Guidelines For Choosing Bridging or Routing
The list below outlines some of the reasons why you might choose to configure the OfficeConnect Remote 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 OfficeConnect Remote 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 OfficeConnect Remote 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 OfficeConnect Remote to connect to the Internet you must configure the unit as a router.
How Bridges Learn
When a bridge is first powered on, it does not know the number or the locations of stations that are connected to the LAN. To minimize the amount of data passed over the bridge it must learn the whereabouts (address) of stations to ensure that it passes only the data that is intended to be passed over the bridge.
Like the envelope of a letter, the header of each frame of data transmitted on the network has a From (source) address and To (destination) address. This ensures that data reaches its destination on the LAN and that the receiving station can reply. The bridge reads every frame of data received at the LAN port and extracts the source address of the frame. From this information it builds an address table of stations it knows to be on the LAN.
To decide if data should be passed over the bridge, the bridge examines the destination address of the frame. If the address is already in its address table, the bridge knows the destination is on the LAN and therefore rejects or filters the frame.
If the destination address is not in the address table, the bridge transmits the data across the bridge. It does this even if the destination device is on the