unfortunately, the VoIP provider answers back on the high port. I learned this is called symmetric NAT.

I disagree.  If the VSP support symetric NAT, then they should be responding with the same ports, 5060.  The only time I've seen a request going OUT with high port numbers is when NAT and/or ALG is enabled on your side and the VSP supports NAT, so this means you are doing double-NAT.

Another thing, you may want to consider turning OFF your modem's ALG. 

g729a

Make sure the VSP has this in writing that they support this codec.

  true

Change this to false.

Not sure if this'll work with your VSP but put 5060 here.  Do this last. 

[slimard001]

Thank you, I will try this evening and let you know

[Leo Laohoo]

Just edited my previous post.

What is ALG?  Read this.

Depending on the make and model of your router, here is the Google search result on modem ALG and how to enable/disable it:  https://www.google.com.au/search?client=opera&q=disable+alg+voip&sourceid=opera&ie=utf-8&oe=utf-8&channel=suggest