3Com OfficeConnect Remote 510 User Manual

Contents

A-2 BRIDGING AND ROUTINGGuidelines For Choosing Bridging or RoutingThe list below outlines some of the reasons why youmight choose to configure the OfficeConnect Remoteas a bridge or a router. Read through the rest of thisappendix for more explanation and to help decidewhich of the above conditions apply to your network.n A bridge is simpler to configure but a router canprovide more security on a busy network and filterunwanted data transmissions more effectively.n If your network consists of only one or two linksbetween different sites and your network is notheavily loaded, in most circumstances you canconfigure your OfficeConnect Remote units asbridges.n If your network structure is complicated and consistsof a mixture of leased line and ISDN links, or if it usesseveral different protocols, you may obtain betterperformance from the OfficeConnect Remote units ifyou configure them as routers.n If you are connecting to a routed corporate networkthat is already running IP and/or IPX protocols or if youare using the OfficeConnect Remote to connect to theInternet you must configure the unit as a router.How Bridges LearnWhen a bridge is first powered on, it does not knowthe number or the locations of stations that areconnected to the LAN. To minimize the amount ofdata passed over the bridge it must learn thewhereabouts (address) of stations to ensure that itpasses only the data that is intended to be passedover the bridge.Like the envelope of a letter, the header of eachframe of data transmitted on the network has a From(source) address and To (destination) address. Thisensures that data reaches its destination on the LANand that the receiving station can reply. The bridgereads every frame of data received at the LAN portand extracts the source address of the frame. Fromthis information it builds an address table of stationsit knows to be on the LAN.To decide if data should be passed over the bridge,the bridge examines the destination address of theframe. If the address is already in its address table,the bridge knows the destination is on the LAN andtherefore rejects or filters the frame.If the destination address is not in the address table,the bridge transmits the data across the bridge. Itdoes this even if the destination device is on theRc.bk : RCAPPA.FRM Page 2 Thursday, July 10, 1997 9:53 AM