ZyXEL Communications MES-2110, Руководство пользователя

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MES-2110 User’s Guide
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C
H A P T E R
7
Loop Detection
7.1 Overview
Loop detection allows you to configure the Switch to shut down a port if it detects
that frames sent out on that port loop back to the Switch.
Loop detection is designed to handle loop problems on the edge of your network.
This can occur when a port is connected to a Switch that is in a loop state. Loop
state occurs as a result of human error. It happens when two ports on a switch are
connected with the same cable. When a switch in loop state sends out broadcast
messages the messages loop back to the switch and are re-broadcast again and
again causing a broadcast storm.
If a switch (not in loop state) connects to a switch in loop state, then it will be
affected by the switch in loop state in the following way:
• It will receive broadcast messages sent out from the switch in loop state.
• It will receive its own broadcast messages that it sends out as they loop back. It
will then re-broadcast those messages again.
The following figure shows port N on switch A connected to switch B . Switch B is
in loop state. When broadcast or multicast frames leave port N and reach switch
B , they are sent back to port N on A as they are rebroadcast from B.
Figure 26 Switch in Loop State
The loop detection feature checks to see if a loop detection enabled port is
connected to a switch in loop state. This is accomplished by periodically sending a
probe frame and seeing if the frame returns on the same port. If this is the case,
the Switch will shut down the port connected to the switch in loop state.
A
B
N