ZyXEL Communications MSC1000G Series, Руководство пользователя

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Chapter 4 Access Control List Screens
Management Switch Card User’s Guide
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4.20 Loop Guard
Configure loop guard to protect against loops on the edge of your network. Loop guard allows you
to configure the system to shut down a port if it detects that packets sent out on that port loop
back to the system. 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 58
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.
The following figure shows port N on system A connected to another switch B . Switch B has
mistakenly two ports, x and y , connected to each other. It forms a loop. When switch B receives
broadcast or multicast frames, they will be broadcast again to senders including port N on system
A .
Modify Select an entry’s Select radio button and click Modify to display the entry in the table
above so you can edit it.
Delete Select an entry’s Select radio button and click Delete to remove the entry.
Table 40
ACL > PPPoE (continued)
LABEL DESCRIPTION
STP
Loop Guard