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New Member

IP Phones over the Internet

What needs to be done to insure that an IP phone can function through a firewall or NAT? I have one working as far as dialing and connecting, but the actual voice traffic is not making it either way. I can use a VPN client and Softphone, but I wanted to use a real IP phone without having to deploy VPN hardware.

New Member

Re: IP Phones over the Internet

If your destination call spans across multiple ISP's then there is nothing you are going to be able to do from a QoS perspective to give strict priority to voice. LLQ and other queuing strategies need to be end to other words, once you hit your first router hop, you'll loose the QoS in place because you don't have control over internet routers. If it is with a single provider, you may be able to work with them on giving you the QoS that UDP voice traffic needs.

Cisco Employee

Re: IP Phones over the Internet

Which side has a fake IP address through NAT?

1) If it's the CM side and they are using an IOS gateway with NAT then you can use 12.1(5)T or later, where IOS NAT supports rewriting packets for Skinny.

2) If it's the CM side and they are using a PIX firewall then you can use 6.x code on the PIX and use the Skinny fixup command.

3) If it's the IP phone side then you would probably need to use a Cisco router running 12.1(5)T or later so that the NAT supports rewriting for Skinny. See:

The only other option I know of if one of these is not the case is a VPN tunnel.