Ok. My external IP is 89.212.176.254...
When I go to cmd.exe, I get the attached window. I guess that by default gateway you mean the 192.168.123.254.
They do not match, so I put it in my browser and the first three hits were these: (I am not really sure what you mean by the configuration page)
http://www.usr.com/support/8000a/800...anual/two.html
http://www.bugmenot.com/view/192.168.123.254
http://www.daniweb.com/forums/thread20228.html#