Peer to Peer Connection Problem across the Internet

My router a Xyxel 660H refuses to allow peer to peer connections across the internet. I have set up numerous rules, added NAT settings and removed them, all, (except once) to no avail. The once worked fine with me hosting a multiplayer session, but with another player on another day it failed. Has anyone done this with a Zyxel router, and what rules did they set up. The Xyxel router is very techie so rules set up with more user friendly, higher level firmware interfaces probably won't help me.For the reord I created a rule to allow my incoming player's WAN IP to pass through my router to my network in the WAN to LAN rules area. In the destination addreses box, I put the range of internal IP addresses of my 3 PCs. The service is UDP 23456.Peter