JNCIS-ENT Spanning Tree Practice Test 3 — 15 Questions

Question 1

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?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

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

Answer

The dynamic MAC address flushing timer

Answer

The portfast edge negotiation protocol

Answer

The root bridge hello timer synchronization protocol

Question 2

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

Accepted Answer

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

Answer

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

Answer

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

Answer

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

Question 3

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

Accepted Answer

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

Answer

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

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

Answer

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

Question 4

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?

Accepted Answer

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

Answer

show spanning-tree bridge detail

Answer

show interfaces diagnostics optics

Answer

show rstp topology-changes

Question 5

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

Accepted Answer

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

Answer

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

Answer

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

Answer

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

Question 6

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

Accepted Answer

set protocols rstp forward-delay 15. The forward delay timer can be configured under protocols rstp or stp using 'set protocols rstp forward-delay <seconds>'.

Answer

set bridge forward-delay 15

Answer

set spanning-tree forward-delay 15

Answer

set protocols rstp delay 15

Question 7

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?

Accepted Answer

set protocols mstp configuration-name RegionA max-hops 20. In Junos OS, the maximum hop count for MSTP is configured under the 'protocols mstp' hierarchy using the 'max-hops' statement.

Answer

set protocols mstp instance 1 hop-limit 20

Answer

set protocols rstp max-hops 20

Answer

set protocols mstp max-age 20

Question 8

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?

Accepted Answer

Root-inconsistent (discarding) state. 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.

Answer

Alternate port state

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Error-disabled state

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Listening state

Question 9

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

Accepted Answer

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

Answer

Master port

Answer

Root port

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Designated port

Question 10

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

Accepted Answer

show spanning-tree interface. 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.

Answer

show bridge spanning-tree status

Answer

show rstp summary

Answer

show protocols spanning-tree summary

Question 11

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

Accepted Answer

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

Answer

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

Answer

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

Answer

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

Question 12

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?

Accepted Answer

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

Answer

show protocols mstp status

Answer

show mstp region detail

Answer

show spanning-tree bridge

Question 13

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

Accepted Answer

VLAN-to-instance mapping table. 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.

Answer

Root bridge MAC address

Answer

Bridge priority value

Question 14

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

Accepted Answer

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

Answer

Bridge priority adjustment

Answer

Hello timer scaling

Answer

Forward delay timer optimization

Question 15

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

Accepted Answer

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

Answer

Blocking

Answer

Listening