Question 159 of 1,819
IP RoutinghardMultiple ChoiceObjective-mapped

Quick Answer

The answer is mismatched HSRP authentication methods. When both routers show the Active state in 'show standby brief', a split-brain scenario occurs because the authentication mismatch prevents them from exchanging valid Hello messages, so each router assumes the other is down and independently takes the Active role for the virtual IP 192.168.1.1. This causes intermittent connectivity as both forward traffic, leading to duplicate frames and ARP confusion. On the CCNA 200-301 v2 exam, this question tests your understanding that HSRP authentication—whether plain-text or MD5—must match exactly to form an adjacency; a common trap is assuming the issue is a priority or preempt misconfiguration, but those cause a single Active router, not a dual-active state. Remember the memory tip: "Auth mismatch, both routers pitch—split-brain glitch."

CCNA IP Routing Practice Question

This 200-301 practice question tests your understanding of ip routing. 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.

A network administrator has configured HSRP between RouterA and RouterB for VLAN 10. End hosts using the virtual IP 192.168.1.1 as their default gateway experience intermittent connectivity losses, and pings to 192.168.1.1 often fail. The output of 'show standby brief' on both routers shows the state as Active. What is the most likely cause?

Clue words in this question

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

  • Clue: "most likely"

    Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1hardmultiple choice
Open the full VLAN trunking answer →

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 routers are configured with mismatched HSRP authentication methods.

When both routers show the HSRP state as Active, a 'dual-active' scenario exists, which causes intermittent connectivity because both routers forward traffic for the virtual IP. Mismatched HSRP authentication methods (e.g., one router using plain-text authentication and the other using MD5) prevent the routers from exchanging proper Hello messages, so they fail to negotiate a single Active router. This is the most likely cause because authentication mismatches break the HSRP adjacency, leading to both routers assuming the Active role.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 virtual IP address is configured on only one router.

    Why it's wrong here

    If the virtual IP is only on one router, that router would become Active and the other would either stay Init or Standby (if it learns of a higher priority), but not both Active. The symptom would be a single point of failure, not intermittent connectivity with both showing Active.

  • The routers are configured with mismatched HSRP authentication methods.

    Why this is correct

    Mismatched authentication (e.g., MD5 vs. text) causes each router to disregard the other's HSRP hellos. Each then assumes no peers exist and becomes Active, leading to both routers claiming the virtual IP and MAC, which results in ARP table flapping and intermittent connectivity.

    Clue confirmation

    The clue word "most likely" in the question point toward this answer.

    Related concept

    Read the scenario before looking for a memorised answer.

  • The HSRP group number on one router is set to 0.

    Why it's wrong here

    Group 0 is a valid HSRPv2 group number. Even if group numbers were mismatched, the routers would belong to different HSRP groups and would not both be Active for the same virtual IP. They would instead form independent standby groups with distinct virtual IPs.

  • The priority on both routers is configured to the same value.

    Why it's wrong here

    Equal priorities result in the router with the higher IP address becoming Active, and the other becoming Standby, as per HSRP election rules. This does not cause a dual-Active condition and would not produce intermittent connectivity.

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.

The routers are configured with mismatched HSRP authentication methods.Correct answer

Why this is correct

Mismatched authentication (e.g., MD5 vs. text) causes each router to disregard the other's HSRP hellos. Each then assumes no peers exist and becomes Active, leading to both routers claiming the virtual IP and MAC, which results in ARP table flapping and intermittent connectivity.

The virtual IP address is configured on only one router.Wrong answer — click to see why

Why this is wrong here

A missing virtual IP on one router does not cause both to be Active; the router without the virtual IP cannot claim the Active role for that address.

The HSRP group number on one router is set to 0.Wrong answer — click to see why

Why this is wrong here

A group number mismatch does not cause both routers to appear as Active for the same virtual IP; they would be in separate groups.

The priority on both routers is configured to the same value.Wrong answer — click to see why

Why this is wrong here

Equal priority does not lead to multiple Active routers; HSRP uses the interface IP address as a tiebreaker to elect a single Active router.

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: answer the scenario, not the keyword

Cisco often tests the concept that HSRP authentication mismatches cause a dual-active failure, while candidates may incorrectly assume that equal priorities or group number 0 are the root cause.

Trap categories for this question

  • Command / output trap

    If the virtual IP is only on one router, that router would become Active and the other would either stay Init or Standby (if it learns of a higher priority), but not both Active. The symptom would be a single point of failure, not intermittent connectivity with both showing Active.

Detailed technical explanation

How to think about this question

HSRP uses a three-state machine (Active, Standby, Listen) and relies on Hello messages sent every 3 seconds (default) to maintain adjacency. Authentication mismatches (e.g., one router configured with 'standby 1 authentication md5 key-string cisco' and the other with 'standby 1 authentication cisco') cause the routers to ignore each other's Hellos, leading to a split-brain condition where both claim Active. In real-world scenarios, this often occurs after a configuration change on one router without updating the peer, and can be diagnosed by checking 'show standby' for 'Authentication mismatch' or 'Hello suppressed' messages.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this 200-301 question test?

IP Routing — This question tests IP Routing — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The routers are configured with mismatched HSRP authentication methods. — When both routers show the HSRP state as Active, a 'dual-active' scenario exists, which causes intermittent connectivity because both routers forward traffic for the virtual IP. Mismatched HSRP authentication methods (e.g., one router using plain-text authentication and the other using MD5) prevent the routers from exchanging proper Hello messages, so they fail to negotiate a single Active router. This is the most likely cause because authentication mismatches break the HSRP adjacency, leading to both routers assuming the Active role.

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

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 25, 2026

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