JNCIS-ENT Practice Test 12 — 15 Questions

Question 1

Which THREE parameters must match across all switches for them to successfully form a single MST region? (Choose three.)

Accepted Answer

VLAN-to-instance mapping table. For switches to form a single MST region, the MST configuration must be identical across all of them, and this is verified by three specific parameters. Option A, the VLAN-to-instance mapping table, must match because it defines which VLANs are mapped to which MST instances (MSTIs), and any difference causes the switches to be in different regions. Option B, the configuration name, is a 32-character alphanumeric string that identifies the MST region and must be identical on all switches. Option C, the revision number, is a 16-bit value that must also match, as it is used together with the configuration name and mapping table to determine region membership. Options D and E are incorrect because bridge priority and hello timer are per-instance or per-port STP parameters that affect root election and BPDU timing, but they are not part of the MST region identifier and do not need to match for region formation.

Answer

Bridge priority value

Answer

Hello timer interval

Question 2

Which THREE conditions must be met to successfully execute an In-Service Software Upgrade (ISSU) on a dual-RE Juniper routing platform? (Choose three)

Accepted Answer

Both Routing Engines must be fully populated with identical hardware models and supported Junos images.. Option A is correct because ISSU requires both Routing Engines to be the same hardware model and to run compatible, supported Junos images so that the upgraded RE can take over cleanly. Option B is correct because Graceful Routing Engine Switchover (GRES) must be enabled and synchronized, allowing the backup RE to assume control without resetting the data plane or losing forwarding state. Option E is correct because Nonstop Active Routing (NSR) or Graceful Restart must be configured for the active routing protocols so that routing adjacencies and protocol state survive the RE switchover during the upgrade. Option C is incorrect because ISSU is designed to avoid taking down all physical interfaces; interfaces remain forwarding during the upgrade. Option D is incorrect because VRRP preemption settings are not a prerequisite for ISSU and do not need to be disabled.

Answer

All physical interfaces must be manually placed in a disabled state prior to upgrade.

Answer

VRRP preemption must be disabled on all routing interfaces.

Question 3

When configuring Layer 2 firewall filters on an EX Series switch, which THREE statements are correct regarding filter structure and application? (Choose three)

Accepted Answer

They are configured under the 'family ethernet-switching' match criteria context.. Option A is correct because Layer 2 firewall filters on EX Series switches are configured within the 'family ethernet-switching' context, which provides the match conditions for Layer 2 fields such as MAC addresses and EtherType. Option C is correct because these filters can match on source and destination MAC addresses and EtherType values, which are fundamental Layer 2 header fields. Option D is correct because Layer 2 filters can be applied to physical switch ports (interfaces) or to VLANs, allowing filtering at the ingress port or across a VLAN. Option B is incorrect because applying filters to logical Layer 3 interfaces (irb or vlan interfaces) using 'family inet' is for Layer 3 filters, not Layer 2. Option E is incorrect because firewall filters evaluate match conditions before any routing lookup occurs; routing lookups happen after a packet is permitted and forwarded.

Answer

They are applied to logical Layer 3 routing interfaces (irb or vlan interfaces) using family inet.

Answer

They execute routing lookups prior to evaluating packet match conditions.

Question 4

You are troubleshooting port security on an EX Series switch. An interface has been configured with 'action-on-violation shutdown', and a violation occurs. What is the default operational state of the interface after the violation, and how is it restored?

Accepted Answer

The interface is disabled and must be manually re-enabled using a clear command or by disabling/re-enabling the interface.. When port security is configured with 'action-on-violation shutdown' on an EX switch, a violation causes the interface to be disabled (err-disabled). It does not automatically recover; the administrator must manually clear the violation using 'clear ethernet-switching port-error' or by disabling and re-enabling the interface. This is the documented default behavior for shutdown action.

Answer

The interface automatically recovers after a default hold-down timer of 300 seconds.

Answer

The interface drops violating packets but remains operationally up until manually disabled.

Answer

The interface transitions to a blocked state and flushes its MAC table every 60 seconds until cleared.

Question 5

Which THREE statements describe the function of the Designated Port in RSTP? (Choose three.)

Accepted Answer

It provides the lowest cost path from the segment back toward the root bridge.. Option A is correct because the designated port is the port on a LAN segment that offers the lowest path cost back toward the root bridge, making it the forwarding port for that segment. Option C is correct because the designated port is responsible for sending (forwarding) BPDUs onto its attached LAN segment, which is how RSTP maintains topology information. Option D is correct because RSTP elects exactly one designated port per active LAN segment to avoid loops and ensure consistent forwarding. Option B is incorrect because designated ports normally forward frames and BPDUs, not remain permanently discarding; discarding is a temporary or alternate/backup port state. Option E is incorrect because the primary root port is the port on a non-root bridge closest to the root bridge, which is a different role from the designated port.

Answer

It remains permanently in the discarding state to prevent loops.

Answer

It acts as the primary root port for the local bridge.

Question 6

Which THREE statements accurately describe the behavior and configuration of VRRP tracking on Junos devices? (Choose three)

Accepted Answer

If the decremented priority falls below the backup router's priority, mastership transitions to the backup router.. Option E is correct because VRRP tracking on Junos is designed to decrement the router's VRRP priority by a configured amount when a tracked interface or route becomes unavailable, reflecting degraded forwarding capability. Option A is correct because once the priority is decremented below that of a backup router, the backup with the higher priority takes over as master, triggering a mastership transition. Option C is correct because Junos VRRP tracking supports monitoring multiple interfaces or reachability paths simultaneously within a single tracking configuration, allowing comprehensive failure detection. Option B is incorrect because tracking only adjusts priority; it does not administratively shut down the tracked interface. Option D is incorrect because tracking has no automatic effect on GRES (Graceful Routing Engine Switchover) and does not disable it.

Answer

Tracking forces the tracked interface to shut down permanently when a failure occurs.

Answer

Tracking automatically disables GRES on the routing engine.

Question 7

Which THREE parameters can be tuned under the VRRP hierarchy in Junos to customize failover timing and behavior? (Choose three)

Accepted Answer

Track interface priority decrement values to lower priority when upstream links fail.. Under the Junos VRRP hierarchy, option B is correct because the track interface configuration lets you specify a priority decrement (for example, track interface ge-0/0/0 priority-cost 30) so the router lowers its VRRP priority when a monitored upstream link fails, triggering a controlled failover. Option C is correct because the advertise-interval statement sets how often VRRP advertisement packets are sent (default 1 second), directly controlling failover detection timing. Option D is correct because the priority value (0–255, default 100) determines which router becomes master, with the higher priority winning and 255 triggering immediate preemption. Option A is not part of the VRRP hierarchy; LACP fast timeout is configured under aggregated Ethernet (lacp periodic fast) and concerns link-bundle heartbeats, not VRRP failover. Option E is also unrelated to VRRP; RE mastership priority is a Virtual Chassis setting (set virtual-chassis member 0 mastership-priority) for controlling Routing Engine roles, not VRRP master election.

Answer

LACP fast timeout timer to manage aggregated link heartbeats.

Answer

Routing engine mastership priority for Virtual Chassis roles.

Question 8

By default, what is the Junos routing protocol preference value assigned to static routes?

Accepted Answer

5. In Junos OS, the default routing protocol preference (also called administrative distance) for static routes is 5. This low value makes static routes highly preferred over routes learned from dynamic protocols like OSPF (preference 10) or BGP (preference 170). The preference value is used to select the active route when multiple routes to the same destination exist from different sources.

Answer

170

Answer

10

Answer

150

Question 9

What is the OSPF router ID format used by Junos OS when initializing the OSPF routing process if no explicit router ID is configured?

Accepted Answer

A 32-bit IPv4 address format (dotted quad). OSPF router IDs are formatted as a 32-bit dotted-quad number, identical in structure to an IPv4 address.

Answer

A 48-bit MAC address

Answer

An integer value between 1 and 65535

Answer

A 128-bit IPv6 address

Question 10

An administrator has configured a forwarding-type routing instance to perform filter-based forwarding. Which configuration statement is mandatory under the routing-instances hierarchy to properly define this instance type?

Accepted Answer

set routing-instances dept-fwd instance-type forwarding. Filter-based forwarding (FBF) on Junos requires a routing instance of type 'forwarding'. This instance type creates a Virtual Routing and Forwarding (VRF) table that is populated only by firewall filter 'then routing-instance' actions, not by a routing protocol. The mandatory statement is therefore 'set routing-instances <name> instance-type forwarding'.

Answer

set routing-instances dept-fwd routing-options interface ge-0/0/0.0

Answer

set routing-instances dept-fwd instance-type virtual-router

Answer

set routing-instances dept-fwd instance-type l3vpn

Question 11

An engineer needs to configure a static IPv4 route on a Juniper Networks MX Series router pointing traffic destined for 192.168.100.0/24 to next-hop 10.0.0.1. Which configuration accomplishes this task?

Accepted Answer

set routing-options static route 192.168.100.0/24 next-hop 10.0.0.1. In Junos, static routes are configured under the [edit routing-options] hierarchy, not under protocols or interfaces. The correct syntax is 'set routing-options static route next-hop

', which installs the route into the inet.0 routing table for IPv4. This is the standard, documented method for defining a static IPv4 route on any Juniper device, including MX Series routers.

Answer

set routing-instances default static route 192.168.100.0/24 next-hop 10.0.0.1

Answer

set protocols static route 192.168.100.0/24 next-hop 10.0.0.1

Answer

set interfaces fxp0 unit 0 family inet static-route 192.168.100.0/24 next-hop 10.0.0.1

Question 12

Which TWO statements are true regarding BGP communities in Junos? (Choose two)

Accepted Answer

Communities are optional transitive path attributes.. Option A is correct because BGP communities are carried as an optional transitive path attribute (attribute type code 8), meaning they are not required in every UPDATE but, when present, are propagated to other BGP speakers. Option E is correct because a standard community is a 32-bit value expressed as two 16-bit numbers in the ASN:value format, for example 65000:100, where the first field is typically the autonomous system number and the second is an administrator-defined value. Option B is wrong because communities are an additional attribute and do not replace AS_PATH, which remains the primary loop-prevention and path-selection attribute. Option C is wrong because community matching is a policy action performed during route evaluation, not a tie-breaker after router ID; the router ID tie-breaker applies only when comparing otherwise equal paths. Option D is wrong because communities can be attached and matched on both eBGP and iBGP sessions, and they are not automatically stripped on iBGP.

Answer

Communities replace the AS_PATH attribute entirely.

Answer

Communities are evaluated after the router ID tie-breaker.

Answer

Communities can only be applied to eBGP sessions and are stripped on iBGP.

Question 13

You are configuring VRRP between two EX4600 switches to provide a default gateway for a VLAN. To ensure that the switch with the higher physical interface capacity assumes the master role, what parameter should you adjust?

Accepted Answer

Increase the VRRP priority value on the preferred switch's interface.. VRRP elects the master based on the highest priority value (default 100, range 1–254, with 255 reserved for the address owner). To ensure the switch with greater capacity becomes master, you increase its VRRP priority above the other switch's. The master then owns the virtual IP and forwards traffic for the VLAN, while the backup monitors advertisements and takes over if the master fails.

Answer

Decrease the VRRP advertisement interval on the backup switch.

Answer

Set the virtual router identifier (VRID) to a lower integer value on the preferred switch.

Answer

Disable the VRRP preempt feature on both routers.

Question 14

Which Junos configuration hierarchy is used to configure secure access port features such as DHCP snooping and Dynamic ARP Inspection?

Accepted Answer

set ethernet-switching-options secure-access-port. In Junos, secure access port features like DHCP snooping, Dynamic ARP Inspection (DAI), and IP source guard are configured under the [edit ethernet-switching-options secure-access-port] hierarchy. This is the correct location for these Layer 2 security features on EX Series switches. The command 'set ethernet-switching-options secure-access-port' enables the configuration stanza where you can then specify VLANs, interfaces, and other parameters for DHCP snooping and DAI.

Answer

set protocols l2-security

Answer

set system security layer2

Answer

set switch-options port-security

Question 15

During the examination of IS-IS packet captures on a multi-access LAN interface, an engineer notices a specific PDU type being transmitted periodically by the Designated Intermediate System (DIS) to maintain synchronized link-state databases. Which PDU type performs this function?

Accepted Answer

Complete Sequence Numbers PDU (CSNP). On a multi-access LAN, the DIS periodically sends Complete Sequence Numbers PDUs (CSNPs) to synchronize link-state databases. CSNPs contain a complete list of LSP IDs and sequence numbers, allowing routers to detect missing or outdated LSPs and request them via PSNPs. This periodic CSNP flooding is the DIS's primary database synchronization mechanism.

Answer

Partial Sequence Numbers PDU (PSNP)

Answer

Intermediate System Hello (IIH)

Answer

Level 1 Link State PDU (LSP)