Advanced Features and Variants Flashcards

What does MSTP (802.1s) allow that RSTP alone does not?

Answer: Multiple VLANs mapped to different spanning tree instances

MSTP allows multiple VLANs to be mapped to separate spanning tree instances, enabling load balancing across redundant links.

In MSTP, what is the Common and Internal Spanning Tree (CIST)?

Answer: A spanning tree that interconnects all MST regions and the CST

The CIST is the single spanning tree that connects all MST regions together and interoperates with 802.1D/RSTP bridges.

Which STP variant was specifically designed to reduce convergence time to under one second by using a proposal/agreement handshake?

Answer: RSTP (802.1w)

RSTP uses a proposal/agreement mechanism between adjacent switches to achieve near-instant convergence without relying on timers.

What is the function of the MST region in MSTP?

Answer: A group of switches sharing the same MST configuration name, revision, and VLAN-to-instance mapping

Switches belong to the same MST region when they share identical configuration name, revision number, and VLAN-to-instance table.

Which STP feature prevents a port from becoming a root port by ignoring received superior BPDUs?

Answer: Root Guard

Root Guard enforces the root bridge placement by placing a port into root-inconsistent state if a superior BPDU is received.

In Rapid PVST+, what happens when a non-edge port receives a BPDU on a port that was previously in Forwarding state due to Dispute mechanism?

Answer: The port is placed in Discarding state to prevent unidirectional link loops

The Dispute mechanism detects unidirectional link failures and places the port in Discarding state to prevent loops.

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.