I have pretty good internet, and so do the people I play with. Matchmaking works fine as does custom games. BUT when I go into Firefight or Forge (online) with a friend, I ALWAYS have around a second of lag. And anytime I play campaign online whether its with randoms or friends I have terrible lag. Is there a way to fix this?
Co-op FF and Campaign lag explained. I personally don’t really know of a way to fix it (and I suffer from it as well), unfortunately. But it’s an explanation at least.
If playing with friends making sure everyone has an open NAT is a good place to start, wireless can be unreliable so try connecting to your mode/ or modem/router using Ethernet.
also search your setting to
GOOD connection
Language
it also increases your chances to meet players in your area with a good connection!
thanks for the help guys
> also search your setting to
>
> GOOD connection
>
> Language
>
> it also increases your chances to meet players in your area with a good connection!
Doesn’t necessarily help. I can do Halo 3 Campaign, ODST Campaign AND Firefight with friends with absolutely no problems. Put in Reach and try to do campaign and FF and lag out. 
Probably due to the fact that maps/game modes have to be rendered/downloaded, which can cause lag, particularly for custom made ones as they are generally more complex. Dedicated servers would probably fix this, but I don’t think they are available.