JNCIS-ENT Layer 2 Switching And VLANs — Timed 20 Questions

Question 1

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?

20 minute time limit — choose an answer to begin.

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 2

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. The command 'show ethernet-switching table' displays the MAC addresses learned by the Junos switch along with their associated VLANs and ports.

Answer

show mac-address-table

Answer

show vlans mac-table

Answer

show bridge-domain mac-table

Question 3

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. VLANs are created at the global [edit vlans] hierarchy in Junos OS.

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 4

You are configuring Q-in-Q tunneling on an enterprise EX4600 switch. The customer-facing edge port must encapsulate incoming customer frames with an outer VLAN tag of 200. Which port mode should be configured on the customer-facing interface?

Accepted Answer

set interfaces et-0/0/0 unit 0 family ethernet-switching interface-mode qinq-access. QinQ tunneling utilizes the 'qinq-access' interface mode on the customer-facing edge port to encapsulate incoming frames with an outer VLAN tag.

Answer

set interfaces et-0/0/0 unit 0 family ethernet-switching interface-mode VPLS

Answer

set interfaces et-0/0/0 unit 0 family ethernet-switching interface-mode trunk

Answer

set interfaces et-0/0/0 unit 0 family ethernet-switching interface-mode access

Question 5

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]

Question 6

You are troubleshooting a connectivity issue between an EX4300 switch access port and an end-host. The port is configured as an access port for VLAN 100, but the host cannot communicate. You run 'show ethernet-switching interface ge-0/0/1' and notice the port status is down/down. Which underlying reason most likely explains this state?

Accepted Answer

The physical cable is disconnected or the transceiver is faulty.. A down/down physical port state is typically a Layer 1 or physical cabling/transceiver issue, rather than a Layer 2 VLAN configuration mismatch.

Answer

The native VLAN ID does not match the upstream trunk switch.

Answer

BPDU protection has disabled the port due to a loop.

Answer

The VLAN 100 has not been created under the [edit vlans] hierarchy.

Question 7

While reviewing the MAC address table on an EX Series switch using 'show ethernet-switching table', you notice a specific MAC address has a 'Flags' field showing 'L'. What does the 'L' flag indicate?

Accepted Answer

The MAC address was learned locally/dynamically on the interface.. In Junos OS, the 'L' flag in the ethernet-switching table indicates that the MAC address was learned dynamically on that interface.

Answer

The MAC address belongs to a local routed interface (VLAN interface IRB).

Answer

The MAC address has looped and triggered a storm control event.

Answer

The MAC address is locked and cannot move to another port.

Question 8

An engineer must configure an EX Series switch trunk port to allow all VLANs while explicitly blocking VLAN 50. Which Junos configuration statement accomplishes this behavior?

Accepted Answer

set interfaces ge-0/0/5 unit 0 family ethernet-switching interface-mode trunk vlan members all except 50. To allow all VLANs except a specific one on a trunk port, you use the member-all statement followed by the except member statement.

Answer

set interfaces ge-0/0/5 unit 0 family ethernet-switching interface-mode trunk vlan members except [ 50 ]

Answer

set interfaces ge-0/0/5 unit 0 family ethernet-switching interface-mode trunk vlan members remove 50

Answer

set interfaces ge-0/0/5 unit 0 family ethernet-switching interface-mode trunk vlan members [ 1-4094 ] drop 50

Question 9

On an EX Series switch, you have configured private VLANs (PVLANs) where community VLAN ports need to communicate with a designated promiscuous port, but not with ports in other community VLANs. Which hierarchical configuration is mandatory to bind the primary VLAN and secondary VLANs together?

Accepted Answer

set vlans primary vlan-id 10 private-vlan community [ 20 30 ]. Private VLANs require defining the primary VLAN and associating the secondary VLANs using the 'private-vlan' configuration statement under the [edit vlans] hierarchy.

Answer

set interfaces vlan unit 0 family ethernet-switching pvlan-mapping primary 10 secondary 20

Answer

set protocols private-vlan primary-vlan 10 secondary-vlan [ 20 30 ]

Answer

set vlans primary-vlan vlan-id 10 isolation-community [ 20 30 ]

Question 10

An engineer configures Selective QinQ on an EX Series switch. Incoming customer frames tagged with VLAN 10 must be mapped to outer VLAN 500, while frames tagged with VLAN 20 must be mapped to outer VLAN 600. Which configuration component is required to achieve this granular mapping?

Accepted Answer

Flexible VLAN Tagging (flexible-vlan-tagging) with input-vlan-map configuration. Selective QinQ requires using VLAN translation profiles or stacked VLAN mapping rules under the interface or VLAN mapping hierarchy.

Answer

Layer 3 firewall filters with rewriting actions on the access port

Answer

Static MAC address binding with Q-in-Q encapsulation rules

Answer

Global native-vlan-id translation tables

Question 11

An enterprise network uses private VLANs. A server connected to an isolated port needs to send traffic out of the primary VLAN. Which statement accurately describes how traffic forwarding operates for an isolated port in Junos?

Accepted Answer

Traffic from an isolated port can only be forwarded to the designated promiscuous port.. Isolated ports can only communicate with the promiscuous port; they cannot communicate with other isolated ports or community ports.

Answer

Traffic from an isolated port can reach other isolated ports within the same secondary VLAN.

Answer

Isolated ports can communicate freely with community ports, but not other isolated ports.

Answer

Traffic from an isolated port is dropped unless a Layer 3 firewall filter explicitly permits it.

Question 12

An administrator wants to verify the configured access VLAN and port mode on interface ge-0/0/2. Which operational command should be used?

Accepted Answer

show ethernet-switching interface ge-0/0/2 detail. To view detailed properties of an Ethernet switching interface, including its mode and member VLANs, you run 'show ethernet-switching interface detail'.

Answer

show vlans interface ge-0/0/2

Answer

show bridge-domain interface

Answer

show interfaces ge-0/0/2 extensive

Question 13

You are configuring a trunk port on an EX Series switch and need to specify that untagged frames received on this port should be placed into VLAN 10. Which command accomplishes this?

Accepted Answer

set interfaces ge-0/0/10 unit 0 family ethernet-switching interface-mode trunk native-vlan-id 10. The native VLAN on an EX switch trunk port is configured using the 'native-vlan-id' statement under the interface ethernet-switching hierarchy.

Answer

set vlans vlan-id 10 native-port ge-0/0/10

Answer

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

Answer

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

Question 14

You are configuring multiple VLANs on an EX Series switch and wish to set the aging time for learned MAC addresses to 600 seconds. Where is this parameter configured?

Accepted Answer

[edit ethernet-switching-options mac-table aging-time 600]. MAC table aging time in Junos is configured under the [edit bridge-options] or [edit ethernet-switching-options] hierarchy depending on the platform.

Answer

[edit vlans default ageing-timer 600]

Answer

[edit protocols l2-learning aging-time 600]

Answer

[edit system mac-address-table aging-time 600]

Question 15

An administrator needs to delete a MAC address entry from the ethernet-switching table on an EX Series switch due to a stuck entry. Which operational command is used?

Accepted Answer

clear ethernet-switching table. The clear ethernet-switching table command is used to flush learned MAC addresses on Junos switches.

Answer

reset mac-table

Answer

delete ethernet-switching table mac-address

Answer

clear bridge-domain mac-address

Question 16

An administrator configures an interface as a trunk port on an EX Series switch, but forgets to specify any VLAN members. By default, how does Junos handle VLAN membership on a newly configured trunk port?

Accepted Answer

All VLANs are allowed by default.. By default, when a trunk interface mode is configured without explicit members in Junos, all VLANs are allowed.

Answer

Only the default native VLAN is allowed.

Answer

Only VLAN 1 is allowed.

Answer

No VLANs are allowed, and traffic is entirely dropped.

Question 17

An enterprise network requires QinQ tunneling where the outer tag EtherType must be explicitly set to 0x88a8 (802.1ad) instead of the standard 0x8100. Where is the custom outer TPID configured on a Junos EX Series switch?

Accepted Answer

set interfaces ge-0/0/0 unit 0 family ethernet-switching outer-tpid 88a8. Custom outer tag protocol identifiers (TPID) for QinQ are configured under the [edit interfaces <interface-name> unit 0 family ethernet-switching outer-tpid] or similar interface/switching options hierarchy.

Answer

set ethernet-switching-options tpid 88a8

Answer

set vlans vlan-id 100 tpid 0x88a8

Answer

set protocols dot1ad tp-id 88a8

Question 18

You need to limit the number of dynamic MAC addresses learned on access interface ge-0/0/5 to a maximum of 10 to prevent MAC flooding attacks. Which configuration accomplishes this?

Accepted Answer

set interfaces ge-0/0/5 unit 0 family ethernet-switching mac-limit 10. MAC limit is configured under the interface-specific ethernet-switching options or secure-access-port settings.

Answer

set switch-options interface ge-0/0/5 maximum-mac 10

Answer

set protocols port-security interface ge-0/0/5 max-mac-addresses 10

Answer

set vlans finance storm-control-limit mac 10

Question 19

An administrator notices that MAC address flapping is occurring between two ports on an EX Series switch due to an unauthorized bridge loop. Which Junos feature can be enabled to automatically detect and action on MAC address movement anomalies?

Accepted Answer

set ethernet-switching-options secure-access-port interface ge-0/0/0 mac-move-limit action shutdown. MAC move detection and port restriction (mac-move-limit) can detect rapid MAC address flapping and disable the offending interface.

Answer

set interfaces ge-0/0/0 family ethernet-switching loop-protect

Answer

set ethernet-switching-options mac-move-limit action errdisable

Answer

set protocols rstp bpdu-protection-recovery

Question 20

An administrator wants to check the total number of active VLANs currently configured on a Junos EX Series switch. Which operational command should be used?

Accepted Answer

show vlans. The 'show vlans' command provides an overview of all configured VLANs, their associated interfaces, and VLAN IDs.

Answer

show ethernet-switching vlan

Answer

show vlans summary

Answer

show bridge-domains