Question 943 of 2,152

Administrative Distance →hardMultiple ChoiceObjective-mapped

Administrative Distance OSPF External vs EIGRP Internal

This 300-410 practice question tests your understanding of administrative distance. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

In a multi-area OSPF network, Router R1 (ABR) is redistributing a static default route into OSPF with 'default-information originate always metric 10'. Router R2, an internal router in Area 1, receives the default route but also learns a more specific route to 0.0.0.0/0 via EIGRP from Router R3 with administrative distance 170. The 'show ip route 0.0.0.0' on R2 shows the EIGRP route as the best path. However, R2's 'show ip ospf database external' shows the OSPF external default route. What is the root cause of R2 preferring the EIGRP route?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

A
The EIGRP route has an administrative distance of 90 because it is an internal EIGRP route, and the OSPF default route is external with AD 110, so EIGRP is preferred.
Why wrong: This option incorrectly claims the EIGRP route is internal with AD 90, but the stem explicitly states it has AD 170.
B
The OSPF default route is not installed because the 'default-information originate always' command requires a 'metric-type' keyword to be set to type-1 for lower AD.
The OSPF default route is not installed because the 'default-information originate always' command requires the 'metric-type' keyword to be set to type-1 for the route to be placed in the routing table. Without it, the route is not considered, allowing the EIGRP route to be preferred despite a higher AD.
C
R2 has a static route with AD 1 that is overriding both dynamic routes.
Why wrong: There is no static route mentioned in the scenario.
D
The EIGRP route is learned from a different VRF, and VRF routes have lower AD by default.
Why wrong: There is no indication of multiple VRFs in the scenario.

Full breakdown with real-world context →

Quick Answer

The answer is that the EIGRP route is preferred because it is an internal EIGRP route with an administrative distance of 90, while the OSPF external default route has an administrative distance of 110. This is the root cause: administrative distance is the tiebreaker when routes from different protocols compete for the routing table, and a lower AD is always preferred. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of the default administrative distance values—specifically that OSPF external routes (including those injected via `default-information originate`) carry an AD of 110, whereas EIGRP internal routes use 90 and EIGRP external routes use 170. A common trap is assuming all EIGRP routes are external when redistributed, but if the redistribution on R3 preserves the internal AD (e.g., via a route-map or if the source is an EIGRP-learned network), the EIGRP route will win over OSPF external. Remember the mnemonic: “EIGRP Internal (90) beats OSPF External (110) every time.”

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The OSPF default route is not installed because the 'default-information originate always' command requires a 'metric-type' keyword to be set to type-1 for lower AD.

The OSPF default route generated by 'default-information originate always' is an external type-2 route with administrative distance 110. However, the installation of this route requires that the route's metric be lower than the best alternative. Since the EIGRP route has an administrative distance of 170, it is actually less preferred than OSPF. The real root cause is that the OSPF route was not installed because the ABR did not generate a type-5 LSA due to the missing 'metric-type' keyword, which is necessary for the route to be considered. Therefore, R2 falls back to the EIGRP route.

Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The EIGRP route has an administrative distance of 90 because it is an internal EIGRP route, and the OSPF default route is external with AD 110, so EIGRP is preferred.
Why it's wrong here
This option incorrectly claims the EIGRP route is internal with AD 90, but the stem explicitly states it has AD 170.
✓
The OSPF default route is not installed because the 'default-information originate always' command requires a 'metric-type' keyword to be set to type-1 for lower AD.
Why this is correct
The OSPF default route is not installed because the 'default-information originate always' command requires the 'metric-type' keyword to be set to type-1 for the route to be placed in the routing table. Without it, the route is not considered, allowing the EIGRP route to be preferred despite a higher AD.
Clue confirmation
The clue word "always" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
R2 has a static route with AD 1 that is overriding both dynamic routes.
Why it's wrong here
There is no static route mentioned in the scenario.
✗
The EIGRP route is learned from a different VRF, and VRF routes have lower AD by default.
Why it's wrong here
There is no indication of multiple VRFs in the scenario.

Common exam traps

Common exam trap: OSPF can fail even when IP connectivity looks correct

OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.

Trap categories for this question

Scenario analysis trap
There is no static route mentioned in the scenario.

Detailed technical explanation

How to think about this question

OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.

KKey Concepts to Remember

OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.

TExam Day Tips

Check area mismatch first when OSPF adjacency fails.
Review passive interfaces when a network is advertised but no neighbour forms.
Use show ip ospf neighbor and show ip route clues carefully.

Key takeaway

OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Real-world example

How this comes up in practice

A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

Visual reference

Quick reference

Routing Protocol Comparison

Protocol	Metric	Max Hops	Algorithm	Type
RIP v2	Hop count	15	Bellman-Ford	Distance vector
OSPF	Cost (bandwidth)	Unlimited	Dijkstra (SPF)	Link state
EIGRP	Composite metric	Unlimited	DUAL	Hybrid
IS-IS	Cost	Unlimited	Dijkstra	Link state
BGP	Policy / attributes	Unlimited	Path vector	Path vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

What to study next

Got this wrong? Here's your next step.

Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 300-410 question test?

Administrative Distance — This question tests Administrative Distance — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The OSPF default route is not installed because the 'default-information originate always' command requires a 'metric-type' keyword to be set to type-1 for lower AD. — The OSPF default route generated by 'default-information originate always' is an external type-2 route with administrative distance 110. However, the installation of this route requires that the route's metric be lower than the best alternative. Since the EIGRP route has an administrative distance of 170, it is actually less preferred than OSPF. The real root cause is that the OSPF route was not installed because the ABR did not generate a type-5 LSA due to the missing 'metric-type' keyword, which is necessary for the route to be considered. Therefore, R2 falls back to the EIGRP route.

What should I do if I get this 300-410 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "always". Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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