Loop Guard; Chapter 27 Loop Guard; Loop Guard Overview - ZyXEL Communications MGS-3712/MES-3728 User Manual

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H A P T E R
This chapter shows you how to configure the Switch to guard against loops on the
edge of your network.

27.1 Loop Guard Overview

Loop guard allows you to configure the Switch to shut down a port if it detects that
packets sent out on that port loop back to the Switch. While you can use Spanning
Tree Protocol (STP) to prevent loops in the core of your network. STP cannot
prevent loops that occur on the edge of your network.
Figure 134 Loop Guard vs. STP

Loop Guard

Loop guard 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.
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Loop Guard
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