Spanning Tree Protocol (STP) Flashcards

In an Aruba switch running MSTP, which command correctly maps VLAN 10 and VLAN 20 to MST instance 1?

Answer: spanning-tree mst 1 vlan 10,20

On Aruba switches, the correct syntax to assign VLANs to an MST instance is 'spanning-tree mst vlan '.

What happens to STP topology when two switches have the same bridge priority and the same MAC address is theoretically used?

Answer: The switch with the lower MAC address becomes root

When bridge priorities are equal, STP uses the MAC address as a tiebreaker, and the numerically lower MAC address wins the root election.

Which STP timer controls how long a switch stores BPDU information before considering the topology stale?

Answer: Max age

Max age (default 20 seconds) is the time a switch retains BPDU information; if no BPDU is received within this period, the port information ages out.

Which feature prevents a non-root bridge from becoming root by blocking superior BPDUs received on a designated port?

Answer: Root Guard

Root Guard places a port in root-inconsistent state if a superior BPDU is received, preventing that port from becoming the root port.

In RSTP, what is the purpose of the Backup port role?

Answer: It provides redundancy to a segment where the switch itself is the designated bridge

An RSTP Backup port is a redundant path to a segment for which the local switch is already the designated bridge, typically seen with hubs.

A network administrator notices frequent topology changes causing MAC table flushes. Which STP enhancement can reduce unnecessary topology change notifications on access ports?

Answer: PortFast

PortFast suppresses Topology Change Notifications (TCNs) on edge ports since link flaps on host ports should not trigger network-wide MAC table flushes.

What is the STP port cost for a 100 Mbps link using the original IEEE 802.1D short path cost method?

Answer: 19

The original IEEE 802.1D short path cost assigns a cost of 19 to a 100 Mbps Fast Ethernet link.