Ultimate Guide to Networking: Part One

Bridges and routers are devices used for linking different LANs or LAN segments together. There are many companies that have LANs at various offices across the world. Routers were originally developed to allow connection of remote LANs across a wide area network (WAN). Bridges can also be used for this purpose. By setting up routers or bridges on two different lans LANs and connecting them together, a user on one LAN can access resources on the other LAN as if they were on the local LAN.

Sample Network Layout With a LAN Switch, Courtesy of Bay Networks

There are maximums on distances between workstations and hubs, hubs and hubs, and stations connected to a single LAN. You can exceed these maximums by linking two LAN segments (groups of users/devices) together using a Bridge or Router.

Bridges
Bridges are simpler and less expensive then routers. Bridges make a simple do/don't decision on which packets to send across two segments they connect. Filtering is done based on the destination address of the packet. If a packet's destination is a station on the same segment where it originated, it is not forwarded. If it is destined for a station on another LAN, it is connected to a different bridge port and forwarded to that port.

Routers
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
Switches are another type of device used to link several LANs and route packets between them. 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.