USG20W-VPN - AT&T - IPSec VPN Troubles - Resolved

Amarand · May 2018

After spending hours on the phone with AT&T business tech support, we finally got the modems situated to the point where the USG20W-VPN on both sides of a site-to-site configuration are working again.

My client took an extended power outage (6+ hours) and their AT&T modem forgot all its settings. So...hours and hours of different techs on different days, we finally got it down to the following setting: IP Passthrough. We used a Passthrough Mode of "DHCPS - Fixed" with a MAC address to IP address binding.

https://www.att.com/esupport/article.html#!/smb-internet/KM1184085

Once you configure both ends of the VPN pipe to this setting, things magically work. All of the ports are opened, like a firehose, to the Zyxel, and it "just works."

I'm posting this information 1) as a BIG THANK YOU to the two engineers at Zyxel who double-checked my configuration work on the units and 2) as a reminder that although AT&T technical support generally sucks, if you know exactly what you need, you can usually get it.

Sadly, I had to use the "my client is going to cancel both Internet services if you don't get this problem resolved" line. But that was after three days of no service for them and an inability for the client to do their job.

I'm hoping that with this post, I can save someone the trouble of having to get mad at someone in a broken organization who's really not that good at their job and just praying for the next dozen "easy" modem reset calls.

As an aside, I've used VPNs professionally on Spectrum and WOW without any issues for years.