7970 behind NAT

Thanks to several on this forum and a few others, I have been able to successfully configure my Cisco 7970 phone.

However, I’m now having a bit of trouble configuring it behind a NAT. Here’s the setup:

Asterisk server is behind NAT. Every device connected locally works wonderfully. If I connect the 7970 locally, it registers without a problem.

The problems enter when I try to connect remotely. The 7970 will simply not register. The Asterisk logs don’t show any record of any register headers getting to the box, so it’s obviously a delivery problem unless I’m missing something or not looking in the right place.

I have a feeling that the problem is within the Cisco configuration, primarily because I can easily connect and talk remotely behind the NAT through various SIP softphones.

Any ideas?

In my configuration file, I have:

my external ip

Is this correct? Also, for any of you who have this working behind NAT, where exactly do those strings above go within the configuration file? I’ve noticed that the phone is rather picky about order and syntax.

Thanks in advance for any guidance.