JNCIS-ENT Practice Test 15 — 15 Questions

Question 1

An administrator implements OSPF on a Junos router with virtual links to span a disconnected non-backbone area across a non-backbone transit area to reach Area 0. What is a key design best practice regarding OSPF virtual links in enterprise networks?

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

Accepted Answer

They should be avoided in permanent designs due to troubleshooting complexity and lack of stability.. OSPF virtual links are a temporary solution to connect a disconnected area to the backbone. Best practice is to avoid them in permanent designs because they add complexity, are difficult to troubleshoot, and can introduce instability. They should only be used during transitional periods, such as when merging networks or during migration, and then replaced with proper physical or logical links.

Answer

They must be configured with a metric of 1 to ensure primary path selection.

Answer

They automatically convert the transit area into an extension of the backbone.

Answer

They require the transit area to be configured as a totally stubby area.

Question 2

You have configured a static route with a next-hop of 10.0.0.1 and a preference of 10. Another static route to the same destination has a next-hop of 10.0.0.2 and a preference of 5. Both next-hops are reachable. Which route will be active in the routing table?

Accepted Answer

The route with next-hop 10.0.0.2 because it has a lower preference.. Junos selects the static route with the lowest preference value. Since the route with next-hop 10.0.0.2 has a preference of 5, which is lower than 10, it becomes the active route. The other route remains in the routing table but is not used for forwarding.

Answer

Both routes will be active and load balancing will occur.

Answer

Neither route will be active because of conflicting preferences.

Answer

The route with next-hop 10.0.0.1 because it has a higher preference.

Question 3

When using authentication in IS-IS, where can you apply the password?

Accepted Answer

At both the interface and global levels.. IS-IS authentication can be applied to the interface level or the global level (area/domain).

Answer

Only on the loopback interface.

Answer

Only at the global level.

Answer

Only at the interface level.

Question 4

A network administrator is configuring IS-IS on a Juniper router. They want to ensure that the router participates in both Level 1 and Level 2 routing. Which configuration statement is correct?

Accepted Answer

By default, IS-IS is enabled for both Level 1 and Level 2 on Juniper routers.. On Juniper routers, IS-IS is enabled for both Level 1 and Level 2 by default when you configure IS-IS on an interface. To restrict the router to a single level, you use the 'level 1 disable' or 'level 2 disable' commands. Since the requirement is to participate in both levels, no additional configuration is needed; the default behavior already satisfies the requirement.

Answer

set protocols isis level 1 disable; set protocols isis level 2 disable

Answer

set protocols isis level 2 disable

Answer

set protocols isis level 1 disable

Question 5

An EX4300 Virtual Chassis has GRES enabled. During a primary Routing Engine failure, what happens to the backup Routing Engine?

Accepted Answer

The backup Routing Engine assumes the primary role without disrupting the forwarding plane or resetting packet forwarding tables.. With GRES enabled, the backup Routing Engine assumes the primary role seamlessly without resetting the forwarding plane or dropping data traffic.

Answer

The backup Routing Engine reboots both engines to synchronize firmware versions.

Answer

The Virtual Chassis splits into independent standalone switches.

Answer

All switch members in the Virtual Chassis are forced into factory default mode.

Question 6

You are configuring a GRE tunnel and want to ensure that integrity checks are performed on the transmitted packets to detect corruption. Which parameter should you add to the tunnel configuration?

Accepted Answer

set interfaces gr-0/0/0 unit 0 tunnel checksum. The tunnel checksum parameter enables GRE header checksumming, which adds a checksum to the GRE header so the receiving endpoint can detect corruption in the encapsulated packet. On Junos, this is configured with 'set interfaces gr-0/0/0 unit 0 tunnel checksum'. It is the only option that maps to a real Junos GRE integrity feature.

Answer

set interfaces gr-0/0/0 unit 0 tunnel verify-integrity

Answer

set protocols gre checksum-validation enable

Answer

set interfaces gr-0/0/0 unit 0 family inet encryption aes256

Question 7

You need to write a Layer 2 firewall filter to drop inbound frames with a specific source MAC address on an EX Series switch. Where must this filter be applied to take effect?

Accepted Answer

Applied to the input of an interface or VLAN under family ethernet-switching.. Layer 2 firewall filters matching MAC addresses or Ethernet headers must be applied to the input of an interface or VLAN using the family ethernet-switching context.

Answer

Applied to the routing-instance forwarding table.

Answer

Applied globally under system services l2-firewall.

Answer

Applied to the output of the VLAN interface under family inet.

Question 8

An administrator needs to verify the exact BGP timers negotiated with an eBGP peer on a Junos device. Which operational command should be used?

Accepted Answer

show bgp neighbor. The 'show bgp neighbor' command provides detailed information about a BGP neighbor session, including negotiated hold time, keepalive interval, state, and message statistics.

Answer

show ospf neighbor

Answer

show bgp summary

Answer

show route advertising-protocol bgp

Question 9

Which Junos routing instance type is best suited when you want to run MPLS L3VPNs on a Provider Edge (PE) router?

Accepted Answer

vrf. L3VPN routing instances are used on PE routers to maintain customer-specific VRF routing tables and exchange VPN-IPv4 routes via MP-BGP.

Answer

forwarding

Answer

virtual-router

Answer

no-structural-instance

Question 10

An organization runs MSTP with multiple instances. A packet belonging to a VLAN that is not explicitly mapped to any MST instance is processed in which manner?

Accepted Answer

It is automatically mapped to Instance 0 (the CIST).. In MSTP (Multiple Spanning Tree Protocol, IEEE 802.1s), VLANs that are not explicitly mapped to a specific MST instance are automatically assigned to the Common and Internal Spanning Tree (CIST), which is MST instance 0. The CIST provides connectivity for all VLANs that are not mapped to other instances and also interconnects MST regions. Therefore, the packet is processed by Instance 0, not dropped or flooded indiscriminately.

Answer

It is processed by the default RSTP instance running outside MSTP.

Answer

It is dropped by the switch because unmapped VLANs are considered invalid in MSTP.

Answer

It floods to all ports regardless of spanning tree port states.

Question 11

An administrator configures a GRE tunnel with a tunnel key enabled for security segmentation between two sites. The tunnel comes up, but traffic fails to pass. Debugging reveals that packets are dropped because the receiving router rejects the packets. What is the most probable configuration mismatch?

Accepted Answer

The tunnel key value configured on one router does not match the tunnel key value configured on the remote peer router.. GRE tunnel keys are used to multiplex multiple GRE tunnels between the same pair of endpoints, and both ends must be configured with the same key value for the receiver to accept the encapsulated packets. If the keys mismatch, the receiving router drops the packets because it cannot match them to the expected tunnel, even though the tunnel interface itself shows as up. This is the classic cause of 'tunnel up but traffic fails' with GRE keys.

Answer

The tunnel source address is using a loopback interface instead of a physical interface.

Answer

The physical interface MTU is set too high on the ingress router.

Answer

The GRE tunnel interface family inet is missing the primary address.

Question 12

When should you consider increasing the 'csnp-interval'?

Accepted Answer

To reduce control traffic overhead on slow links.. Increasing the interval is useful on slow or congested links to reduce the frequency of full database synchronization traffic.

Answer

To improve convergence time.

Answer

To increase the maximum LSP size.

Answer

To fix adjacency flapping.

Question 13

Which of the following are true regarding the IS-IS 'hello-interval'? (Choose TWO)

Accepted Answer

It determines how often Hello PDUs are sent.. Option B is correct because the IS-IS hello-interval directly controls the frequency with which a router transmits IS-IS Hello PDUs (IIHs) on an interface, which is its fundamental purpose. Option D is correct because the adjacency hold time is derived from the hello-interval multiplied by the hello-multiplier (by default, hold time = hello-interval × 3), so changing the hello-interval changes how long a neighbor waits before declaring the adjacency down. Option A is wrong because the SPF interval is governed by separate SPF timers (e.g., spf-interval), not the hello-interval. Option C is wrong because the default hello-interval varies by interface type and network type (for example, 10 seconds on broadcast and 3 seconds on point-to-point by default on many platforms), so it is not always 10 seconds. Option E is wrong because Hello PDUs and the hello-interval apply to both broadcast and point-to-point links, not only point-to-point.

Answer

It is used to calculate the SPF interval.

Answer

It is always 10 seconds.

Answer

It is only used on point-to-point links.

Question 14

An OSPF area contains routers running Junos OS where external routes must be imported into the OSPF domain from a BGP core. However, the area must not accept external AS-external LSAs (Type 5) from other areas, but must allow routers within this area to originate external routes themselves. Which area type fulfills this requirement?

Accepted Answer

Not-So-Stubby Area (NSSA). A Not-So-Stubby Area (NSSA) is designed to allow external routes to be imported into the OSPF domain from a non-OSPF protocol (like BGP) while preventing Type 5 AS-external LSAs from other areas. NSSAs use Type 7 LSAs for external routes originated within the area, which are translated to Type 5 at the NSSA ABR. This fulfills the requirement: the area does not accept Type 5 LSAs from other areas, but routers within can originate external routes.

Answer

Backbone Area (Area 0)

Answer

Totally Stubby Area

Answer

Standard Stub Area

Question 15

An engineer is preparing to perform an In-Service Software Upgrade (ISSU) on a pair of dual-RE MX240 routers. Which condition must be met to ensure the ISSU succeeds without dropping traffic?

Accepted Answer

Graceful Route Engine Switchover (GRES) and Nonstop Active Routing (NSR) must be enabled and functioning.. ISSU requires specific hardware compatibility (matching RE models, line card types), GRES and NSR configured and operating, and a supported Junos image path.

Answer

The backup Routing Engine must be physically removed from the chassis during the upgrade.

Answer

All physical interfaces must be manually disabled prior to issuing the request system software in-service command.

Answer

All routing protocols must be migrated from OSPF to IS-IS before starting ISSU.