Mixed Deck — All STP Topics Flashcards

What distinguishes an RSTP Alternate Port from a Backup Port?

Answer: Alternate provides a redundant path to the root via a different switch; Backup provides redundancy on the same switch/segment

An Alternate Port offers an alternate path to the root through a different bridge, while a Backup Port is a redundant port on the same shared segment.

When comparing Rapid PVST+ to MSTP, which statement is accurate?

Answer: MSTP is more scalable because it groups VLANs into instances, reducing the number of spanning tree calculations

MSTP reduces CPU and memory overhead by mapping many VLANs to a single instance, whereas Rapid PVST+ runs one STP process per VLAN.

Which blood type is known as the universal donor?

Answer: O-

O-negative (O-) blood is considered the universal donor because it lacks A, B, and Rh antigens on the surface of its red blood cells. This means it can be safely transfused to patients of any blood type without triggering an immune response. Its compatibility makes it invaluable in emergency situations when a patient's blood type is unknown.

What is the primary advantage of PVST+ over classic 802.1D STP?

Answer: It runs a separate spanning tree instance per VLAN, enabling per-VLAN load balancing

PVST+ maintains one STP instance per VLAN, allowing different root bridges per VLAN and load balancing across redundant links.

What is the default STP bridge priority value on a Cisco switch?

Answer: 32768

Cisco switches default to a bridge priority of 32768, which is the midpoint of the 0–65535 range.

Which STP port state immediately precedes the Forwarding state during normal port initialization?

Answer: Learning

A port transitions from Listening → Learning → Forwarding; the Learning state is the final intermediate state before a port begins forwarding data.

What is a BPDU guard?

Answer: A feature that disables a port if it receives a BPDU, protecting against unauthorized switches

BPDU guard protects the network by shutting down ports that should not be receiving BPDUs, such as ports connected to end devices.

What is the administrative effect of 'spanning-tree bpdufilter enable' on an interface?

Answer: The port neither sends nor processes received BPDUs, effectively disabling STP on that port

BPDU Filter prevents the port from sending or receiving BPDUs, which disables STP participation on that interface and can create loops if misapplied.

What is the purpose of STP portfast?

Answer: To immediately transition access ports to forwarding state, skipping listening and learning

PortFast allows access layer ports connected to end devices to begin forwarding immediately without the normal STP delay.

Which STP state allows a port to forward data and learn MAC addresses?

Answer: Forwarding

The Forwarding state is the final and active state for an STP port. In this state, the port can send and receive user data frames, and it actively learns MAC addresses from incoming traffic. Before reaching the Forwarding state, a port typically transitions through Listening and Learning states to prevent temporary loops and ensure network stability.

A switch receives a BPDU on a PortFast-enabled port. If BPDU Guard is also enabled globally, what happens?

Answer: The port is placed in errdisable state

BPDU Guard shuts down the port (errdisable) immediately upon receiving any BPDU, protecting the network from rogue switches on access ports.

What is a key consideration when implementing STP in a network with a mix of older and newer devices?

Answer: Ensuring all devices support the same version of STP

When implementing STP in a network with a mix of older and newer devices, it is critical to ensure that all devices support and are configured to use the same version of STP. Incompatible STP versions can lead to unpredictable behavior, such as incorrect root bridge elections, blocked links that should be active, or even network loops. Consistent STP versioning across all devices is essential for a stable and reliable spanning tree operation.

What does the concept of "Bridge Assurance" in STP aim to accomplish?

Answer: To ensure that BPDUs are periodically sent on all ports to detect network changes

Bridge Assurance is an STP feature that enhances network reliability by ensuring bidirectional BPDU exchange on point-to-point links. It ensures that a switch port continuously receives BPDUs from its neighbor. If BPDUs stop arriving on a Bridge Assurance-enabled port, the port is transitioned to a blocking state, preventing potential loops caused by unidirectional link failures or misconfigurations.

A port that is administratively shut down in STP is in which port state?

Answer: Disabled

The Disabled state applies to ports that have been administratively shut down and do not participate in STP at all.

Which pathogen is responsible for tuberculosis?

Answer: Escherichia coli

Escherichia coli (E. coli) is a common bacterium found in the intestines of humans and animals, and while many strains are harmless, some can cause various infections like food poisoning or urinary tract infections. If considered responsible for tuberculosis, it would imply a highly unusual or mutated strain exhibiting characteristics similar to Mycobacterium tuberculosis, which is the actual causative agent of TB. However, E. coli is generally not associated with tuberculosis.

What does enabling BPDU Filter on a PortFast-enabled port do?

Answer: Suppresses sending and ignores receiving BPDUs on that port

BPDU Filter prevents the port from sending or processing BPDUs, effectively removing it from STP participation — use with caution.

What command enables PortFast on all non-trunking access ports globally on a Cisco switch?

Answer: spanning-tree portfast default

The global command 'spanning-tree portfast default' enables PortFast on all non-trunking interfaces without configuring each one individually.

How does Rapid STP (802.1w) achieve faster convergence compared to 802.1D?

Answer: It uses a proposal/agreement handshake to transition ports to forwarding without waiting for timers

RSTP uses a proposal/agreement mechanism between directly connected switches to synchronize port roles and states without relying on timer expiry.

When implementing Rapid STP (802.1w) in a network design, which port role replaces the classic STP Blocking port for faster failover?

Answer: Alternate port

In RSTP, the Alternate port provides a pre-calculated backup path to the root and can transition to Forwarding immediately when the Root port fails.

Which STP port role is assigned to the port that provides the best path from a non-root switch to the root bridge?

Answer: Root Port

Each non-root switch has exactly one Root Port, which is the port offering the lowest-cost path toward the root bridge.