JNCIS-ENT Layer 2 Switching And VLANs Practice Test 3 — 15 Questions

Question 1

An administrator wants to remove an interface from an access VLAN and clear its configuration. Which TWO configuration commands are required to clean up the interface? (Choose two.)

Accepted Answer

delete interfaces ge-0/0/5 unit 0 family ethernet-switching. Removing an interface configuration in Junos involves using the delete command for the ethernet-switching family or specific interface mode statements.

Answer

delete vlans finance interface ge-0/0/5

Answer

set interfaces ge-0/0/5 unit 0 family ethernet-switching interface-mode access vlan members none

Answer

clear interfaces ge-0/0/5

Question 2

An administrator needs to configure two access ports on an EX Series switch for VLAN 100 named 'engineering'. Which TWO configuration commands are required? (Choose two.)

Accepted Answer

set vlans engineering vlan-id 100. Option C, 'set vlans engineering vlan-id 100', is required because it defines the VLAN named 'engineering' and maps it to VLAN ID 100, which is the foundational step for creating the VLAN on an EX Series switch. Option E, 'set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode access vlan members 100', is required because it configures the physical interface as an access port and assigns it to VLAN 100, which is exactly what the administrator needs for the access ports. Option A is incorrect because it assigns an IP address to an interface rather than configuring VLAN membership, which is not needed for access ports. Option B is incorrect because 'bridge-domain' is not the correct VLAN configuration syntax on EX Series switches. Option D is incorrect because 'protocols vlan' is not valid EX Series configuration syntax for assigning interfaces to a VLAN.

Answer

set interfaces ge-0/0/1 unit 0 family inet address 192.168.100.1/24

Answer

set bridge-domain engineering vlan-id 100

Answer

set protocols vlan engineering interface ge-0/0/1

Question 3

You are troubleshooting a MAC address flapping issue on an EX Series switch. Which TWO operational commands help diagnose the source and frequency of MAC moves? (Choose two.)

Accepted Answer

show ethernet-switching table. Option A, 'show ethernet-switching table', is correct because it displays the Layer 2 forwarding database (MAC table) with each MAC address, its associated VLAN, and the learned interface, allowing you to spot the same MAC appearing on multiple ports—the hallmark of a flapping condition. Option D, 'show ethernet-switching table extensive', is correct because it provides the same MAC table entries plus additional detail such as the entry's age, flags, and learning history, which helps identify how frequently a MAC is moving and from which interfaces. Together these operational commands let you confirm the source and frequency of MAC moves on an EX Series switch. Option B, 'show interfaces diagnostics optics', is unrelated because it reports optical transceiver parameters like Rx/Tx power and temperature, not MAC learning. Option C, 'show bridge-domain mac-table', is not the correct EX Series operational syntax for this purpose (bridge domains are used in EVPN/VXLAN contexts, and the standard EX MAC table command is show ethernet-switching table). Option E, 'show route forwarding-table', displays Layer 3 routing/forwarding entries and does not show Layer 2 MAC move information.

Answer

show interfaces diagnostics optics

Answer

show bridge-domain mac-table

Answer

show route forwarding-table

Question 4

An engineer is configuring a trunk port on an EX Series switch and needs to manage untagged traffic, allowed VLANs, and native VLAN tagging behavior. Which THREE configurations are valid in Junos for a trunk interface? (Choose three.)

Accepted Answer

set interfaces ge-0/0/9 unit 0 family ethernet-switching vlan members [ 10 20 30 ]. Option C is correct because setting 'interface-mode trunk' under the ethernet-switching family is the standard Junos command that places the port into trunk mode, which is required to carry multiple VLANs. Option A is correct because 'vlan members [ 10 20 30 ]' is the valid Junos syntax for specifying the list of allowed VLANs on a trunk interface. Option B is correct because 'native-vlan-id 10' is the valid Junos parameter that defines the native VLAN for untagged traffic on a trunk port, controlling how untagged frames are handled. Option D is not valid because 'trunk-encapsulation dot1q-only' is not a supported Junos ethernet-switching parameter on EX Series switches. Option E is not valid because 'access-vlan' is not a Junos trunk configuration statement; access VLANs are configured differently and are not used to manage trunk allowed VLANs.

Answer

set interfaces ge-0/0/9 unit 0 family ethernet-switching trunk-encapsulation dot1q-only

Answer

set interfaces ge-0/0/9 unit 0 family ethernet-switching access-vlan 10

Question 5

An administrator is configuring a new Juniper EX Series switch and needs to configure an access port for a VoIP phone and a connected PC. Which Juniper feature should be used to support both the voice and data VLAN on the same physical port?

Accepted Answer

Voice VLAN. Juniper's Voice VLAN feature (configured with 'set vlans interface ' or via 'voice-vlan' under the interface) allows a single access port to carry both untagged data traffic for the PC and tagged voice traffic for the IP phone. The phone tags its traffic with the voice VLAN ID, while the PC's untagged frames are placed in the data VLAN. This is the standard Juniper mechanism for converged voice/data access ports.

Answer

Q-in-Q tunneling

Answer

Private VLAN

Answer

Native VLAN

Question 6

A network engineer has configured a trunk port between an EX4300 switch and a third-party switch. The native VLAN traffic is dropping between the switches. Upon troubleshooting, the engineer discovers that the Juniper switch is tagging native VLAN egress traffic, while the peer device expects untagged traffic. Which configuration statement corrects this behavior while preserving trunking?

Accepted Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode trunk native-vlan-id 10 no-native-vlan-tagging. By default, Junos tags native VLAN traffic on trunk ports. Using the 'no-native-vlan-tagging' statement ensures that native VLAN traffic egresses untagged.

Answer

set vlans vlan-trust untagged-native-vlan

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching native-vlan-tagging

Answer

set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode access vlan members 10

Question 7

You are configuring Q-in-Q tunneling (VLAN stacking) on an EX Series switch where customer traffic with VLANs 10 through 20 needs to be encapsulated into a service provider VLAN 100. Which configuration correctly applies the provider VLAN tag to incoming customer VLANs on a trunk interface?

Accepted Answer

set interfaces xe-0/0/0 flexible-vlan-tagging
set interfaces xe-0/0/0 encapsulation q-in-q-tunneling
set interfaces xe-0/0/0 unit 0 family ethernet-switching interface-mode trunk vlan-members 100. It uses the Juniper EX-specific Q-in-Q configuration: enabling flexible-vlan-tagging on the physical interface, setting encapsulation to q-in-q-tunneling, and then configuring a logical unit with family ethernet-switching in trunk mode with the provider VLAN (100) as a member. This combination allows the switch to accept incoming frames that already carry customer VLAN tags (10–20) and push an outer provider VLAN tag (100) on egress, while preserving the inner tag. The flexible-vlan-tagging statement is mandatory for any interface that must handle double-tagged frames.

Answer

set interfaces xe-0/0/0 encapsulation ethernet-bridge
set interfaces xe-0/0/0 unit 0 family bridge vlan-id-list 10-20

Answer

set interfaces xe-0/0/0 unit 0 family ethernet-switching interface-mode access vlan members 100

Answer

set vlans provider-vlan q-in-q-service
set interfaces xe-0/0/0 unit 0 family ethernet-switching vlan members provider-vlan

Question 8

An administrator needs to restrict MAC learning on a specific access port (ge-0/0/5) on an EX Series switch to a maximum of 2 learned MAC addresses to prevent MAC flooding attacks. Where is this limit configured in Junos?

Accepted Answer

set interfaces ge-0/0/5 unit 0 family ethernet-switching port-security max-mac-count 2. MAC limit is configured under the interface-specific ethernet-switching-options hierarchy within the bridge-domains or vlans configuration, or directly under the interface if using port security.

Answer

set forwarding-options storm-control interface ge-0/0/5 mac-limit 2

Answer

set protocols l2-learning global-max-mac-count 2 interface ge-0/0/5

Answer

set bridge-domains vlan-data interface ge-0/0/5 mac-limit 2

Question 9

You are troubleshooting connectivity issues on a private VLAN deployment on an EX4600 switch. Server A resides in an isolated VLAN and needs to communicate with the promiscuous gateway, but it should not be able to reach Server B, which is in the same isolated VLAN. However, Server A can successfully ping Server B. What is the most likely cause of this behavior?

Accepted Answer

The promiscuous port is missing the trunk-allowed VLAN list for the isolated VLAN.. Isolated VLAN ports can normally communicate with promiscuous ports. If isolated hosts can talk to each other, private VLAN isolation is broken, typically because the isolation was misconfigured or the ports are assigned to community VLANs instead.

Answer

MAC address aging timer is set too high, causing stale entries in the forwarding table.

Answer

No-root-port is enabled on the STP instance affecting the VLAN.

Question 10

An administrator wants to prevent unauthorized switches from being connected to user access ports on an EX Series switch. Which feature should be implemented to drop BPDUs received on access ports while keeping the port active for end-user devices?

Accepted Answer

BPDU protection (bpdu-block). BPDU protection (bpdu-block) drops incoming BPDUs on access ports to prevent unauthorized switches from altering the spanning tree topology.

Answer

Loop protection (loop-protection)

Answer

BPDU guard (bpdu-guard) on trunk ports

Answer

Root protection (root-protection)

Question 11

Which TWO configuration statements are required when configuring a trunk port on an EX Series switch to allow specific VLANs while blocking others? (Choose two.)

Accepted Answer

set interfaces ge-0/0/0 unit 0 family ethernet-switching interface-mode trunk. Option A is correct because on EX Series switches the interface must first be placed into trunk mode with 'set interfaces ge-0/0/0 unit 0 family ethernet-switching interface-mode trunk'; without this, the port remains in access mode and cannot carry multiple VLANs. Option B is correct because 'set interfaces ge-0/0/0 unit 0 family ethernet-switching vlan members [ vlan-10 vlan-20 ]' explicitly defines which VLANs are allowed on the trunk, thereby allowing vlan-10 and vlan-20 while blocking all other VLANs not listed. Option C is incorrect because 'encapsulation access' is not a valid Junos ethernet-switching statement and would not configure trunking. Option D is incorrect because 'port-mode hybrid' is not valid EX Series syntax; the correct keyword is 'interface-mode' with values access or trunk. Option E is incorrect because 'set protocols l2-learning trunk-vlan-restriction' is not a real Junos command and does not restrict VLANs on a trunk.

Answer

set interfaces ge-0/0/0 unit 0 family ethernet-switching encapsulation access

Answer

set interfaces ge-0/0/0 unit 0 family ethernet-switching port-mode hybrid

Answer

set protocols l2-learning trunk-vlan-restriction

Question 12

You are configuring a new access port on an EX2300 switch for a printer that must be placed in VLAN 30. The VLAN 30 already exists on the switch. Which configuration correctly assigns the port to VLAN 30?

Accepted Answer

set interfaces ge-0/0/10 unit 0 family ethernet-switching vlan members 30. The correct configuration uses 'vlan members 30' under the ethernet-switching family without specifying an interface mode, which defaults to access mode when a single VLAN is assigned. This places the printer's untagged traffic into VLAN 30. Adding a native VLAN ID or setting trunk mode is unnecessary and would misconfigure the port for a standard access device.

Answer

set interfaces ge-0/0/10 unit 0 family ethernet-switching port-mode access vlan 30

Answer

set interfaces ge-0/0/10 unit 0 family ethernet-switching vlan members 30 interface-mode trunk

Answer

set interfaces ge-0/0/10 unit 0 family ethernet-switching vlan members 30 native-vlan-id 30

Question 13

An administrator needs to view the MAC address learning table on an EX Series switch to verify which switchport a specific server is connected to. Which operational command should be used?

Accepted Answer

show ethernet-switching table. On Juniper EX Series switches, the MAC address learning table is exposed through the ethernet-switching subsystem, so the correct operational command is 'show ethernet-switching table'. This command displays learned MAC addresses, their associated VLANs, and the egress switchport, allowing the administrator to map a server's MAC to the exact interface it is connected to.

Answer

show mac-address-table

Answer

show vlans mac-table

Answer

show bridge-domain mac-table

Question 14

An administrator needs to create a VLAN named 'voice' with a VLAN ID of 50 on a Junos EX Series switch. Which configuration path achieves this?

Accepted Answer

set vlans voice vlan-id 50. On Junos EX Series switches, VLANs are configured under the [edit vlans] hierarchy with the syntax 'set vlans vlan-id '. This creates a VLAN named 'voice' with VLAN ID 50, which can then be associated with access or trunk interfaces.

Answer

set ethernet-switching-options vlans voice id 50

Answer

set bridge-domains voice vlan-id 50

Answer

set interfaces vlan unit 50 name voice

Question 15

An administrator is configuring a new EX Series switch running Junos OS and needs to assign an access port to VLAN finance. Which configuration hierarchy is used to assign an interface to a specific VLAN?

Accepted Answer

[edit interfaces unit 0 family ethernet-switching]. In Junos OS, access and trunk interface properties for Layer 2 switching are configured under the [edit interfaces unit 0 family ethernet-switching] hierarchy.

Answer

[edit vlans finance]

Answer

[edit bridge-domains finance]

Answer

[edit protocols l2-learning]