I’m not sure at what point, but some time over the past week or two, my 2Wire 3800 HGV-B router was upgraded to new firmware (by AT&T of course), version 22.214.171.124 or rather 126.96.36.199-enh.tm. I’m not positive this fixed it or if AT&T upgraded their firewall policy, but for whatever reason, my NAT loopback works now. This has been a major complaint by both tech-ey customers and AT&T tech’s on various forums I’ve read ever since U-Verse started it’s roll-out a couple of years ago. It’s a pain to work around if you’re doing any port-forwarding on the outside of the firewall and then attempt to access those open ports from the inside of the network outward. Well, if you get upgraded to the latest version or get the latest firewall rules from AT&T, you should be good now.
Public IP scanned from the internal network