JNCIP-ENT Ethernet Switching And Spanning Tree — 10 Questions

Question 1

You are configuring VSTP (VLAN Spanning Tree Protocol) on Juniper EX switches to interoperate with legacy third-party switches running PVST+. Which operational command allows you to verify the VSTP bridge identifier and root bridge status per VLAN?

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

Accepted Answer

show vstp vlan. The command 'show vstp vlan' displays the VSTP state, root bridge, and port roles for each VLAN.

Answer

show ethernet-switching vstp

Answer

show spanning-tree vlan detail

Answer

show bridge vstp-status

Question 2

You are reviewing the MSTP configuration on an EX4300 switch. You want to assign VLANs 10 through 50 to Multiple Spanning Tree Instance (MSTI) 2. Which syntax under 'protocols mstp' is correct?

Accepted Answer

set protocols mstp configuration-name Region1 instance instance2 vlan [ 10..50 ] or set protocols mstp region-name Region1 instance instance2 vlan 10-50. MSTP instance configuration maps VLAN lists to specific MSTI numbers in Junos.

Answer

set protocols mstp configuration-name Region1 revision 1 instance msti2 vlan [ 10-50 ]

Answer

set protocols mstp region-name Region1 instance-map instance-2 vlan 10 to 50

Answer

set protocols mstp msti-instance 2 vlan-members 10-50

Question 3

An enterprise network uses VSTP. During a topology change, network administrators notice excessive flooding of broadcast traffic. Which Juniper configuration statement under 'protocols vstp' prevents unnecessary topology change flooding by restricting TCN propagation?

Accepted Answer

set protocols vstp interface ge-0/0/1 bpdu-guard. Root guard and BPDU guard protect ports, but for VSTP tuning, bpdu-block-on-edge or restricted role configuration helps. However, setting interface parameters correctly prevents topology shifts. The correct parameter to prevent TCNs on access ports is bpdu-guard or no-root-port.

Answer

set protocols vstp flood-suppression enable

Answer

set protocols vstp disable-tcn-propagation

Answer

set protocols vstp interface ge-0/0/1 no-root-port

Question 4

You are troubleshooting a Q-in-Q tunneling implementation on an MX Series router where customer VLAN tags are being stripped instead of preserved across the service provider core. Under which configuration hierarchy should the 'vlan-tagging' and 'pop-pop' or 'push' actions be applied on the interface?

Accepted Answer

set interfaces ge-0/0/1 flexible-vlan-tagging. For Q-in-Q tunneling on Juniper routing and switching platforms, flexible VLAN tagging is configured under 'interfaces <interface> flexible-vlan-tagging'.

Answer

set protocols l2-learning interface ge-0/0/1 q-in-q

Answer

set bridge-domains bd vlan-id-list 10

Answer

set interfaces ge-0/0/1 encapsulation flexible-ethernet-services

Question 5

An enterprise network engineer needs to configure a trunk port on a Juniper EX Series switch running Junos OS to allow multiple VLANs while explicitly blocking VLAN 99. Which configuration statement under 'interfaces ge-0/0/1 unit 0 family ethernet-switching' correctly achieves this?

Accepted Answer

vlan-members except 99;. The 'vlan-members none' or explicitly listing allowed VLANs excludes unspecified ones, but to explicitly prune a VLAN while allowing others, the 'vlan-members except' option is used.

Answer

exclude-vlan-members 99;

Answer

block-vlan 99;

Answer

vlan-members [ vlan-members except 99 ];

Question 6

An administrator needs to enable BPDU protection on edge access ports in a VSTP environment to prevent loops caused by unauthorized switches. Which command under 'protocols vstp' accomplishes this globally or per-interface?

Accepted Answer

set protocols vstp interface ge-0/0/1 bpdu-guard. bpdu-guard under interface configuration in VSTP drops or disables the port upon receiving BPDUs.

Answer

set protocols vstp interface ge-0/0/1 disable-on-bpdu

Answer

set protocols vstp interface ge-0/0/1 edge-port protect

Answer

set protocols vstp interface ge-0/0/1 drop-bpdu

Question 7

An enterprise network runs MSTP across an EX Series core. An administrator wants to ensure that a specific core port never becomes the root port for any MSTI, protecting the upstream core path. Which command achieves this?

Accepted Answer

set protocols mstp interface ge-0/0/0 no-root-port. Root protection in MSTP is enabled via the 'no-root-port' or 'root-protection' statement under interface configuration in MSTP. In Junos, 'no-root-port' is used.

Answer

set protocols mstp interface ge-0/0/0 root-guard

Answer

set protocols mstp interface ge-0/0/0 priority 0

Answer

set protocols mstp interface ge-0/0/0 restrict-role root

Question 8

You are configuring selective Q-in-Q stacking on an MX Series router. Unlike standard Q-in-Q where all customer VLANs are encapsulated into a single provider VLAN, selective Q-in-Q allows you to map specific customer VLAN ranges to different provider VLANs. Which configuration element enables this granularity?

Accepted Answer

vlan-map match statement with specific input VLAN ID filters. Flexible VLAN tagging combined with 'vlan-map' statements defining match criteria allows selective Q-in-Q.

Answer

protocols l2-learning selective-stacking

Answer

global bridge-domain vlan-translation enable

Answer

routing-instance forwarding-options selective-qinq

Question 9

An enterprise network operates VSTP across 150 VLANs. The network engineering team notices high CPU utilization on the Routing Engine due to VSTP BPDU processing. Which Junos command or feature can mitigate this control-plane load while keeping VSTP operational?

Accepted Answer

set protocols vstp hello-time 5. BPDU rate-limiting or adjusting VSTP hello timers helps reduce control-plane processing overhead. In Junos, VSTP timer tuning and bpdu processing limits control overhead.

Answer

set system pfe bpdu-bypass enable

Answer

set forwarding-options storm-control interfaces all vstp

Answer

set protocols vstp no-bpdu-generation

Question 10

An administrator needs to configure a port on an EX series switch to act as a Designated Port in MSTP, forcing it to forward traffic regardless of incoming superior BPDUs from an untrusted switch. Which feature should be enabled on this port?

Accepted Answer

Loop guard. Loop guard or root guard protects ports. Specifically, loop guard prevents alternate or backup ports from becoming designated ports when BPDUs are lost.

Answer

Root guard

Answer

STP disable

Answer

BPDU guard