3Com 3C840 - Manual (Page 167)

How Bridges Learn A-5
not be placed on LAN A. Therefore, frames passing between LAN B and
LANs C or D will not impact the overall performance of the LAN.
Figure A–2 Multiple Remote Bridge
Multiple Paths
Between Bridge LANs
With only a single physical path between LANs, the network is
susceptible to link and bridge failures. In the event of a failure, the
connection between any of the LANs upstream or downstream from the
point of failure will be broken. A more resilient network of
interconnected LANs can be established by providing more than one link
between any two of the LANs.
Normally, this network would soon encounter serious problems resulting
from a loop, around which frames could endlessly travel if precautions
aren't taken by the bridges. To prevent loops, you can enable the
Spanning Tree Protocol (STP).
When STP is enabled, the bridges send out frames to inquire if there are
other bridges on the network. By exchanging information, the bridges
block ports that cause the loops and ensure that there is only ever one
active path through the network. If one of the links or bridges fail, the
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