I have Tomato on a wl520 gu and have the Loopback set to All only on the firewall. In the past I have had no issues using the external IP address to access devices on the LAN while being on the LAN too. I am facing a problem now where I have another subnet behind the router and a static route setup to access that subnet. Port forwarding works fine and I can access the devices remotely if I am Offsite, but if I am on the LAN and try to access the devices with the port number it doesn't work, and I have no idea why.
Loopback on another subnet?