Network Authentication
Network Authentication is what happens when you have a computer connected in a network, but, to actually make use of its resources you must perform authentication against a server machine which is running a network authentication service. The windows network authentication happens when you have a server running the Active Directory service so that the users who seek wired network authentication will have to present a user-name and a password to the server.
This network authentication system prevents any sort of physical or wireless intrusion since all users must be previously registered into the Active Directory. Without a valid login any attempt to join the Domain will be bounced off and thus disallowing use of the network resources without any additional network authentication protocols. If the network authentication failed several times in a row, the user attempting the login will also have its system blocked for a few minutes, preventing a breach attempt by brute force.
In addition to the wired network authentication, there's also the Wi-Fi network authentication, which allows users to join the Local Area Network through wireless devices, but in addition to the windows XP network authentication, you'll have to do an authentication check against the router. It will be running one of several possible protocols: Network authentication WEP, WPA, WPA2 or BBRAS based.
When it comes to wireless network authentication methods, WEP is probably the worst there is these days since it can literally be cracked in minutes. WPA and WPA2 come second, but they are already very strong encryption systems that so far haven't been broken and the only way to pierce it is through picking up certain packets, the so called handshake packets, and try to brute force crack them. Ultimately you have the BBRAS system, where the router is linked to a server machine with a series of user-names and passwords much like if it was the Windows Active Directory records and use those network authentication settings to welcome the users to the local network.
Other network authentication software that can be used to login into a network is VPN software. You can be outside of a LAN, but as long as this network has a Internet connection you can connect into a machine on the inside through a Virtual Private Network system, which means that you'll connect to a computer that is within the LAN and use it just like if you were there. You will of course still have to perform authentication against the Active Directory settings as well.
These are the only real network authentication methods that matter the most when trying to construct a network that is actually safe but very functional still. It will allow everyone who uses the local computers to be protected and your servers won't be accessed by anyone else other than specified by you, provided there is no security breach from part of the persons who use the computers. In case a user-name and password set is provided to a stranger, that's all that's needed to try and break in into the network system.