JNCIP-ENT Ethernet Switching And Spanning Tree Practice Test 4 — 15 Questions

Question 1

Which THREE features or protocols are used in Juniper enterprise switching environments to prevent Layer 2 bridging loops while avoiding traditional Spanning Tree blocking ports? (Choose three)

Accepted Answer

Virtual Chassis technology. MC-LAG, Virtual Chassis, and EVPN-VXLAN eliminate loops via active-active multi-pathing or distributed control planes without traditional STP blocking links.

Answer

Rapid PVST+ with bridge priority overrides

Answer

MSTP with MSTI region mapping

Question 2

Which TWO actions can be triggered when a MAC address limit is exceeded on a Juniper switch interface configured with MAC limiting? (Choose two)

Accepted Answer

drop. Configurable actions on MAC limit violation include drop and log, or drop and shutdown (disable) the interface.

Answer

quarantine

Answer

reboot

Answer

isolate-vlan

Question 3

When configuring advanced Q-in-Q tunneling on Juniper MX Series routers, which THREE encapsulation or tagging parameters must be correctly aligned between the customer edge and provider edge interfaces? (Choose three)

Accepted Answer

VLAN action rules (pop, push, or swap). Q-in-Q alignment requires matching flexible-vlan-tagging, TPID values (EtherType), and VLAN tag preservation/manipulation rules.

Answer

MSTP region name configuration

Answer

IGMP snooping version compatibility

Question 4

Which TWO parameters are part of the standard MSTP configuration digest computed across switches in an MST region? (Choose two)

Accepted Answer

MST configuration name. The MST configuration digest includes region name, revision number, and the VLAN-to-instance allocation table.

Answer

Bridge priority value

Answer

Interface MAC addresses

Answer

Hello time and max age timers

Question 5

Which TWO security features can be configured on Juniper EX switches to prevent DHCP spoofing and ARP poisoning attacks on Layer 2 access ports? (Choose two)

Accepted Answer

DHCP snooping. DHCP snooping and Dynamic ARP Inspection (DAI) prevent DHCP spoofing and ARP poisoning respectively.

Answer

Storm control

Answer

BPDU guard

Answer

MACsec encryption

Question 6

Which TWO statements describe the behavior of VSTP (VLAN Spanning Tree Protocol) on Juniper EX Series switches? (Choose two)

Accepted Answer

VSTP can interoperate with Cisco's PVST+ protocol.. VSTP runs an independent spanning tree instance per VLAN and interoperates with PVST+.

Answer

VSTP is incompatible with RSTP fallback modes.

Answer

VSTP automatically disables all trunk ports if BPDU guard is triggered globally.

Answer

VSTP requires all VLANs to be mapped into a single master MSTI region.

Question 7

You are designing an enterprise network running Multiple Spanning Tree Protocol (MSTP) across multiple data center switches. To ensure that switches belong to the same MST region, which three parameters must match identically across all switches in that region?

Accepted Answer

Region name, revision number, and VLAN-to-instance mapping. According to IEEE 802.1s, switches belong to the same MST region if and only if they share the exact same configuration name, revision number, and VLAN-to-instance mapping table.

Answer

VLAN-to-instance mapping, bridge priority, and MAC address

Answer

Bridge priority, region name, and maximum age timer

Answer

Root bridge ID, region name, and revision number

Question 8

An engineer is configuring a QinQ tunnel where the service provider bridge needs to transparently carry customer control traffic (like STP BPDUs) through the core without processing them. What feature must be enabled on the provider edge access ports?

Accepted Answer

Layer 2 Protocol Tunneling (L2PT). Layer 2 Protocol Tunneling (L2PT) encapsulates customer BPDUs into specific multicast destination MAC addresses at the ingress edge, tunnels them across the provider core, and un-encapsulates them at the egress edge.

Answer

VLAN Translation

Answer

Rapid Spanning Tree Protocol (RSTP)

Answer

BPDU Protection (bpdu-block)

Question 9

When designing advanced enterprise campus VLAN architectures with Juniper EX Series switches, which TWO considerations are critical for large-scale Layer 2 domains? (Choose two)

Accepted Answer

Configuring bridge assurance on all point-to-point links running MSTP to protect against unidirectional link failures.. In large-scale Layer 2 networks, keeping broadcast domains small and controlling failure domains via multi-chassis link aggregation (MC-LAG or EVPN-VXLAN) and limiting spanning tree blast radius are essential design principles.

Answer

Disabling BPDU protection on core inter-switch links to allow unexpected root bridges to take over seamlessly.

Answer

Enabling spanning tree globally across all VLANs without instance mapping to ensure all switches share a single root bridge.

Answer

Setting the forward delay timer to 4 seconds across all switches to accelerate MSTP topology convergence.

Question 10

When configuring advanced Layer 2 tunneling (Q-in-Q) on Juniper EX Series switches, which THREE statements are correct regarding VLAN stacking behavior and limitations? (Choose three)

Accepted Answer

MTU sizes across the core must be adjusted to account for the extra 4 bytes of the added outer VLAN tag.. QinQ on Juniper EX switches involves specific encapsulation requirements like flexible-ethernet-services, stacking VLAN tags on ingress and popping on egress, and preserving inner customer VLAN tags transparently.

Answer

Layer 2 Protocol Tunneling (L2PT) is automatically enabled for all protocols without additional configuration when QinQ is active.

Answer

QinQ tunneling requires standard access mode encapsulation on all core-facing uplink ports.

Question 11

You are troubleshooting a Juniper EX Series switch running RSTP. The network experiences intermittent loops. You suspect that BPDU guard is not functioning as expected on an edge port. Which statement is correct about BPDU guard behavior on EX Series switches?

Accepted Answer

When a BPDU is received on a port with BPDU guard enabled, the port is disabled and placed in the err-disabled state, and can be recovered automatically if err-disable recovery is configured.. BPDU guard protects the network by disabling a port that receives a BPDU, which should not happen on an edge port. On EX Series switches, the port goes into err-disabled state. Automatic recovery can be configured using 'errdisable recovery' commands, allowing the port to be re-enabled after a specified time. This prevents loops while allowing recovery from transient misconfigurations.

Answer

BPDU guard disables the port permanently when a BPDU is received, requiring manual intervention to re-enable.

Answer

BPDU guard is enabled by default on all edge ports configured with the 'edge' keyword.

Answer

BPDU guard only works on trunk ports, not on access ports.

Question 12

You are configuring a Juniper EX Series switch to support a VoIP deployment. You want to ensure that voice traffic from IP phones is placed in VLAN 100 and data traffic in VLAN 200, with the phone tagging voice packets with 802.1p priority 5. Which feature should you configure?

Accepted Answer

Voice VLAN with VLAN ID 100 and 802.1p priority 5, and data VLAN 200 on the access port.. The voice VLAN feature on Juniper EX Series switches enables automatic assignment of voice traffic to a specific VLAN and can set 802.1p priority. By configuring voice VLAN 100 with priority 5 and data VLAN 200, the switch will recognize VoIP traffic (via LLDP-MED or MAC address) and place it in the correct VLAN with the appropriate priority, ensuring QoS for voice.

Answer

Private VLAN with primary VLAN 100 and secondary VLAN 200.

Answer

MSTP with MSTI 1 for VLAN 100 and MSTI 2 for VLAN 200.

Answer

Q-in-Q tunneling with outer VLAN 100 and inner VLAN 200.

Question 13

You are deploying a Juniper EX Series switch as an access layer device in a campus network. The uplink port ge-0/0/1 connects to a distribution switch and is expected to carry traffic for VLANs 10, 20, and 30. You want to prevent the access switch from becoming the root bridge for any of these VLANs and ensure that the uplink is preferred for forwarding. Which configuration should you apply on the access switch?

Accepted Answer

Set the bridge priority to 61440 on the access switch and configure the uplink port with a lower path cost.. To prevent the access switch from becoming the root bridge, a high bridge priority such as 61440 is appropriate. To ensure the uplink is preferred for forwarding, a lower path cost on that port is necessary. Together, these settings control both root bridge election and path selection, aligning with best practices for access layer switches in a campus network.

Answer

Enable RSTP on the access switch and set the uplink port as an edge port to prioritize forwarding.

Answer

Set the bridge priority to 4096 on the access switch and configure the uplink port as the root port using the root-port command.

Answer

Configure the uplink port with a higher path cost and set the bridge priority to 61440 on the access switch.

Question 14

An engineer is deploying VSTP (VLAN Spanning Tree Protocol) on a Juniper EX Series switch in a network that also includes RSTP bridges. The engineer wants to ensure that VSTP BPDUs are properly handled and that the network converges quickly. Which statement about VSTP operation is correct?

Accepted Answer

VSTP is compatible with RSTP and can interoperate using RSTP BPDUs on a per-VLAN basis.. VSTP runs a separate spanning-tree instance for each VLAN, using RSTP BPDU format. It can interoperate with RSTP bridges by sending standard RSTP BPDUs on a per-VLAN basis, often using 802.1Q tags to identify the VLAN. This allows a VSTP-enabled switch to participate in an RSTP network while maintaining per-VLAN topologies. The correct statement highlights this interoperability, which is essential for mixed-vendor or mixed-protocol environments.

Answer

VSTP BPDUs are encapsulated in 802.1Q tags with a special EtherType to differentiate them from RSTP BPDUs.

Answer

VSTP uses a single spanning-tree instance for all VLANs, similar to MSTP.

Answer

VSTP requires all switches in the network to run VSTP; it cannot interoperate with RSTP.

Question 15

You are configuring a Juniper EX Series switch to prevent loops in a VSTP environment. An access port connected to an end-user device is receiving BPDUs from an unauthorized switch. You want to automatically disable the port if BPDUs are received. Which feature should you enable on the access port?

Accepted Answer

BPDU protection. BPDU protection is specifically designed to disable edge ports that receive BPDUs, preventing loops caused by unauthorized switches. When enabled on an access port, any BPDU received will cause the port to enter an err-disabled state. This is the standard best practice for end-user ports in a VSTP or RSTP environment. Root protection and loop protection serve different purposes, and storm control does not address BPDU reception.

Answer

Loop protection

Answer

Storm control

Answer

Root protection