Routers are more complex and more expensive than bridges. They use information within each packet to route it from one LAN to another, and communicate with each other and share information that allows them to determine the best route through a complex network of many LANs.

Switches are another type of device used to link several LANs and route packets between them. They are very similar to routers.

A switch has multiple ports, each of which can support either a single station or an entire Ethernet or Token Ring LAN.
With a different LAN connected to each of the ports, it can switch packets between LANs as needed.

Routers interconnect networks at the internetwork layer level and routes packets between them. The router must understand the addressing structure associated with the networking protocols it supports and take decisions on whether, or how, to forward packets.
Routers are able to select the best transmission paths and optimal packet sizes.

The basic routing function is implemented in the IP layer of the TCP/IP protocol stack, so any host or workstation running TCP/IP over more than one interface could, in theory and also with most of today's TCP/IP implementations, forward IP datagrams.
However, dedicated routers provide much more sophisticated routing than the minimum functions implemented by IP.

Because IP provides this basic routing function, the term "IP router," is often used. Other, older terms for router are "IP gateway," "Internet gateway," and "gateway." The term gateway is now normally used for connections at a higher layer than the internetwork layer.

A router is said to be visible to IP. That is, when a host sends an IP datagram to another host on a network connected by a router, it sends the datagram to the router so that it can forward it to the target host.