CCNA Spanning Tree Questions

MCQmedium

You notice that an EX Series switch is experiencing frequent topology changes, causing intermittent packet drops across VLANs. Which command helps identify which specific interface is generating the topology changes?

A.show spanning-tree bridge detail

B.show interfaces diagnostics optics

C.show rstp topology-changes

D.show spanning-tree statistics

AnswerD

Per-interface topology change counters help identify unstable links causing TC floods.

Why this answer

The command 'show spanning-tree statistics' displays topology change counts per interface, enabling administrators to isolate the unstable port.

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Multi-Selectmedium

Which THREE parameters are included when calculating the MST region configuration digest? (Choose three.)

Select 3 answers

A.VLAN-to-instance mapping table

B.Configuration name

C.Root bridge MAC address

D.Bridge priority value

E.Revision number

AnswersA, B, E

VLAN allocations to MST instances dictate the digest hash.

Why this answer

The MST configuration digest is an MD5 hash calculated from the region configuration name, the revision number, and the complete VLAN-to-instance mapping table.

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MCQhard

An administrator is configuring MSTP on a Junos device and needs to map VLANs 10 through 20 to MST instance 2. Which configuration hierarchy is required to achieve this?

A.set vlans vlan-range 10-20 mst-instance 2

B.set protocols msti instance-id 2 vlan-list 10-20

C.set protocols rstp instance 2 vlan 10-20

D.set protocols mstp configuration region-name Corp revision 1 instance 2 vlan 10-20

AnswerD

This command correctly maps VLANs 10 through 20 to instance 2 within the specified MST configuration block.

Why this answer

In Junos, MSTP region configuration parameters including VLAN mappings are defined under protocols mstp configuration.

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MCQeasy

When verifying RSTP operation on a Junos switch, which operational command should you use to view the bridge identifier, root bridge identifier, and local port states?

A.show rstp bridge

B.show rstp statistics interface

C.show bridgestp detail

D.show spanning-tree summary

AnswerA

show rstp bridge displays the bridge identifier, root bridge details, and timers.

Why this answer

The command 'show rstp bridge' provides detailed bridge-level statistics and state information for RSTP on Juniper devices.

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MCQeasy

What is the primary function of the RSTP port role known as the 'Backup' port?

A.It forwards traffic when the primary trunk fails without triggering a topology change.

B.It acts as a backup for the root port towards the root bridge.

C.It acts as a backup for a designated port on the same segment.

D.It is an operational state used exclusively during edge port transitions.

AnswerC

Backup ports exist on segments where the local bridge already has a designated port.

Why this answer

A backup port provides a redundant path to a segment and is a backup for a designated port, receiving superior BPDUs from its own bridge on the same segment.

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MCQhard

An operator configures RSTP across multiple EX Series switches. A rogue switch running legacy STP is connected to an RSTP switch. How does the RSTP switch handle interaction with the legacy STP switch?

A.The port receiving legacy BPDUs is immediately placed into a permanent error-disabled state.

B.The legacy STP BPDUs are dropped and logged as protocol violations.

C.The entire switch converts its spanning tree mode to legacy STP.

D.The RSTP switch falls back to legacy STP behavior on that specific interface.

AnswerD

Per-port protocol migration allows interoperability by downgrading to 802.1D on ports receiving legacy BPDUs.

Why this answer

RSTP switches have a migration mechanism that automatically detects legacy STP BPDUs on a per-port basis and falls back to running legacy 802.1D STP behavior on that specific port.

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MCQmedium

You are configuring an EX Series switch and want to set the forward delay timer to 15 seconds. Which command is used?

A.set protocols rstp forward-delay 15

B.set bridge forward-delay 15

C.set spanning-tree forward-delay 15

D.set protocols rstp delay 15

AnswerA

This command sets the forward delay timer for RSTP state transitions.

Why this answer

The forward delay timer can be configured under protocols rstp or stp using 'set protocols rstp forward-delay <seconds>'.

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MCQhard

An enterprise network runs MSTP. Instance 0 is always reserved for which specific purpose?

A.The Internal Regional Boundary instance (IRBI)

B.The Designated Root Backup instance (DRB)

C.The Common and Internal Spanning Tree (CIST) instance

D.The Vlan-to-Instance Mapping table (VIM)

AnswerC

Instance 0 serves as the CIST instance for MSTP operation and regional management.

Why this answer

Instance 0 in MSTP is the Common and Internal Spanning Tree (CIST) instance, which maintains connectivity across the entire bridged network and communicates with legacy STP/RSTP regions.

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Multi-Selecthard

Which TWO conditions will cause an MSTP boundary port to drop BPDUs or recognize a region separation? (Choose two.)

Select 2 answers

A.A mismatch in the bridge priority of the regional root

B.A mismatch in the local bridge MAC address of the root bridge

C.Exceeding the maximum configured regional hop count

D.Receipt of a legacy 802.1D or RSTP BPDU from outside the region

E.Receipt of a BPDU with a mismatched MST configuration digest

AnswersD, E

Legacy BPDUs indicate connection to a non-MST region.

Why this answer

MSTP boundary ports detect region separation when there is a mismatch in configuration digests or when legacy STP/RSTP BPDUs are received from outside the region.

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MCQmedium

You suspect that a network loop has formed due to a misconfigured RSTP topology on your EX Series switches. Which command shows real-time topology change notifications and counts on the switch?

A.show bridge mac-table

B.show spanning-tree interface detail

C.show rstp neighbor

D.show spanning-tree statistics

AnswerD

This command provides counts for topology changes and BPDU packets processed.

Why this answer

The command 'show spanning-tree statistics' displays counters related to topology changes, BPDU transmission, and reception per interface.

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Multi-Selectmedium

Which THREE actions are performed by an RSTP switch when a topology change is detected? (Choose three.)

Select 3 answers

A.Starting a TC while timer to flood notifications

B.Sending topology change notifications out of active designated and root ports

C.Electing a new root bridge automatically

D.Resetting all edge ports to the discarding state

E.Clearing dynamic MAC address entries associated with non-edge ports

AnswersA, B, E

A TC while timer controls the duration of notification flooding.

Why this answer

When an RSTP topology change occurs, the switch starts a TC while timer, clears dynamic MAC entries on non-edge ports, and floods TC notifications to active designated and root ports.

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Multi-Selectmedium

Which THREE parameters must match across all switches for them to successfully form a single MST region? (Choose three.)

Select 3 answers

A.VLAN-to-instance mapping table

B.Configuration name

C.Revision number

D.Bridge priority value

E.Hello timer interval

AnswersA, B, C

VLAN allocations to MST instances must be identical across region members.

Why this answer

MST region membership requires matching configuration names, revision numbers, and VLAN-to-instance mapping tables.

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MCQmedium

You need to ensure that a core switch retains its position as the root bridge even if a new switch with a manually lowered bridge priority is added to the network. Which feature should you configure on the core switch's ports facing the downstream switches?

A.Loop protection

B.BPDU guard

C.Root protection

D.Edge port configuration

AnswerC

Root protection enforces that the designated root port stays designated, rejecting superior BPDUs.

Why this answer

Root protection prevents a designated port from becoming a root port, ensuring that if a superior BPDU arrives on that port, the port transitions to a root-inconsistent (discarding) state rather than yielding the root role.

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Multi-Selecthard

Which TWO mechanisms are utilized by RSTP to achieve rapid convergence compared to legacy 802.1D STP? (Choose two.)

Select 2 answers

A.Proposal-agreement handshake mechanism

B.Mandatory 15-second listening timer enforcement

C.Centralized root bridge polling

D.Support for point-to-point link synchronization

E.Periodic topology change broadcasting by root bridges

AnswersA, D

The proposal-agreement handshake allows immediate downstream state transitions.

Why this answer

RSTP achieves rapid convergence through the proposal-agreement handshake and the explicit support of point-to-point full-duplex links.

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MCQmedium

When a topology change occurs in an RSTP network, how are MAC address forwarding table entries affected across the switches?

A.MAC addresses are relearned only after the root bridge sends a direct clearing command.

B.MAC address entries are retained until the standard 300-second aging timer expires.

C.MAC address tables are completely cleared for all ports, including edge ports.

D.MAC address table entries associated with non-edge ports are flushed immediately.

AnswerD

RSTP flushes dynamic MAC entries to quickly adapt to the new topology without waiting for aging timers.

Why this answer

Unlike legacy STP, RSTP immediately flushes MAC address entries associated with non-edge ports on receiving a topology change notification, speeding up convergence.

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MCQeasy

What is the primary purpose of the Hello timer in RSTP?

A.It sets the interval between topology change notifications.

B.It determines the maximum time a switch waits before declaring a neighbor dead.

C.It defines the duration of the listening and learning states during convergence.

D.It dictates how often configuration BPDUs are generated and sent by the root bridge.

AnswerD

The Hello timer controls the interval between transmitted BPDUs.

Why this answer

The Hello timer defines how often a bridge generates and sends configuration BPDUs. In RSTP, it is typically set to 2 seconds by default.

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Multi-Selecteasy

Which TWO commands are valid Junos configuration hierarchy paths for setting up RSTP? (Choose two.)

Select 2 answers

A.set bridge rstp mode rapid-pvst

B.set protocols stp rstp-version true

C.set protocols rstp bridge-priority 4096

D.set protocols rstp interface ge-0/0/1.0 edge

E.set spanning-tree rstp enable

AnswersC, D

Valid command to set bridge priority under protocols rstp.

Why this answer

RSTP configuration in Junos is performed under 'protocols rstp' hierarchy.

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MCQeasy

What is the default bridge priority value assigned to Juniper EX Series switches when RSTP is enabled?

A.61440

B.0

C.32768

D.4096

AnswerC

32768 is the IEEE default bridge priority value used across JUNOS routing and switching platforms.

Why this answer

The default bridge priority for JUNOS devices running STP, RSTP, or MSTP is 32768.

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MCQhard

When configuring MSTP, how is the regional maximum hop count enforced across switches within the same MST region?

A.The regional root periodically floods drop-commands if the network diameter exceeds the limit.

B.BPDUs carry a hop count that is decremented by each bridge; when it reaches zero, the BPDU is dropped.

C.Switches drop any incoming BPDUs that exceed the statically configured Max Age timer.

D.Ports exceeding the hop count are automatically placed into the error-disabled state.

AnswerB

MSTP uses a hop count mechanism similar to IP TTL to limit BPDU propagation within a region.

Why this answer

Each switch decrements the hop count field in the MSTP BPDU before forwarding it; if the hop count reaches zero, the BPDU is discarded, preventing loops in large MSTP deployments.

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MCQhard

An organization runs MSTP with multiple instances. A packet belonging to a VLAN that is not explicitly mapped to any MST instance is processed in which manner?

A.It is processed by the default RSTP instance running outside MSTP.

B.It is dropped by the switch because unmapped VLANs are considered invalid in MSTP.

C.It is automatically mapped to Instance 0 (the CIST).

D.It floods to all ports regardless of spanning tree port states.

AnswerC

Instance 0 acts as the default catch-all instance for any unmapped VLANs.

Why this answer

Any unmapped VLANs in MSTP are automatically mapped to Instance 0, which is the CIST (Common and Internal Spanning Tree).

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Multi-Selecteasy

Which TWO parameters are typically configured when tuning RSTP timers on Junos EX Series switches? (Choose two.)

Select 2 answers

A.forward-delay-timer-scale

B.edge-port-delay

C.max-age

D.topology-change-interval

E.hello-time

AnswersC, E

Controls BPDU expiration timeout.

Why this answer

Administrators can tune RSTP behavior using timers such as hello-time and max-age under the protocols rstp hierarchy.

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MCQeasy

An administrator needs to configure a Juniper EX Series switch to participate in an existing Spanning Tree topology without risking the switch becoming the root bridge. Which command should be used to achieve this?

A.set protocols rstp bridge-priority 61440

B.set protocols rstp forward-delay 30

C.set protocols rstp root-protection

D.set protocols rstp disable

AnswerA

Setting the bridge priority to a higher numerical value (such as 61440, default is 32768) ensures the switch loses root bridge elections.

Why this answer

Configuring a bridge priority higher than the current root (e.g., 61440) or setting a lower priority makes it less likely to become root, but the definitive best practice for non-core switches to prevent them from becoming root is manipulating the bridge priority to a high value like 61440.

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MCQhard

An administrator configures root protection on a designated port. If that port subsequently receives a superior BPDU from another switch, what exact state does the port transition into?

A.Alternate port state

B.Error-disabled state

C.Root-inconsistent (discarding) state

D.Listening state

AnswerC

The port becomes root-inconsistent and stops forwarding traffic until the superior BPDU ceases.

Why this answer

When root protection is violated by receiving a superior BPDU, the port transitions into the root-inconsistent state, placing it in discarding mode to protect the root bridge position.

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Multi-Selecteasy

Which TWO features help protect an RSTP topology from unauthorized switches or misconfigurations on access ports? (Choose two.)

Select 2 answers

A.Bridge priority adjustment

B.Hello timer scaling

C.Root protection

D.Forward delay timer optimization

E.BPDU guard

AnswersC, E

Root protection prevents designated ports from accepting superior BPDUs.

Why this answer

BPDU guard and root protection are standard security mechanisms used to protect spanning tree topologies against unauthorized BPDUs and superior root bridge injections.

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Multi-Selectmedium

Which THREE parameters can be configured manually to influence root bridge selection in an RSTP network? (Choose three.)

Select 3 answers

A.Bridge priority increments (multiples of 4096)

B.Interface port cost

C.Configuration revision number

D.Bridge priority

E.MST regional configuration name

AnswersA, B, D

Priority values are adjusted in multiples of 4096.

Why this answer

Root bridge selection is primarily determined by bridge priority and MAC address. In Junos, administrators configure bridge priority, and can influence port/path costs or use MAC address manipulation indirectly. Specifically, bridge priority is the primary direct control.

Let's list valid configuration parameters affecting STP path selection: bridge priority, path cost, and interface cost.

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Multi-Selecthard

Which TWO port roles are defined in Rapid Spanning Tree Protocol (RSTP) but did not exist in legacy 802.1D STP? (Choose two.)

Select 2 answers

A.Master port

B.Root port

C.Backup port

D.Designated port

E.Alternate port

AnswersC, E

Backup ports provide redundant backup paths for designated ports on shared segments.

Why this answer

RSTP introduced the Alternate and Backup port roles to replace the legacy blocking state and accelerate convergence.

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MCQmedium

You notice that an access switch running RSTP is continually dropping user traffic because a connected end-user device is sending inferior BPDUs that trigger topology changes. Which Juniper feature should you configure on the access ports to protect against this behavior?

A.set protocols rstp interface ge-0/0/1.0 loop-protection

B.set protocols rstp interface ge-0/0/1.0 bpdu-protection

C.set protocols rstp interface ge-0/0/1.0 root-protection

D.set protocols rstp interface ge-0/0/1.0 no-root-port

AnswerB

Enabling bpdu-protection on edge ports shuts down the port if a BPDU is received, protecting against rogue devices.

Why this answer

BPDU protection (bpdu-protection) on Junos edge ports puts the port in an error-disabled state if any BPDU is received, preventing unauthorized switches or loops.

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Multi-Selecteasy

Which TWO commands can be used to view spanning tree information on a Juniper EX Series switch? (Choose two.)

Select 2 answers

A.show bridge spanning-tree status

B.show spanning-tree interface

C.show spanning-tree bridge

D.show rstp summary

E.show protocols spanning-tree summary

AnswersB, C

Displays per-interface spanning tree states, roles, and port types.

Why this answer

The commands 'show spanning-tree interface' and 'show spanning-tree bridge' are standard operational commands used to inspect spanning tree status and bridge parameters on Junos devices.

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Multi-Selectmedium

Which THREE statements describe the function of the Designated Port in RSTP? (Choose three.)

Select 3 answers

A.It provides the lowest cost path from the segment back toward the root bridge.

B.It remains permanently in the discarding state to prevent loops.

C.It forwards BPDUs onto the attached LAN segment.

D.There is exactly one designated port for every active LAN segment.

E.It acts as the primary root port for the local bridge.

AnswersA, C, D

The designated bridge for a segment is responsible for forwarding traffic toward the root.

Why this answer

A designated port forwards BPDUs onto a segment, provides the lowest cost path to reach the root bridge for that segment, and exists on every segment connected to the bridge where it acts as the forwarding interface.

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MCQhard

An EX Series switch running MSTP receives a BPDU from an upstream switch in a different MST region. How does the receiving switch identify the boundary between the two regions?

A.When the incoming BPDU contains an instance count greater than the local switch capacity.

B.When the CIST external path cost exceeds the maximum hop count.

C.By comparing the received MST configuration digest and region parameters with its own.

D.By detecting a mismatch in the system MAC address of the root bridge.

AnswerC

Mismatch in configuration digests or region names identifies an MST boundary port.

Why this answer

Boundary ports are identified when a switch receives a CIST BPDU where the regional configuration (digest, name, revision) or regional root differs from its own, or when it receives a legacy STP BPDU.

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MCQeasy

Which RSTP port role replaces the legacy STP blocking and listening port states to provide rapid convergence?

A.Alternate and Backup roles

B.Disabled and Discarding roles

C.Master and Slave roles

D.Root and Designated roles

AnswerA

Alternate and Backup roles provide immediate standby paths without waiting for listening/learning timers.

Why this answer

In RSTP, the Alternate and Backup roles replace the blocking state, while the discarding state replaces blocking, listening, and disabled states.

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Multi-Selectmedium

Which TWO parameters are included when a Junos switch calculates the MST configuration digest? (Choose two.)

Select 2 answers

A.Bridge priority of Instance 0

B.Revision number

C.System MAC address

D.Configuration name

E.Hello timer interval

AnswersB, D

The integer revision number is included in the digest computation.

Why this answer

The MST digest is computed using the configuration name, revision number, and the VLAN-to-instance allocation table.

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MCQmedium

You need to modify the bridge priority of an EX Series switch running RSTP to ensure it becomes the root bridge. Which configuration command correctly sets the bridge priority to 4096?

A.set spanning-tree priority 4096

B.set protocols rstp priority 4096

C.set bridge-priority 4096

D.set protocols rstp bridge-priority 4096

AnswerD

This command sets the bridge priority to 4096, which is lower than the default of 32768.

Why this answer

To set the RSTP bridge priority on a Junos device, you use the 'set protocols rstp bridge-priority <value>' command.

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MCQeasy

Which command allows you to verify whether a specific interface on an EX Series switch is operating as an edge port?

A.show protocols rstp edge

B.show spanning-tree edge-ports

C.show spanning-tree interface

D.show interfaces edge

AnswerC

This command displays port status, role, state, and edge port operational status.

Why this answer

The 'show spanning-tree interface' command provides detailed parameters for each port, including whether it is operating as an edge port.

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MCQeasy

Which command is used to display comprehensive spanning tree status, including port roles, states, and priorities across all interfaces on an EX Series switch?

A.show spanning-tree interface

B.show protocols rstp status

C.show spanning-tree summary

D.show bridge spanning-tree

AnswerA

This command displays detailed per-interface spanning tree status and role assignments.

Why this answer

The 'show spanning-tree interface' command provides detailed status, roles, and states for all interfaces participating in spanning tree.

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Multi-Selecteasy

Which TWO actions occur when you configure an interface as an edge port in RSTP? (Choose two.)

Select 2 answers

A.The port does not generate topology change notifications when its link goes up or down.

B.The port automatically becomes a backup port.

C.The port transitions immediately to the forwarding state.

D.The port's bridge priority is automatically set to 0.

E.The port stops transmitting BPDUs entirely under all circumstances.

AnswersA, C

Edge port state changes do not trigger TCNs.

Why this answer

Edge ports transition immediately to the forwarding state and do not trigger topology changes when their link status changes.

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MCQhard

An administrator implements MSTP and wants to configure a maximum hop count of 20 for instance 1. Which configuration command is used in Junos OS?

A.set protocols mstp instance 1 hop-limit 20

B.set protocols mstp configuration-name RegionA max-hops 20

C.set protocols rstp max-hops 20

D.set protocols mstp max-age 20

AnswerB

The max-hops command sets the regional maximum hop limit in MSTP.

Why this answer

In Junos OS, the maximum hop count for MSTP is configured under the 'protocols mstp' hierarchy using the 'max-hops' statement.

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MCQmedium

You want to disable spanning tree protocol entirely on a specific access interface (ge-0/0/10.0) of an EX Series switch while keeping RSTP active globally. Which configuration command achieves this?

A.delete protocols rstp

B.set protocols rstp interface ge-0/0/10.0 disable

C.set interfaces ge-0/0/10.0 spanning-tree disable

D.set protocols rstp interface ge-0/0/10.0 mode off

AnswerB

This command disables RSTP on the specified interface while leaving it active on other ports.

Why this answer

To disable RSTP on a specific interface while running it globally, you can deactivate or disable the interface under the rstp protocols hierarchy, or configure it appropriately. In Junos, you can use 'disable' under protocols rstp interface.

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MCQhard

An enterprise network uses MSTP. What is the function of the Internal Root in an MST region?

A.It acts as the root switch for a specific MSTI within the local MST region.

B.It translates MST BPDUs into legacy STP BPDUs at the regional boundary.

C.It manages the CIST instance across all connected foreign MST regions.

D.It serves as the sole bridge responsible for generating the MST configuration digest.

AnswerA

Each MSTI has an internal root responsible for path calculations inside the region.

Why this answer

The Internal Root is the switch within a specific MST instance that has the lowest path cost to the regional root or CIST root, serving as the root for that particular MSTI within the region.

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MCQeasy

Which command allows an operator to view the designated root bridge identifier and port roles for all active VLANs under RSTP?

A.show spanning-tree bridge

B.show spanning-tree statistics

C.show spanning-treemstp region

D.show spanning-tree interface detail

AnswerA

This command shows the root bridge ID, bridge priority, and designated root parameters.

Why this answer

The command 'show spanning-tree interface' or 'show spanning-tree bridge' displays root bridge information. Specifically, 'show spanning-tree bridge' displays the root bridge identifier.

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MCQhard

An administrator configures link aggregation (ae0) using LACP between two EX Series switches running RSTP. How does RSTP treat the aggregated interface ae0?

A.RSTP places all member links except the primary active link into a permanent discarding state.

B.RSTP disables itself on aggregated links to prevent conflicts with LACP.

C.RSTP treats the aggregate interface as a single logical port.

D.RSTP runs an independent spanning tree instance on each physical member link of the aggregate.

AnswerC

LACP aggregation hides individual physical links from RSTP, which treats ae0 as a single port.

Why this answer

RSTP treats an aggregated Ethernet bundle (LACP) as a single logical port, running spanning tree calculations on the bundle rather than individual physical member links.

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MCQeasy

What is the primary benefit of enabling edge port configuration on switch access ports connected to end devices?

A.It forces the port to operate exclusively in full-duplex mode.

B.It allows the port to transition immediately to the forwarding state, avoiding startup delays.

C.It increases the interface bandwidth by disabling spanning tree calculations entirely.

D.It enables automatic detection of unauthorized rogue bridges on access links.

AnswerB

Edge ports bypass learning and listening phases for rapid connectivity.

Why this answer

Edge port configuration allows access ports to skip the listening and learning states, transitioning immediately to forwarding and preventing DHCP or client timeout issues.

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MCQmedium

While examining an RSTP topology, you notice that a designated port has suddenly stopped receiving BPDUs from its upstream neighbor, causing the port to transition into a discarding state to prevent potential loops. Which feature is actively providing this protection?

A.Loop protection

B.Root protection

C.BPDU guard

D.TC protection

AnswerA

Loop protection places a port in a discarding state if BPDUs stop arriving unexpectedly.

Why this answer

Loop protection detects when BPDUs are missing on a point-to-point link and places the port into a discarding state to prevent loops caused by unidirectional link failures.

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Multi-Selecthard

Which TWO operational commands are useful for troubleshooting MSTP configuration mismatches and instance status on Junos switches? (Choose two.)

Select 2 answers

A.show spanning-tree interface

B.show bridge-domain mstp-status

C.show mstp topology-digest

D.show spanning-tree mstp configuration

E.show protocols mstp neighbors detail

AnswersA, D

Displays per-interface roles and states across instances.

Why this answer

To troubleshoot MSTP, 'show spanning-tree mstp configuration' and 'show spanning-tree interface' provide essential visibility into regional parameters and port states across instances.

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MCQeasy

What action does the 'set protocols rstp max-age <seconds>' command perform on a Juniper switch?

A.It sets the maximum time a port can remain in the discarding state during bootup.

B.It limits the maximum age of MAC table entries learned via spanning tree.

C.It restricts the maximum number of hops an MSTP BPDU can traverse.

D.It defines how long BPDU information is stored before being considered expired.

AnswerD

Max Age sets the expiration timeout for stored BPDU data.

Why this answer

It configures the Max Age parameter, which determines how long a switch waits without receiving BPDUs before considering the stored BPDU information expired.

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MCQhard

An EX Series switch running RSTP receives BPDUs with superior path cost information from an unauthorized access switch. Which feature should you enable on access-facing ports to prevent these unauthorized BPDUs from altering the spanning tree topology?

A.set protocols rstp interface ge-0/0/5.0 bpdu-guard

B.set protocols rstp interface ge-0/0/5.0 no-root-port

C.set protocols rstp interface ge-0/0/5.0 root-protection

D.set protocols rstp interface ge-0/0/5.0 loop-protection

AnswerA

BPDU guard ensures that ports configured as edge ports will error-disable if they receive a BPDU.

Why this answer

BPDU protection (bpdu-guard) disables a designated edge port if it receives a BPDU, protecting the network from unauthorized switches attempting to inject themselves into the topology.

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MCQmedium

You need to verify the regional configuration name and revision number currently active on an EX Series switch running MSTP. Which operational command should you use?

A.show protocols mstp status

B.show mstp region detail

C.show spanning-tree bridge

D.show spanning-tree mstp configuration

AnswerD

This command shows active MST region parameters, revision, and mappings.

Why this answer

The command 'show spanning-tree mstp configuration' displays the MST region name, revision number, and VLAN-to-instance mapping table.

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MCQeasy

An administrator has deployed a new EX Series switch running RSTP and notices that access ports connected to end-user workstations take up to 30 seconds to transition to the forwarding state. Which configuration command should be applied to immediately resolve this delay for access ports?

A.set protocols rstp interface ge-0/0/1.0 edge

B.set protocols rstp force-version stp

C.set protocols rstp interface ge-0/0/1.0 mode point-to-point

D.set protocols rstp bridge-priority 0

AnswerA

Designating the interface as an edge port skips the listening and learning states, immediately placing it into the forwarding state.

Why this answer

In RSTP, edge ports transition directly to the forwarding state, bypassing the discarding and learning states. Configuring 'no-root-port' or designating the port as an edge port using 'set protocols rstp interface <interface> edge' allows workstations to connect without experiencing STP convergence delay.

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Multi-Selecthard

Which TWO statements are correct regarding the operation of MSTP instance 0 (CIST)? (Choose two.)

Select 2 answers

A.It handles any VLANs that are not explicitly mapped to another user-defined MST instance.

B.It operates independently without any interaction with external RSTP switches.

C.It is limited strictly to a maximum hop count of 1.

D.It acts as the Common and Internal Spanning Tree (CIST).

E.It prohibits the use of root protection on instance 0 ports.

AnswersA, D

Unmapped VLANs automatically default to Instance 0.

Why this answer

Instance 0 in MSTP is known as the Common and Internal Spanning Tree (CIST), and it manages unmapped VLANs while maintaining backward compatibility with legacy STP/RSTP regions.

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MCQeasy

In an RSTP-enabled network, which port role immediately transitions to the forwarding state upon failure of the designated port on the segment, bypassing the traditional listening and learning states?

A.Root port

B.Disabled port

C.Designated port

D.Alternate port

AnswerD

An alternate port maintains a backup path to the root and can transition immediately without delay.

Why this answer

The Alternate port in RSTP serves as a backup to the root port and transitions directly to forwarding if the root port fails.

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MCQhard

While troubleshooting an RSTP topology on EX Series switches, you notice that a designated port has stopped receiving BPDUs from its upstream neighbor due to a unidirectional link failure. Which feature should you enable to prevent this port from transitioning to a Designated Forwarding state and causing a loop?

A.set protocols rstp interface ge-0/0/5.0 bpdu-protection

B.set protocols rstp interface ge-0/0/5.0 loop-protection

C.set protocols rstp interface ge-0/0/5.0 no-negotiation

D.set protocols rstp interface ge-0/0/5.0 error-disable

AnswerB

Loop protection guards against unidirectional link failures by placing the port in a discarding state if BPDUs stop arriving.

Why this answer

Loop protection checks for the continued receipt of BPDUs on root and alternate ports. If BPDUs are lost, the port transitions to a loop-inconsistent blocking state.

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Multi-Selecteasy

Which TWO statements are true regarding loop protection in RSTP? (Choose two.)

Select 2 answers

A.It increases the bridge priority of the local switch to maintain root status.

B.It requires MSTP instances to be fully mapped before activation.

C.It protects against loops caused by unidirectional link failures.

D.It places a port into a discarding state if BPDUs stop arriving unexpectedly.

E.It shuts down access ports immediately upon receiving any BPDU.

AnswersC, D

Unidirectional links cause BPDUs to stop arriving in one direction, which loop protection catches.

Why this answer

Loop protection guards against unidirectional link failures and missing BPDUs, placing the affected port into a discarding state.

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MCQmedium

You are troubleshooting an RSTP topology where a port remains in the discarding state. You suspect a proposal-agreement handshake is failing. Which mechanism is responsible for accelerating this handshake in RSTP?

A.The dynamic MAC address flushing timer

B.The proposal-agreement handshake mechanism

C.The portfast edge negotiation protocol

D.The root bridge hello timer synchronization protocol

AnswerB

Proposal and agreement flags in BPDU headers allow rapid, synchronized link transitions.

Why this answer

RSTP uses a proposal-agreement handshake mechanism between designated and root ports to achieve rapid transition to forwarding without waiting for timers.

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MCQeasy

What is the role of the Root Port in an RSTP topology?

A.It forwards traffic between two different MST regions.

B.It connects the root bridge to all downstream non-root switches.

C.It provides the lowest-cost path from a non-root switch to the root bridge.

D.It serves as the backup forwarding path when the designated port fails.

AnswerC

Every non-root switch has exactly one root port pointing toward the root bridge.

Why this answer

The root port is the port on a non-root switch that provides the lowest cost path to the root bridge.

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MCQhard

When configuring MSTP, what purpose does the regional configuration digest serve?

A.It encrypts the BPDU payload to prevent tampering by unauthorized access switches.

B.It allows neighboring switches to verify if they belong to the same MST region.

C.It acts as a dynamic bridge priority modifier for internal instance root selection.

D.It determines the Designated Master Bridge within the CIST instance.

AnswerB

Switches compare the received digest with their own calculated digest to ensure region parameter consistency.

Why this answer

The configuration digest is an MD5 hash calculated from the region name, revision, and VLAN-to-instance mapping, included in BPDUs to verify that neighboring switches share the exact same region configuration.

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MCQmedium

You are troubleshooting a suboptimal spanning tree topology where an EX4300 switch is chosen as the STP Root Bridge despite having a high bridge priority. What command helps verify the current bridge priority and local bridge identifier parameters?

A.show spanning-tree bridge

B.show spanning-tree statistics

C.show spanning-tree interface

D.show spanning-treemstp configuration

AnswerA

This command displays the local bridge parameters including priority and MAC address.

Why this answer

The 'show spanning-tree bridge' command displays the local bridge identifier, bridge priority, and root bridge information, allowing administrators to inspect active STP parameters.

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MCQmedium

You are configuring MSTP and want to assign VLANs 10 through 50 to MST instance 2. Which configuration hierarchy is correct in Junos OS?

A.set bridge-domains domain1 mstp-instance 2 vlan 10-50

B.set protocols mstp configuration-name RegionA revision 1 instance msti2 vlan 10-50

C.set protocols rstp msti 2 vlan-list 10-50

D.set vlans vlan-range 10-50 mstp instance 2

AnswerB

This command correctly specifies the region configuration name, revision, instance name, and associated VLANs.

Why this answer

In Junos OS, MSTP instances and their associated VLAN mappings are defined under the 'protocols mstp' hierarchy.

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Multi-Selectmedium

Which THREE states are defined in Rapid Spanning Tree Protocol (RSTP)? (Choose three.)

Select 3 answers

A.Blocking

B.Discarding

C.Learning

D.Forwarding

E.Listening

AnswersB, C, D

Discarding replaces blocking, listening, and disabled states in RSTP.

Why this answer

RSTP streamlines operational states into three distinct states: Discarding, Learning, and Forwarding. Legacy states like listening and blocked were combined into discarding.

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