What "ethernet port" does airport utility use for "remote administration"

Question

I have a friend who was recently evangelized to Macs and bought a Macbook Pro and an Apple Airport Extreme (gigabit) Router, hereinafter called AE. The place where he lives has cable modem internet access and an older Linksys wireless-G router for the building, and I am trying to configure his new AE, prior to making it the primary router in the network (e.g. connected to the cable modem).
When the AE is completely configured the Linksys will be retired.
I remotely manage and maintain the network and some other computers in that house. The Linksys is configured for Remote Administration so I can manage it. I manage several PC's and Macs using Timbuktu Pro 8, with the necessary ports forwarded through to TB2 on those machines.
I am trying to configure the Airport so it also can be managed remotely, so from a workstation on that network (accessed from where I am using TB2) and running Airport Utility, I have checked "Allow setup over WAN" on the Airport/BaseStation page. Now I would like to test whether I can connect and remotely administer that Airport Extreme from Airport Utility on my Mac.
I assume that, if I can rout packets from my Airport Utility here through the internet to the public IP of the Linksys router there, I should be able to connect. But I can't.
My setup is this. The target AE has its WAN port connected to an ethernet port on the Linksys, as is the LAN in the remote building. Nothing is connected to the AE's ethernet ports at this time. The Linksys is the DHCP server, and the AE has an IP from it, as does all the other ethernet- and wireless-connected computers, printers, etc. The AE's wireless is active and the wireless-connected devices in the building can connect to either its base station or to that of the Linksys. When the Linksys is retired the AE will be the only wireless in the building.
I attempt to connect in the following way: On my Mac, I run Airport Utility. From the file menu I select "Configure other" and enter the public IP address of the remote Linksys, and give AE's password. There is a long wait
Reading the Airport wireless device configuration....
while Airport Utility tried to discover AE, and then
An error occurred while reading the configuration..... (-6753)
I suspect that my remote connection problem is due to the fact that the AE is behind the Linksys, and the proper port forwarding is not in place on it to pass the Airport Utility's packets through to the Wan port of the AE. This might be that I have not entered into the Linksys the correct port number to forward on to the AE. I've tried the three numbers in the list:
"Well known TCP and UDP ports used by Apple software products" found at
http://support.apple.com/kb/ts1629
that are mentioned as possibly being involved with Airport Utility; 192, 4500 and 5009.
Advice will be appreciated.
Bob

Answer 1

One example, and there may be others, is the (free) DynDNS dynamic DNS service which publishes a domain name for the WAN port of your router which can then be resolved, like all other domain names, to the actual IP address of the WAn port of your router. This service provides a solution to the problem of having a proper domain name in cases where your public IP address changes over time. Unless you pay for a static IP address, virtually all ISPs change your public IP address over time.
So, you can register for a free DynDNS account at www.dyndns.com and that is how you come up with the User: and Password: information; use whatever User and Password you register at dyndns.com with.
The first part of the hostname you can define as you wish, subject only to someone else having used it previously, and the remaining parts of the domain name might be "dyndns.org" or one of the other domain names provided by the DynDNS service. So, you could publish, via DynDNS, the name of your public IP address as, for example, joehlam.dyndns.org however you might want something less descriptive or more vague.