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PPENDIX
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RIDGING
AND
R
OUTING
Guidelines for
Choosing Bridging or
Routing
The list below outlines some of the reasons you might choose to
configure the OfficeConnect Remote 840 as a bridge or a router. Read
through the rest of this section 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 is not heavily loaded, in most circumstances you can
configure your OfficeConnect Remote 840 units as bridges.
■
If your network structure is complicated and consists of a mixture of
leased-line and modem links, or if it uses several different protocols,
you may obtain better performance from the OfficeConnect Remote
840 units if you configure them as routers.
■
If you are connecting to a routed corporate network that is already
routing the IP protocol, or if you are using the OfficeConnect Remote
840 to connect to the Internet, you must configure the unit as a
router.
■
If you want to link networks that the OfficeConnect Remote 840 is
not routing, you must configure bridging. The OfficeConnect Remote
840 may serve as an IP router and a bridge simultaneously.
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
necessary 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 a 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
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