Which of the following commands can be issued without interfering with the operation of loop guard?

Which of the following commands 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:
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 enabled on the entire switched network. Loop guard prevents alternate and root ports from becoming designated ports, and spanning tree does not send BPDUs on root or alternate ports.

You can enable this feature by using the spanning-tree loopguard default global configuration command.

When the switch is operating in PVST+ or rapid-PVST+ mode, loop guard prevents alternate and root ports from becoming designated ports, and spanning tree does not send BPDUs on root or alternate ports.

When the switch is operating in MST mode, BPDUs are not sent on nonboundary ports only if the interface is blocked by loop guard in all MST instances. On a boundary port, loop guard blocks the interface in all MST instances.