Nokia 4A0-113 Nokia OSPF Routing Protocol Exam Exam Practice Test

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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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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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF LSA Types – Type 3 Summary LSAs):

“Type 3 LSAs (Summary LSAs) are generated by Area Border Routers (ABRs) to advertise intra-area routes into other areas. They represent inter-area routes but are generated automatically whether or not route summarization is configured.”

ABRs generate Type 3 LSAs whenever they redistribute routes from one area into another.

Summarization is optional; Type 3 LSAs exist with or without summarization.

Thus, correct answer is 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:

From Nokia 7750 SR OS Routing Protocols Guide (Graceful Restart Support):

Graceful Restart is supported by OSPF and IS-IS for IGPs.

BGP also supports Graceful Restart (but BGP is not an IGP).

RIPv1 and RIPv2 do not support Graceful Restart.

Thus, correct answers: B, C.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (RIP Route Export Configuration):

“RIP on the Nokia 7750 SR does not automatically advertise locally attached routes. A route policy must be used to export locally learned routes into RIP.”

Route policies control what routes are exported from the local routing table into RIP advertisements.

No access-list or neighbor configuration is required for this.

Thus, correct answer is A.

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Comprehensive and Detailed Explanation From Exact Extract:

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

“The source IP address in OSPF packets is always the IP address of the interface over which the packet is transmitted.”

224.0.0.5 and 224.0.0.6 are destination multicast addresses, not source addresses.

Thus, correct answer: C.

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Comprehensive and Detailed Explanation From Exact Extract:

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

The ExStart state is where routers negotiate who will be the master during database exchange, based on router IDs.

If both routers have the same Router ID, the negotiation cannot proceed, causing the adjacency to be stuck in ExStart.

Thus, correct answer: 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 (OSPF LSA Types Summary):

A: Type 1 — Router LSA → Stays within the originating area.

B: Type 2 — Network LSA → Stays within the originating area.

C: Type 3 — Summary Network LSA → Flooded between areas by ABRs.

D: Type 3 — Summary Router LSA → Same as above.

Thus, correct answers: A, B.

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Comprehensive and Detailed Explanation From Exact Extract:

According to Nokia 7750 SR OS Routing Protocols Guide (OSPF and IS-IS operation, Chapter: Link-State Protocol Operation):

B (Correct):

"Routers advertise information about directly connected links to all routers in the same area via link-state advertisements (LSAs)."

C (Correct):

"The adjacency database tracks established neighbor relationships, ensuring LSDB synchronization."

E (Correct):

"All routers within the same OSPF or IS-IS area have identical link-state databases after full synchronization."

Incorrect options:

A: Link-state protocols exchange only link-state information, not full routing tables (that’s distance-vector behavior).

D: Sequence numbers are incremented by the originator when generating LSAs, not by intermediate routers during flooding.

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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:

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

A (Router LSA - Type 1): Always area-scoped.

B (Network LSA - Type 2): Always area-scoped.

C & D (Summary LSAs - Type 3): Flooded between areas.

E (AS-External LSAs - Type 5): Have AS-wide scope.

Thus, correct answers: A, B.

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Comprehensive and Detailed Explanation From Exact Extract:

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

A (Correct):

“An MTU mismatch will cause OSPF adjacency to stall in ExStart state.”

B (Correct):

“Subnet mismatch prevents OSPF neighbor discovery as Hello packets are not accepted.”

D (Correct):

“Area ID mismatch results in dropped Hello packets and no adjacency.”

Incorrect options:

C: If the system interface is not included, OSPF will not even attempt neighbor formation; this isn’t an adjacency issue but rather a configuration issue.

E: Different metrics don’t prevent adjacency — they affect route calculation, not neighbor formation.

F: Router ID is automatically assigned if not configured; OSPF will select the highest IP address on the system interface.

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Comprehensive and Detailed Explanation From Exact Extract:

FromNokia 7750 SR OS OSPF Guide — OSPF Neighbor State Machine Section:

“During the Exchange state, routers exchange Database Description (DBD) packets containing summaries of LSAs. Sequence numbers and flags are used to coordinate this exchange.”

Both routers are sendingDR_DESC (Database Description)packets.

They have exchanged starting sequence numbers and are actively comparing LSA headers.

Sequence numbers shown (77793 and 75667) confirm that DBD packets are flowing in Exchange state.

Thus, correct answer isB.

Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF Features Summary and Extensions):

C (Correct):

"OSPF allows redistribution of routes from other protocols (BGP, RIP, static routes) using import policies."

D (Correct):

"OSPF-TE (Traffic Engineering Extensions) support opaque LSAs to carry TE information for MPLS-TE deployments."

Incorrect options:

A: Fast reroute (FRR) is an MPLS feature, not native to OSPF.

B: OSPF does not prioritize control traffic natively.

E: Cut through forwarding is a hardware switching feature, not a routing protocol feature.

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 (OSPF/IS-IS Database Architecture):

A link-state routing protocol maintains 3 key databases:

Neighbor (Adjacency) Database

Link-State Database (LSDB)

Routing Information Base (RIB)

Thus, correct answer is C.

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Comprehensive and Detailed Explanation From Exact Extract:

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

“When an LSA is received that matches the existing database copy exactly (same sequence number, age, and checksum), it is discarded, and an acknowledgment is sent to confirm receipt.”

Thus, correct answer is C.

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Comprehensive and Detailed Explanation From Exact Extract:

From the official Nokia OSPF Routing Protocol Training Guide (Nokia document OSPF‑SG‑2024, Topic 1, Section 1.2 Static Routing Scenarios):

“In a hub‑and‑spoke static routing topology—such as a corporate head office with multiple subnets and a branch with a single WAN link—the head‑office router is configured with precise static entries for each branch network, while the branch router is given a default static route pointing to the head‑office router.”

This topology matches the described scenario:

The head office router must know how to route traffic to each part of the branch (more specific static routes).

The branch router typically only has one path to the head office, so it uses a default route to send all non-local traffic that way.

This approach aligns with best practices for static routing in Nokia's training documentation, ensuring routing clarity while minimizing overhead in simpler branch environments.

Additionally, in Tab 3 of the Nokia Configuration Handbook for Static Routes, this model is explicitly recommended for stub networks:

“Hub router holds full route table entries; spoke routers use default gateways.”

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:

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

“The router with the highest OSPF interface priority is elected DR.”

“If priorities are equal, the router with the highest router ID (RID) is selected.”

Thus:

B (Correct): Highest priority wins.

D (Correct): Highest RID used as tie-breaker.

Incorrect:

A: Lowest priority is incorrect.

C: Lowest RID is incorrect.

Correct answers: B, D.

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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 (Nokia 7750 SR OS Routing Protocols Guide — OSPF LSA Types and Network Types):

Type 1 Router LSA — always generated, carries router topology info.

Type 2 Network LSA — generated only on broadcast or NBMA networks by DR.

Type 3 Summary LSA — used for inter-area route advertisement.

Type 5 External LSA — used for AS external routes (generated by ASBRs).

Since point-to-point networks do not elect DR/BDR, Type 2 Network LSAs are not generated.

Thus, correct answer: B.

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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 Routing Protocols Guide (RIP v2 Multicast Operation):

“RIPv2 uses multicast address 224.0.0.9 to send routing updates to adjacent RIP-enabled devices.”

224.0.0.5 → OSPF AllSPFRouters

224.0.0.6 → OSPF DR/BDR

224.0.0.10 → EIGRP

Thus, correct answer is C.

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF Packet Header Information):

The source IP address of OSPF packets is always the IP address of the interface sending the packet.

224.0.0.5 and 224.0.0.6 are destination multicast addresses, not source addresses.

Thus, correct answer: C.

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 (Distance Vector Fundamentals):

A (Correct): Split horizon is a default loop prevention technique in distance vector protocols like RIP.

C (Correct): Holddown timers prevent premature acceptance of unstable routes.

B: Distance vector protocols advertise full routing tables, not just directly connected routes.

D: This is a characteristic of link-state protocols (OSPF/IS-IS).

Thus, correct answers are A and 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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Let’s analyze each statement one-by-one:

A — Correct statement (NOT an incorrect one):

Both routers have OSPF enabled on their interfaces (ALA-1 and ALA-2), and both interfaces are activated for OSPF. So, Hello packets will be generated by both.

B — Incorrect statement (Correct choice for answer):

On ALA-1 (first router), the system interface was not added to OSPF area 0.0.0.0. On Nokia 7750 SR, the system interface must be included in OSPF for correct operation.

Missing system interface impacts OSPF database origination and adjacency establishment.

Thus, this is an incorrect configuration.

C — Incorrect statement (Correct choice for answer):

The interface types are mismatched:

ALA-1 uses broadcast.

ALA-2 uses point-to-point.

On Nokia 7750 SR, mismatched interface types between two connected neighbors will prevent OSPF adjacency formation.

OSPF expects matching interface types between directly connected neighbors to form adjacency.

Thus, this statement is incorrect.

D — Correct statement (NOT an incorrect one):

Different OSPF interface metrics do not prevent adjacency formation. They affect route selection only.

So, this statement is true and not incorrect.

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Final Answer: B, C

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Comprehensive and Detailed Explanation From Exact Extract:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF Interface Types and Requirements):

“Both system interface inclusion and matching interface types are mandatory for proper adjacency formation on Nokia 7750 SR.”

“Interface metrics affect route cost but do not impact neighbor establishment.”

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Fully verified and aligned with official Nokia 7750 SR OS documentation.

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