ZyXEL Communications XS3800-28, User Manual, Page: 285 / 789

Chapter 41 Loop Guard
XS3800-28 User’s Guide
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Loop Guard
41.1 Loop Guard Overview
This chapter shows you how to configure the Switch to guard against loops on the edge of your network.
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 198 Loop Guard vs. STP
Refer to Section 41.1.2 on page 285 for more information.
41.1.1 What You Can Do
Use the Loop Guard screen ( Section 41.2 on page 287 ) to enable loop guard on the Switch and in
specific ports.
41.1.2 What You Need to Know
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:
• The switch (not in loop state) will receive broadcast messages sent out from the switch in loop state.
• The switch (not in loop state) will receive its own broadcast messages that it sends out as they loop
back. It will then re-broadcast those messages again.