JNCIS-ENT Layer 2 Switching And VLANs — 15 Questions

Question 1

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?

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

Accepted Answer

set interfaces et-0/0/0 unit 0 family ethernet-switching interface-mode qinq-access. For Q-in-Q tunneling on a customer-facing edge port, the port must be configured as 'qinq-access' (also known as 'dot1q-tunnel' in some vendors). This mode encapsulates incoming customer frames with an outer VLAN tag (the S-VLAN) specified by the service provider. The correct configuration is 'set interfaces et-0/0/0 unit 0 family ethernet-switching interface-mode qinq-access'.

Answer

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

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

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

Question 2

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).

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

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

Question 3

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. The correct Junos syntax to allow all VLANs except VLAN 50 on a trunk port is 'vlan members all except 50'. This uses the 'all' keyword to include every VLAN and the 'except' keyword to explicitly exclude VLAN 50. This is the standard Junos way to express an exclusion list on a trunk interface.

Answer

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

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

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

Question 4

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 ]. On Junos EX Series switches, private VLANs are configured hierarchically under the primary VLAN using the 'private-vlan' statement, which binds secondary VLANs (community or isolated) to the primary VLAN. The correct syntax is 'set vlans vlan-id private-vlan community [ ]', which creates the primary/secondary association required for PVLAN operation.

Answer

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

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

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

Question 5

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. Flexible VLAN Tagging with input-vlan-map allows granular mapping of incoming customer VLAN tags to different outer VLAN tags on a per-VLAN basis. This is exactly what Selective QinQ requires: mapping VLAN 10 to outer VLAN 500 and VLAN 20 to outer VLAN 600. The input-vlan-map configuration specifies the rewrite action for each customer VLAN, enabling this selective encapsulation.

Answer

Layer 3 firewall filters with rewriting actions on the access port

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

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Global native-vlan-id translation tables

Question 6

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

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show bridge-domain interface

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show interfaces ge-0/0/2 extensive

Question 7

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. On Juniper EX Series switches, the native VLAN for a trunk port is configured using the `native-vlan-id` statement under the interface's ethernet-switching family. The correct command, `set interfaces ge-0/0/10 unit 0 family ethernet-switching interface-mode trunk native-vlan-id 10`, sets the port to trunk mode and assigns VLAN 10 as the native VLAN for untagged frames. This is the standard Junos syntax for this requirement.

Answer

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

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

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

Question 8

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]

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

Question 9

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

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delete ethernet-switching table mac-address

Answer

clear bridge-domain mac-address

Question 10

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.

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Only VLAN 1 is allowed.

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No VLANs are allowed, and traffic is entirely dropped.

Question 11

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

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set vlans vlan-id 100 tpid 0x88a8

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set protocols dot1ad tp-id 88a8

Question 12

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. On Junos EX switches, the MAC limit for port security is applied under the interface's ethernet-switching family using the 'mac-limit' statement. The correct syntax 'set interfaces ge-0/0/5 unit 0 family ethernet-switching mac-limit 10' binds the limit directly to the logical interface, capping dynamically learned MAC addresses at 10 and dropping frames from additional MACs (or taking the configured violation action). This is the documented Junos method for per-port MAC limiting.

Answer

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

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

Answer

set vlans finance storm-control-limit mac 10

Question 13

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. The feature that automatically detects and actions on MAC address movement anomalies is configured with `set ethernet-switching-options secure-access-port interface ge-0/0/0 mac-move-limit action shutdown`. This enables MAC move limiting on the interface, and when the limit is exceeded, the specified action (shutdown) is taken. This helps detect and mitigate MAC flapping caused by loops or attacks.

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 14

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 on Junos EX Series switches displays all configured VLANs, including their names, VLAN IDs, interfaces, and active status. It is the standard operational command to verify the total number of active VLANs and their membership. The output includes a summary line showing the total VLAN count.

Answer

show ethernet-switching vlan

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show vlans summary

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show bridge-domains

Question 15

An engineer is deploying Selective QinQ where customer inner VLAN tags must be preserved while the outer tag is swapped or added based on ingress port rules. Which Junos statement enables tag preservation?

Accepted Answer

set interfaces ge-0/0/0 unit 0 family ethernet-switching input-vlan-map push. The `input-vlan-map push` statement is used in Junos to add an outer VLAN tag to incoming frames while preserving the existing inner tag, which is the essence of Selective QinQ. When applied to an interface, it pushes a new VLAN tag onto the frame as it enters the switch, leaving the original customer tag intact. This allows service providers to multiplex multiple customer VLANs over a single outer VLAN, maintaining customer separation. The other options either remove tags, use an incorrect encapsulation, or reference a non-existent statement.

Answer

set interfaces ge-0/0/0 unit 0 family ethernet-switching input-vlan-map pop

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set interfaces ge-0/0/0 unit 0 family ethernet-switching encapsulation qinq-transparent

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set interfaces ge-0/0/0 unit 0 family ethernet-switching vlan-translation preserve-inner