Minimum Internet connection requirements
The minimum requirements to run theHunter Multiplayer is a 256Kbps (for clients) and a 1Mbps (for game hosts) ADSL or broadband Internet connection. Dial-up Internet connections will not work.
Depending on your router configuration, you may experience problems when connecting to some games. You will get a black screen saying "Could not connect to host".
Internet uses IP addresses to communicate between computers. Currently Internet uses IP v4 which has a limited amount of IP addresses, which means all computers / devices on the Internet cannot get an unique IP address. Routers is one solution to the problem. A router has (usually) _one_ external IP address on the Internet and then gives internal addresses for all computers / devices connected to it. Routers use NAT (Network Address Translation) or NAPT (Network Address And Port translation) to translate an external IP address and port to a specific computer / device. Some NAT types have problems to translate addresses from some NAT types.
Read more about NAT ans how it affects online connectivity: (http://en.wikipedia.org/wiki/Network_address_translation)
NAT (Network Address Translation) Types
Open: can connect to any of the three types.
Moderate: can only connect to open and moderate.
Strict: can ONLY connect to open.
Strict NATs are a difficult problem with multiplayer games that don’t use dedicated servers. Since most people don't have open NATs, the player with a strict NAT won't be able to find many joinable games. Another problem is that sometimes the ISP (Internet Service Provider) is also NAT'd which often means even if you have a direct connection to the Internet (without a router/firewall), the ISP still acts as a strict NAT.
These are some recommendations to improve your connectivity
Enable uPnP (universal plug and play) on your router. The game can use this to automatically forward a port from the router to the computer.
Port forward UDP port 32303. Guides to how you can forward ports: http://portforward.com
Here are some additional tips
Make sure your router's firmware is upgraded the latest version.
Unplug your router for 10 minutes and plug it back in. Some older routers degrade in performance over time until it is rebooted, similar to a PC.
Disable any firewall or other network filtering for the game.
On Windows Vista, the network driver security service pack sometimes breaks network packets for the game. This service pack should be rolled back, and not installed.
3rd Party Tools
If the above tips do not resolve you issues, try using a third party tool.
You can create your own virtual private network as if your computers would be located next to each other. This tools helps you to connect to each other and resolve the connection issues.