STP Advanced Features and Variants 4

Question 1

What is the purpose of Loop Guard in STP?

Accepted Answer

To protect against loops caused by unidirectional link failures on non-designated ports

Answer

To prevent root bridge election from being influenced by unauthorized switches

Answer

To block ports that receive superior BPDUs from downstream switches

Answer

To speed up convergence on uplink ports at the access layer

Question 2

Which feature detects unidirectional fiber link failures at the physical layer, complementing Loop Guard at the STP layer?

Accepted Answer

UDLD (UniDirectional Link Detection)

Answer

PortFast

Answer

BPDU Filter

Answer

Backbone Fast

Question 3

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

Accepted Answer

Suppresses sending and ignores receiving BPDUs on that port

Answer

Sends BPDUs at double the normal interval for faster detection

Answer

Converts BPDUs into LLDP frames before forwarding

Answer

Forces the port into root port role regardless of cost

Question 4

In Rapid PVST+, what type of port can transition directly to Forwarding without going through Discarding and Learning states?

Accepted Answer

Edge Port (PortFast-enabled) when link comes up

Answer

Root Port when receiving a superior BPDU

Answer

Alternate Port when the root port fails

Answer

Designated Port on a point-to-point link after proposal/agreement

Question 5

What happens to a PortFast-enabled port if BPDU Guard is active and a BPDU is received?

Accepted Answer

The port is placed in err-disabled state immediately

Answer

The port ignores the BPDU and remains in Forwarding state

Answer

The port transitions to Blocking but stays up

Answer

The port sends an RLQ to verify root reachability

Question 6

How does STP handle a topology change in RSTP compared to classic 802.1D?

Accepted Answer

RSTP flushes MAC tables and sends TC BPDUs for twice the Hello time; 802.1D propagates TCNs to the root first

Answer

RSTP floods TCN BPDUs to all ports for MaxAge seconds; 802.1D uses a fast flush

Answer

Both protocols use identical topology change mechanisms

Answer

RSTP ignores topology changes on edge ports; 802.1D notifies the root for all changes

Question 7

Which MSTP concept describes the role of an MST region boundary port connecting to another region or a legacy STP bridge?

Accepted Answer

Boundary Port

Answer

Edge Port

Answer

IST Master Port

Answer

Regional Root Port