3com 520 用户手册
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Introduction
During the initial configuration of the OfficeConnect
Remote you must decide whether to configure the
unit as a bridge or as a router although we may help
you with this choice with our Quick Configuration
options. If you are unsure which option you should
choose, read this appendix to help you decide.
Bridges and routers are used to connect networks
together. The cost of connecting networks together
is generally proportional to the distance over which
the network extends and the amount of bandwidth
required. Large amounts of bandwidth can be
provided easily within a LAN by connecting different
segments together with a local bridge. However, it
becomes impractical and expensive to extend this
bandwidth over larger distances, and it is, therefore,
usual to interconnect local high speed networks
using bridges or routers connecting over slower
speed terrestrial and satellite links.
In the following sections we describe the concepts
behind bridging and routing, and discuss the
different ways in which LANs can be configured and
operated to optimize performance and minimize
disruption of traffic on each individual LAN.
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.
Rc.bk : RCAPPA.FRM Page 1 Thursday, July 10, 1997 9:53 AM