Nokia 4A0-113 - Nokia OSPF Routing Protocol Exam

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:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF vs. IS-IS Comparison):

C (Correct):

“Both OSPF and IS-IS support hierarchical design through the use of areas (OSPF Area 0 backbone; IS-IS Level 1/Level 2 hierarchy).”

D (Correct):

“Both protocols support variable length subnet masks (VLSM) and Classless Inter-Domain Routing (CIDR).”

Incorrect options:

A: Both use cost-based metrics, not hop count.

B: Both protocols converge quickly (they are link-state protocols).

E: IS-IS uses Layer 2 (CLNS) for communication, not Layer 3 multicast.

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These answers are fully in line with Nokia’s official service router certification curriculum.

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 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:

From Nokia 7750 SR OS Routing Protocols Guide (OSPF and IS-IS LSA Aging Rules):

A (Correct): OSPF starts LSAs with age 0, IS-IS starts with age 1200 seconds.

C (Correct): LSA/LSP age is incremented both during database retention and while being flooded.

Thus, correct answers are A and C.

Comprehensive and Detailed Explanation From Exact Extract:

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

An ASBR can exist in any OSPF area — including stub or NSSA areas.

There is no requirement that an ASBR be directly connected to area 0.

Thus, correct answer: B (False).

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According to the official Nokia exam prep documentation for classful routing logic (mirrored in the Nokia 4A0‑101 study guide), routers R1, R2, and R3 run a classful routing protocol. When R1 advertises its directly connected subnets 10.1.1.0/24 and 10.1.2.0/24, the classful nature of the protocol means the subnet mask is not included in the update. The entire classful network portion is advertised instead. Since both your /24s fall within the same Class A network (10.0.0.0/8), router R3 does not distinguish the smaller subnets; it only learns the classful network 10.0.0.0/8.

From the guide:

“Routers R1, R2, and R3 are running a classful routing protocol. Router R1 advertises the directly connected networks 10.1.1.0/24 and 10.1.2.0/24. In router R3's routing table, these networks will be represented by a single entry of 10.0.0.0/8.”

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:

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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