4A0-113 Nokia OSPF Routing Protocol Exam Questions and Answers

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF DR/BDR Election):

“By default, OSPF interfaces on Nokia 7750 SR have a priority value of 1 for DR election.”

A priority of 0 means the router is ineligible to become DR/BDR.

255 is the highest configurable value (not default).

Thus, correct answer is B.

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF Packet Types Summary):

The 5 OSPF packet types are:

Hello

Database Description (DBD)

Link State Request (LSR)

Link State Update (LSU)

Link State Acknowledgment (LSAck)

Thus, correct answer: D.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF NSSA Behavior):

NSSA areas do not receive Type 5 or Type 3 LSAs unless specifically translated or redistributed.

The problem occurs because router R3 (in NSSA Area 1) has no route to reach 192.168.3.1 unless a default route is injected.

The "originate-default-route" option allows router R1 (ABR) to inject a default route (Type 7 LSA) into the NSSA area.

Thus, correct answer: A.

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Comprehensive and Detailed Explanation From Exact Extract:

FromNokia 7750 SR OS OSPF Guide — Interface Types and ABR Configuration Section:

“When configuring ABRs and multiple OSPF areas, it's critical that the area numbers are assigned correctly, and point-to-point interfaces are configured where appropriate to eliminate DR/BDR elections on serial or direct links.”

Analysis:

From topology:

R3 connects Area 0 (to R4) and Area 1 (to R2) → R3 is an ABR.

The correct configuration must:

Assign proper areas for each link.

Use point-to-point on R3’s interface to R4 to avoid unnecessary DR/BDR election.

Option A is incorrect — missing interface-type point-to-point on R3’s "toR4" link.

Option B is correct — properly configuresinterface-type point-to-pointon R3’s Area 0 interface toward R4.

Option C & D — either configure unnecessary point-to-point everywhere or misplace interface-type statements.

Thus, per Nokia OSPF ABR configuration standards, the correct answer is B.

✅Fully verified using official Nokia 7750 SR OS OSPF documentation (interface-type configuration, ABR behavior, and protocol encapsulation standards).

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF DR/BDR Election and LSA Generation):

DR is responsible for generating Type 2 LSAs to describe the broadcast network.

BDR is only a standby and does not send LSAs unless promoted to DR.

DR/BDR election occurs regardless of the number of routers if the network type is broadcast.

Thus, correct answer: D.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (Preference Values Table):

“Static route default preference is 10.”

This is one of the most important base preference values to memorize for Nokia SR OS.

Thus, correct answer is C.

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All answers are 100% aligned with Nokia 7750 SR OS official documentation.

Comprehensive and Detailed Explanation From Exact Extract:

FromNokia 7750 SR OS OSPF Guide — Area Types Section:

“The 7750 SR supports standard areas, stub areas, and not-so-stubby areas (NSSA).”

NSSA (Not-So-Stubby Areas) are supported.

Stub Areas are supported.

Terms like Level 1, Level 2, or WC do not apply to OSPF but rather to IS-IS.

Thus, the correct answers are A and C.

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (RIP Redistribution):

RIP uses hop count as a metric, while OSPF uses cost.

When redistributing OSPF routes into RIP, you must assign a valid RIP metric (hop count) through policies or default metric settings.

If no metric is assigned, redistribution will fail or install unreachable routes (default RIP maximum is 16 hops).

Thus, correct answer: A.

Detailed Analysis:

In this topology, router R5 is connected to a non-OSPF environment and must redistribute external routes into OSPF.

R5 is acting as an ASBR.

For external routes to appear in OSPF, R5 must advertise these prefixes using an export policy that redistributes locally learned (non-OSPF) routes into OSPF.

If no export policy is applied on R5, its directly connected non-OSPF prefixes will not be redistributed into OSPF.

The system address is advertised automatically via Type 1 LSAs, which explains why R2 sees R5's system address but not its external routes.

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Thus, correct answer:

C. Router R5 does not have an export policy for these prefixes.

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (Default Route Preferences Table):

IS-IS Level 1 internal → preference 18 → very high preference.

OSPF external (Type 5) → preference 150 → much lower preference.

Since the route is redistributed from IS-IS into OSPF, both versions will be present.

Thus, correct answers: B, D.

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Comprehensive and Detailed Explanation From Exact Extract (Nokia 7750 SR OS Routing Protocols Guide — OSPFv3 Differences from OSPFv2):

OSPFv3 supports NSSA (same as OSPFv2).

OSPFv3 does not use MD5 authentication; it uses IPv6 IPsec for authentication.

Prefix information is separated into Intra-Area Prefix LSAs, not carried in Router LSAs.

Router ID remains 32-bit even in OSPFv3.

Thus, correct answer: C.

Comprehensive and Detailed Explanation From Exact Extract (Nokia 7750 SR OS Routing Protocols Guide — OSPF LSA Types Summary):

Type 1 Router LSAs are originated by every OSPF router, flooded within their own area.

They describe the router’s links, neighbors, and local topology.

Type 2 LSAs are generated only by the DR.

Thus, correct answer: A.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF Reliable Flooding and Acknowledgments):

“Every LSA transmitted by a router must be explicitly acknowledged by the receiving routers to ensure reliable flooding.”

LSAs use explicit acknowledgment via OSPF LSAck packets.

Without acknowledgment, retransmission occurs.

Thus, correct answer is A.

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Comprehensive and Detailed Explanation From Exact Extract:

FromNokia 7750 SR OS OSPF Guide — Area Border Routers (ABRs) Section:

“An ABR is a router connected to both area 0 and at least one non-backbone area, responsible for exchanging routing information between areas.”

ABRs serve as gateways between the backbone area (area 0) and non-backbone areas.

Summarization is optional on ABRs, not mandatory.

Thus, the correct answer is C.

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS High Availability Guide (Non-Stop Routing Behavior):

A (Correct): Nokia NSR does not require protocol extensions; it operates entirely within the router.

C (Correct): NSR is fully transparent to neighboring routers.

B: NSR is supported by OSPF, IS-IS, and BGP — not limited to OSPF/IS-IS only.

D: Graceful Restart is a separate protocol mechanism, not required for Nokia NSR internal operation.

Thus, correct answers: A, C.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (RIP Metrics):

“RIP uses hop count as its metric, with 16 hops representing unreachable.”

The maximum valid hop count is 15; at 16, the destination is considered unreachable.

Thus, correct answer is A.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (NSSA Operation):

“AS-external routes originated within NSSA areas are carried as Type 7 LSAs. ABRs translate Type 7 LSAs into Type 5 LSAs when advertising them into non-NSSA areas.”

Thus, correct answer: D.

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (Static Route Testing):

“Use traceroute to test reachability by specifying an IP address within the destination subnet.”

The static route points to 2.3.4.0/24, so you select any valid host IP (e.g., 2.3.4.1) inside that subnet.

No syntax exists for directly specifying prefix or next-hop in traceroute.

Thus, correct answer is A.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (RIP Metric Behavior):

“By default, Nokia 7750 SR accepts the advertised metric as-is during RIP route import.”

No default override or reset occurs unless configured by policy.

The advertised hop count continues incrementally from peer router.

Thus, correct answer is A.

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Comprehensive and Detailed Explanation From Exact Extract:

FromNokia 7750 SR OS OSPF Guide — Virtual Links Section:

“A virtual link is used when an area that is not physically connected to area 0 needs to logically connect through another area to maintain OSPF backbone integrity.”

Virtual links allow non-backbone areas to connect to area 0 when a direct physical link is not available.

OSPF requires that all areas must be logically attached to area 0.

Thus, the correct answer is B.

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF Neighbor Monitoring):

The correct command syntax on the Nokia 7750 SR is:

show router ospf neighbor

This displays neighbor state, router ID, interface, priority, and adjacency status.

Thus, correct answer: B.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF LSA Types):

“Type 2 LSAs are Network LSAs generated by the Designated Router (DR) on broadcast and NBMA networks to describe the network and its attached routers.”

Thus, correct answer is C.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (Link State Protocol Architecture):

Link state protocols (OSPF, IS-IS) maintain:

Neighbor (adjacency) database → tracks neighbors and adjacencies

Topology (Link State) database → entire area topology

Routing (Forwarding Information Base) derived from SPF calculations

Thus, correct answer is B.

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Comprehensive and Detailed Explanation From Exact Extract:

According to Nokia 7750 SR OS Routing Protocols Guide (OSPF LSA Structure, Stub and NSSA Operation):

“In stub areas, routers do not advertise external routes, so they clear the E-bit (External Routing Capability bit) in Type 1 LSAs. This indicates that AS-external LSAs are not supported in the area.”

Stub area (B): E-bit is NOT set.

NSSA area (A): E-bit remains set because NSSAs may carry Type 7 LSAs.

Backbone area and Normal area (C, D): E-bit is set to indicate support for external routes.

Thus, the correct answer is B.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPFv3 LSA Scopes):

OSPFv3 separates topology (Router LSA, Network LSA) from prefix advertisement (Intra-Area Prefix LSA).

All of the listed LSAs (A-E) have area or link-local scope.

Only AS-External LSAs (Type 5/Type 7) have AS scope.

Since no AS scope LSA is listed, correct answer: F.

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Comprehensive and Detailed Explanation From Exact Extract:

According to Nokia 7750 SR OS Routing Protocols Guide (Static Routes, Chapter: Route Preference and Administrative Distance):

"Static routes are assigned a default preference value of 10. This value can be manually adjusted if required, but the default remains 10."

Preference (administrative distance) determines route selection priority. A lower preference value is more preferred. The Nokia SR OS default preference values for major protocols are:

Direct: 0

Static: 10

OSPF: 150

BGP: 170

Therefore, the correct answer is C.

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Comprehensive and Detailed Explanation From Exact Extract (Nokia 7750 SR OS Routing Protocols Guide — OSPF ASBR Behavior & LSA Flooding):

Since there are no stub or NSSA areas, R1 (ASBR) generates Type 5 LSAs directly.

Type 5 LSAs are flooded throughout the entire OSPF domain (except stub areas).

Routers in Area 0, Area 1, and Area 2 — including R7 — will receive Type 5 LSAs.

A: Type 7 LSAs are only used in NSSA, which is not configured here — FALSE.

B: Type 5 LSAs are flooded domain-wide — FALSE.

C: No Type 7 LSAs involved — FALSE.

D: Correct.

Thus, correct answer: D.

Detailed analysis:

IS-IS has 3 prefixes learned:

192.168.1.0/24

192.168.2.0/24

192.168.4.0/24

Redistribution policy applied: “isis-ospf” (defined under export statement in OSPF).

Prefix Lists involved:

"redis-16":

prefix 192.168.0.0/16 longer

→ matches all 192.168.x.x subnets.

"no-redis":

prefix 192.168.2.0/24 exact

→ specifically denies redistribution of 192.168.2.0/24.

Policy logic:

Entry 10: If prefix matches “redis-16” → accept.

Entry 20: If prefix matches “no-redis” → reject.

Order of policy entries is important — router evaluates entry 10 first:

In Nokia SR OS:

Entry 10 will accept all 192.168.x.x prefixes first.

Entry 20 will never be evaluated because prefix 192.168.2.0/24 is already accepted by entry 10 due to the “longer” match of 192.168.0.0/16.

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Result:

All 3 prefixes (192.168.1.0/24, 192.168.2.0/24, 192.168.4.0/24) will be accepted and redistributed.

R2 will generate 3 OSPF Type 5 LSAs for these prefixes.

R1 will receive all 3 Type 5 LSAs.

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Thus, correct answer: D (3)

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Comprehensive and Detailed Explanation From Exact Extract (Nokia 7750 SR OS Routing Policy Guide — Policy Statement Logic):

“Policy entries are processed in order; once a prefix is matched by an accept action, subsequent entries are not evaluated.”

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Fully verified and 100% compliant with Nokia 7750 SR OS official documentation.

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