User's Manual

Table Of Contents
251
Users Manual of CS-6306R
20.1.2.8 Configuring Loop Guard
You can use loop guard to prevent alternate or root ports from becoming designated ports because of a failure
that leads to a unidirectional link. This feature is most effective when it is configured on the entire switched
network. Loop guard operates only on interfaces that are considered point-to-point by the spanning tree.
Loop Guard feature acts differently somehow in SSTP/PVST. In SSTP/PVST mode,, the designated port is
always blocked by Loop Guard. In RSTP/MSTP, the designated port is always blocked by Loop Guard. In
RSTP/MSTP mode, the port will be blocked only when it changes into the designated port because of
inaccessibility to receiving BPDU. A port which is provided with the designated role due to receiving the lower
level BPDU will not be blocked by Loop Guard.
Follow these steps to enable loop guard in global configuration mode.:
Command Purpose
spanning-tree loopguard default Globally enables loop guard feature. It is
valid to all interfaces.
no spanning-tree loopguard default Globally disables loop guard.
Follow these steps to enable loop guard in the interface configuration mode.:
Command Purpose
spanning-tree guard loop Enables loop guard feature on the
interface.
no spanning-tree guard Disables root guard and loop guard
feature on the interface.
spanning-tree guard none Disables root guard and loop guard on the
interface.