3Com S7906E Configuration Manual page 123

S7900e family release 6600 series
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Follow these steps to enable root guard:
To do...
Enter system view
Enter Ethernet
interface view, or
Enter
Layer 2
interface view
aggregate
or port group
interface view
view
Enter port group
view
Enable the root guard function for
the port(s)
Enabling Loop guard
By keeping receiving BPDUs from the upstream device, a device can maintain the state of the root port
and blocked ports. However, due to link congestion or unidirectional link failures, these ports may fail to
receive BPDUs from the upstream devices. In this case, the downstream device will reselect the port
roles: Those ports in forwarding state that failed to receive upstream BPDUs will become designated
ports, and the blocked ports will transition to the forwarding state, resulting in loops in the switched
network. The loop guard function can suppress the occurrence of such loops.
With loop guard enabled on a port, all instances on it are in the discarding state initially. Upon receiving
BPDUs, it can transition its role normally; if receiving no BPDU, it stays in the discarding state, thus
avoiding loops.
Do not enable loop guard on ports connecting to terminals, such as PCs. Otherwise, such ports will
always stay in the discarding state because they cannot receive BPDUs.
Make this configuration on the root port or an alternate port of a device.
Follow these steps to enable loop guard:
To do...
Enter system view
Enter Ethernet
interface view, or
Enter
Layer 2
interface view
aggregate
or port group
interface view
view
Enter port group
view
Enable the loop guard function for
the ports
Use the command...
system-view
interface interface-type
interface-number
port-group manual
port-group-name
stp root-protection
Use the command...
system-view
interface interface-type
interface-number
port-group manual
port-group-name
stp loop-protection
1-36
Remarks
Required
Use either command.
Required
Disabled by default
Remarks
Required
Use either command.
Required
Disabled by default

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