Technical information

AX Series L2 Loop Detection Configuration Guide (Edition 2)
Copyright © 2008, 2010, ALAXALA Networks Corporation. All rights reserved.
12
2. Examples of the Basic Usage of the L2 Loop Detection
Functionality
The efficient use of each functionality for preventing L2 loops can stop the occurrence of L2 loops or reduce the
impact of L2 loops to a minimum, if they occur.
This chapter specifically describes examples of the basic configurations and operations of the L2 loop detection
functionality.
2.1 Example of an application configuration
The following figure shows an example of the application of the L2 loop detection functionality in a
configuration with core switches and access switches connected redundantly with STP, as a general network
system.
Figure 2.1-1 General core and access network
STP and other protocols are available to control redundant configurations between network devices on a core
network configured at the Layer 2 level. Such L2 redundancy protocols also play a role to prevent loops between
network devices. In addition, as configurations of such networks are modified by the network administrator in most
cases, the occurrence rate of incorrect settings or incorrect connections is considered to be low.
Therefore, networks with redundant configuration between network devices, as represented by core networks,
are considered loop-free, reducing the necessity of using the functionality for preventing L2 loops.
However, for endpoints that connect to access switch destinations, terminals, servers, and hubs, and that do not
support L2 redundancy protocols, L2 redundancy protocols are not necessarily enabled. In addition, connection
ports are often open to general users, which increases the possibility of loops due to the invalid line cable
connections.
As such, it is most effective to enable the L2 loop control functionality at access edges.
The following is an example of using the L2 loop detection functionality on a switch used as an access edge.
Core switch o
r
distribution switch
Core network
- Unseen from general users
- Redundancy protocol is enabled.
Access switch
Device E1
- Accessible by general users
- Out of control range of
redundancy protocols
↓
High risk of loops!
Small-sca
le hub
A
ccess networ
k
To prevent this ↓
No redundancy control
≈ Vulnerable to loops
Application of L2 loop
detection functionalit
y
Redundant
configuration with STP