Yesterday via Twitter it was revealed by a 343 Industries employee, Che Chou Franchise Manager at 343 Industries, that Halo: The Master Chief Collection will support LAN (or System Link). Che Chou was responding to tweets about how the upcomming Gamescom Halo 2 Anniversary tournament would work and Che Chou replied through “Custom Games on LAN”
Two more tweets clarified that for LAN to work there still needs to be a connection to the internet. The internet connection doesn’t have to be major, it’s just so the Xbox One consoles can make a “handshake” and ping to Xbox Live.
Chief Canuck - Video Game News 
WTF!!!!!!! Is the point of ****ing lan support if you need an internet ready connection,, its not difficult to just support system link, games are getting really bad because guess what????? One day the servers will be shut down and you have a game that supports lan but can’t use it?!?!? Nice job
It’s to make sure that you own the game. It won’t require a robust connection at all. Plus with dedicated servers it won’t go down… which by the way you won’t need dedicated servers if you’re using a LAN connection to play with a friend.