JNCIS-ENT OSPF Practice Test 2 — 15 Questions

Question 1

Which THREE types of routers can act as an OSPF Autonomous System Boundary Router (ASBR)? (Choose three)

Accepted Answer

An Area Border Router (ABR) redistributing BGP routes into OSPF. An ASBR is any OSPF router that injects external routing information into the OSPF domain via redistribution, regardless of its other roles. Option A is correct because an ABR that redistributes BGP routes into OSPF performs ASBR functionality in addition to its ABR duties. Option C is correct because a non-backbone internal router redistributing connected routes into OSPF originates Type 5 LSAs and thus becomes an ASBR. Option E is correct because a backbone router in Area 0 redistributing static routes into OSPF also generates external LSAs and acts as an ASBR. Option B is wrong because a router exclusively in a totally stubby area cannot originate external LSAs (Type 5 is blocked), so it cannot be an ASBR. Option D is wrong because a router running only RIP without OSPF enabled is not part of the OSPF domain and cannot function as an OSPF ASBR.

Answer

A router operating exclusively in a totally stubby area

Answer

A router running only RIP without OSPF enabled

Question 2

Which TWO commands can an administrator use on a Junos device to verify OSPF interface configurations and operational status? (Choose two)

Accepted Answer

show ospf interface. Option D, 'show ospf interface', is correct because it displays the OSPF operational status of each interface, including the interface name, area, DR/BDR, and state, which directly verifies OSPF interface configuration and status. Option E, 'show ospf interface detail', is correct because it provides the same OSPF interface verification with additional parameters such as timers, authentication, and neighbor counts, giving deeper operational detail. Option A, 'show ospf bgp-neighbors', is not a valid Junos command and mixes OSPF with BGP. Option B, 'show interfaces terse', only shows generic interface up/down and addressing information, not OSPF-specific configuration or state. Option C, 'show route protocol bgp', displays BGP routes rather than OSPF interface information.

Answer

show ospf bgp-neighbors

Answer

show interfaces terse

Answer

show route protocol bgp

Question 3

Which TWO LSA types are flooded throughout a single OSPF area and do not cross ABRs into other areas? (Choose two)

Accepted Answer

Type 1 (Router LSA). Type 1 (Router LSA) is correct because every OSPF router generates a Router LSA for each area it belongs to, and these LSAs are flooded only within that single area and are not propagated across an ABR into other areas. Type 2 (Network LSA) is correct because it is generated by the DR on a multi-access segment, describes the subnet and attached routers, and is flooded only within the area containing that segment, never crossing an ABR. Type 5 (AS-external LSA) is incorrect because it is flooded throughout the entire OSPF domain (all areas) unless it encounters a stub area, so it does cross ABRs. Type 4 (ASBR Summary LSA) is incorrect because it is generated by an ABR to advertise the ASBR's location and is flooded into areas other than the one containing the ASBR. Type 3 (Summary LSA) is incorrect because it is generated by an ABR specifically to advertise inter-area routes from one area into another, so by definition it crosses ABRs.

Answer

Type 5 (AS-external LSA)

Answer

Type 4 (ASBR Summary LSA)

Answer

Type 3 (Summary LSA)

Question 4

Which THREE Junos configuration elements are required when setting up OSPF authentication using MD5 on a broadcast interface? (Choose three)

Accepted Answer

set protocols ospf area interface authentication md5. Configuring MD5 authentication on a Junos OSPF interface requires setting the authentication type to md5, defining the key ID, and providing the secret key string.

Answer

Disabling all OSPF hello timers across the area

Question 5

Which TWO factors directly influence the calculation of the OSPF Shortest Path First (SPF) algorithm tree? (Choose two)

Accepted Answer

Interface cost metrics assigned to links. The SPF algorithm computes the shortest path tree using Link-State Advertisements (LSAs) in the LSDB and interface cost metrics assigned to links.

Answer

Interface MTU sizes configured on the links

Answer

OSPF hello and dead timer values

Question 6

Which TWO troubleshooting commands help identify OSPF route installation issues in the Junos routing table? (Choose two)

Accepted Answer

show route protocol ospf. Option D, show route protocol ospf, is correct because it filters the Junos routing table to display only routes whose protocol is OSPF, directly revealing whether OSPF routes were installed and their preference/next-hop state. Option E, show route terse, is correct because it gives a compact listing of all routing-table entries, letting you quickly confirm whether expected OSPF prefixes are present or missing without the verbosity of full route detail. Options A, B, and C do not belong: clear ospf database only resets/refreshes the OSPF link-state database rather than showing route installation, show ospf neighbor detail verifies adjacency and neighbor state but not routing-table installation, and show ospf database summary displays link-state advertisement counts, not installed routes.

Answer

clear ospf database

Answer

show ospf neighbor detail

Answer

show ospf database summary

Question 7

Which TWO packet types are sent reliably (requiring acknowledgment) by OSPF routers during communication? (Choose two)

Accepted Answer

Link-State Update (LSU) packets. Options C and D are correct because OSPF uses reliable delivery for Link-State Update (LSU) and Link-State Request (LSR) packets: both are transmitted with acknowledgment mechanisms (via LSAck) to ensure reliable flooding and database synchronization. LSU packets carry LSAs and must be acknowledged to guarantee every router receives the updated topology information, while LSR packets request specific LSAs from neighbors and are also sent reliably so the request is not lost. The unmarked options do not belong: Type 0 heartbeat packets (A) are not an OSPF packet type, Hello packets (B) are sent periodically and unreliably to discover/maintain neighbors, and Link-State Acknowledgment (LSAck) packets (E) are the acknowledgment mechanism itself rather than a packet type that requires acknowledgment.

Answer

Type 0 heartbeat packets

Answer

Hello packets

Answer

Link-State Acknowledgment (LSAck) packets

Question 8

An administrator is reviewing OSPF link-state database entries using the Junos command 'show ospf database'. Which THREE LSA types appear in the output of a standard non-backbone area router? (Choose three)

Accepted Answer

Type 1 (Router LSA). Type 1 (Router LSA) is correct because every OSPF router in an area originates a Router LSA describing its links and interface states, so it always appears in the link-state database of a standard non-backbone area router. Type 3 (Summary LSA) is correct because Area Border Routers (ABRs) flood inter-area prefix information into the area, and a normal non-backbone area router receives these Type 3 LSAs from its ABR. Type 5 (AS-external LSA) is correct because external routes redistributed into OSPF are flooded throughout all normal (non-stub, non-NSSA) areas as Type 5 LSAs, which a standard area router will display. Type 8 (OSPFv3 Inter-Area Prefix LSA) does not belong because it is an OSPFv3 (IPv6) LSA type and this scenario concerns OSPFv2 link-state database output. Type 7 (NSSA LSA) does not belong because Type 7 LSAs are only generated and flooded within Not-So-Stubby Areas, which is not the standard non-backbone area described here.

Answer

Type 8 (OSPFv3 Inter-Area Prefix LSA)

Answer

Type 7 (NSSA LSA)

Question 9

An administrator is troubleshooting an OSPF adjacency issue on an interface connecting two Juniper vMX routers. Both routers are stuck in the 2-Way state on a broadcast segment. Which configuration parameter must match on both routers for the adjacency to progress beyond 2-Way?

Accepted Answer

The hello-interval and dead-interval timers must match. OSPF neighbors on a broadcast segment must agree on hello-interval and dead-interval timers to form and maintain an adjacency. If these timers mismatch, the routers will not progress past Init or 2-Way (or will drop the adjacency), because each router considers the other's hellos stale. Matching hello/dead timers is a fundamental OSPF adjacency requirement, along with matching area ID, authentication, MTU, and stub flags.

Answer

The interface metric must be identical

Answer

The interface priority must be set to zero on both nodes

Answer

The router-id must be identical on both routers

Question 10

When examining an OSPF link-state database on a Junos device, which THREE LSA types are flooded exclusively within the local area and do not cross Area Border Routers (ABRs) into other areas? (Choose three.)

Accepted Answer

Type 2 Network LSA. Type 1 Router LSAs (option D) are generated by every OSPF router to describe its links and are flooded only within the originating area, never crossing an ABR. Type 2 Network LSAs (option A) are produced by the DR on a multi-access segment and are likewise scoped strictly to the local area. Type 7 NSSA LSAs (option B) are originated by ASBRs inside a not-so-stubby area and are flooded only within that NSSA, being translated to Type 5 by the ABR at the area boundary. Type 3 Summary LSAs (option E) are generated by ABRs to advertise inter-area routes and are explicitly flooded between areas, and Type 4 Summary LSAs (option C) are also ABR-generated to advertise ASBR reachability across areas, so neither is confined to a single area.

Answer

Type 4 Summary LSA

Answer

Type 3 Summary LSA

Question 11

You are troubleshooting an OSPF adjacency between two Juniper routers in area 0. The routers are directly connected and can ping each other, but the adjacency remains in the ExStart state. You suspect an MTU mismatch. Which Junos configuration statement on the interface resolves the issue without changing the physical MTU?

Accepted Answer

set interfaces ge-0/0/0 unit 0 family inet mtu 1500. OSPF routers include the interface MTU in Database Description packets and will not proceed past ExStart if the values do not match. In Junos, the relevant MTU is the logical interface MTU configured under family inet. Setting it to match the peer resolves the mismatch and allows the adjacency to transition to Exchange and then Full.

Answer

set interfaces ge-0/0/0 mtu 1500

Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 mtu 1500

Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 ignore-mtu

Question 12

You are configuring OSPF on a Juniper MX Series router. The router has two interfaces in the same OSPF area: ge-0/0/0 and ge-0/0/1. You want to ensure that the router ID is always 10.1.1.1, regardless of interface IP addresses or the order in which interfaces become active. Which configuration statement accomplishes this?

Accepted Answer

set routing-options router-id 10.1.1.1. The OSPF router ID is a 32-bit value that uniquely identifies the router in the OSPF domain. In Junos, it is explicitly configured under the [edit routing-options] hierarchy with the router-id statement. This setting takes precedence over any interface-derived router ID, providing deterministic behavior. Configuring it per interface or under protocols ospf is invalid syntax and will not achieve the desired result.

Answer

set protocols ospf router-id 10.1.1.1

Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 router-id 10.1.1.1

Answer

set interfaces lo0 unit 0 family inet address 10.1.1.1/32

Question 13

You are configuring OSPF on a Juniper router and want to advertise a loopback interface into OSPF so that its address is always reachable. Which configuration statement correctly places the loopback interface into OSPF area 0?

Accepted Answer

set protocols ospf area 0.0.0.0 interface lo0.0. To advertise a loopback interface in OSPF on Junos, you reference the logical interface lo0.0 under the OSPF area hierarchy. This causes the loopback address to be advertised as a stub network, ensuring it is reachable. The network statement is not used in Junos OSPF configuration.

Answer

set protocols ospf area 0.0.0.0 interface lo0

Answer

set protocols ospf area 0.0.0.0 interface lo0.0 passive

Answer

set protocols ospf area 0.0.0.0 network 127.0.0.1/32

Question 14

You are configuring OSPF on a Junos router. You want to influence the DR/BDR election on a broadcast network so that a specific router becomes the DR. Which two interface parameters can you set to increase the likelihood of a router being elected as DR? (Choose two.)

Accepted Answer

Configure a higher router ID on the router.. The DR/BDR election on a broadcast network is determined first by OSPF interface priority, and then by router ID as a tiebreaker. To increase the likelihood of a router becoming DR, you can either increase its interface priority above others, or ensure it has the highest router ID if priorities are equal. Interface cost and other parameters do not affect the election. Setting priority to 0 makes a router ineligible.

Answer

Enable OSPF demand circuits on the interface.

Answer

Change the network type to point-to-point.

Answer

Set the OSPF interface cost to a lower value.

Question 15

You are troubleshooting an OSPF network where a Juniper router is not installing a route to a remote network in its routing table. You verify that the route is present in the OSPF database as a Type 5 LSA. The router is an ABR connected to area 0 and area 1. What is the most likely reason the route is not being installed?

Accepted Answer

The forwarding address in the Type 5 LSA is unreachable.. A Type 5 LSA with an unreachable forwarding address will not be used to install a route, even though the LSA is present in the OSPF database. The forwarding address must be reachable via an intra-area or inter-area route for the LSA to be considered valid for route installation.

Answer

The Type 5 LSA is being filtered by an OSPF export policy on the ABR.

Answer

The Type 5 LSA is not allowed in area 1 because it is a stub area.

Answer

The OSPF route preference is higher than the preference of another routing protocol.