Cisco IP Phone NAT

[Abdu]

Hi

I have CME with two IP Phone

IP Phone1: 172.16.15.5

CME: 172.16.15.6

IP Phone2: 10.10.10.2

IP Phone2 have 10.10.10.2 and after NAT have 172.16.15.8, the problem I faced is the phone 2 can ring but not receive any Media only send, 

How I make Phone2 receive the RTP Media?, 

Thanks

[Mohammed al Baqari]

Hi,

Are they two subnets on same router or different sites? With natting there are very limited options to get media working. Therefore, I suggest to avoid it

[Abdu]

It is two sites, I can't avoid NAT, is there any workaround..

[Mohammed al Baqari]

Are both sites using same CME or two CMEs with trunk between them (e.g. SIP Trunk). If SIP trunk is used, then the solution will be enabling nat detection on both CMEs using the config

sip-ua

nat symmetric check-media-src

[Abdu]

Both site using same CME

[Mohammed al Baqari]

In this case nat won't work. You need to have SIP trunk between CMEs to get nat working with the feature I mentioned.

A work around is to register phone 2 to CME using natted IP not the original IP. This case CME won't know the original IP and will ask phone 1 to send rtp stream natted IP

[Abdu]

How I make Phone2 registered in CME using natted IP?

[JustForVoice_2]

I do not if this could help. If you are using firewall for nat then you have to disable SIP inspection in the firewall.

[Mohammed al Baqari]

Hi,

This is a routing config using combination of nat, local policy route map and loopback. It will do natting for phone IP before it hits cme.

I thought about one more thing, are you using ephones. If so, apply the command mtp under each ephone and reset the phones then test

[Abdu]

i used SIP Phone not sccp, is there any config. i can do in CME or sip phone to allow using nat ip for phone to solve issue?

[Abdu]

if possible to give me steps, How I can fix this issue?

[Gordon Ross]

SIP & NAT don't work.

Can you use, say, an IPSEC VPN between the two systems?

GTG

[Abdu]

Hi

I tried asterisk with soft-phones SIP same scenario, and it works fine!! 

Thanks

[Gordon Ross]

Asterix is probably using a system such as STUN. Not sure if CME (or CUCM) supports STUN.

GTG

[Abdu]

Hi

Is the STUN will work if there is not Internet?

Thanks