What is the "technical" definition of LAN and WAN Most of explanations on internet contend by saying "lan" is over smaller distance, while "Wan" covers wider geography. To make question more clear ? 1. If two computers are on the same "LAN" what is it that they share in common to be on that `single LAN` they belong to ? Is it that they share a common router/switch/subnet ? Technically what is that that unifies under a LAN ? 2. If two computers are on the same "WAN" what is it that they share in common to be on that `same WAN` they belong to ? Is it that they share a common router/ subnet ? Technically what is that that unifies under a WAN ? 3. Is single datacenter considered a `Lan` ?

Wikipedia is your friend:

LAN: A local area network (LAN) is a computer network that user interconnects computers in a limited area such as a home, school, computer laboratory, or office building using network media.

In simple words, what unifies devices on one LAN: they are situated in the same area. Most commonly, one LAN is behind one router (not talking about backup routers and redundancy routers).

WAN: A wide area network (WAN) is a network that covers a broad area (i.e., any telecommunications network that links across metropolitan, regional, or national boundaries) using private or public network transports.

Again, in simple words: a WAN connection is connecting LAN's over a bigger area.

Example: LAN + internet/network + LAN = WAN (when talking about bigger area's)