JNCIP-ENT Ethernet Switching And Spanning Tree Practice Test 3 — 15 Questions

Question 1

You are configuring an EX Series switch to participate in a spanning tree topology. You want to ensure that the switch has the lowest priority in the network so that it becomes the root bridge. Which configuration command should you use?

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

Accepted Answer

set protocols rstp bridge-priority 0. To make a switch the root bridge, you must set its bridge priority to the lowest value in the network. The bridge priority is a 4-bit field in the BPDU, with lower values indicating higher priority. Setting it to 0 ensures the switch will win the root election. Interface priority and cost affect port roles and path selection, not the root bridge election. Edge port configuration is for access ports and does not influence root election.

Answer

set protocols rstp interface all cost 0

Answer

set protocols rstp interface all priority 0

Answer

set protocols rstp interface all edge

Question 2

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?

Accepted Answer

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

Answer

VLAN stripping

Answer

VLAN push

Answer

VLAN pop

Question 3

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?

Accepted Answer

Multi-Chassis Link Aggregation (MC-LAG) with ICCP. 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.

Answer

Layer 2 Tunneling Protocol (L2TPv3) bridging

Answer

Rapid PVST+ with root guard on all access ports

Answer

Virtual Chassis with spanning-tree disabled

Question 4

An administrator implements MSTP (Multiple Spanning Tree Protocol) in a large data center using Juniper switches. Region boundaries must be maintained strictly. Which three parameters must match identically across all switches for them to be considered part of the same MST region?

Accepted Answer

Region name, revision number, and VLAN-to-instance mapping. MST region configuration requires identical configuration name, revision number, and VLAN-to-instance mapping table.

Answer

MAC address, revision number, and region name

Answer

Bridge priority, hello time, and max age

Answer

Extended system ID, region name, and forward delay

Question 5

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?

Accepted Answer

Under the logical interface unit configuration using input/output vlan-map. VLAN maps or rewriting rules are applied on the logical interface (subinterface) inbound or outbound directions.

Answer

Under the routing-instance bridge-domain configuration

Answer

Under protocols l22-control configuration hierarchy

Answer

Under the physical interface encapsulation statement

Question 6

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?

Accepted Answer

Isolated VLAN. Isolated VLAN ports can only communicate with promiscuous ports.

Answer

Primary VLAN

Answer

Community VLAN

Answer

Target VLAN

Question 7

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?

Accepted Answer

The switch drops packets from the new MAC address and optionally logs or generates an SNMP trap.. 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.

Answer

The switch immediately reboots the line card to protect the control plane.

Answer

The switch forwards the frame and clears the oldest learned MAC entry from the forwarding table.

Answer

The switch dynamically converts the port into a routed Layer 3 interface.

Question 8

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?

Accepted Answer

Two switches are elected as Master and Backup Routing Engines, while remaining switches act as line cards.. A Virtual Chassis designates a Routing Engine (RE) Master and Backup across designated members, while all switches participate in the distributed forwarding plane.

Answer

Every switch runs its own independent Spanning Tree instance to prevent loops across the virtual backplane.

Answer

Control traffic is load-balanced across all 10 member switches using ECMP across the dedicated stacking ports.

Answer

All 10 switches run independent routing engines with separate control planes and synchronized MAC tables.

Question 9

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?

Accepted Answer

MSTP boundary ports detect RSTP BPDUs and operate in RSTP compatibility mode on that specific port.. MSTP bridge ports connected to RSTP regions automatically downgrade their communication mode to interoperate with RSTP/STP BPDUs.

Answer

MSTP boundary ports drop all RSTP BPDUs and treat the link as a point-to-point blocked topology.

Answer

The entire MSTP region converts its configuration digest to match the RSTP region's default region name.

Answer

MSTP isolates the RSTP region into a separate MSTI instance automatically.

Question 10

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?

Accepted Answer

LLDP-MED with voice VLAN assignment. Voice VLAN feature on EX switches automatically assigns voice traffic from known MAC OUIs to the designated voice VLAN.

Answer

MAC-based RADIUS dynamic VLAN assignment

Answer

Layer 2 protocol tunneling (L2PT)

Answer

IEEE 802.1X supplicant authentication

Question 11

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?

Accepted Answer

The switch with the numerically lowest MAC address is selected as the root bridge.. Spanning tree tie-breaking checks the bridge priority first, and if tied, compares the lowest MAC address of the switches.

Answer

The switch with the highest interface count operational status wins.

Answer

The switch with the higher serial number stored in EEPROM is chosen.

Answer

MSTP triggers a randomized tie-breaker algorithm using the system uptime.

Question 12

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?

Accepted Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching storm-control. Storm control is applied under 'interfaces <interface-name> unit 0 family ethernet-switching storm-control'.

Answer

set vlans default storm-control

Answer

set protocols l2-learning storm-control interface ge-0/0/1

Answer

set forwarding-options storm-control interface ge-0/0/1

Question 13

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?

Accepted Answer

Layer 2 Protocol Tunneling (L2PT). 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.

Answer

MSTP region boundary enforcement

Answer

BPDU filter across all bridging domains

Answer

VLAN translation swapping on inner tags

Question 14

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

Accepted Answer

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

Answer

show vstp topology-change

Answer

show spanning-tree vstp-status

Answer

show ethernet-switching vstp-neighbors

Question 15

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?

Accepted Answer

Both switches must have identical pre-shared keys (connectivity association keys) and matching cipher suites configured.. MACsec requires pre-shared keys (PSK) or MKA (MACsec Key Agreement) with matching connectivity association keys (CAK) and cipher suites.

Answer

Both switches must run RSVP-TE to reserve bandwidth for encrypted frames prior to session establishment.

Answer

Both switches must disable Spanning Tree Protocol on the MACsec-secured interface.

Answer

Both switches must be configured as part of the same VSTP region.