JNCIP-ENT Ethernet Switching And Spanning Tree Practice Test 2 — 15 Questions

Question 1

Which THREE mechanisms are provided by Juniper switches running MSTP to protect against bridging loops caused by unidirectional link failures or misbehaving switches? (Choose three)

Accepted Answer

Root guard. Loop guard, root guard, and bpdu guard are standard STP/MSTP protection features available on Juniper switches.

Answer

Storm control broadcast filtering

Answer

MACsec cryptographic validation

Question 2

When designing a high-scale enterprise campus network using Juniper EX Series switches, which THREE best practices should be followed for Spanning Tree Protocol design? (Choose three)

Accepted Answer

Enable BPDU guard and loop guard on all edge access ports.. Best practices include placing root bridges at the core/distribution layer, using edge protection features, and maintaining consistent region parameters.

Answer

Use default bridge priority values on all core switches to allow automated root election.

Answer

Disable Spanning Tree entirely on all access ports to ensure faster convergence.

Question 3

An engineer is configuring QinQ (802.1ad) tunneling on a Juniper EX Series switch to transport customer VLANs across a service provider core. The customer-facing access port receives tagged frames with outer VLAN ID 100 and inner VLAN ID 200. Which configuration statement correctly defines the interface encapsulation and VLAN mapping?

Accepted Answer

set interfaces ge-0/0/1 encapsulation vlan-stacking and set interfaces ge-0/0/1 unit 0 family ethernet-switching input-vlan-map push and set interfaces ge-0/0/1 unit 0 family ethernet-switching output-vlan-map pop. To configure Q-in-Q tunneling on Juniper switches, the customer-facing port requires 'flexible-ethernet-services' encapsulation and a 'vlan-map' configuration that maps the incoming outer VLAN to the provider core VLAN.

Answer

set interfaces ge-0/0/1 encapsulation flexible-ethernet-services and set interfaces ge-0/0/1 unit 0 family ethernet-switching vlan-tagging

Answer

set interfaces ge-0/0/1 encapsulation flexible-ethernet-services and set interfaces ge-0/0/1 unit 0 family ethernet-switching interface-mode access

Answer

set interfaces ge-0/0/1 encapsulation qinq-access and set interfaces ge-0/0/1 unit 0 family ethernet-switching vlan-members 100

Question 4

An enterprise network running VSTP (VLAN Spanning Tree Protocol) across Juniper EX Series switches experiences unexpected loops because a newly added switch does not participate in VSTP for VLAN 50. Upon investigation, you discover the VSTP BPDU multicast destination MAC address is being dropped by a third-party non-Juniper intermediate switch. What is the standard VSTP MAC address used for BPDU transmission?

Accepted Answer

01:00:0c:cc:cc:cd. VSTP utilizes the PVST+ proprietary destination MAC address of 01:00:0c:cc:cc:cd to interoperate and transmit per-VLAN spanning tree BPDUs.

Answer

01:80:c2:00:00:08

Answer

01:80:c2:00:00:00

Answer

01:80:c2:00:00:0f

Question 5

When designing large-scale Layer 2 networks using VSTP, you notice high CPU utilization on the Routing Engine due to the large number of topology changes and BPDU processing across 150 VLANs. Which command can you apply globally or per-interface in Junos to optimize VSTP performance and mitigate CPU load?

Accepted Answer

Migrate from VSTP to MSTP to consolidate multiple VLAN spanning trees into a single or few MST instances.. To limit the impact of excessive VSTP instances, Junos allows tuning BPDU transmission intervals or disabling VSTP on unnecessary ports, but more importantly, optimizing BPDU processing or utilizing MSTP is recommended. However, bpdu-block and interface tuning are key features. Wait, let's look at the options.

Answer

set protocols vstp bpdu-block-on-edge

Answer

set forwarding-options spanning-tree-processor offload

Answer

set protocols vstp no-normalization-check

Question 6

An administrator wants to configure MSTP on Juniper switches and needs to assign VLANs 10 through 50 to MST Instance 2. Which configuration command hierarchy is correct in Junos?

Accepted Answer

set protocols mstp configuration-name CORP msti 2 vlan 10-50. In Junos, MST configuration parameters such as instance mappings, revision numbers, and names are defined under the 'protocols mstp configuration-name' hierarchy.

Answer

set protocols mstp configuration-name CORP instance-name msti2 vlan 10-50

Answer

set protocols spanning-tree mst instance 2 vlan-members 10-50

Answer

set protocols mstp region-name CORP revision 1 instance msti2 vlan [ 10-50 ]

Question 7

You are troubleshooting a switching loop issue in an enterprise core utilizing MSTP. You run 'show mstp interface' and notice that a specific port is stuck in the discarding state for MSTI 1. Which command should you run to verify if root guard has been triggered on this port?

Accepted Answer

show mstp interface detail. The command 'show mstp interface detail' provides detailed port-level status including whether root guard has tripped and placed the port into a inconsistent/discarding state.

Answer

show spanning-tree inconsistent-ports

Answer

show bridge root-guard status

Answer

show ethernet-switching security-guard

Question 8

An engineer is deploying VSTP on a Juniper EX Series network. Which THREE characteristics or limitations of VSTP should be considered during the design phase? (Choose three)

Accepted Answer

VSTP configuration requires enabling vstp under protocols and can be applied selectively per VLAN or globally.. VSTP operates per-VLAN, maintains full compatibility with Cisco PVST+, and scales linearly with the number of VLANs, which can consume significant CPU resources if not properly sized.

Answer

VSTP requires all switches in the topology to belong to the exact same named MST region.

Answer

VSTP automatically aggregates all VLAN spanning trees into a single BPDU transmission to save bandwidth.

Question 9

You are designing a Layer 2 network using Juniper EX Series switches with MSTP. You need to map multiple VLANs to a single spanning-tree instance while ensuring that the region configuration is consistent across all switches. Which MSTP configuration parameter must be identical on all switches within an MSTP region?

Accepted Answer

The MSTP region name and VLAN-to-instance mapping. MSTP regions require that all switches share the same region name, configuration revision level, and VLAN-to-instance mapping. These parameters form the region identifier and ensure consistent spanning-tree instances. The region name and mapping are especially critical because they determine which VLANs are handled by which MST instance. Without this consistency, switches will not form a single region, leading to separate topologies and potential loops.

Answer

The bridge priority value

Answer

The hello time and forward delay timers

Answer

The configuration revision level

Question 10

You are implementing MSTP on a Juniper EX Series switch. You need to map VLANs 10, 20, and 30 to MSTI 1, and VLANs 40, 50, and 60 to MSTI 2. Which configuration correctly accomplishes this?

Accepted Answer

set protocols mstp msti 1 vlan 10,20,30 set protocols mstp msti 2 vlan 40,50,60. In Junos OS, to map VLANs to an MSTI, you use the 'set protocols mstp msti vlan ' command. The VLAN list can be a comma-separated list of VLAN IDs or a range using a hyphen (e.g., '10-30'). However, the hyphen range is only valid if the syntax supports it; in this case, the correct answer uses a comma-separated list, which is always valid. Both methods are acceptable, but the comma-separated list is unambiguous.

Answer

set protocols mstp msti 1 vlan 10-20-30
set protocols mstp msti 2 vlan 40-50-60

Answer

set protocols mstp msti 1 vlan 10-30
set protocols mstp msti 2 vlan 40-60

Answer

set protocols mstp msti 1 vlan-id 10-30
set protocols mstp msti 2 vlan-id 40-60

Question 11

You are troubleshooting a Juniper EX Series switch running RSTP in a network with a mix of Juniper and third-party switches. The topology has redundant links, and you notice that a port on the EX switch remains in the discarding state even though it should be forwarding. You have verified that the port is not an alternate or backup port. Which RSTP mechanism should you investigate to determine why the port is not transitioning to forwarding?

Accepted Answer

The port is waiting for a proposal/agreement handshake to complete, and the downstream switch is not sending an agreement.. In RSTP, a designated port uses the proposal/agreement handshake to rapidly transition to forwarding. If the downstream bridge does not send an agreement, the port remains in discarding. This is common when interoperating with third-party switches that may not fully support or correctly implement RSTP's rapid transition mechanisms. Investigating the handshake and checking compatibility settings is essential.

Answer

The port is experiencing a topology change notification storm, which prevents it from transitioning to forwarding.

Answer

The port is configured as an edge port and is receiving BPDUs, causing it to lose its edge status and remain in discarding.

Answer

The port is in a blocking state because of a misconfigured bridge priority, causing it to never become a designated port.

Question 12

You are deploying a Juniper EX Series switch in a campus network that must interoperate with a third-party switch running Rapid Spanning Tree Protocol (RSTP). The EX switch is currently configured with the default spanning-tree protocol. You need to ensure the EX switch can form a spanning tree with the third-party switch without any compatibility issues. Which configuration should you apply on the EX switch?

Accepted Answer

set protocols rstp interface all. The correct approach is to explicitly enable RSTP on the EX switch. Juniper EX switches support RSTP, MSTP, and VSTP. When connecting to a third-party RSTP switch, enabling RSTP ensures both devices speak the same protocol and can form a rapid spanning tree. This provides fast convergence and avoids compatibility issues that arise from protocol mismatches, such as the default protocol being different.

Answer

set protocols stp interface all

Answer

set protocols vstp interface all

Answer

set protocols mstp interface all

Question 13

You are configuring MSTP on a Juniper EX Series switch to map multiple VLANs to different spanning-tree instances. You want VLANs 10 and 20 to use instance 1, and VLANs 30 and 40 to use instance 2. Which configuration correctly accomplishes this?

Accepted Answer

set protocols mstp configuration-name region1
set protocols mstp revision-level 1
set protocols mstp msti 1 vlan [10 20]
set protocols mstp msti 2 vlan [30 40]. The correct configuration sets the MSTP region name and revision level, then maps VLANs to specific MSTIs using the 'msti' keyword with space-separated VLAN lists in brackets. This ensures that VLANs 10 and 20 use instance 1, and VLANs 30 and 40 use instance 2, as required. Consistency in region name and revision level across all switches is critical for MSTP to function.

Answer

set protocols mstp region-name region1
set protocols mstp revision 1
set protocols mstp instance 1 vlan [10 20]
set protocols mstp instance 2 vlan [30 40]

Answer

set protocols mstp configuration-name region1
set protocols mstp revision-level 1
set protocols mstp msti 1 vlan 10,20
set protocols mstp msti 2 vlan 30,40

Answer

set protocols mstp configuration-name region1
set protocols mstp revision-level 1
set protocols mstp msti 1 vlan all
set protocols mstp msti 2 vlan all

Question 14

You are configuring VSTP on a Juniper EX Series switch. You want to ensure that VSTP uses a specific VLAN (VLAN 10) as the management VLAN for the spanning tree instance. Which configuration is required?

Accepted Answer

set protocols vstp vlan 10. VSTP on Juniper EX switches is enabled per VLAN. To have VLAN 10 participate in VSTP, you must configure 'set protocols vstp vlan 10'. This creates a separate spanning tree instance for that VLAN. Other options either enable VSTP globally, on an interface, or configure a protection feature, none of which specifically enable VSTP for VLAN 10 as required.

Answer

set protocols vstp vlan all

Answer

set protocols vstp interface ge-0/0/1.0

Answer

set protocols vstp bpdu-block-on-edge

Question 15

You are configuring a Juniper EX Series switch to participate in a VSTP (VLAN Spanning Tree Protocol) environment. You need to ensure that VSTP is enabled for VLAN 100 and that the switch uses a specific bridge priority for that VLAN. Which configuration statement set achieves this?

Accepted Answer

set protocols vstp vlan 100 bridge-priority 4096. VSTP in Junos OS is configured under the 'protocols vstp' hierarchy, with per-VLAN parameters specified using the 'vlan' keyword. Setting the bridge priority for VLAN 100 to 4096 is done with the command 'set protocols vstp vlan 100 bridge-priority 4096'. This enables VSTP for that VLAN and sets the priority, which influences root bridge election for the VLAN-specific spanning-tree instance.

Answer

set protocols vstp vlan-id 100 bridge-priority 4096

Answer

set protocols rstp vlan 100 bridge-priority 4096

Answer

set protocols mstp vlan 100 bridge-priority 4096