Alaxala AX2200S Series Configuration Manual page 364

19 Spanning Tree Protocol
PortFast Configuration definition
Functiona
lity
Configuration for each port
(spanning-tree guard)
Root guard is set (root)
No command specified
Disabled Loop guard is set (loop)
Guard disabled (none)
Root guard is set (root)
No command specified
Legend:
Y: Supported, --: Not supported
(2) Notes on loop guards
Loop guards cannot be used for Multiple Spanning Tree.
After loop guard functionality is set, when the following events occur, the loop guard runs to
block ports. Loop guards are not cleared until a BPDU is received.

Starting the switch

A port goes up (including due to link aggregation)

The type of Spanning Tree Protocol changes (to STP or high-speed STP, PVST+ or
high-speed PVST+)
Configure loop guard functionality not only on designated ports, but also on partner
switches. When it is configured only on designated ports, even when the above events
occur, the designated ports might not receive BPDUs. In cases like this, removing loop
guards might take a long time. This is because removing a loop guard requires waiting for
BPDU transmission after a BPDU reception timeout is detected on a port on the partner
switch.
Also, even if loop guards are set for both ports, removing the loop guard on a designated
port might take a long time if no BPDUs are received. Specifically, this happens when a
bridge, port priority, or path cost is changed so that the opposing port becomes a
designated port, in which case a BPDU timeout is detected on the opposing port, and loop
guard operation is performed. If this port is a designated port, BPDUs might not be received,
and removing loop guards might take a long time.
When loop guard functionality is set during operation, the loop guard will not run
immediately, but instead will run when a BPDU reception timeout occurs.
When a switch that does not forward BPDUs exists between the Switch and a partner
switch, and a port is linked up while loop guard functionality is set on both ports, loop
guards will continue running on both ports. To perform recovery, BPDU forwarding
342
Configuration for each
switch
(spanning-tree loopguard
default)
command specified
No command specified
(Priority is given to the
configuration for each port.)
Command specified
No command specified
Loop guard
operation
--
--
--
Y
--
--
Y
--