3Com AccessBuilder 500 User Manual - page 74

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Bridging and Routing Concepts

A bridge connects one or more LANs together. It examines each data 

frame received at a LAN port and forwards any frames that it assumes are 

for a destination device not connected to that LAN port. The bridge is able 

to do this by learning which devices are connected to each LAN port.

A router learns much more about the networks connected to it and is 

able to be much more selective about the data it passes on to other 

networks and to which networks it transmits. By default routers reject or 

filter

 data unless it matches predefined attributes (for example specific 

protocols or destination network addresses). In large interconnected 

networks a router selects the best route for data to travel.

Guidelines For Choosing Bridging or Routing

The list below outlines some of the reasons why you might choose to 

configure the AccessBuilder 500 as a bridge or a router. Read through 

the rest of this appendix for more explanation and to help decide 

which of the above conditions apply to your network.

■

A bridge is simpler to configure but a router can provide more security on 

a busy network and filter unwanted data transmissions more effectively.

■

If your network consists of only one or two links between different sites 

and your network is not heavily loaded, in most circumstances you can 

configure your AccessBuilder 500 units as bridges.

■

If your network structure is complicated and consists of a mixture of 

leased line and ISDN links, or if it uses several different protocols, you 

may obtain better performance from the AccessBuilder 500 units if you 

configure them as routers.

■

If you are connecting to a routed corporate network that is already running 

IP and/or IPX protocols or if you are using the 

AccessBuilder 500

 to 

connect to the Internet you must configure the unit as a router.