Sams Teach Yourself Network Troubleshooting in 24 Hours, Second Edition

Routers and Switches

Just as every phone in a corporation might have the same prefix, and allow for in-house, four-digit dialing without hitting the phone company’s switching equipment, so too do networks have the concept of local network versus remote network. NICs on a local network can communicate with each other without needing remote-capable equipment. To communicate with a NIC on a remote network, a router is required.

To make it easier for routers to differentiate between networks, each network (in modern times, usually referred to as a VLAN, or Virtual Local Area Network) is given a network number. It will come as no surprise, because a router is connected to more than one network, that a router has more than one NIC in it. Its function ...