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IP Routing →mediumConfigurationObjective-mapped

Quick Answer

The correct configuration is ip route 192.168.0.0 255.255.252.0 Null0, because the three /24 subnets—192.168.1.0, 192.168.2.0, and 192.168.3.0—fall within the 192.168.0.0/22 summary range, which covers addresses 192.168.0.0 through 192.168.3.255. By pointing a static summary route to Null0, any traffic destined for the summary block that does not match a more specific directly connected route is silently discarded, preventing potential routing loops that could occur if the summary were advertised without a black-hole route. On the CCNA 200-301 v2 exam, this tests your ability to calculate a proper CIDR summary and apply it with a Null0 next-hop, a common design pattern for loop prevention in route summarization. A frequent trap is choosing a summary that is too broad (e.g., /21) or too narrow (e.g., /23), so always verify the block size covers all subnets exactly. Memory tip: think of Null0 as a "digital trash can" for any traffic that hits the summary but misses the specifics—it keeps your routing table clean and loop-free.

CCNA IP Routing Practice Question

This 200-301 practice question tests your understanding of ip routing. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.

You are connected to R1 via console. R1 has three directly connected subnets: 192.168.1.0/24 (G0/0), 192.168.2.0/24 (G0/1), and 192.168.3.0/24 (G0/2). You need to configure a summary route to be advertised to a neighbor via a static route pointing to Null0 to prevent routing loops. The summary should cover all three subnets.

Question 1mediumConfiguration
Review the full subnetting walkthrough →

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

✓

ip route 192.168.0.0 255.255.252.0 Null0

The three subnets 192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24 can be summarized as 192.168.0.0/22, which covers 192.168.0.0 to 192.168.3.255. A static route to Null0 ensures that traffic matching the summary but not a more specific route is dropped, preventing routing loops.

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.

  • ✓

    ip route 192.168.0.0 255.255.252.0 Null0

    Why this is correct

    This is correct because 192.168.0.0/22 covers 192.168.0.0 to 192.168.3.255, which includes all three subnets. The static route to Null0 drops traffic that matches the summary but not a more specific route, preventing routing loops.

    Related concept

    OSPF neighbours must agree on key parameters.

  • ✗

    ip route 192.168.1.0 255.255.252.0 Null0

    Why it's wrong here

    This is incorrect because 192.168.1.0/22 covers 192.168.1.0 to 192.168.4.255, which includes 192.168.4.0/24 (not directly connected) and excludes 192.168.0.0/24. The summary address should start at 192.168.0.0 to properly cover all three subnets.

  • ✗

    ip route 192.168.0.0 255.255.255.0 Null0

    Why it's wrong here

    This is incorrect because 192.168.0.0/24 only covers 192.168.0.0 to 192.168.0.255, which does not include 192.168.1.0/24, 192.168.2.0/24, or 192.168.3.0/24. The mask is too specific.

  • ✗

    ip route 192.168.0.0 255.255.254.0 Null0

    Why it's wrong here

    This is incorrect because 192.168.0.0/23 covers 192.168.0.0 to 192.168.1.255, which includes only 192.168.1.0/24 and 192.168.2.0/24, but not 192.168.3.0/24. The mask is too large (prefix length too long) to cover all three subnets.

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

✓ip route 192.168.0.0 255.255.252.0 Null0Correct answer▾

Why this is correct

This is correct because 192.168.0.0/22 covers 192.168.0.0 to 192.168.3.255, which includes all three subnets. The static route to Null0 drops traffic that matches the summary but not a more specific route, preventing routing loops.

✗ip route 192.168.1.0 255.255.252.0 Null0Wrong answer — click to see why▾

Why this is wrong here

The network address is wrong; the summary must start at 192.168.0.0, not 192.168.1.0.

Why candidates choose this

Candidates might think the summary should start at the first subnet (192.168.1.0) but forget that the summary network address must be aligned to the subnet boundary.

✗ip route 192.168.0.0 255.255.255.0 Null0Wrong answer — click to see why▾

Why this is wrong here

The subnet mask /24 is too small; it does not summarize the three subnets.

Why candidates choose this

Candidates might confuse the summary route with a static route to a specific subnet, or think that using the first subnet's mask is sufficient.

✗ip route 192.168.0.0 255.255.254.0 Null0Wrong answer — click to see why▾

Why this is wrong here

The subnet mask /23 is too specific; it only covers two of the three subnets.

Why candidates choose this

Candidates might miscalculate the summary mask, thinking that /23 covers 192.168.0.0 to 192.168.3.255, but it actually only covers up to 192.168.1.255.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

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.

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.

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 200-301 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 200-301 question test?

IP Routing — This question tests IP Routing — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: ip route 192.168.0.0 255.255.252.0 Null0 — The three subnets 192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24 can be summarized as 192.168.0.0/22, which covers 192.168.0.0 to 192.168.3.255. A static route to Null0 ensures that traffic matching the summary but not a more specific route is dropped, preventing routing loops.

What should I do if I get this 200-301 question wrong?

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 200-301 OSPF questions on adjacency and route selection.

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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Last reviewed: Jun 7, 2026

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This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.