Xbox 360 system link

me and my friends used to have halo 2 parties every weekend back in the day. we would plug up to 4 360s into one of our routers, and play system link. but with xbox 360 games, it doesnt work. we have to direct link them instead of putting them into a router, or else it wont work. anyone else have this problem?

i mean

it works for halo 2

but not for halo 3 or gears of war

Well, if it still works, just in a different way, what's the problem?