Configuring Loop Guard - 3Com 4500 Configuration Manual

Configuration procedure
Follow these steps to configure the root guard function in system view:
To do...
Enter system view
Enable the root guard function
on specified ports
Follow these steps to enable the root guard function in Ethernet port view:
To do...
Enter system view
Enter Ethernet port view
Enable the root guard function
on the current port
Configuration example
# Enable the root guard function on Ethernet 1/0/1.
1) Perform this configuration in system view
<Sysname> system-view
[Sysname] stp interface Ethernet 1/0/1 root-protection
2) Perform this configuration in Ethernet port view
<Sysname> system-view
[Sysname] interface Ethernet 1/0/1
[Sysname-Ethernet1/0/1] stp root-protection

Configuring Loop Guard

A switch maintains the states of the root port and other blocked ports by receiving and processing
BPDUs from the upstream switch. These BPDUs may get lost because of network congestions or
unidirectional link failures. If a switch does not receive BPDUs from the upstream switch for certain
period, the switch selects a new root port; the original root port becomes a designated port; and the
blocked ports turns to the forwarding state. This may cause loops in the network.
The loop guard function suppresses loops. With this function enabled, if link congestions or
unidirectional link failures occur, both the root port and the blocked ports become designated ports and
turn to the discarding state. In this case, they stop forwarding packets, and thereby loops can be
prevented.
Use the command...
system-view
stp interface interface-list
root-protection
Use the command...
system-view
Interface interface-type
interface-number
stp root-protection
1-36
Remarks
—
Required
The root guard function is
disabled by default.
Remarks
—
—
Required
The root guard function is
disabled by default.