4 Spanning Tree Protocol Free Online FlashCards

How does STP prevent Layer 2 loops?

STP prevents Layer 2 loops by placing redundant paths in a standby state while preserving a loop-free forwarding path.

What can STP do when an active link fails?

If an active link fails, STP can recalculate the topology and activate a redundant path.

How does PVST+ handle spanning trees across VLANs?

In common Cisco PVST+ and Rapid PVST+ deployments, STP calculates a separate spanning tree for each VLAN.

What are BPDUs used for in STP?

Switches exchange BPDUs to compare paths and determine the active spanning-tree topology.

How is the STP root bridge elected?

The switch with the lowest bridge ID wins: lower bridge priority is preferred, then the lower MAC address breaks a priority tie.

What is distinctive about the root bridge’s port roles?

The root bridge is the reference point for path-cost calculations and has no root port.

What does a root port do?

A root port is the port on a non-root switch that provides its best path toward the root bridge.

What is the role of a designated port?

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

What does an RSTP alternate port provide?

In RSTP, an alternate port is a standby port that offers another path toward the root and normally discards data frames.

How do an STP port’s role and state differ?

A port’s role describes its function; its state describes what it is doing. Forwarding ports carry traffic, while discarding ports do not; learning ports learn MAC addresses without forwarding user traffic.

How does path cost influence STP path selection?

STP normally prefers the path with the lower total cost. Lowering an interface’s cost makes that path more attractive and can change which redundant link blocks.

Where should PortFast be used?

PortFast is for end-device ports, such as those connected to PCs or printers, and lets them enter forwarding quickly. It is not a replacement for STP on switch-to-switch links.