3 Spanning Tree Free Online FlashCards

What problem does STP prevent on networks with redundant switch links?

STP prevents Layer 2 loops by creating a loop-free logical topology and placing redundant paths in a nonforwarding state.

What information do BPDUs help switches exchange?

Switches exchange Bridge Protocol Data Units (BPDUs) to share information used to build the loop-free topology.

How does PVST+ handle spanning-tree topology across VLANs?

In Per-VLAN STP modes such as PVST+, each VLAN has its own spanning-tree instance and may have a different topology.

Which switch becomes the STP root bridge?

The switch with the lowest Bridge ID (BID) becomes the root bridge for that STP instance.

How does STP break a tie between Bridge IDs?

STP compares the complete BID numerically: lower priority wins; if priorities tie, the lower MAC address wins.

How does STP choose between paths with different costs?

STP prefers the path with the lower total path cost. A path with fewer physical links may still lose if its total cost is higher.

What is a root port?

On a non-root switch, the root port is the single port with the best path toward the root bridge. The root bridge itself has no root port.

What does a designated port do for its segment?

A designated port is the forwarding port selected for a network segment; it advertises that segment's best path toward the root.

How do alternate and backup ports differ?

An alternate port is a standby path toward the root. A backup port is standby on a segment where another port on the same switch already provides the designated connection.

Which port states does RSTP use, and what does discarding combine?

Traditional 802.1D STP uses blocking, listening, learning, forwarding, and disabled states. RSTP uses discarding, learning, and forwarding; discarding combines several traditional nonforwarding states.

What does PortFast do, and where is it intended to be used?

PortFast, also called edge-port behavior, lets a host-facing port enter forwarding promptly; it does not disable STP and should not substitute for correct switch-to-switch STP configuration.

What happens when BPDU Guard detects a BPDU on an edge port?

BPDU Guard disables an edge port when a BPDU arrives, guarding against an unexpected switch or loop on a host-facing connection.