Dasan V5808 - Topology Change Detection; Loop Guard

UMN:CLI User Manual
V5808
312
8.3.9 Loop Guard
An STP loop is created when an STP blocking port in an redundant topology erroneously
transitions to the forwarding state. This usually happens because one of the ports in a
physically redundant topology no longer receives BPDUs. In this case, the designated
port transmits BPDUs, and the non-designated port receives BPDUs. As a result, the
blocking port from the alternate or backup port eventually becomes designated and
moves to forwarding state. This might cause a loop if the reason for not receiving BPDUs
has been other than actual failure of a link. If BPDUs are not received on a non-
designated port when loop guard is enabled, that port is moved into the STP loop-
inconsistent blocking state, instead of the listening / learning / forwarding state. Without
the loop guard feature, the port assumes the designated port role. The port moves to the
STP forwarding state and creates a loop.
To enable/disable the loop guard on the specified port, use the following command.
Command
Mode
Description
spanning-tree port PORTS
guard loop
Bridge
Enables the loop guard on the ports
spanning-tree port PORTS
guard none
Disables the loop guard on the ports.
To enable/disable the loop guard on all the ports, use the following command.
Command
Mode
Description
spanning-tree loopguard default
Bridge
Enables loop guard function on all the ports.
no spanning-tree loopguard
default
Disables loop guard function on all the ports.
8.3.10 Topology Change Detection
The ability to detect topology changes can be enabled or disabled on a per-port. If the
TCN guard function is enabled on a port, it detects its STP topology change.
To configure TCN Guard on the ports, use the following command.
Command
Mode
Description
spanning-tree port PORTS
tcnguard enable
Bridge
Enables a guard for STP topology change notification.
spanning-tree port PORTS
tcnguard disable
Disables a guard for STP topology change notification..