JNCIS-ENT Layer 2 Switching And VLANs Practice Test 2 — 15 Questions

Question 1

You are configuring an access port on an EX Series switch and want to ensure that if a MAC address is learned on the port, it persists even after a switch reboot or aging timer expiration. Which configuration attribute achieves this?

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

Accepted Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching static-mac-address <mac-address>. Static MAC addresses can be configured on an interface using the static statement under the interface or ethernet-switching hierarchy.

Answer

set vlans finance static-learning enable

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching filter input static-mac

Answer

set ethernet-switching-options persistent-mac interface ge-0/0/1

Question 2

An EX Series switch is configured with a private VLAN primary VLAN 10 and secondary isolated VLAN 20. An administrator wants to verify the active private VLAN port associations and mappings. Which operational command displays this information?

Accepted Answer

show vlans extensive. Private VLAN operational state and port mappings are verified using 'show ethernet-switching vlan' or specialized PVLAN operational commands.

Answer

show private-vlan mapping

Answer

show ethernet-switching vlan private-vlan

Answer

show bridge-options private-vlan

Question 3

An administrator needs to remove VLAN 20 from a trunk port that currently allows all VLANs. Which configuration command correctly prunes VLAN 20?

Accepted Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode trunk vlan members all except 20. To exclude a specific VLAN from a trunk port that allows all VLANs, you configure member-all except.

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode trunk vlan prune 20

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode trunk vlan members remove 20

Answer

delete interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode trunk vlan members 20

Question 4

You are troubleshooting an issue where devices on VLAN 10 cannot communicate across switches because frames are dropping. You suspect a native VLAN mismatch on the interconnecting trunk link. Which operational command helps identify the native VLAN configuration on all trunk ports?

Accepted Answer

show ethernet-switching interfaces trunk. The command 'show ethernet-switching interfaces trunk' displays trunk port information, including the native VLAN configuration for each trunk interface. This allows the administrator to quickly identify any native VLAN mismatches on trunk links.

Answer

show vlans detail

Answer

show interfaces native-vlan

Answer

show protocols spanning-tree interface

Question 5

You are configuring voice and data VLANs on an EX Series access port. You want the IP phone to process tagged voice traffic for VLAN 50 and pass untagged data traffic from a connected PC into access VLAN 10. Which configuration achieves this?

Accepted Answer

set interfaces ge-0/0/3 unit 0 family ethernet-switching interface-mode access vlan members 10 voice-vlan 50. Configuring a voice VLAN alongside an access VLAN on an interface allows handling both tagged voice and untagged data traffic.

Answer

set interfaces ge-0/0/3 unit 0 family ethernet-switching interface-mode dual-access vlan 10 50

Answer

set interfaces ge-0/0/3 unit 0 family ethernet-switching ip-phone vlan-data 10 vlan-voice 50

Answer

set interfaces ge-0/0/3 unit 0 family ethernet-switching interface-mode trunk native-vlan-id 10 vlan members 50

Question 6

An engineer needs to configure a Layer 2 protocol tunneling (L2PT) feature on an EX Series switch trunk port to tunnel BPDU frames from a customer switch across a service provider network. Where is L2PT enabled in Junos?

Accepted Answer

set protocols layer2-control tunneling interface ge-0/0/1 stp. On Junos EX Series switches, Layer 2 Protocol Tunneling (L2PT) is configured under the [edit protocols layer2-control] hierarchy using the 'tunneling' stanza, with the interface and the protocol to tunnel (stp, vtp, or lacp) specified. The correct syntax is 'set protocols layer2-control tunneling interface ge-0/0/1 stp', which enables BPDU tunneling on that trunk port. This allows customer STP BPDUs to be encapsulated and forwarded transparently across the service provider network.

Answer

set protocols l2pt interface ge-0/0/1 peer-protocol stp

Answer

set ethernet-switching-options bpdu-tunneling interface ge-0/0/1

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching l2pt-profiles

Question 7

An administrator needs to modify the name of an existing VLAN from 'sales' to 'retail' without changing its VLAN ID 40. Which command accomplishes this?

Accepted Answer

rename vlans sales to retail. On Junos devices, VLANs are configured under the [edit vlans] hierarchy. To rename an existing VLAN while preserving its VLAN ID, you use the 'rename' command within configuration mode. The correct syntax is 'rename vlans to ', which changes the VLAN's name from 'sales' to 'retail' without altering its associated VLAN ID (40). This command is specific to Junos and is the standard way to rename any configuration object.

Answer

edit vlans sales vlan-name retail

Answer

change vlans sales name retail

Answer

set vlans retail vlan-id 40

Question 8

You are troubleshooting intermittent packet drops on an enterprise switch trunk link. You notice that the MTU configured on the core switch trunk port is 1500, but QinQ double-tagged frames are traversing the link. What is the impact of this MTU configuration?

Accepted Answer

Frames exceeding 1500 bytes are dropped due to MTU mismatch/exceeding standard size.. QinQ double-tagging adds an outer 802.1Q tag (4 bytes) plus the original inner tag (4 bytes), increasing the frame size beyond the standard 1500-byte payload. If the trunk port MTU is left at 1500, frames that exceed this size (due to the extra tag overhead) are dropped. To support QinQ, the MTU must be increased (typically to 1504 or higher, often 1522 or 9100 for jumbo) to accommodate the additional tag bytes.

Answer

The switch strips the outer tag automatically to fit the 1500 MTU limit.

Answer

The switch automatically fragments the Layer 2 Ethernet frames into smaller segments.

Answer

The interface automatically negotiates a higher MTU using LLDP.

Question 9

An administrator wants to configure MAC-based VLAN assignment on an EX Series switch so that specific client devices are automatically placed into VLAN 20 based on their source MAC address regardless of which port they plug into. Where is MAC-based VLAN assignment configured in Junos?

Accepted Answer

set ethernet-switching-options mac-based-vlan interface ge-0/0/1 vlan 20. MAC-based VLAN classification is configured under the [edit ethernet-switching-options mac-based-vlan] hierarchy.

Answer

set protocols vlan-assignment mac <mac> vlan-id 20

Answer

set vlans vlan-id 20 mac-address-match <mac>

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching dynamic-vlan 20

Question 10

You are configuring a trunk port on an EX Series switch and need to explicitly define the allowed VLAN list as VLANs 10, 20, and 30. Which configuration statement is correct?

Accepted Answer

set interfaces ge-0/0/4 unit 0 family ethernet-switching interface-mode trunk vlan members [ 10 20 30 ]. The correct Junos syntax for a trunk port with an explicit VLAN member list is 'set interfaces ge-0/0/4 unit 0 family ethernet-switching interface-mode trunk vlan members [ 10 20 30 ]'. This sets the interface mode to trunk and restricts the allowed VLANs to the specified list. The brackets denote a Junos list, and 'vlan members' is the correct keyword.

Answer

set vlans members ge-0/0/4 [ 10 20 30 ]

Answer

set interfaces ge-0/0/4 unit 0 family ethernet-switching trunk-vlan 10,20,30

Answer

set interfaces ge-0/0/4 unit 0 family ethernet-switching interface-mode trunk allowed-vlans 10 20 30

Question 11

An administrator is troubleshooting a scenario where broadcast traffic from a specific VLAN is flooding a Layer 2 domain and causing high CPU utilization on EX Series switches. Which feature can be configured to limit unknown unicast, broadcast, and multicast (BMC) traffic per VLAN or interface?

Accepted Answer

set ethernet-switching-options storm-control interface ge-0/0/1 broadcast level percentage 20. The correct Junos configuration for storm control on EX Series switches uses the 'ethernet-switching-options storm-control' hierarchy, specifying the interface and the traffic type (broadcast, multicast, or unknown-unicast) with a level as a percentage or packets per second. Option C matches this syntax exactly, applying a 20% broadcast storm control level on ge-0/0/1.

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching storm-control level 80

Answer

set forwarding-options storm-control profile default bandwidth-percentage 50

Answer

set protocols storm-protection vlan 10 max-rate 1000pps

Question 12

An administrator wants to examine Layer 2 switching status and MAC learning tables on an EX Series switch. Which TWO operational commands can be used to gather this information? (Choose two.)

Accepted Answer

show ethernet-switching interface. Option C, 'show ethernet-switching interface', is correct because on EX Series switches it displays Layer 2 switching status per interface, including the interface's VLAN membership, switching state (up/down, tagged/untagged), and related Ethernet switching parameters. Option E, 'show ethernet-switching table', is correct because it displays the MAC learning table (the Ethernet switching forwarding database), showing learned MAC addresses, their associated VLANs, and the interfaces/next hops through which they were learned. Option A, 'show vlans summary', is not an operational command that provides MAC learning or interface-level Layer 2 switching status in this context. Option B, 'show bridge-domain forwarding-table', is not a valid EX Series Junos operational command for this purpose. Option D, 'show ip route bridge', is not a valid command and relates to IP routing rather than Layer 2 switching or MAC tables.

Answer

show vlans summary

Answer

show bridge-domain forwarding-table

Answer

show ip route bridge

Question 13

You are configuring Q-in-Q tunneling on an enterprise network using EX Series switches. Which THREE configuration elements are essential for implementing Q-in-Q successfully? (Choose three.)

Accepted Answer

Enabling flexible-vlan-tagging on the customer-facing interface.. Option A is correct because enabling flexible-vlan-tagging on the customer-facing interface allows the EX Series switch to accept and process frames with two VLAN tags (inner customer tag plus outer service tag), which is the foundation of Q-in-Q tunneling. Option C is correct because the core transit switch ports must be configured as trunk ports so they can carry the outer VLAN tag (the service-provider S-VLAN) across the provider network between edge switches. Option E is correct because setting the customer-edge interface to interface-mode qinq-access makes that port a Q-in-Q access port that maps the customer's C-VLAN into the provider's S-VLAN and pushes the outer tag on ingress. Option B is incorrect because disabling MAC learning globally is not required and would break normal switching; Q-in-Q relies on standard MAC learning within each S-VLAN. Option D is incorrect because OSPF is a routing protocol and has nothing to do with Q-in-Q tagging or Layer 2 tunneling configuration.

Answer

Disabling all MAC learning globally across the entire switch.

Answer

Configuring the access ports with routing protocol OSPF enabled.

Question 14

An engineer is configuring MAC security features on an EX Series switch access port to protect against unauthorized devices. Which THREE features or parameters can be configured under the interface secure-access-port options? (Choose three.)

Accepted Answer

persistent-learning to retain learned MAC addresses across reboots.. The question asks which features can be configured under the secure-access-port hierarchy on an EX Series switch access port. Option C, persistent-learning, is correct because it is a secure-access-port parameter that saves dynamically learned MAC addresses to the configuration so they survive a reboot, preventing relearning of unauthorized devices. Option D, mac-limit, is correct because it is configured under secure-access-port to cap the number of dynamic MAC addresses learned on the interface, dropping or logging traffic once the limit is exceeded. Option E, mac-move-limit, is correct because it is a secure-access-port parameter that detects MAC address flapping and can take an action such as shutting down or logging when the threshold is exceeded. Option A, bgp-multihop, is incorrect because it is a BGP neighbor parameter, not a secure-access-port option, and BGP is not configured on an access port. Option B, stp-root-guard, is incorrect because root guard is an STP feature configured under the interface's spanning-tree protocol options, not under secure-access-port.

Answer

bgp-multihop to secure BGP control plane neighbors on the access port.

Answer

stp-root-guard to prevent unauthorized switches from becoming root.

Question 15

An administrator needs to verify the VLAN configuration and port mappings on a Junos EX Series switch. Which TWO operational commands provide this information? (Choose two.)

Accepted Answer

show vlans extensive. VLAN details and membership are verified using 'show vlans' and 'show vlans extensive'.

Answer

show ethernet-switching vlans

Answer

show interfaces switching-table

Answer

show bridge-table