I've been using a Lynksys PAP2T-NA ATA off and on for at least a few months now. I get my VoIP service from Les.net and I'm pretty happy with it. Les has been making some improvements even over the short time I've been using the service and just today the servers started checking for some common device configuration problems on the customer side that cause network issues. Well, I was an offender. My problem was that the PAP2 was set up to send NAT Keep Alive messages every 15 seconds. I'm pretty sure this was the default setting out of the box, but apparently it's overkill. The recommendation was to set the time up to between 60 seconds and 120 seconds. I don't think it was a major issue and it was easy for me to fix, so I thought I'd write down all the details of it.

If you have the same box and aren't impressed with the manual that Linksys offers, here's all I did to set my NAT Keep Alive Interval up to a more friendly 90 seconds (click the images for bigger screenshots).

In a web browser on the same LAN as the PAP2, open the configuration page for the PAP2. I think the default address is http://192.168.0.109/ but I moved mine to 192.168.3.109. To find out for sure what IP address your PAP2-NA is set to, pick up a phone and dial ****110#. The four asterisks (****) starts the IVR menu, 110 is the command to get the IP address. You will hear the address read back to you.

Click Admin Login. There's no password by default to switch to the Admin view on the unlocked PAP2-NA.

Click the little "(switch to advanced view)" link.

Click the SIP tab circled in the picture below.

You should now be at a screen something like this

My firmware version as of this writing is 5.1.2(LS), some options might move around a little on other versions. Down at the bottom of the page, you can find the option that we actually want to set. It's called "NAT Keep Alive Intvl" on here and it appears to be the time betweeen NAT keep alive messages measured in seconds. In the screenshot below I've already adjusted mine to 90 seconds.

After adjusting it be sure to click the "Save Settings" button at the bottom. The PAP2 will save all the settings and reset.

That's all there is to it. I set mine up about an hour or so ago and it seems to work fine. The one consequence I imagine this could have is that when my external,ISP-assigned dynamic IP address changes, it could take up to 90 seconds for the ATA to figure it out. That part's just a guess so don't quote me on it. If you know differently then leave a comment below.