JNCIS-ENT OSPF Practice Test 4 — 15 Questions

Question 1

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 2

During OSPF database synchronization, two Junos routers exchange Database Description (DBD) packets. One router repeatedly sends DBD packets with the master/slave bit set incorrectly or encounters sequence number mismatches, causing the adjacency to loop in the Exchange state. Which OSPF packet type is immediately sent by a router to request missing link-state information once the ExStart/Exchange transition completes?

Accepted Answer

Link-State Request (Type 3). Once the ExStart/Exchange transition completes, a router sends Link-State Request (Type 3) packets to request specific link-state advertisements (LSAs) that are missing or outdated. This occurs after the Database Description exchange, where routers identify which LSAs they need. The Link-State Request is used to request the full LSA from the neighbor.

Answer

Hello (Type 1)

Answer

Database Description (Type 2)

Answer

Link-State Update (Type 4)

Question 3

What is the primary function of the OSPF Designated Router (DR) on a broadcast network segment?

Accepted Answer

To minimize the number of adjacencies and LSA flooding traffic on a multi-access segment. The DR reduces network traffic and LSA flooding overhead by acting as a central focal point for exchanging routing information and generating the Network LSA (Type 2) on multi-access segments.

Answer

To translate Type 7 LSAs into Type 5 LSAs for the backbone

Answer

To authenticate OSPF hello packets across interfaces

Answer

To act as the sole exit gateway for all external traffic in the AS

Question 4

An enterprise network runs OSPF across multiple areas. A Junos routing device receives an LSA with an aging timer approaching MaxAge (3600 seconds). Under what condition does a router purge or flush an LSA from its link-state database?

Accepted Answer

When the LSA reaches 3600 seconds (MaxAge) and is flooded across the area to flush it. An LSA is purged or flushed from the link-state database when it reaches MaxAge (3600 seconds). At that point, the router floods the LSA with the MaxAge timer set across the area to ensure all routers remove it from their databases. This is part of OSPF's aging mechanism to remove stale LSAs.

Answer

When the SPF algorithm recalculates the routing table

Answer

When a hello packet is missed three times consecutively

Answer

When the OSPF dead timer expires on the local interface

Question 5

You are troubleshooting an OSPF network and notice that a router's OSPF state is stuck in 'ExStart'. What is the most common reason for this adjacency state issue?

Accepted Answer

An MTU mismatch between the neighboring OSPF interfaces. OSPF adjacency stuck in ExStart is almost always caused by an MTU mismatch between the two neighbors. During ExStart, routers exchange DBD packets to elect a master/slave and agree on the initial sequence number; if the interface MTUs differ, the larger DBD packets are dropped, and the routers keep retransmitting without progressing to Exchange. This is the classic ExStart/Exchange hang.

Answer

Duplicate OSPF router IDs in the network

Answer

Different authentication passwords on the links

Answer

A mismatch in the OSPF area ID configuration

Question 6

Which command is used on a Junos device to clear the OSPF database and force a re-synchronization with neighbors?

Accepted Answer

clear ospf database. The 'clear ospf database' command clears the OSPF link-state database and forces the router to re-synchronize with its neighbors by re-exchanging LSAs. This is used to recover from database corruption or to force a refresh. It does not reset the OSPF process itself.

Answer

restart ospf-protocol

Answer

clear ospf neighbor

Answer

reset routing-protocol ospf

Question 7

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 8

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?

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 9

Which Junos command displays detailed information about OSPF neighbor states, including dead timer countdowns and address bindings?

Accepted Answer

show ospf neighbor detail. The command 'show ospf neighbor detail' displays comprehensive information about each OSPF neighbor, including neighbor state (Full, 2-Way, etc.), neighbor ID, interface address, dead timer countdown, and area. This is the go-to command for verifying adjacency health and troubleshooting OSPF neighbor issues on Junos devices.

Answer

show ospf statistics

Answer

show route table inet.0

Answer

show ospf database detail

Question 10

Which TWO states are valid OSPF operational adjacency states seen in Junos operational outputs? (Choose two)

Accepted Answer

2-Way. Option A (2-Way) is correct because in OSPF, 2-Way is a valid adjacency state where bidirectional communication between two routers is confirmed; on broadcast and NBMA networks, routers remain in 2-Way with non-DR/BDR neighbors, and it appears in Junos outputs such as 'show ospf neighbor'. Option D (Full) is correct because Full is the final OSPF adjacency state, indicating that the link-state databases of the two routers are fully synchronized, and it is likewise displayed in Junos operational output. The unmarked options do not belong: Listen is an OSPF interface state (not an adjacency/neighbor state), Connected is not an OSPF state at all, and Active is not a valid OSPF neighbor state (it is associated with other protocols such as EIGRP or PIM).

Answer

Listen

Answer

Connected

Answer

Active

Question 11

Which TWO actions occur during OSPF link-state database flooding on a Junos routing device? (Choose two)

Accepted Answer

The router updates its link-state database (LSDB) with the received LSA and acknowledges it.. Option D is correct because when a Junos router receives an LSA during OSPF flooding, it installs the LSA into its link-state database (LSDB), runs the SPF algorithm if the topology changed, and sends a Link State Acknowledgment back to the sender to confirm reliable receipt. Option E is correct because OSPF flooding requires the router to forward (flood) the received LSA out all other OSPF-enabled interfaces in the same area, excluding the interface on which the LSA was received, so that every router in the area maintains an identical LSDB. Option A is wrong because OSPF LSAs are never converted into BGP path attributes; OSPF and BGP are separate protocols with independent databases and attributes. Option B is wrong because flooding an LSA does not cause static routes to be deleted from the routing table. Option C is wrong because OSPF flooding does not reset all neighbor adjacencies on the device; adjacencies remain up and only the LSDB is updated and the LSA is re-flooded.

Answer

The router converts the link-state database into BGP path attributes.

Answer

The router immediately deletes all static routes from the routing table.

Answer

The router resets all active neighbor adjacencies across the entire device.

Question 12

Which TWO features characterize OSPFv3 compared to OSPFv2? (Choose two)

Accepted Answer

OSPFv3 router IDs remain 32-bit unsigned integers, formatted identically to IPv4 addresses.. Option B is correct because OSPFv3, like OSPFv2, still uses a 32-bit unsigned router ID that is written in dotted-decimal IPv4 format, even though OSPFv3 runs over IPv6; the router ID is not an IPv6 address. Option D is correct because OSPFv3 forms adjacencies and sends hello packets using IPv6 link-local addresses (fe80::/10) on each interface, which is a key operational difference from OSPFv2's use of interface IPv4 addresses. Option A is incorrect because OSPFv3 does not exclusively use MD5 in the OSPF header; it relies on IPv6 IPsec (AH/ESP) for authentication, and later RFCs also define OSPFv3 authentication trailer options. Option C is incorrect because OSPFv3 still requires a backbone area, Area 0, for multi-area topologies just like OSPFv2. Option E is incorrect because OSPFv3 dynamically learns inter-area routes through LSAs and the SPF calculation; it does not require manual static routes for inter-area paths.

Answer

OSPFv3 exclusively uses MD5 authentication embedded in the OSPF packet header.

Answer

OSPFv3 eliminates the need for Area 0 in multi-area topologies.

Answer

OSPFv3 requires manual static routing for all inter-area paths.

Question 13

An administrator wants to configure an OSPF Not-So-Stubby Area (NSSA) on a Junos router. Which THREE characteristics distinguish an NSSA from a standard OSPF Stub Area? (Choose three)

Accepted Answer

An NSSA blocks incoming Type 5 AS-external LSAs from the backbone area.. Option A is correct because, like a standard stub area, an NSSA blocks Type 5 AS-external LSAs from entering the area from the backbone, keeping the area's LSDB free of external routes. Option C is correct because the defining feature of an NSSA is that routers within it can originate external routes as Type 7 NSSA-external LSAs, which is not permitted in a standard stub area. Option D is correct because the NSSA ABR translates those Type 7 LSAs into Type 5 LSAs before flooding them into the backbone, allowing external reachability to propagate beyond the NSSA. Option B is wrong because NSSA is an area-type attribute and has nothing to do with automatically converting internal links to broadcast point-to-multipoint networks. Option E is wrong because an NSSA can support multiple ABRs; there is no such prohibition.

Answer

An NSSA automatically converts all internal links into broadcast point-to-multipoint networks.

Answer

An NSSA is prohibited from supporting multiple ABRs.

Question 14

A network engineer wants to inject external routes into an OSPF domain using Junos OS. The routes originate from an external BGP process. Which OSPF LSA type is generated by the ASBR to describe these external destinations?

Accepted Answer

Type 5 AS-external LSA. When an ASBR redistributes external routes (such as those learned via BGP) into an OSPF domain, it originates a Type 5 AS-external LSA to describe each external destination. Type 5 LSAs are flooded throughout the OSPF area (except stub/NSSA areas) and carry the external metric and forwarding address. This is the standard mechanism for injecting non-OSPF routes into OSPF.

Answer

Type 7 NSSA LSA

Answer

Type 3 Summary LSA

Answer

Type 4 Summary LSA

Question 15

You are configuring OSPF on a Junos device and notice that Type 3 LSAs are not being generated or propagated into a specific area. When examining the configuration under protocols ospf, you see that the area is defined with the no-summaries parameter. Which area type has been configured?

Accepted Answer

Totally Stubby Area. In Junos OS, the 'no-summaries' parameter under 'set protocols ospf area' defines a Stub area as a totally stubby area, which suppresses Type 3 summary LSAs from being injected into the area by the ABR.

Answer

Not-So-Stubby Area (NSSA)

Answer

Transit Area

Answer

Standard OSPF Area