CCNA Practice Quiz | Spanning Tree Protocol

Here is the 50 MCQ quizzes on Spanning Tree Protocol for CCNA Exam practice.

Question 1

What is the default STP cost for a 10 Gbps (TenGigabitEthernet) interface under the legacy IEEE 802.1D-1998 (Short) path cost method?

A) 1

B) 2

C) 4

D) 19

  • Correct Answer: B
  • Explanation: In the original 802.1D standard (Short path cost), a 10 Mbps link has a cost of 100, 100 Mbps is 19, 1 Gbps is 4, and 10 Gbps is 2. Because 10 Gbps and higher speeds began to saturate the available values, the IEEE updated this in 802.1w (Long path cost) where a 10 Gbps link has a default cost of 2,000.

Question 2

A network engineer enables PortFast on a switch port connected to a user workstation. Which of the following states does the port bypass when transitioning to the Forwarding state?

A) Blocking and Listening

B) Listening and Learning

C) Learning and Forwarding

D) Discarding and Learning

  • Correct Answer: B
  • Explanation: Standard STP transitions a port through Blocking -> Listening (15s) -> Learning (15s) -> Forwarding. PortFast allows an access port to bypass the Listening and Learning states, moving immediately from Blocking to Forwarding to prevent DHCP timeouts on end devices.

Question 3

Two Catalyst switches are connected via two parallel Ethernet links. Neither switch has been configured with a custom bridge priority. Which criteria will the switches use first to break the tie and select the Root Bridge?

A) The lowest MAC address

B) The highest MAC address

C) The lowest port number

D) The highest interface bandwidth

  • Correct Answer: A
  • Explanation: The Bridge ID (BID) consists of Bridge Priority + Extended System ID + MAC Address. Since both switches have identical default priorities (32768) and identical Extended System IDs (assuming the same VLAN), the switch with the numerically lowest MAC address will become the Root Bridge.

Question 4

In Rapid Spanning Tree Protocol (RSTP, 802.1w), what role is assigned to a port that offers an alternative path to the Root Bridge from a different upstream switch but is currently blocked?

A) Designated Port

B) Backup Port

C) Alternate Port

D) Edge Port

  • Correct Answer: C
  • Explanation: An Alternate port receives BPDUs from another switch and acts as a backup to the Root Port. A Backup port receives BPDUs from the same switch (via a hub or redundant loop to the same segment) and acts as a backup to a Designated port.

Question 5

An administrator configures the command spanning-tree mode rapid-pvst. Which operational states from traditional 802.1D STP are combined or eliminated into the single “Discarding” state in RSTP?

A) Disabled, Blocking, and Listening

B) Blocking, Listening, and Learning

C) Disabled, Listening, and Learning

D) Blocking and Learning

  • Correct Answer: A
  • Explanation: RSTP simplifies the port states from five down to three: Discarding, Learning, and Forwarding. The operational states of Disabled, Blocking, and Listening from 802.1D are all functionally merged into Discarding.

Question 6

A switch receives a configuration BPDU from its neighbor. What is the default Hello Timer value contained within this BPDU?

A) 1 second

B) 2 seconds

C) 5 seconds

D) 15 seconds

  • Correct Answer: B
  • Explanation: By default, the Root Bridge originates BPDUs every 2 seconds. This timer dictates how frequently configuration BPDUs are propagated down the STP topology tree.

Question 7

Which STP feature is designed to prevent a non-root switch from unexpectedly becoming the Root Bridge if a rogue switch with a priority of 0 is plugged into an access port?

A) BPDU Guard

B) Loop Guard

C) Root Guard

D) EtherChannel

  • Correct Answer: C
  • Explanation: Root Guard is enabled on ports facing devices that should never become the Root Bridge. If the port receives a superior BPDU (a lower Bridge ID), Root Guard puts the port into a “root-inconsistent” state, effectively blocking traffic until the superior BPDUs stop.

Question 8

What is the exact Bridge Priority value of a switch configured for VLAN 10 using the command spanning-tree vlan 10 root primary, assuming no other switches have altered priorities?

A) 24576

B) 24586

C) 32768

D) 32778

  • Correct Answer: B
  • Explanation: The root primary macro attempts to lower the priority to 24576 (calculated as $32768 – 8192$). Because of the Extended System ID, the VLAN ID is added to this base priority: $24576 + 10 = 24586$.

Question 9

Under 802.1D STP, what happens immediately after a non-root switch detects a link failure on one of its designated ports?

A) It transmits a Topology Change Notification (TCN) BPDU out its Root Port toward the Root Bridge.

B) It immediately sets the TC bit flag in its own configuration BPDUs.

C) It clears its local MAC address table instantly.

D) It enters the forwarding state on all alternate paths.

  • Correct Answer: A
  • Explanation: Non-root switches cannot generate configuration BPDUs with the Topology Change (TC) bit set. Instead, they notify the Root Bridge by sending a TCN BPDU up the tree. The Root Bridge then sets the TC flag in its next configuration BPDU to inform the entire network.

Question 10

When a network is informed of a topology change via an active TC bit in a BPDU, how do the switches adjust their MAC address aging timers?

A) They increase the timer to 600 seconds to prevent frame flooding.

B) They temporarily reduce the aging timer from 300 seconds down to the Forward Delay timer value (15 seconds).

C) They completely freeze the MAC address table until a new Root Bridge is elected.

D) They clear the entire table immediately without waiting for a timer.

  • Correct Answer: B
  • Explanation: Shortening the aging timer to the Forward Delay value ensures that stale MAC address entries (which might now point to broken or changed paths) are flushed quickly without completely wiping the table instantly.

Question 11

Which RSTP mechanism allows a port to transition to the forwarding state rapidly by actively negotiating a handshake with its neighbor instead of waiting for passive timers?

A) BackboneFast

B) UplinkFast

C) The Proposal and Agreement process

D) PortFast

  • Correct Answer: C
  • Explanation: RSTP uses a fast handshake mechanism on point-to-point links. A switch sends a proposal with the Designated bit set; if the downstream switch agrees (after syncing its other ports), it returns an agreement, allowing the upstream port to move to Forwarding immediately without waiting for timers.

Question 12

If a port configured with BPDU Guard receives an 802.1D configuration BPDU, what operational state is the port placed into?

A) disabled

B) blocking

C) listening

D) err-disabled

  • Correct Answer: D
  • Explanation: BPDU Guard is an access-layer security feature. If any BPDU is received on a protected port (typically combined with PortFast), the switch shuts down the port immediately and logs an error, moving it to the err-disabled state.

Question 13

What is the command to globally enable Rapid PVST+ on a Cisco Catalyst switch?

A) spanning-tree mode rapid-pvst

B) spanning-tree rapid-pvst enable

C) spanning-tree mode rstp

D) spanning-tree mode mst

  • Correct Answer: A
  • Explanation: Cisco switches default to PVST+ (spanning-tree mode pvst). To transition the entire chassis to run the rapid implementation per-VLAN, the global configuration command spanning-tree mode rapid-pvst must be executed.

Question 14

Which mathematical formula defines the calculation of the Bridge ID (BID) in a network utilizing the Extended System ID?

A) $\text{Bridge ID} = \text{Bridge Priority} \times \text{MAC Address} + \text{VLAN ID}$

B) $\text{Bridge ID} = \text{Bridge Priority (multiple of 4096)} + \text{System ID (VLAN ID)} + \text{MAC Address}$

C) $\text{Bridge ID} = \text{Base MAC Address} + \text{VLAN ID}$

D) $\text{Bridge ID} = \text{Bridge Priority} + \text{Port Priority} + \text{MAC Address}$

  • Correct Answer: B
  • Explanation: To support per-VLAN spanning tree without needing thousands of unique MAC addresses, the original 16-bit Bridge Priority field was split into a 4-bit Priority field (multiples of 4096) and a 12-bit Extended System ID field to carry the VLAN ID.

Question 15

What is the default Max Age timer value for IEEE 802.1D Spanning Tree?

A) 2 seconds

B) 15 seconds

C) 20 seconds

D) 30 seconds

  • Correct Answer: C
  • Explanation: The Max Age timer dictates how long a switch will retain saved BPDU information received on a port before discarding it. If a switch stops receiving BPDUs from its neighbor, it waits 20 seconds before initiating a topology calculation.

Question 16

Switch A has a Root Port with an accumulated path cost of 19. It sends a BPDU out of its Designated Port toward Switch B over a 1 Gbps link (Long path cost method). What path cost value is advertised inside that outbound BPDU?

A) 0

B) 4

C) 19

D) 20017

  • Correct Answer: C
  • Explanation: A switch always advertises its own current cumulative path cost to the Root Bridge inside outward-facing BPDUs. The receiving switch (Switch B) will then add the cost of its local inbound interface to that advertised value when calculating its total path cost.

Question 17

What mechanism does Loop Guard use to detect a unidirectional link failure and prevent Layer 2 loops?

A) It injects loopback frames to test bidirectional integrity.

B) It monitors the continuous receipt of BPDUs on non-designated ports; if BPDUs stop arriving without a topology change, it places the port into a loop-inconsistent state.

C) It actively shuts down any port that transmits more than 100 BPDUs per second.

D) It relies on PortFast notifications to shut down redundant trunks.

  • Correct Answer: B
  • Explanation: Unidirectional links cause loops because a blocking port stops receiving BPDUs, assumes the neighbor is dead, and transitions to forwarding. Loop Guard catches this: if BPDUs stop on a blocking/root port without a valid reason, it blocks the port instead of allowing it to transition.

Question 18

In Multiple Spanning Tree Protocol (MSTP, 802.1s), what three parameters must match exactly on two switches for them to belong to the same MST Region?

A) Domain Name, Password, and VTP Version

B) MST Region Name, MST Revision Number, and the VLAN-to-Instance mapping table

C) Bridge Priority, Max Age, and Hello Timer values

D) Local MAC address, VLAN ID, and System ID

  • Correct Answer: B
  • Explanation: MSTP groups multiple VLANs into logical spanning tree instances to save CPU cycles. Switches recognize each other as members of the same region only if their Name, Revision Number, and explicit VLAN-to-Instance digest match perfectly.

Question 19

A switch port is manually configured with the command spanning-tree portfast disable under interface configuration mode. If the global command spanning-tree portfast default is active, what is the PortFast status of this specific interface?

A) PortFast is globally enabled but interface-disabled, meaning it remains active.

B) PortFast is explicitly disabled on this interface, and it will follow normal STP transitions.

C) The port will enter the err-disabled state due to a command conflict.

D) The interface will ignore the command and default to dynamic trunking.

  • Correct Answer: B
  • Explanation: Interface-specific commands always override global configuration defaults. Even if PortFast is globally enabled for all access ports, an interface-level disable command forces that specific port to use normal STP transition states.

Question 20

What destination MAC address is used by Cisco PVST+ BPDUs transmitted over an 802.1Q trunk port for non-default/tagged VLANs?

A) 01-80-C2-00-00-00

B) 01-00-5E-00-00-02

C) 01-00-0C-CC-CC-CD

D) FF-FF-FF-FF-FF-FF

  • Correct Answer: C
  • Explanation: Standard IEEE BPDUs use the multicast address 01-80-C2-00-00-00. However, Cisco’s proprietary PVST+ uses a shared multicast address called the Shared Spanning Tree Protocol (SSTP) MAC address (01-00-0C-CC-CC-CD) to flood BPDUs across trunks for VLANs other than VLAN 1.

Question 21

Which RSTP port role is assigned to an interface that connects to an end-user device like a PC or server, behaving identically to an STP port with PortFast enabled?

A) Alternate Port

B) Backup Port

C) Designated Port

D) Edge Port

  • Correct Answer: D
  • Explanation: In RSTP terminology, a port configured for PortFast is called an Edge Port. It immediately transitions to the forwarding state upon link-up because it assumes no switches or loops exist downstream.

Question 22

If a switch port transitions sequentially through the states of Discarding, Learning, and Forwarding, which spanning tree flavor is operating on the switch?

A) Traditional 802.1D STP

B) PVST+

C) RSTP (802.1w) or Rapid PVST+

D) Cisco UplinkFast

  • Correct Answer: C
  • Explanation: The absence of the “Listening” and “Blocking” terminology, replaced directly by “Discarding,” confirms that the switch is operating an 802.1w-based protocol (RSTP) rather than legacy 802.1D.

Question 23

What is the lowest allowable non-zero custom Bridge Priority value you can manually configure on a Cisco switch VLAN?

A) 1

B) 1024

C) 4096

D) 32768

  • Correct Answer: C
  • Explanation: While 0 is technically the absolute lowest priority (which guarantees a switch becomes the root bridge), the priority must be configured in increments of 4096 due to the 12-bit Extended System ID truncation. Therefore, the lowest configured step above 0 is 4096.

Question 24

You have two switches connected via an EtherChannel bundle consisting of four 1 Gbps interfaces. How does STP treat this bundle by default?

A) It blocks three out of the four physical links to prevent a loop.

B) It treats the bundle as a single logical link with a single path cost.

C) It disables the entire bundle because parallel paths are detected.

D) It forces the bundle into a loop-inconsistent state.

  • Correct Answer: B
  • Explanation: One of the main benefits of EtherChannel is that spanning tree views the entire logical bundle as a single link. Instead of blocking three of the four parallel links to prevent a loop, all links stay active, and the composite interface gets a lower cumulative STP cost.

Question 25

Which command would you use to verify which specific ports on a switch are currently acting as the Root Port or Designated Ports for VLAN 20?

A) show ip route vlan 20

B) show spanning-tree vlan 20

C) show mac address-table vlan 20

D) show interface status

  • Correct Answer: B
  • Explanation: The show spanning-tree vlan [X] command provides an interface breakdown showing the port roles (Root, Altn, Desg), port states (FWD, BLK, LRN), path costs, and edge designations specific to that VLAN instance.

Question 26

What problem does the BackboneFast feature address in legacy 802.1D environments?

A) It protects access ports from rogue BPDUs.

B) It allows dual-homed access switches to achieve sub-second convergence.

C) It bypasses the Max Age timeout (20 seconds) when an indirect link failure occurs.

D) It bundles up to eight parallel links into a single logical channel.

  • Correct Answer: C
  • Explanation: BackboneFast is a Cisco-proprietary feature for 802.1D. When a switch detects an indirect failure (e.g., a link down between two other switches), it uses Root Link Queries (RLQ) to verify if the root bridge is still reachable, skipping the 20-second Max Age wait time if the link is truly broken.

Question 27

If a switch port is in the Learning state, can it forward user data frames, and can it populate its MAC address table?

A) It can forward data frames, but cannot populate its MAC table.

B) It can neither forward data frames nor populate its MAC table.

C) It cannot forward user data frames, but it can populate its MAC address table.

D) It can both forward data frames and populate its MAC table.

  • Correct Answer: C
  • Explanation: During the Learning state, the switch processes the source MAC addresses of frames entering the port to build its MAC table, preventing massive flooding when the port finally transitions to the Forwarding state. However, it drops all transit payload traffic.

Question 28

Why is the default path cost value for a 10 Mbps link higher than the path cost value for a 100 Mbps link?

A) Faster links are penalized with lower metrics.

B) Lower metrics indicate higher cost paths.

C) Spanning Tree paths prefer higher bandwidth; therefore, faster links are assigned lower cost metrics so the path calculation favors them.

D) High-speed links naturally experience more data degradation, requiring manual overrides.

  • Correct Answer: C
  • Explanation: STP path cost calculation is inversely proportional to bandwidth. Lower costs indicate more desirable paths. A 10 Mbps link has a cost of 100, while a faster 100 Mbps link has a lower cost of 19.

Question 29

A network design includes a core switch and an access switch. The link between them is configured as an 802.1Q trunk line. If a native VLAN mismatch occurs across this trunk, what spanning tree problem can arise?

A) The switches will completely turn off the physical interfaces due to duplex mismatch.

B) Traffic leaking between different VLANs or STP blocking the ports entirely due to PVID inconsistency checks.

C) Spanning tree will automatically disable itself across the entire chassis.

D) BPDUs will be permanently converted into regular data payloads.

  • Correct Answer: B
  • Explanation: Cisco PVST+ includes a feature that checks the VLAN ID inside BPDUs. If a native VLAN mismatch occurs (e.g., VLAN 1 on one side and VLAN 99 on the other), BPDUs from one VLAN leak into another, causing PVST+ to put the ports into a broken / inconsistent state to prevent loops.

Question 30

Which command enables BPDU Guard globally on all interfaces that have PortFast enabled?

A) spanning-tree portfast bpduguard default

B) spanning-tree bpduguard enable

C) spanning-tree portfast enable bpduguard

D) clear spanning-tree bpduguard

  • Correct Answer: A
  • Explanation: The global command spanning-tree portfast bpduguard default targets any interface currently running PortFast. If an interface transitions away from an access/PortFast status, the guard is removed automatically from that port.

Question 31

How does a switch operating under RSTP handle a Topology Change (TC) differently than a switch running legacy 802.1D?

A) The switch must wait for the Root Bridge to send a specific clear command before making updates.

B) The switch detecting the change immediately floods TC-marked BPDUs out of all non-edge designated ports and its root port, rather than relying on a TCN exchange to the Root Bridge first.

C) It disables all interfaces for 30 seconds to allow the network to drain.

D) It completely stops sending BPDUs until the Max Age timer expires.

  • Correct Answer: B
  • Explanation: RSTP dramatically speeds up topology convergence. Instead of a slow 2-step process (TCN up to Root -> Config with TC bit down to all switches), any RSTP switch can initiate a topology change notification that sweeps through the active network topology within a few hellos.

Question 32

What is the default bridge priority value for any Cisco Catalyst switch before customization?

A) 0

B) 4096

C) 32768

D) 65535

  • Correct Answer: C
  • Explanation: The standard base priority for all industry-standard and Cisco switches is 32768. This acts as the mid-point value, allowing administrators to easily lower priorities to force root election or raise them to prevent it.

Question 33

Two parallel cables connect Switch X and Switch Y. Switch X is elected as the Root Bridge. On Switch Y, both interfaces receive BPDUs with identical path costs and identical Sender Bridge IDs. What third tie-breaker will Switch Y use to determine its single Root Port?

A) The lowest local Port ID on Switch Y

B) The lowest Sender Port ID (Priority + Port Number) received from Switch X

C) The highest MAC address of Switch Y’s own ports

D) The physical length of the connected cables

  • Correct Answer: B
  • Explanation: When choosing a Root Port, the selection order is: 1. Lowest cumulative path cost to root, 2. Lowest neighbor Bridge ID, 3. Lowest neighbor Port ID advertisement, 4. Lowest local Port ID. Since 1 and 2 are tied, Switch Y looks at the Port ID of Switch X’s transmitting ports.

Question 34

What happens if an operational Edge Port running RSTP receives a valid BPDU from a newly attached device?

A) It enters the err-disabled state immediately.

B) It ignores the BPDU entirely to maintain performance optimization.

C) It loses its Edge Port status, loses PortFast optimization, and becomes a standard STP port.

D) It reboots the local switch linecard to protect the processor.

  • Correct Answer: C
  • Explanation: An Edge Port assumes no switches exist downstream. If it receives a BPDU, that assumption is invalidated. The port immediately converts to a normal spanning tree port to prevent loops, unless BPDU Guard is active (which would shut it down).

Question 35

Which command forces a Cisco switch interface to treat its attached medium as a point-to-point link for rapid convergence, regardless of its duplex settings?

A) spanning-tree link-type point-to-point

B) spanning-tree mode point-to-point

C) spanning-tree edge point-to-point

D) switchport mode point-to-point

  • Correct Answer: A
  • Explanation: RSTP’s proposal/agreement process requires a point-to-point link topology. By default, a switch assumes full-duplex links are point-to-point and half-duplex links are shared. You can override an automated detection using spanning-tree link-type point-to-point.

Question 36

What is the purpose of the MST (Multiple Spanning Tree) configuration revision number?

A) It identifies how many VLANs exist inside the global network database.

B) It tracks how many times the switch has rebooted since installation.

C) It acts as a version-control tracking number to ensure all switches within an MST region share the exact same configuration layout.

D) It forces priority overrides over traditional PVST+ environments.

  • Correct Answer: C
  • Explanation: Because a cryptographic digest of the VLAN-to-Instance table is validated between neighbors, the Revision Number allows administrators to change configurations and ensure switches map to instances identically across the region.

Question 37

If you configure a switch with spanning-tree vlan 10 root secondary, what base priority value does the switch attempt to set?

A) 0

B) 4096

C) 28672

D) 32768

  • Correct Answer: C
  • Explanation: The root secondary macro drops the priority value down one standard increment below the default ($32768 – 4096 = 28672$). If the primary root bridge fails, this switch will easily take over as the root bridge.

Question 38

Which modern STP feature prevents a port from transitioning to a forwarding loop by expecting a continuous bidirectional stream of BPDUs on critical links, placing the port into an inconsistent state if BPDUs cease?

A) Root Guard

B) Loop Guard

C) Bridge Assurance

D) UplinkFast

  • Correct Answer: C
  • Explanation: Bridge Assurance (supported on newer MSTP/RPVST+ deployments) turns BPDUs into a bidirectional keepalive. If a port stops receiving BPDUs on an assurance link, the port is placed into an inconsistent state rather than transitioning to clear data loops.

Question 39

What type of BPDU is generated exclusively by the Root Bridge every 2 seconds to maintain the active loop-free tree topology?

A) Topology Change Notification (TCN) BPDU

B) Link-State BPDU

C) Configuration BPDU

D) Keepalive BPDU

  • Correct Answer: C
  • Explanation: The Root Bridge generates Configuration BPDUs periodically. Non-root switches receive them, update the path cost and sender fields, and forward them down through their own designated ports to sustain the active state topology.

Question 40

A network engineer sees that a port is listed as “Altn BLK” in the output of show spanning-tree. What does this indicate about the port’s role and state?

A) The port role is Designated, and its operational state is Blocking.

B) The port role is Alternate, and its operational state is Blocking.

C) The port role is Backup, and its operational state is Learning.

D) The port role is Root, and its operational state is Forwarding.

  • Correct Answer: B
  • Explanation: This output means the interface is a backup path to the Root Bridge through an upstream switch. It is currently blocked to prevent loop formation but stands ready to immediately transition if the primary root port fails.

Question 41

What value is added to the base priority when calculating the bridge ID for VLAN 100 on a switch running PVST+?

A) 1

B) 10

C) 100

D) 4096

  • Correct Answer: C
  • Explanation: The Extended System ID incorporates the specific VLAN identification number directly into the 16-bit Priority field block. Thus, the system adds exactly 100 to whatever base multiple of 4096 is configured.

Question 42

What is the functional difference between an RSTP Alternate Port and an RSTP Backup Port?

A) Alternate ports connect to end hosts; Backup ports connect to switches.

B) Alternate ports are active paths; Backup ports are always disabled.

C) An Alternate port provides a backup path to the root from a different upstream switch; a Backup port provides a redundant path to the same network segment from the same switch.

D) Alternate ports operate at Layer 3; Backup ports operate at Layer 2.

  • Correct Answer: C
  • Explanation: Alternate ports back up Root Ports (different upstream neighbors). Backup ports back up Designated Ports on the same switch (usually occurring when multiple ports on the same switch connect to an old-style shared hub).

Question 43

Under IEEE 802.1D, what is the default length of time a port spends in the Listening state?

A) 2 seconds

B) 15 seconds

C) 20 seconds

D) 30 seconds

  • Correct Answer: B
  • Explanation: The Forward Delay timer dictates the duration of both the Listening and Learning states. By default, Forward Delay is set to 15 seconds, making the transition from Listening to Learning take exactly 15 seconds.

Question 44

If you clear the MAC address table on a switch manually using the CLI, does it trigger an STP Topology Change Notification (TCN)?

A) Yes, it forces the entire network to recalculate paths.

B) No, it affects only the local control plane database without indicating a physical interface change.

C) Yes, but only for the default native VLAN 1.

D) No, unless PortFast is disabled on all access lines.

  • Correct Answer: B
  • Explanation: Manually clearing the MAC address table affects only the local control plane database. It does not indicate a physical interface link state drop or structure change; therefore, no TCN BPDU is triggered or transmitted.

Question 45

Which command is used to completely disable spanning tree execution globally for a single specific VLAN?

A) spanning-tree vlan [vlan-id] disable

B) no spanning-tree vlan [vlan-id]

C) clear spanning-tree vlan [vlan-id]

D) shutdown spanning-tree vlan [vlan-id]

  • Correct Answer: B
  • Explanation: Executing no spanning-tree vlan X stops all STP processing for that particular VLAN. Warning: Doing this on links with physical redundancy will immediately cause an unchecked layer 2 broadcast storm.

Question 46

What field inside an 802.1Q frame header is used by Per-VLAN Spanning Tree Plus (PVST+) to run independent spanning tree instances over trunks?

A) Type of Service (ToS) field

B) Preamble field

C) The VLAN ID (VID) tag field

D) Destination MAC Address field

  • Correct Answer: C
  • Explanation: PVST+ replicates standard STP operations by sending unique BPDUs separated inside each individual tagged trunk encapsulation, tracking topology alterations independently per VLAN tag.

Question 47

Which standard introduced Multiple Spanning Tree Protocol (MSTP) to consolidate resource usage across high-VLAN enterprises?

A) IEEE 802.1D

B) IEEE 802.1w

C) IEEE 802.1q

D) IEEE 802.1s

  • Correct Answer: D
  • Explanation: IEEE 802.1s standardized MSTP, which was later incorporated into the roll-up IEEE 802.1Q standard. It maps numerous VLANs into a few instance structures to decrease switch CPU loads.

Question 48

What role does a Designated Port play in an STP topology?

A) It is the single interface on a switch that has the absolute lowest path cost to the Root Bridge.

B) It is the port on a network segment that has the lowest path cost back to the Root Bridge, responsible for forwarding traffic onto that segment.

C) It is a blocked port that stands ready to take over if the Root Port fails.

D) It is an access port connected straight to end-user workstations.

  • Correct Answer: B
  • Explanation: Every network segment between switches must have exactly one Designated Port. This port handles frame forwarding for that segment. All ports on a Root Bridge are Designated Ports by default.

Question 49

What is the total default convergence time for an unoptimized port under legacy 802.1D STP when it transitions from initial link-up to the forwarding state?

A) 2 seconds

B) 15 seconds

C) 30 seconds

D) 50 seconds

  • Correct Answer: C
  • Explanation: Without enhancements like PortFast, a port must cycle through the Listening state (15 seconds) and the Learning state (15 seconds) before reaching the Forwarding state, resulting in a total delay of 30 seconds.

Question 50

If Switch 1 has a Bridge Priority of 4096 and Switch 2 has a Bridge Priority of 8192, which switch will win the election to become the Root Bridge?

A) Switch 1, because a lower Bridge ID priority value is always superior.

B) Switch 2, because higher numbers take absolute precedence.

C) Neither; the switch with the higher MAC address will win automatically.

D) They will negotiate an equal load-balanced multi-root topology.

  • Correct Answer: A
  • Explanation: In Spanning Tree Protocol elections, a lower Bridge ID value is always superior. Since 4096 is lower than 8192, Switch 1 wins the election, regardless of the MAC addresses of the two devices.