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CCNA Ethernet Switching And Spanning Tree Questions

40 questions · Ethernet Switching And Spanning Tree topic · All types, answers revealed

1
MCQeasy

You are troubleshooting MAC address learning on an EX Series switch and want to display dynamic MAC entries learned specifically on interface ge-0/0/5. Which operational command should you use?

A.show mac-address-table interface ge-0/0/5
B.show ethernet-switching table port ge-0/0/5
C.show l2-learning interface ge-0/0/5 macs
D.show bridge mac-table interface ge-0/0/5
AnswerD

This command filters the bridging table by the specified interface.

Why this answer

The command 'show bridge mac-table interface ge-0/0/5' displays MAC addresses learned on that interface.

2
MCQeasy

You are configuring private VLANs (PVLANs) on a Juniper EX switch to isolate customer ports from one another while sharing a common gateway. Which VLAN type is configured to allow communication only with promiscuous ports?

A.Primary VLAN
B.Community VLAN
C.Isolated VLAN
D.Target VLAN
AnswerC

Isolated VLAN ports can only communicate with the promiscuous port.

Why this answer

Isolated VLAN ports can only communicate with promiscuous ports.

3
MCQmedium

You are troubleshooting a Q-in-Q tunneling implementation on an MX Series router where customer VLAN tags are being stripped instead of preserved across the service provider core. Under which configuration hierarchy should the 'vlan-tagging' and 'pop-pop' or 'push' actions be applied on the interface?

A.set interfaces ge-0/0/1 flexible-vlan-tagging
B.set protocols l2-learning interface ge-0/0/1 q-in-q
C.set bridge-domains bd vlan-id-list 10
D.set interfaces ge-0/0/1 encapsulation flexible-ethernet-services
AnswerA

flexible-vlan-tagging is required on the physical interface to process multiple VLAN tags.

Why this answer

For Q-in-Q tunneling on Juniper routing and switching platforms, flexible VLAN tagging is configured under 'interfaces <interface> flexible-vlan-tagging'.

4
MCQmedium

You are configuring MACsec (Media Access Control Security) on an EX Series switch interface to secure Layer 2 links between two enterprise buildings. Which requirement is mandatory for MACsec to establish a secure session successfully between the two switches?

A.Both switches must run RSVP-TE to reserve bandwidth for encrypted frames prior to session establishment.
B.Both switches must have identical pre-shared keys (connectivity association keys) and matching cipher suites configured.
C.Both switches must disable Spanning Tree Protocol on the MACsec-secured interface.
D.Both switches must be configured as part of the same VSTP region.
AnswerB

MACsec encryption relies on matching security keys (CAK/CKN) and negotiated cipher suites.

Why this answer

MACsec requires pre-shared keys (PSK) or MKA (MACsec Key Agreement) with matching connectivity association keys (CAK) and cipher suites.

5
MCQeasy

You want to configure voice VLAN functionality on a Juniper EX switch so that IP phones automatically place voice traffic into VLAN 50 while passing PC data through unchanged. Which feature should you configure?

A.MAC-based RADIUS dynamic VLAN assignment
B.Layer 2 protocol tunneling (L2PT)
C.LLDP-MED with voice VLAN assignment
D.IEEE 802.1X supplicant authentication
AnswerC

LLDP-MED provides network policy advertisement, allowing IP phones to discover the voice VLAN.

Why this answer

Voice VLAN feature on EX switches automatically assigns voice traffic from known MAC OUIs to the designated voice VLAN.

6
MCQmedium

You are configuring Ethernet switching on an EX4300 switch and need to implement storm control to prevent broadcast, multicast, and unknown unicast traffic from overwhelming access links. Where is storm-control applied in the Junos configuration hierarchy?

A.set interfaces ge-0/0/1 unit 0 family ethernet-switching storm-control
B.set vlans default storm-control
C.set protocols l2-learning storm-control interface ge-0/0/1
D.set forwarding-options storm-control interface ge-0/0/1
AnswerA

Storm control is configured directly under the ethernet-switching family on the interface.

Why this answer

Storm control is applied under 'interfaces <interface-name> unit 0 family ethernet-switching storm-control'.

7
MCQhard

An enterprise network operates VSTP across 150 VLANs. The network engineering team notices high CPU utilization on the Routing Engine due to VSTP BPDU processing. Which Junos command or feature can mitigate this control-plane load while keeping VSTP operational?

A.set system pfe bpdu-bypass enable
B.set forwarding-options storm-control interfaces all vstp
C.set protocols vstp no-bpdu-generation
D.set protocols vstp hello-time 5
AnswerD

Increasing the hello-time interval reduces the frequency of BPDU transmissions and processing overhead.

Why this answer

BPDU rate-limiting or adjusting VSTP hello timers helps reduce control-plane processing overhead. In Junos, VSTP timer tuning and bpdu processing limits control overhead.

8
Multi-Selecteasy

Which TWO operational commands are valid for troubleshooting VSTP on Juniper EX switches? (Choose two)

Select 2 answers
A.show vstp topology-change
B.show spanning-tree vstp-status
C.show vstp vlan
D.show vstp interface
E.show ethernet-switching vstp-neighbors
AnswersC, D

Displays VSTP status per VLAN.

Why this answer

show vstp and show vstp vlan are valid operational commands for VSTP.

9
MCQhard

In a Juniper Virtual Chassis scaling deployment comprising 10 EX4600 switches, how are control and management planes structured across member switches to maintain high availability and failover resilience?

A.Two switches are elected as Master and Backup Routing Engines, while remaining switches act as line cards.
B.Every switch runs its own independent Spanning Tree instance to prevent loops across the virtual backplane.
C.Control traffic is load-balanced across all 10 member switches using ECMP across the dedicated stacking ports.
D.All 10 switches run independent routing engines with separate control planes and synchronized MAC tables.
AnswerA

The Virtual Chassis architecture assigns Routing Engine roles to two members for redundancy, with the rest acting as line-card members.

Why this answer

A Virtual Chassis designates a Routing Engine (RE) Master and Backup across designated members, while all switches participate in the distributed forwarding plane.

10
MCQeasy

An administrator needs to verify the operational state of an MSTP instance named 'MSTI-1' on an EX Series switch, including its designated root and regional parameters. Which operational command should be executed?

A.show ethernet-switching mstp detail
B.show bridge mstp-status instance-1
C.show spanning-tree instance msti-1
D.show mstp instance detail
AnswerD

show mstp instance provides detailed operational parameters for MSTP instances.

Why this answer

The command 'show mstp instance detail' or 'show spanning-tree mstp instance' displays instance details. In Junos, it is 'show mstp instance [name]'.

11
MCQmedium

You are configuring MAC limiting on an EX Series switch interface to restrict the maximum number of learned MAC addresses to 10. What happens when the 11th unique MAC address attempts to communicate through the interface?

A.The switch drops packets from the new MAC address and optionally logs or generates an SNMP trap.
B.The switch immediately reboots the line card to protect the control plane.
C.The switch forwards the frame and clears the oldest learned MAC entry from the forwarding table.
D.The switch dynamically converts the port into a routed Layer 3 interface.
AnswerA

Exceeding the MAC limit triggers the configured action, typically dropping new source MACs and logging.

Why this answer

By default, MAC limit drop or log actions occur. The standard configurable action when a limit is exceeded includes dropping the packet or shutting down the port.

12
Multi-Selecthard

Which THREE features or protocols are used in Juniper enterprise switching environments to prevent Layer 2 bridging loops while avoiding traditional Spanning Tree blocking ports? (Choose three)

Select 3 answers
A.Rapid PVST+ with bridge priority overrides
B.Virtual Chassis technology
C.Ethernet VPN (EVPN) with VXLAN data plane
D.MSTP with MSTI region mapping
E.Multi-Chassis Link Aggregation (MC-LAG)
AnswersB, C, E

Virtual Chassis combines multiple physical switches into a single logical device, eliminating internal loops.

Why this answer

MC-LAG, Virtual Chassis, and EVPN-VXLAN eliminate loops via active-active multi-pathing or distributed control planes without traditional STP blocking links.

13
MCQhard

In a Juniper Q-in-Q deployment, customer frames are received with an EtherType of 0x8100 (IEEE 802.1Q). The service provider network uses a custom provider EtherType of 0x9100 for outer tags. Where and how is this custom EtherType configured on an MX Series router?

A.Under 'protocols l2-learning provider-tpid 0x9100'
B.Under 'system ethernet-switching tpid-table add 0x9100'
C.Under 'routing-instances bd bridge-options tpid 0x9100'
D.Under 'interfaces ge-0/0/1 tpid 0x9100' on the physical interface
AnswerD

Configuring the TPID on the physical interface allows the router to recognize non-standard outer tag EtherTypes.

Why this answer

Custom inner/outer TPIDs (Tag Protocol Identifiers) are configured on the physical interface using 'tpid 0x9100'.

14
Multi-Selectmedium

Which TWO parameters are part of the standard MSTP configuration digest computed across switches in an MST region? (Choose two)

Select 2 answers
A.Bridge priority value
B.Interface MAC addresses
C.MST configuration name
D.Hello time and max age timers
E.MST revision number
AnswersC, E

Region name is included in the digest.

Why this answer

The MST configuration digest includes region name, revision number, and the VLAN-to-instance allocation table.

15
Multi-Selectmedium

Which TWO actions can be triggered when a MAC address limit is exceeded on a Juniper switch interface configured with MAC limiting? (Choose two)

Select 2 answers
A.drop
B.quarantine
C.shutdown
D.reboot
E.isolate-vlan
AnswersA, C

Drops frames from unauthorized source MAC addresses.

Why this answer

Configurable actions on MAC limit violation include drop and log, or drop and shutdown (disable) the interface.

16
Multi-Selectmedium

An engineer is deploying VSTP on a Juniper EX Series network. Which THREE characteristics or limitations of VSTP should be considered during the design phase? (Choose three)

Select 3 answers
A.VSTP configuration requires enabling vstp under protocols and can be applied selectively per VLAN or globally.
B.VSTP allows interoperability with Cisco switches running PVST+ or Rapid-PVST+.
C.VSTP requires all switches in the topology to belong to the exact same named MST region.
D.VSTP automatically aggregates all VLAN spanning trees into a single BPDU transmission to save bandwidth.
E.VSTP creates a separate spanning tree instance for every defined VLAN, which can increase Routing Engine CPU load in very large VLAN environments.
AnswersA, B, E

VSTP can be enabled globally or enabled/disabled on a per-VLAN basis within the Junos configuration hierarchy.

Why this answer

VSTP operates per-VLAN, maintains full compatibility with Cisco PVST+, and scales linearly with the number of VLANs, which can consume significant CPU resources if not properly sized.

17
Multi-Selectmedium

Which TWO statements describe the behavior of VSTP (VLAN Spanning Tree Protocol) on Juniper EX Series switches? (Choose two)

Select 2 answers
A.VSTP can interoperate with Cisco's PVST+ protocol.
B.VSTP is incompatible with RSTP fallback modes.
C.VSTP automatically disables all trunk ports if BPDU guard is triggered globally.
D.VSTP runs a separate Spanning Tree instance for each configured VLAN.
E.VSTP requires all VLANs to be mapped into a single master MSTI region.
AnswersA, D

VSTP is designed to interoperate with PVST/PVST+ using standard Cisco-compatible PVST BPDUs.

Why this answer

VSTP runs an independent spanning tree instance per VLAN and interoperates with PVST+.

18
Multi-Selecthard

When configuring advanced Layer 2 tunneling (Q-in-Q) on Juniper EX Series switches, which THREE statements are correct regarding VLAN stacking behavior and limitations? (Choose three)

Select 3 answers
A.Layer 2 Protocol Tunneling (L2PT) is automatically enabled for all protocols without additional configuration when QinQ is active.
B.MTU sizes across the core must be adjusted to account for the extra 4 bytes of the added outer VLAN tag.
C.Incoming customer frames have an outer VLAN tag pushed onto them at the provider edge ingress port.
D.The inner customer VLAN tags remain entirely untouched and transparent as the frames traverse the provider core.
E.QinQ tunneling requires standard access mode encapsulation on all core-facing uplink ports.
AnswersB, C, D

Because stacked tags add overhead (an extra 4 bytes per tag), core link MTU must be increased to prevent frame fragmentation or drops.

Why this answer

QinQ on Juniper EX switches involves specific encapsulation requirements like flexible-ethernet-services, stacking VLAN tags on ingress and popping on egress, and preserving inner customer VLAN tags transparently.

19
MCQmedium

You are troubleshooting a switching loop issue in an enterprise core utilizing MSTP. You run 'show mstp interface' and notice that a specific port is stuck in the discarding state for MSTI 1. Which command should you run to verify if root guard has been triggered on this port?

A.show spanning-tree inconsistent-ports
B.show bridge root-guard status
C.show mstp interface detail
D.show ethernet-switching security-guard
AnswerC

In Junos, 'show mstp interface detail' displays comprehensive port state information including root guard status and inconsistent port flags.

Why this answer

The command 'show mstp interface detail' provides detailed port-level status including whether root guard has tripped and placed the port into a inconsistent/discarding state.

20
MCQmedium

An administrator wants to configure MSTP on Juniper switches and needs to assign VLANs 10 through 50 to MST Instance 2. Which configuration command hierarchy is correct in Junos?

A.set protocols mstp configuration-name CORP instance-name msti2 vlan 10-50
B.set protocols spanning-tree mst instance 2 vlan-members 10-50
C.set protocols mstp configuration-name CORP msti 2 vlan 10-50
D.set protocols mstp region-name CORP revision 1 instance msti2 vlan [ 10-50 ]
AnswerC

The correct Junos syntax is 'set protocols mstp configuration-name <name> msti <id> vlan <vlan-list>'.

Why this answer

In Junos, MST configuration parameters such as instance mappings, revision numbers, and names are defined under the 'protocols mstp configuration-name' hierarchy.

21
MCQhard

An enterprise network engineer is designing a redundant Layer 2 topology with MSTP across Juniper EX switches. Two switches have identical bridge priorities and MAC addresses that result in a tie for regional root. How does MSTP deterministically break the tie to select the regional root bridge?

A.The switch with the highest interface count operational status wins.
B.The switch with the numerically lowest MAC address is selected as the root bridge.
C.The switch with the higher serial number stored in EEPROM is chosen.
D.MSTP triggers a randomized tie-breaker algorithm using the system uptime.
AnswerB

When bridge priorities are tied, the switch with the lowest base MAC address wins the election.

Why this answer

Spanning tree tie-breaking checks the bridge priority first, and if tied, compares the lowest MAC address of the switches.

22
MCQeasy

You are configuring VSTP (VLAN Spanning Tree Protocol) on Juniper EX switches to interoperate with legacy third-party switches running PVST+. Which operational command allows you to verify the VSTP bridge identifier and root bridge status per VLAN?

A.show ethernet-switching vstp
B.show spanning-tree vlan detail
C.show vstp vlan
D.show bridge vstp-status
AnswerC

show vstp vlan provides per-VLAN spanning tree operational status.

Why this answer

The command 'show vstp vlan' displays the VSTP state, root bridge, and port roles for each VLAN.

23
Multi-Selecthard

When designing advanced enterprise campus VLAN architectures with Juniper EX Series switches, which TWO considerations are critical for large-scale Layer 2 domains? (Choose two)

Select 2 answers
A.Configuring bridge assurance on all point-to-point links running MSTP to protect against unidirectional link failures.
B.Keeping failure domains small by limiting the physical span of a single VLAN or transitioning to routed access / EVPN-VXLAN architectures.
C.Disabling BPDU protection on core inter-switch links to allow unexpected root bridges to take over seamlessly.
D.Enabling spanning tree globally across all VLANs without instance mapping to ensure all switches share a single root bridge.
E.Setting the forward delay timer to 4 seconds across all switches to accelerate MSTP topology convergence.
AnswersA, B

Bridge assurance ensures that switches actively send BPDUs on all point-to-point operational ports, preventing loops caused by unidirectional link failures.

Why this answer

In large-scale Layer 2 networks, keeping broadcast domains small and controlling failure domains via multi-chassis link aggregation (MC-LAG or EVPN-VXLAN) and limiting spanning tree blast radius are essential design principles.

24
Multi-Selecteasy

Which TWO security features can be configured on Juniper EX switches to prevent DHCP spoofing and ARP poisoning attacks on Layer 2 access ports? (Choose two)

Select 2 answers
A.Storm control
D.MACsec encryption
AnswersC, E

DHCP snooping builds a binding database to prevent rogue DHCP servers and IP spoofing.

Why this answer

DHCP snooping and Dynamic ARP Inspection (DAI) prevent DHCP spoofing and ARP poisoning respectively.

25
MCQmedium

An engineer is configuring QinQ (802.1ad) tunneling on a Juniper EX Series switch to transport customer VLANs across a service provider core. The customer-facing access port receives tagged frames with outer VLAN ID 100 and inner VLAN ID 200. Which configuration statement correctly defines the interface encapsulation and VLAN mapping?

A.set interfaces ge-0/0/1 encapsulation flexible-ethernet-services and set interfaces ge-0/0/1 unit 0 family ethernet-switching vlan-tagging
B.set interfaces ge-0/0/1 encapsulation vlan-stacking and set interfaces ge-0/0/1 unit 0 family ethernet-switching input-vlan-map push and set interfaces ge-0/0/1 unit 0 family ethernet-switching output-vlan-map pop
C.set interfaces ge-0/0/1 encapsulation flexible-ethernet-services and set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode access
D.set interfaces ge-0/0/1 encapsulation qinq-access and set interfaces ge-0/0/1 unit 0 family ethernet-switching vlan-members 100
AnswerB

vlan-stacking encapsulation with input-vlan-map push and output-vlan-map pop correctly handles Q-in-Q encapsulation on Juniper EX switches.

Why this answer

To configure Q-in-Q tunneling on Juniper switches, the customer-facing port requires 'flexible-ethernet-services' encapsulation and a 'vlan-map' configuration that maps the incoming outer VLAN to the provider core VLAN.

26
MCQmedium

You are configuring Q-in-Q tunneling on an MX Series router where customer frames arrive with VLAN tag 100, and you need to encapsulate them with a service provider outer VLAN tag 3000 using 'vlan-map'. Where is the VLAN map applied?

A.Under the routing-instance bridge-domain configuration
B.Under the logical interface unit configuration using input/output vlan-map
C.Under protocols l22-control configuration hierarchy
D.Under the physical interface encapsulation statement
AnswerB

VLAN maps for tag manipulation are applied under logical interface units.

Why this answer

VLAN maps or rewriting rules are applied on the logical interface (subinterface) inbound or outbound directions.

27
MCQhard

An enterprise network uses Q-in-Q tunneling over an MX Series provider network. Customer BPDUs must pass transparently across the provider core without being processed by the provider's own VSTP/MSTP instances. Which feature must be enabled on the provider switch access ports to achieve this?

A.MSTP region boundary enforcement
B.BPDU filter across all bridging domains
C.VLAN translation swapping on inner tags
D.Layer 2 Protocol Tunneling (L2PT)
AnswerD

L2PT encapsulates BPDUs into proprietary multicast frames at the ingress edge and strips them at the egress edge.

Why this answer

Layer 2 protocol tunneling (L2PT) or BPDU tunneling is required to encapsulate L2 control frames (like STP BPDUs) into multicast destination MAC addresses so they cross the core transparently.

28
Multi-Selecthard

When configuring advanced Q-in-Q tunneling on Juniper MX Series routers, which THREE encapsulation or tagging parameters must be correctly aligned between the customer edge and provider edge interfaces? (Choose three)

Select 3 answers
A.VLAN action rules (pop, push, or swap)
B.MSTP region name configuration
C.Tag Protocol Identifier (TPID) EtherType values
D.Flexible VLAN tagging enabled on physical interfaces
E.IGMP snooping version compatibility
AnswersA, C, D

Tag manipulation actions must mirror each other for proper tag processing.

Why this answer

Q-in-Q alignment requires matching flexible-vlan-tagging, TPID values (EtherType), and VLAN tag preservation/manipulation rules.

29
MCQeasy

An engineer is configuring a QinQ tunnel where the service provider bridge needs to transparently carry customer control traffic (like STP BPDUs) through the core without processing them. What feature must be enabled on the provider edge access ports?

A.VLAN Translation
C.Layer 2 Protocol Tunneling (L2PT)
D.BPDU Protection (bpdu-block)
AnswerC

L2PT allows customer bridge protocol data units (BPDUs) to be tunneled transparently across a service provider network.

Why this answer

Layer 2 Protocol Tunneling (L2PT) encapsulates customer BPDUs into specific multicast destination MAC addresses at the ingress edge, tunnels them across the provider core, and un-encapsulates them at the egress edge.

30
Multi-Selecthard

Which THREE mechanisms are provided by Juniper switches running MSTP to protect against bridging loops caused by unidirectional link failures or misbehaving switches? (Choose three)

Select 3 answers
A.Storm control broadcast filtering
E.MACsec cryptographic validation
AnswersB, C, D

Root guard prevents unauthorized switches from becoming root.

Why this answer

Loop guard, root guard, and bpdu guard are standard STP/MSTP protection features available on Juniper switches.

31
MCQeasy

When configuring advanced VLAN mapping on a Juniper MX Series router using flexible VLAN tagging, which term describes the action of replacing an incoming inner VLAN tag with a new tag before forwarding into the provider core?

A.VLAN stripping
B.VLAN swap
C.VLAN push
D.VLAN pop
AnswerB

Swap replaces an existing tag with a new tag value.

Why this answer

VLAN translation or swapping replaces the incoming tag with a mapped tag.

32
MCQhard

An enterprise network running VSTP (VLAN Spanning Tree Protocol) across Juniper EX Series switches experiences unexpected loops because a newly added switch does not participate in VSTP for VLAN 50. Upon investigation, you discover the VSTP BPDU multicast destination MAC address is being dropped by a third-party non-Juniper intermediate switch. What is the standard VSTP MAC address used for BPDU transmission?

A.01:00:0c:cc:cc:cd
B.01:80:c2:00:00:08
C.01:80:c2:00:00:00
D.01:80:c2:00:00:0f
AnswerA

VSTP uses the Cisco/PVST+ compatible multicast MAC address 01:00:0c:cc:cc:cd.

Why this answer

VSTP utilizes the PVST+ proprietary destination MAC address of 01:00:0c:cc:cc:cd to interoperate and transmit per-VLAN spanning tree BPDUs.

33
Multi-Selecthard

When designing a high-scale enterprise campus network using Juniper EX Series switches, which THREE best practices should be followed for Spanning Tree Protocol design? (Choose three)

Select 3 answers
A.Use default bridge priority values on all core switches to allow automated root election.
B.Enable BPDU guard and loop guard on all edge access ports.
C.Disable Spanning Tree entirely on all access ports to ensure faster convergence.
D.Manually position root and secondary root bridges at the core or distribution layer.
E.Keep MSTP region configurations (name, revision, VLAN mapping) identical across all switches in the region.
AnswersB, D, E

Protecting edge ports prevents unauthorized loops and topology manipulation.

Why this answer

Best practices include placing root bridges at the core/distribution layer, using edge protection features, and maintaining consistent region parameters.

34
MCQeasy

An administrator needs to enable BPDU protection on edge access ports in a VSTP environment to prevent loops caused by unauthorized switches. Which command under 'protocols vstp' accomplishes this globally or per-interface?

A.set protocols vstp interface ge-0/0/1 disable-on-bpdu
B.set protocols vstp interface ge-0/0/1 edge-port protect
C.set protocols vstp interface ge-0/0/1 drop-bpdu
D.set protocols vstp interface ge-0/0/1 bpdu-guard
AnswerD

bpdu-guard protects edge ports by error-disabling them when BPDUs are detected.

Why this answer

bpdu-guard under interface configuration in VSTP drops or disables the port upon receiving BPDUs.

35
Multi-Selectmedium

Which TWO configuration statements are required when setting up an MSTP region on a Juniper EX Series switch? (Choose two)

Select 2 answers
A.set protocols mstp revision 1
B.set protocols mstp configuration-name RegionA
C.set protocols mstp msti-priority 4096
D.set protocols mstp region-type standard
E.set protocols mstp force-version 802.1s
AnswersA, B

The revision number is a mandatory component of the MST region configuration digest.

Why this answer

MSTP configuration requires defining a configuration name and a revision number within the mstp protocol hierarchy.

36
MCQhard

An enterprise network runs MSTP across an EX Series core. An administrator wants to ensure that a specific core port never becomes the root port for any MSTI, protecting the upstream core path. Which command achieves this?

A.set protocols mstp interface ge-0/0/0 no-root-port
B.set protocols mstp interface ge-0/0/0 root-guard
C.set protocols mstp interface ge-0/0/0 priority 0
D.set protocols mstp interface ge-0/0/0 restrict-role root
AnswerA

The 'no-root-port' statement ensures the interface is never selected as a root port.

Why this answer

Root protection in MSTP is enabled via the 'no-root-port' or 'root-protection' statement under interface configuration in MSTP. In Junos, 'no-root-port' is used.

37
MCQhard

An engineer is troubleshooting a large-scale enterprise network with multiple MSTP regions connected by a legacy RSTP region. How do boundary switches running MSTP interact with RSTP switches on shared segments?

A.MSTP boundary ports drop all RSTP BPDUs and treat the link as a point-to-point blocked topology.
B.The entire MSTP region converts its configuration digest to match the RSTP region's default region name.
C.MSTP boundary ports detect RSTP BPDUs and operate in RSTP compatibility mode on that specific port.
D.MSTP isolates the RSTP region into a separate MSTI instance automatically.
AnswerC

MSTP bridges automatically migrate ports connecting to RSTP/STP regions to legacy mode for compatibility.

Why this answer

MSTP bridge ports connected to RSTP regions automatically downgrade their communication mode to interoperate with RSTP/STP BPDUs.

38
MCQeasy

An enterprise network engineer needs to configure a trunk port on a Juniper EX Series switch running Junos OS to allow multiple VLANs while explicitly blocking VLAN 99. Which configuration statement under 'interfaces ge-0/0/1 unit 0 family ethernet-switching' correctly achieves this?

A.exclude-vlan-members 99;
B.block-vlan 99;
C.vlan-members except 99;
D.vlan-members [ vlan-members except 99 ];
AnswerC

Using 'vlan-members except' allows all other VLANs except the one specified.

Why this answer

The 'vlan-members none' or explicitly listing allowed VLANs excludes unspecified ones, but to explicitly prune a VLAN while allowing others, the 'vlan-members except' option is used.

39
MCQmedium

You are configuring selective Q-in-Q stacking on an MX Series router. Unlike standard Q-in-Q where all customer VLANs are encapsulated into a single provider VLAN, selective Q-in-Q allows you to map specific customer VLAN ranges to different provider VLANs. Which configuration element enables this granularity?

A.vlan-map match statement with specific input VLAN ID filters
B.protocols l2-learning selective-stacking
C.global bridge-domain vlan-translation enable
D.routing-instance forwarding-options selective-qinq
AnswerA

Matching specific inner VLAN IDs enables selective Q-in-Q mapping.

Why this answer

Flexible VLAN tagging combined with 'vlan-map' statements defining match criteria allows selective Q-in-Q.

40
MCQhard

You need to design a scalable Layer 2 architecture across multiple data center buildings using Juniper switches, avoiding single points of failure while preventing bridging loops. Which scaling mechanism allows Active-Active multihoming without running Spanning Tree Protocol across the core?

A.Layer 2 Tunneling Protocol (L2TPv3) bridging
B.Multi-Chassis Link Aggregation (MC-LAG) with ICCP
C.Rapid PVST+ with root guard on all access ports
D.Virtual Chassis with spanning-tree disabled
AnswerB

MC-LAG uses ICCP to coordinate forwarding between two peer switches, enabling active-active uplinks without STP loops.

Why this answer

MC-LAG (Multi-Chassis Link Aggregation Group) or EVPN-VXLAN provides active-active multihoming and eliminates spanning tree loops. Among traditional Layer 2 tools, MC-LAG is the direct multi-chassis active-active solution.

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