JNCIS-ENT Practice Test 4 — 25 Questions

Question 1

What is the function of the DIS in an IS-IS broadcast network?

Accepted Answer

To generate pseudonode LSPs.. The DIS (Designated Intermediate System) is responsible for generating pseudonode LSPs to represent the broadcast network.

Answer

To authenticate all neighbors.

Answer

To perform path calculation for all routers.

Answer

To act as the routing controller for the area.

Question 2

An administrator configures a Link Aggregation Group (LAG) using LACP between two EX series switches. The link fails to aggregate, and the log shows 'LACP status: Expired'. What does the 'Expired' state indicate?

Accepted Answer

The local port has stopped receiving LACP packets from the remote peer within the timeout window.. The 'Expired' state in LACP means the local port has stopped receiving LACP packets from the remote peer within the expected timeout period.

Answer

The Virtual Chassis primary routing engine license has expired.

Answer

The Junos software license for aggregated Ethernet has expired.

Answer

The GRES synchronization timer has timed out.

Question 3

Which Junos command displays the active DHCP snooping binding database entries on an EX Series switch?

Accepted Answer

show ethernet-switching dhcp-snooping binding. The operational command to view DHCP snooping bindings is 'show ethernet-switching dhcp-snooping binding'.

Answer

show dhcp-snooping binding

Answer

show system dhcp-snooping database

Answer

show bridge dhcp bindings

Question 4

An administrator runs 'show vlans' and notices that a particular VLAN has the status 'Active' but no interfaces listed under it. What does this indicate?

Accepted Answer

The VLAN is defined in the configuration and has an active IRB interface or routing instance, but no physical switch ports assigned.. An active VLAN without interfaces means the VLAN is defined in the database and associated with an IRB (Layer 3 interface) or routing instance, but no physical switch ports are members.

Answer

The VLAN has been disabled by Spanning Tree Protocol.

Answer

The switch memory is full and cannot display interface memberships.

Answer

The VLAN configuration has a syntax error.

Question 5

When a topology change occurs in an RSTP network, how are MAC address forwarding table entries affected across the switches?

Accepted Answer

MAC address table entries associated with non-edge ports are flushed immediately.. When a topology change occurs in RSTP, MAC address table entries associated with non-edge ports are flushed immediately. This allows the switches to relearn MAC addresses on the new topology, preventing forwarding to stale locations. Edge ports are not flushed because they connect to end devices and are not affected by topology changes.

Answer

MAC addresses are relearned only after the root bridge sends a direct clearing command.

Answer

MAC address entries are retained until the standard 300-second aging timer expires.

Answer

MAC address tables are completely cleared for all ports, including edge ports.

Question 6

You are configuring a Link Aggregation Group (LAG) on an EX series switch. Which statement is correct regarding LACP active mode?

Accepted Answer

The interface will actively transmit LACP packets to initiate and negotiate the aggregation with the peer device.. In LACP active mode, the interface actively transmits LACP packets to the remote peer to negotiate the link aggregation.

Answer

The interface will only respond to LACP packets and never transmit them.

Answer

Active mode can only be used when connecting Juniper switches to non-Juniper servers.

Answer

LACP active mode requires static pinning of member links and disables dynamic hash selection.

Question 7

Which of the following is required for two routers to form a Level 2 adjacency?

Accepted Answer

Matching Level 2 support.. For two routers to form a Level 2 adjacency in IS-IS, both must be configured to support Level 2 routing. This is achieved by configuring the interfaces with 'level 2' or 'level 1-2' (the default). If one router is configured as Level 1 only, it will not form a Level 2 adjacency with a Level 2-capable router. The other options are not required: hostnames can differ, area addresses only need to match for Level 1 adjacencies, and System IDs must be unique, not identical.

Answer

Identical hostname configurations.

Answer

Matching Area Addresses.

Answer

Identical System IDs.

Question 8

When configuring Filter-Based Forwarding (FBF), which THREE components are absolutely mandatory for successful operation? (Choose three)

Accepted Answer

A firewall filter with 'then routing-instance ' action.. Option A is correct because FBF requires a firewall filter that matches traffic and uses the 'then routing-instance ' action to redirect matching packets into the alternate routing table. Option B is correct because that action must reference a routing instance of type 'forwarding' (or 'virtual-router'), which provides the separate routing table where the redirected traffic is resolved. Option C is correct because the filter must be applied as an input filter on the ingress interface so that packets are classified and redirected before the normal destination lookup occurs. Option D is incorrect because BGP multipath is a load-balancing feature and is not required for FBF to function. Option E is incorrect because RSVP-TE LSPs are an MPLS traffic-engineering mechanism and are unrelated to the mandatory FBF configuration components.

Answer

BGP multipath enabled across all core interfaces.

Answer

An RSVP-TE LSP tunnel configured between the routers.

Question 9

Which CLI command displays the packet statistics, errors, and drop counters for a Link Aggregation Group (LAG) named ae0?

Accepted Answer

show interfaces ae0. The 'show interfaces ae0' command displays general interface statistics, error counts, and drops for the aggregated interface.

Answer

show chassis interface-drops ae0

Answer

show virtual-chassis interface ae0

Answer

show lacp statistics ae0

Question 10

When configuring a GRE tunnel source and destination address on a Junos device, which configuration hierarchy is used?

Accepted Answer

set interfaces gr-0/0/0 unit 0 tunnel source destination . On Junos, GRE tunnel source and destination addresses are configured under the tunnel interface unit hierarchy using 'set interfaces gr-0/0/0 unit 0 tunnel source destination '. This is the standard syntax for GRE tunnels, where the tunnel interface is a gr- interface and parameters are applied at the unit level.

Answer

set routing-options tunnels source destination

Answer

set protocols gre source destination

Answer

set system tunnel source destination

Question 11

You are configuring OSPF on a Junos device and need to ensure that the router prefers internal OSPF intra-area paths over inter-area paths, and inter-area paths over external paths. According to OSPF route preference rules, what is the evaluation order?

Accepted Answer

Intra-area > Inter-area > External Type 1 > External Type 2. OSPF route preference follows a strict order: intra-area (O) routes are most preferred, then inter-area (O IA), then external Type 1 (E1), and finally external Type 2 (E2). This order is based on the OSPF path selection algorithm, where routes within the same area are considered most reliable and external routes least.

Answer

Inter-area > Intra-area > External Type 2 > External Type 1

Answer

External Type 1 > Intra-area > Inter-area > External Type 2

Answer

External Type 2 > External Type 1 > Inter-area > Intra-area

Question 12

Which command displays the IS-IS interface parameters?

Accepted Answer

show isis interface. 'show isis interface' shows the configuration and state of IS-IS interfaces.

Answer

show isis configuration

Answer

show interfaces isis

Answer

show protocols isis interface

Question 13

Which THREE parameters are included when calculating the MST region configuration digest? (Choose three.)

Accepted Answer

VLAN-to-instance mapping table. The MST region configuration digest is an MD5 hash computed over the region's configuration attributes, and it includes the VLAN-to-instance mapping table (A), the configuration name (B), and the revision number (E) — these three define the region's identity and ensure all switches agree on the same MST region. The VLAN-to-instance mapping (A) determines which VLANs belong to which MST instances, the configuration name (B) is the alphanumeric region identifier, and the revision number (E) is the 16-bit value that must match across all switches in the region. The root bridge MAC address (C) and bridge priority value (D) are not part of the digest; they are per-instance spanning-tree parameters used for root election and topology calculation, not region configuration attributes.

Answer

Root bridge MAC address

Answer

Bridge priority value

Question 14

An administrator needs to configure an OSPF stub area on a Juniper router. Which THREE characteristics apply to a standard OSPF stub area? (Choose three.)

Accepted Answer

The ABR injects a default route (0.0.0.0/0) into the area. In a standard OSPF stub area, the ABR blocks Type 5 AS-external LSAs from being flooded into the area (option C), which is the defining restriction that keeps external routing information out of the stub. To still provide reachability to external destinations, the ABR injects a default route (0.0.0.0/0) into the stub area via a Type 3 summary LSA (option B), so internal routers can forward traffic toward the ABR. Because Type 5 LSAs are blocked and external connectivity depends on that default route, ASBRs cannot reside inside a stub area, and virtual links cannot transit a stub area (option D) since a virtual link requires the transit area to carry Type 5 LSAs and cannot be configured through a stub. Option A is incorrect because Type 3 summary LSAs are still permitted in a standard stub area (only totally stubby areas block Type 3 LSAs, except the default route). Option E is incorrect because an ASBR inside the area would generate Type 5 LSAs, which are not allowed in a stub area.

Answer

Type 3 summary LSAs are blocked from entering the area

Answer

ASBRs are permitted to reside directly inside the stub area

Question 15

An administrator configures a BGP policy to reject routes with an AS_PATH containing a specific AS number. Which match condition in a Junos routing policy is used to evaluate the AS_PATH?

Accepted Answer

as-path. In Junos, the as-path match condition evaluates routes against a defined as-path regular expression.

Answer

pref

Answer

metric

Answer

community

Question 16

Which statement is true regarding the behavior of storm control when the traffic rate exceeds the configured threshold?

Accepted Answer

Excess traffic exceeding the threshold is dropped by the switch hardware.. When storm control thresholds are exceeded, Junos drops the excess traffic matching the storm control criteria until the rate drops below the threshold.

Answer

Traffic is rate-shaped and buffered in the output queue until congestion clears.

Answer

The interface is immediately shut down and placed in an error-disabled state.

Answer

The switch sends SNMP traps and forwards the traffic with a low-priority CoS marking.

Question 17

You are verifying BGP Graceful Restart helper mode on a Juniper router. A peering router restarts its control plane. What output or verification command confirms that your router is acting as a Graceful Restart helper for the peer?

Accepted Answer

Run 'show bgp neighbor' and verify that the 'Graceful Restart' capability is advertised and received, and observe the restart state flags.. Using 'show bgp neighbor' displays the graceful restart capabilities negotiated and whether the peer is currently in restart state.

Answer

Run 'show chassis routing-engine' to verify that the remote neighbor has updated its local RE priority.

Answer

Run 'show lacp statistics ae0' to see if LACP packets are being suppressed during restart.

Answer

Run 'show vrrp summary' to check if the BGP neighbor has assumed the master VRRP role.

Question 18

You are reviewing the configuration of an EX Series switch and notice that interface ge-0/0/15 is configured with 'interface-mode access' but has no explicit 'vlan members' statement defined. Which VLAN does the interface default to?

Accepted Answer

VLAN 1 (default VLAN). On Juniper EX Series switches, when an interface is configured with 'interface-mode access' and no explicit 'vlan members' statement is present, the interface automatically becomes a member of the default VLAN, which is VLAN ID 1. This default VLAN is created by the system and is named 'default'. The interface will forward untagged traffic into VLAN 1, allowing connectivity without additional configuration.

Answer

VLAN 0 (null VLAN)

Answer

The port remains shut down until a VLAN is explicitly assigned.

Answer

It drops all traffic until a VLAN membership is added.

Question 19

Which OSPF area is mandatory in any multi-area OSPF routing architecture?

Accepted Answer

Area 0 (Backbone Area). Area 0, also known as the backbone area, is mandatory in multi-area OSPF architectures. All other areas must connect directly or via virtual links to Area 0.

Answer

Area 1

Answer

A totally stubby area

Answer

An NSSA area

Question 20

You have configured multiple static routes to the same destination with different preference values. When does Junos install a static route into the forwarding table (FIB)?

Accepted Answer

Only the static route with the lowest preference value is installed into the FIB.. Junos uses preference (administrative distance) to rank routes from the same or different protocols; the route with the lowest preference value is preferred and installed into the forwarding table (FIB). If multiple static routes to the same destination have equal preference, all can be installed for ECMP, but when preferences differ, only the lowest-preference route wins. This mirrors the standard 'lower is better' convention used by Junos for route preference.

Answer

Only the static route with the highest preference value is installed into the FIB.

Answer

All static routes are installed into the FIB, and traffic is automatically load-balanced across them.

Answer

All valid static routes are installed into the FIB regardless of preference values.