The answer is an HSRP group number mismatch between R1 and R2. This is the most likely cause because HSRP relies on matching group numbers to establish a neighbor relationship and exchange hello messages; when the group numbers differ, each router operates in isolation, believing it is the active router for its own virtual instance, so neither detects the other’s state, and failover never occurs. On the CCNA 200-301 v2 exam, this scenario tests your understanding of HSRP’s fundamental requirement for consistent group identifiers across peers, often appearing in troubleshooting questions where show standby output displays each router as active with no standby router listed—a classic trap where you might overlook the group number field. Remember the memory tip: “Group must groove together” to recall that matching group numbers are essential for HSRP neighbor formation and seamless failover.
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.
Exhibit
R1# show standby brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vlan10 10 110 Active local 192.168.10.2 192.168.10.1
R2# show standby brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vlan10 20 100 Active local unknown 192.168.10.1
Two routers, R1 and R2, have been configured with HSRP for VLAN 10 to provide default gateway redundancy to hosts. The virtual IP address is 192.168.10.1. After configuration, end hosts report inconsistent connectivity to the gateway, and a failover test reveals that when the active router is shut down, connectivity is lost. The network administrator checks the HSRP status on both routers. Based on the output shown, what is the most likely cause of the redundancy failure?
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.
R1# show standby brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vlan10 10 110 Active local 192.168.10.2 192.168.10.1
R2# show standby brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vlan10 20 100 Active local unknown 192.168.10.1
A
R2 has a lower HSRP priority than R1, so it cannot become standby.
Why wrong: A lower priority does not prevent a router from becoming standby; it simply makes it less likely to become the active router if preemption is enabled. Here the issue is not priority—both routers are active in different groups.
B
The HSRP group number is mismatched between R1 and R2.
R1 uses group 10, while R2 uses group 20. This creates two isolated HSRP processes with no shared virtual MAC or failover capability, which directly explains the redundancy failure.
C
The HSRP authentication strings do not match.
Why wrong: An authentication mismatch typically places the router in the Init state, preventing it from becoming Active. However, the output shows both routers in the Active state, ruling out this issue.
D
HSRP version 1 is used on R1 while version 2 is used on R2.
Why wrong: A version mismatch would cause the routers to ignore each other’s hello packets and both become active, but they would still be in the same configured group number. The output shows different group numbers (10 vs 20), which is a more explicit misconfiguration.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The HSRP group number is mismatched between R1 and R2.
HSRP uses the group number to identify the virtual router instance. If the group numbers on R1 and R2 do not match, they will not form a neighbor relationship or exchange HSRP messages, so neither router will know the other exists. This prevents failover: when the active router goes down, the standby router does not take over because it never learned about the active router's state. The output would show that each router believes it is the active router (or that no standby exists), confirming the mismatch.
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.
✗
R2 has a lower HSRP priority than R1, so it cannot become standby.
Why it's wrong here
A lower priority does not prevent a router from becoming standby; it simply makes it less likely to become the active router if preemption is enabled. Here the issue is not priority—both routers are active in different groups.
✓
The HSRP group number is mismatched between R1 and R2.
Why this is correct
R1 uses group 10, while R2 uses group 20. This creates two isolated HSRP processes with no shared virtual MAC or failover capability, which directly explains the redundancy failure.
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 authentication strings do not match.
Why it's wrong here
An authentication mismatch typically places the router in the Init state, preventing it from becoming Active. However, the output shows both routers in the Active state, ruling out this issue.
✗
HSRP version 1 is used on R1 while version 2 is used on R2.
Why it's wrong here
A version mismatch would cause the routers to ignore each other’s hello packets and both become active, but they would still be in the same configured group number. The output shows different group numbers (10 vs 20), which is a more explicit misconfiguration.
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 HSRP group number is mismatched between R1 and R2.Correct answer▾
Why this is correct
R1 uses group 10, while R2 uses group 20. This creates two isolated HSRP processes with no shared virtual MAC or failover capability, which directly explains the redundancy failure.
✗R2 has a lower HSRP priority than R1, so it cannot become standby.Wrong answer — click to see why▾
Why this is wrong here
The output shows R2 is Active in its own group (20); priority only affects role election within the same group. The real problem is separate group numbers.
✗The HSRP authentication strings do not match.Wrong answer — click to see why▾
Why this is wrong here
With mismatched authentication, the state would not be Active. The exhibit clearly shows Active on both routers, so authentication is not the cause.
✗HSRP version 1 is used on R1 while version 2 is used on R2.Wrong answer — click to see why▾
Why this is wrong here
Version mismatch would not change the displayed group number; the group number discrepancy is the direct evidence shown in the exhibit.
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 HSRP group number mismatch as a subtle cause of redundancy failure because candidates focus on priority or authentication and overlook the fundamental requirement that the group number must be identical on all routers in the same virtual router group.
Trap categories for this question
Command / output trap
An authentication mismatch typically places the router in the Init state, preventing it from becoming Active. However, the output shows both routers in the Active state, ruling out this issue.
Detailed technical explanation
How to think about this question
HSRP group numbers must match on all routers in the same standby group because the group number is used to derive the virtual MAC address (0000.0c07.acXX where XX is the group number in hex) and to identify the HSRP session. If group numbers differ, each router forms its own virtual router instance with a different virtual MAC, so hosts may receive conflicting ARP replies, and failover cannot occur because the routers do not recognize each other as part of the same group. In real-world troubleshooting, the 'show standby' command output will show the group number and the state; a mismatch is easily spotted when one router shows 'Standby router is unknown' while the other shows itself as active.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
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 HSRP group number is mismatched between R1 and R2. — HSRP uses the group number to identify the virtual router instance. If the group numbers on R1 and R2 do not match, they will not form a neighbor relationship or exchange HSRP messages, so neither router will know the other exists. This prevents failover: when the active router goes down, the standby router does not take over because it never learned about the active router's state. The output would show that each router believes it is the active router (or that no standby exists), confirming the mismatch.
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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