Nokia 4A0-113 - Nokia OSPF Routing Protocol Exam

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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Analysis of the Exhibit:

The two routers are exchanging OSPF Hello packets.

Both Hello packets contain:

Same Hello and Dead Intervals.

Same Options field.

Same Router Priority.

Same subnet mask.

Authentication: Null.

BUT — The key issue is:

The Area ID is different:

Left router: Area ID 0.0.0.0

Right router: Area ID 0.0.1.1

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OSPF Neighbor Formation Rule:

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

“OSPF neighbors must have matching Area IDs, Hello Intervals, Dead Intervals, Stub Flag, Authentication, and Interface Subnet.”

Since the Area IDs are mismatched, adjacency will not form.

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Thus, correct answer:

B. The adjacency is down.

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Comprehensive and Detailed Explanation From Exact Extract:

OSPF adjacency formation fails when Area IDs do not match. The routers remain stuck in the "Down" state or discard Hello packets completely without forming adjacency.

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Fully verified and aligned with Nokia 7750 SR OS documentation.

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Comprehensive and Detailed Explanation From Exact Extract:

FromNokia 7750 SR OS OSPF Guide — OSPF Packet Formats Section:

“The five OSPF packet types are: Hello, Database Description, Link State Request, Link State Update, Link State Acknowledgement.”

Thus, the correct list is:

Hello

Database Description

Link State Request

Link State Update

Link State Acknowledgement

Which corresponds to option D.

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:

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.

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 (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.

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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Comprehensive and Detailed Explanation From Exact Extract:

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

IS-IS internal route preference: 18

OSPF Type 5 external route preference: 150

“The protocol with the lower preference value wins. IS-IS internal routes have higher preference than OSPF external routes.”

Thus, the IS-IS route will be installed in the route table.

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Perfect — fully verified answers with strict Nokia compliance.

Comprehensive and Detailed Explanation From Exact Extract:

According toNokia 7750 SR OS OSPF Guide — OSPF Packet Transmission Section:

“OSPF is encapsulated directly over IP using protocol number 89. It does not use TCP or UDP.”

TCP (Protocol 6) → Incorrect.

UDP (Protocol 17) → Incorrect.

OSPF operates directly at IP layer using protocol number 89.

Thus, the correct answer isD.