yeah the most likely thing is your firewall may be preventing people from connecting to you i have had this before but it is also upto you if you want to risk disabling your protection to allow people to join your server either that or you can try and configure all your protection to allow halo but it depends on what protection you use. You might be better off just connecting to other peoples games or finding some mates that can direct connect to your i.p address then you know you are more safe
i have the same problem so i disable my firewall but still does not work i have heard of this program called Xfire that peaple use to play but i dont know what it is exacly.
it could be anything even my adware program stopped me from playing online it doesn't just have to be your firewall and my spyware program stopped it and i am not risking disabling all my protection. To be honest with you most of the time it is nothing to do with your protection it is to do with one thing and that is: Nobody wants to join a server with 1 person lol i have left a server open for ages and no one joined because believe it or not it is pretty hard to get the server running with lots of people. Its generally the servers that are running 24/7 that people tend to join becasue they know the server but you may get lucky you just have to be patient or ask your friend to join your server
Xfire is a chat program that's popular with my friends. Basically it tells you when your friends are playing games and shows their servers for games like CSS (and all the other steam games), Battlefield, etc etc. It also has a click to join the server your friend is playing in. If you're behind a router that might also be a problem.
You can have exceptions in your firewall. Halo automatically adds itself though. You could have some problems with your internet server, like latency but most people don't.