Incorrect Statements Regarding OSPF Router ID Requirements

H12-811 By islever Editorial Last updated

OSPF Principles and Configuration

Short answer

ABC These statements are incorrect because OSPF requires unique Router IDs everywhere, allows automatic selection rather than mandatory manual config or strict interface mapping.

Question

Which of the following statements regarding the router ID in OSPF are incorrect?
  1. The router IDs of OSPF routers in the same area must be the same, but can be different in different areas. Correct Answer
  2. The router ID must be the IP address of an OSPF router interface. Correct Answer
  3. The router ID must be configured manually. Correct Answer
  4. A router running OSPF must have a router ID for it to operate properly.

Key Takeaways

The question tests the distinction between optional/flexible mechanisms (automatic ID election, manual override) and strict requirements (global uniqueness).

Identify the incorrect assertions about OSPF Router IDs: uniqueness is global, and assignment can be automatic or manual, not strictly tied to interface IPs or forced manual entry.

Common mistake: Candidates often select only one option by focusing on the most obvious error (like A) while missing the subtle 'must' traps in B and C regarding automatic vs. manual configuration.

Expert Analysis

The Requirement for a Unique Router ID

OSPF relies on the Router ID to uniquely identify each router within an OSPF domain. This identifier is critical for building the Link-State Database (LSDB) and exchanging routing information. A fundamental rule of OSPF operation is that every router must possess a unique Router ID. If two routers share the same ID, it leads to confusion in LSAs and potential network instability. Therefore, the statement that Router IDs can be duplicated across different areas (Option A) is factually incorrect; uniqueness is required globally within the OSPF autonomous system, not just locally per area.

Flexibility in Router ID Selection

The second major trap involves how the Router ID is determined. Option B claims it "must" be an interface IP address. While OSPF often selects the highest IP address from active interfaces or loopbacks automatically, the protocol allows for manual configuration of any valid 32-bit number that does not conflict with other routers. It does not strictly have to map to a physical interface's IP. Similarly, Option C states it "must" be configured manually. This is false because if no manual configuration exists, the OSPF process will automatically elect a Router ID based on available interface IPs. Thus, both "must" conditions in B and C are incorrect constraints.

Operational Necessity vs. Configuration Method

Option D states that a router "must have a router ID for it to operate properly." This is a true statement. Without a valid Router ID, an OSPF process cannot form adjacencies or function correctly. Since the question asks for the incorrect statements, Options A, B, and C are the correct selections. They impose rigid "must" requirements that contradict the flexible, auto-assignable nature of the OSPF Router ID mechanism.

Exam Strategy

When faced with questions asking for 'incorrect' or 'false' statements involving OSPF parameters, scrutinize absolute words like 'must'. OSPF is generally designed with fallback mechanisms (e.g., automatic ID election). If an option says a feature 'must' be done a specific way (manual, specific type), it is likely incorrect unless it is a hard security or stability constraint like uniqueness.

Frequently Asked Questions

Does an OSPF Router ID have to be an actual interface IP?

No. While OSPF often picks the highest IP from a loopback or physical interface, you can manually configure any valid 32-bit value as long as it is unique.

Can OSPF Router IDs be duplicated in different areas?

No. The Router ID must be unique across the entire OSPF autonomous system, regardless of which area the routers belong to.

Is manual configuration of the Router ID mandatory?

No. If not manually configured, OSPF will automatically select a Router ID from the available interface IPs on the device.

More H12-811 FAQ →

Community Votes

A
75%
D
25%

75% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 13 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 13

  1. buggybombastis10 👍 4
    The answer is A
  2. izzraihan 👍 2 Answered D
    I mean the correct Answer is D, cause the OSPF Router ID can be selected based on Lower IP Address on the router.
  3. Silveira 👍 2 Answered A
    A afirmação incorreta é a questão (A)
  4. IBB90704 👍 2
    Respuesta es la A,B,C
  5. surveycorps969 👍 2 Answered A
    Answer is A
Show 8 more comments
  1. Fmoura17 👍 1 Answered A
    A, B, C are incorrect. ❌ A — Incorrect Every OSPF router must have a unique Router ID, both within the same area and across different areas. Duplicate IDs cause network conflicts. ❌ B — Incorrect The Router ID does not have to be an actual interface IP. It can be any manually configured 32-bit value, or automatically selected from a Loopback/physical interface. ❌ C — Incorrect The Router ID can be selected automatically by the router (highest Loopback IP or highest active interface IP). Manual configuration is not required. ✅ D — Correct A Router ID is mandatory for OSPF to function. Without it, OSPF cannot operate.
  2. Allenrok 👍 1
    This is a multiple choice question. You are asking for the wrong thing, it would be A, B and C.
  3. Chleong 👍 1
    CCCCCC OSPF router id can be manually specified or automatically assigned by system.
  4. Tibi99 👍 1
    Answer is D. C and B incorrect because "must be"
  5. eeadbff 👍 1
    A,B,C incorrect, D correct.
  6. cha_dadi_exams 👍 1
    A,B,C incorrect
  7. hafizhou 👍 1
    B is correct
  8. Jrmelo 👍 1
    Answer is D

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