Loop Protection; Loop Detection - Allied Telesis SwitchBlade x908 Series Software Reference Manual

Switching Introduction

Loop Protection

Loop protection is a general term that embraces several different methods you can apply to
protect your network from effects such as broadcast storms that can result from data loops or
equipment malfunction. Presently two methods of loop protection are available:
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Loop Detection

Loop Detection

Feature
Introduction
This feature is used loop test frames to detect loops within the layer two path, and then to
apply selected protection mechanisms to limit their effect. The loop protection mechanisms can
applied either to the port at which the loop is detected or to the VLAN within which the loop
was detected.
Limiting
You can configure loop detection to apply one of the following mechanisms when a loop
Actions condition is detected:
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Operation
To detect loops this feature operates by transmitting a series of Loop Detection Frames (LDFs)
from each switch port out into the network. If no loops exist, then none of these frame should
ever return. If a frame returns to its original port, the detection mechanism assumes that there
is a loop somewhere in the network and offers a number of protective options.
Each LDF is a layer 2 LLC frame that contains the following components:
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You can set the detection mechanism to remember the LDF ID of up to 5 of the most recently
transmitted LDF frames. Each of the 5 most recently transmitted frames is compared with
every frame that arrives at that same port.
14.14
Loop Detection
Thrash Limiting
New vs_531 %flag
Disable all MAC address learning.
Block all traffic on the port (or aggregated link) that detected the loop, and take down the
link.
Block all traffic on the port (or aggregated link) that detected the loop, but keep the link in
the up state.
Block all traffic on a vlan. Note that setting this parameter will also enable ingress filtering.
This is the default action.
Take no action, but log the details.
Take no action.
the source MAC address of the originating switch
the destination MAC address of the non-existent end station 00-00-F4-27-71-01
VLAN ID (where the port is a tagged member of a VLAN).
a randomly generated LDF ID number.
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1

Loop Protection

This feature senses network loops and applies a selected corrective action.
C613-50007-01 REV B