The answer is an HSRP failover group number mismatch. This is the most likely cause because HSRP requires both routers to share the same group number to form a single virtual router; if the numbers differ, each router creates its own isolated HSRP group, preventing them from recognizing each other as peers. When the primary router fails, the DR router cannot assume the active role because it is not part of the same group, so the failover fails entirely. On the CISA exam, this tests your understanding of network redundancy configuration and the importance of consistent parameters in high-availability protocols—a common trap is to blame IP addressing or routing protocols instead of the group number. A quick memory tip: think of HSRP group numbers like a team jersey number—if both players don’t wear the same number, they can’t play on the same team.
CISA Practice Question: Information Systems Operations and Business Resilience
This CISA practice question tests your understanding of information systems operations and business resilience. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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
Refer to the exhibit.
interface GigabitEthernet0/1
description Link to Primary Site
ip address 10.1.1.1 255.255.255.252
standby 1 ip 10.1.1.2
standby 1 priority 110
standby 1 preempt
!
interface GigabitEthernet0/2
description Link to DR Site
ip address 10.2.2.1 255.255.255.252
standby 2 ip 10.2.2.2
standby 2 priority 100
!
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
!
ip route 0.0.0.0 0.0.0.0 10.1.1.2
An organization has configured HSRP as shown. During a failover test, the primary router (G0/1) is shut down, but the DR site router does not become active. What is the MOST likely reason?
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.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Refer to the exhibit.
interface GigabitEthernet0/1
description Link to Primary Site
ip address 10.1.1.1 255.255.255.252
standby 1 ip 10.1.1.2
standby 1 priority 110
standby 1 preempt
!
interface GigabitEthernet0/2
description Link to DR Site
ip address 10.2.2.1 255.255.255.252
standby 2 ip 10.2.2.2
standby 2 priority 100
!
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
!
ip route 0.0.0.0 0.0.0.0 10.1.1.2
A
The default route on the primary router points to the wrong next-hop
Why wrong: The default route is not the cause of the HSRP failover failure.
B
The preempt command is missing on the DR router
Why wrong: Preempt causes the higher priority router to take over; the DR router has lower priority and would not preempt anyway.
C
The OSPF routing protocol is not redistributing the default route
Why wrong: OSPF is not related to HSRP failover; the issue is with HSRP configuration.
D
The HSRP group numbers on the two interfaces do not match
HSRP group 1 is on G0/1 and group 2 on G0/2; they should be the same group to provide redundancy for the same virtual IP.
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 numbers on the two interfaces do not match
HSRP requires that both routers participating in the same virtual IP address use the same group number to form a single HSRP group. If the group numbers on the two interfaces do not match, each router will form its own separate HSRP group, and neither will recognize the other as a peer. Consequently, when the primary router fails, the DR router does not assume the active role because it is not part of the same HSRP group.
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 default route on the primary router points to the wrong next-hop
Preempt causes the higher priority router to take over; the DR router has lower priority and would not preempt anyway.
✗
The OSPF routing protocol is not redistributing the default route
Why it's wrong here
OSPF is not related to HSRP failover; the issue is with HSRP configuration.
✓
The HSRP group numbers on the two interfaces do not match
Why this is correct
HSRP group 1 is on G0/1 and group 2 on G0/2; they should be the same group to provide redundancy for the same virtual IP.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse HSRP group number mismatch with missing preempt or routing issues, but Cisco specifically tests the fundamental requirement that HSRP group numbers must match for the protocol to establish adjacency.
Detailed technical explanation
How to think about this question
HSRP uses a multicast address (224.0.0.2 for version 1, 224.0.0.102 for version 2) and UDP port 1985 to exchange hello messages. The group number is embedded in the HSRP packet header; mismatched group numbers cause each router to ignore the other's hellos, effectively creating two isolated HSRP groups. In a real-world scenario, this misconfiguration often goes unnoticed during normal operation because both routers may still forward traffic via their own virtual IPs, but failover fails silently.
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.
Information Systems Operations and Business Resilience — This question tests Information Systems Operations and Business Resilience — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The HSRP group numbers on the two interfaces do not match — HSRP requires that both routers participating in the same virtual IP address use the same group number to form a single HSRP group. If the group numbers on the two interfaces do not match, each router will form its own separate HSRP group, and neither will recognize the other as a peer. Consequently, when the primary router fails, the DR router does not assume the active role because it is not part of the same HSRP group.
What should I do if I get this CISA 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", "primary". 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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