Server not working externally

I installed bukkit server so that my friends can get on and play on a private server. They are able to connect anywhere via the same LAN as the server is on but not remotely. Here is how I have it setup:

I have a linksys router that has port forwarding enabled to the computer running the server, the router is connected to a cable modem that also has port forwarding enabled for that port to the router (By now someone should be able to enter my ip and connect). I also have a dynamic dns service setup through the router itself to give me a static ip address and I own a custom domain that points to that static ip address.

The server is running on Ubuntu Linux 64-bit using the recommended build of craftbukkit.

The problem is, despite that, people still aren't able to connect. There's no particular error message it just acts like the server is offline displaying the following message "Can't reach server".

I've tried from my custom domain, my static ip, even directly typing in my dynamic ip address. I've double and triple checked everything.

 

Try doing a port check on all IPs. Is 25565 open or closed while the server is running?

 

Externally using subnetonline.com it says
"Connection Refused"

Internally (localhost) using nmap it says
"open"

Well I got a temporary work-around which explains where the problem lies. The workaround was to enable dmz mode for the cable modem to the router and dmz mode for the router to the pc. The upside is now it works like a charm, the downside is dmz creates a huge security hole and is overkill for what I need it for.

That means, despite the fact that I forwarded the proper ports, the signal still stopped at either the cable modem or the router. The best guess I can come up with is some other port that I didn't know about that needs forwarding.

EDIT by Moderator: merged posts, please use the edit button instead of double posting.