JNCIS-ENT OSPF — 30 Questions

Question 1

An engineer needs to prevent Type 4 and Type 5 LSAs from entering a specific OSPF area while still allowing external routes to be summarized via default routing. Which area type should be configured?

Accepted Answer

Totally Stubby Area. A Totally Stubby Area (TSA) blocks Type 3, 4, and 5 LSAs from entering the area, and the ABR injects a single default route (Type 3) into the area. This prevents Type 4 (ASBR Summary) and Type 5 (AS-external) LSAs from flooding in, while still allowing external reachability via the default route. This is exactly what the question describes.

Answer

Standard OSPF Area

Answer

Not-So-Stubby Area (NSSA)

Answer

Standard Stub Area

Question 2

You are configuring an OSPF interface on a Junos router and want to ensure that the interface never participates in DR/BDR election, always acting as a point-to-point connection. Which interface type should you explicitly configure?

Accepted Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 interface-type p2p. Setting the OSPF interface-type to 'p2p' forces the interface to operate as point-to-point, which by definition does not participate in DR/BDR election and sends LSAs without network mask information. This is the explicit Junos configuration to achieve the stated requirement. The 'interface-type p2p' statement under the OSPF interface hierarchy is the correct syntax.

Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 passive

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set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 point-to-multipoint

Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 no-dr-election

Question 3

You need to configure an OSPF interface as passive on a Junos routing platform so that it advertises connected subnets without sending OSPF hello packets. Which configuration command achieves this?

Accepted Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/1.0 passive. In Junos, an OSPF interface is marked passive by using the 'passive' statement under the specific OSPF interface configuration block.

Answer

set protocols ospf disable-adjacency interface ge-0/0/1.0

Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/1.0 no-hellos

Question 4

An OSPF network running on Junos has multiple equal-cost paths to a destination. By default, how many equal-cost paths does Junos OSPF install into the forwarding table (inet.0)?

Accepted Answer

16. By default, Junos OSPF installs up to 16 equal-cost next-hops into the inet.0 forwarding table for a given destination. This is controlled by the 'maximum-paths' setting under the OSPF protocol configuration, and 16 is the default value on most Junos platforms.

Answer

1

Answer

32

Answer

4

Question 5

An administrator needs to modify the OSPF cost on a specific Junos interface to influence traffic engineering without changing the reference bandwidth globally. Which command accomplishes this?

Accepted Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/2.0 metric 50. In Junos OSPF, the per-interface cost is set with the 'metric' statement under the OSPF interface hierarchy, not 'cost'. The command 'set protocols ospf area 0.0.0.0 interface ge-0/0/2.0 metric 50' correctly overrides the default cost for that interface without changing the global reference bandwidth. This influences SPF path selection for traffic engineering.

Answer

set protocols ospf area 0.0.0.0 interface ge-0/0/2.0 cost 50

Answer

set protocols ospf reference-bandwidth 10g

Answer

set interfaces ge-0/0/2.0 ospf-cost 50

Question 6

You need to verify the router ID elected by OSPF on a Junos routing device. Which operational command provides this information quickly?

Accepted Answer

show ospf overview. The 'show ospf overview' command on Junos displays the OSPF router ID along with other global OSPF parameters such as area information, SPF timers, and reference bandwidth. It is the quickest single command to verify the elected router ID because it summarizes the OSPF instance state at a glance. The router ID is chosen as the highest loopback address, or highest interface address if no loopback exists, unless explicitly configured.

Answer

show system router-id

Answer

show route summary

Answer

show ospf interface detail

Question 7

An enterprise network has redundant ABRs connecting Area 1 to Area 0. To prevent suboptimal routing and unnecessary Type 3 LSA flooding, an administrator decides to filter inter-area summary routes on the ABR using a Junos policy. Which configuration component is required to apply an export policy to OSPF summary routes on an ABR?

Accepted Answer

set protocols ospf area 0.0.0.1 prefix-export . On Junos, inter-area summary LSAs (Type 3) generated by an ABR are controlled by the area-level prefix-export statement, not by the global OSPF export policy. The command 'set protocols ospf area 0.0.0.1 prefix-export ' attaches a policy that filters which prefixes from other areas are summarized into the specified area. This is the only mechanism that specifically targets Type 3 LSA generation on an ABR.

Answer

set protocols ospf import <policy-name>

Answer

set routing-options export <policy-name>

Answer

set protocols ospf export <policy-name>

Question 8

What information is contained within an OSPF Type 1 (Router LSA)?

Accepted Answer

The router's active interfaces, interface types, costs, and neighbor states within an area. An OSPF Type 1 (Router LSA) contains information about the router's active interfaces, interface types (e.g., point-to-point, broadcast), costs, and neighbor states within a specific area. It is flooded within an area and used to build the shortest path tree. Each router generates a Type 1 LSA for each area it belongs to.

Answer

Summary prefixes imported from external autonomous systems

Answer

Inter-area summary routes generated by ABRs

Answer

Networks attached to a designated router on a broadcast segment

Question 9

You are configuring OSPF redistribution on a Junos router and want to ensure that external routes imported from a static routing table retain an escalating external metric. Which external route metric type (E1 or E2) should you choose if you want the internal cost to be added to the external cost during path selection?

Accepted Answer

Type 1 (E1). In OSPF, external routes can be advertised as Type 1 (E1) or Type 2 (E2). E1 routes have a metric that is the sum of the external cost and the internal cost to reach the ASBR. E2 routes have a metric that is only the external cost, and internal cost is not added. Therefore, to have the internal cost added to the external cost during path selection, you should choose Type 1 (E1).

Answer

Type 7 (NSSA)

Answer

Type 3 (E3)

Answer

Type 2 (E2)

Question 10

A Junos router running OSPF is configured with graceful restart helper mode enabled. What is the primary role of an OSPF graceful restart helper router during a control plane restart of a neighboring router?

Accepted Answer

To maintain neighbor adjacencies and continue forwarding packets without recalculating the SPF tree while the neighbor restarts. The primary role of an OSPF graceful restart helper router is to maintain neighbor adjacencies and continue forwarding packets without recalculating the SPF tree while the neighboring router restarts its control plane. This allows the restarting router to re-establish OSPF sessions without disrupting traffic, as the helper router assumes the restarting router's forwarding state remains valid.

Answer

To translate Type 7 LSAs into Type 5 LSAs during the helper window

Answer

To purge all LSAs originated by the restarting router from the LSDB

Answer

To take over the role of Designated Router immediately upon detecting control plane failure

Question 11

Which TWO statements correctly describe OSPF Area Border Routers (ABRs) in a Junos environment? (Choose two)

Accepted Answer

An ABR maintains a separate link-state database for each area to which it connects.. Option B is correct because an OSPF ABR, by definition, has interfaces in multiple areas and therefore runs a separate link-state database (LSDB) per attached area, synchronizing LSAs only within each area. Option D is correct because in standard OSPF design an ABR must have at least one interface in Area 0 (the backbone); it connects non-backbone areas to the backbone and generates Type 3 summary LSAs between them. Option A is wrong because generating Type 3 summary LSAs is precisely a core ABR function, not a prohibition. Option C is wrong because ABRs do not convert Type 5 external LSAs into Type 1 router LSAs; Type 5 LSAs are flooded by ASBRs, and Type 1 LSAs describe routers within an area. Option E is wrong because an ABR and an ASBR are distinct roles, and a router is not exclusively an ASBR merely by being an ABR.

Answer

An ABR is prohibited from generating Type 3 summary LSAs.

Answer

An ABR automatically converts all Type 5 LSAs into Type 1 LSAs.

Answer

An ABR functions exclusively as an Autonomous System Boundary Router (ASBR).

Question 12

Which TWO criteria are used by Junos OS to select the OSPF router ID if no explicit router ID is configured under [edit routing-options]? (Choose two)

Accepted Answer

The highest IPv4 address configured on any active physical interface. Junos OS selects the OSPF router ID without an explicit [edit routing-options] router-id by first preferring the highest IPv4 address configured on an active loopback interface (lo0), which is option B, because loopback addresses are stable and always up. If no loopback address is available, it falls back to the highest IPv4 address on any active physical interface, which is option A. Options C, D, and E are incorrect because Junos does not use the lowest transit-interface address, the management interface MAC address, or the BGP AS number for OSPF router ID selection.

Answer

The lowest IPv4 address configured on a transit interface

Answer

The lowest MAC address assigned to the management interface (fxp0)

Answer

The router's configured BGP Autonomous System number

Question 13

Which THREE LSA types are blocked from entering a standard OSPF Stub Area? (Choose three)

Accepted Answer

Type 4 (ASBR summary LSAs). In a standard OSPF stub area, the ABR blocks Type 5 (AS-external LSAs), so option C is correct because external routes are not flooded into the stub area; instead the ABR injects a default route. Option A is correct because Type 4 (ASBR summary LSAs) are also blocked, since without Type 5 externals there is no need to advertise a route to an ASBR inside the stub area. Option E is correct because Type 7 (NSSA external LSAs) are not allowed in a standard stub area — Type 7 LSAs exist only in NSSAs, and a standard stub area does not permit them. Options B and D are incorrect because Type 1 (Router LSAs) and Type 2 (Network LSAs) are still flooded within the stub area to build the intra-area topology. Thus the three blocked LSA types are Type 4, Type 5, and Type 7.

Answer

Type 1 (Router LSAs)

Answer

Type 2 (Network LSAs)

Question 14

Which THREE conditions must match between neighboring OSPF routers for an adjacency to successfully transition from Init to ExStart/Exchange? (Choose three)

Accepted Answer

Subnet mask and network prefix length. To progress past the Init state and establish an adjacency, neighbors must agree on the Area ID, Hello/Dead intervals, and authentication credentials. Subnet mask/network matching is also required.

Question 15

Which TWO packet types are utilized during the OSPF database synchronization process after neighbor adjacencies are established? (Choose two)

Accepted Answer

Database Description (DBD) packets. Database Description (DBD) packets (option C) are correct because they are exchanged during the OSPF database synchronization phase to summarize the contents of the link-state database, allowing routers to determine which LSAs they need from each other. Link-State Request (LSR) packets (option E) are also correct because after comparing DBD summaries, a router sends LSRs to explicitly request the specific LSAs it is missing or has stale. Link-State Acknowledgment (LSAck) packets (option A) are used to acknowledge receipt of LSAs, but they are not one of the two packet types specifically asked for in the database synchronization exchange described here. Routing Information Protocol (RIP) updates (option B) are irrelevant because RIP is a separate distance-vector routing protocol and does not participate in OSPF synchronization. Hello packets (option D) are used to discover neighbors and maintain adjacencies, which occurs before the database synchronization process, not during it.

Answer

Link-State Acknowledgment (LSAck) packets

Answer

Routing Information Protocol (RIP) updates

Answer

Hello packets

Question 16

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 17

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 18

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 19

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 20

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