ZyXEL Communications ES-2108, User Manual, Page: 175 / 284

ES-2108 Series User’s Guide
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Loop Guard
This chapter shows you how to configure the Switch to guard against loops on the edge of
your network.
22.1 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 98 Loop Guard vs STP
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.
• It will receive its own broadcast messages that it sends out as they loop back. It will then
re-broadcast those messages again.
STP
Loop Guard