Which command can be issued without interfering with the operation of loop guard?
A.
Switch(config-if)#spanning-tree guard root
B.
Switch(config-if)#spanning-tree portfast
C.
Switch(config-if)#switchport mode trunk
D.
Switch(config-if)#switchport mode access
Explanation:
The spanning-tree guard root cannot be enabled together with loop guard. The loop guard
feature is supposed to be used on the port receiving BPDU and guard root will shutdown the
port as soon as the first BPDU comes to that port.
Configuring portfast on the port connected to the other switch can create temporal loop.
Configuring access mode on the port can filter BPDU from other VLANs from coming to the
port and force loop guard feature to put this port into error-disabled state.
So the only command that can be issued without interfering with the operation of loop guard
is “switchport mode trunk”.
Reference:
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094640.shtml