Easy slice, then.
Do this:
1. Open your browser.
2. In the address bar, type: 192.168.1.1
3. Default Username should be admin. Password should be admin or blank, depending on the router.
4. Go to the wireless section.
5. Go to the Port forwarding Section.
6. Open another Window in another tab. Google the port forwarding settings for this particular P2P site.
7. Enter those values in the Port Forwarding section.
8. Save the changes
Should fix it. If not, I highly recommend you go to http://dd-wrt.com , go to the Supported Routers section, find your model, and download their custom firmware. To upload it to the router:
1. In the address bar, go to 192.168.1.1
2. User Name is admin. Password is blank or Admin
3. Go to the Admin or Advanced Tab
4. Click on Firmware Update.
5. Upload the .bin file you got from dd-wrt
6. Go into Tools - > Internet Options (Tools -> Options if Firefox)
7. Clear Cookies
8. Restart the Browser
That should take care of it. The DD-WRT firmware is top notch.