The answer is that R2 is advertising its loopback prefix as a /24 network instead of a /32 host route. This occurs because OSPF, by default, advertises loopback interfaces as /32 host routes, but if the network type is changed or the interface is misconfigured, OSPF may advertise the actual configured prefix length—in this case, a /24—causing a mismatch in the routing table. On the CCNA 200-301 v2 exam, this scenario tests your understanding of OSPF loopback prefix advertisement and the longest-prefix match rule: R1 sees a /24 route for 10.0.0.0/24 via a different next-hop, but when pinging 10.0.0.1/32, it looks for a more specific /32 route, which is missing, so the ping fails. A common trap is assuming OSPF always advertises loopbacks as /32, but the actual prefix length depends on the `ip ospf network point-to-point` command or the interface configuration. Memory tip: "Loopbacks love /32—unless you change the network type, they stay a host route."
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. 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
R1# show ip route 10.0.0.1
% Network not in table
R1# show ip route 10.0.0.0
Routing entry for 10.0.0.0/24
Known via "eigrp", distance 90, metric 30720, type internal
Redistributing via eigrp 1
Last update from 192.168.1.2 on GigabitEthernet0/0, 00:12:34 ago
Routing Descriptor Blocks:
* 192.168.1.2, from 192.168.1.2, 00:12:34 ago, via GigabitEthernet0/0
Route metric is 30720, traffic share count is 1
R1# show ip route 10.0.0.0 255.255.255.0
Routing entry for 10.0.0.0/24
Known via "connected", distance 0, metric 0 (connected)
Redistributing via eigrp 1
Directly connected via GigabitEthernet0/1
R1# show ip route 10.0.0.1 255.255.255.255
% Network not in table
A network engineer notices that hosts on VLAN 100 (192.168.10.0/24) cannot ping the loopback interface (10.0.0.1/32) of a directly connected router R2. The engineer checks R1's routing table and sees an entry for 10.0.0.0/24 via a different next-hop, but no entry for 10.0.0.1/32. What is the most likely reason for the connectivity 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 ip route 10.0.0.1
% Network not in table
R1# show ip route 10.0.0.0
Routing entry for 10.0.0.0/24
Known via "eigrp", distance 90, metric 30720, type internal
Redistributing via eigrp 1
Last update from 192.168.1.2 on GigabitEthernet0/0, 00:12:34 ago
Routing Descriptor Blocks:
* 192.168.1.2, from 192.168.1.2, 00:12:34 ago, via GigabitEthernet0/0
Route metric is 30720, traffic share count is 1
R1# show ip route 10.0.0.0 255.255.255.0
Routing entry for 10.0.0.0/24
Known via "connected", distance 0, metric 0 (connected)
Redistributing via eigrp 1
Directly connected via GigabitEthernet0/1
R1# show ip route 10.0.0.1 255.255.255.255
% Network not in table
A
The loopback interface on R2 is administratively down.
Why wrong: If the interface were down, R2 would not advertise any route for 10.0.0.0/24, but R1 shows a /24 route via EIGRP, so the interface is up.
B
R2 is advertising the loopback as a /24 network, not a /32 host route.
The loopback address 10.0.0.1/32 is typically advertised as a /32. If R2's loopback is configured with a /24 mask, it advertises 10.0.0.0/24. R1 then has a /24 route but no /32 route, so when trying to reach 10.0.0.1, the longest-prefix match fails, and the router drops the packet.
C
R1 has a route for 10.0.0.0/24 via a different next-hop, causing a routing loop.
Why wrong: While R1 has two routes for 10.0.0.0/24 (one connected, one via EIGRP), the connected route is more specific (directly connected) but still a /24. The issue is not a loop but the lack of a /32 route.
D
The EIGRP metric for the /24 route is too high, so R1 prefers the connected route.
Why wrong: The EIGRP metric is 30720, which is normal, and the connected route has a lower administrative distance (0 vs 90), so R1 uses the connected route for 10.0.0.0/24. However, neither route is a /32, so the problem remains.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
R2 is advertising the loopback as a /24 network, not a /32 host route.
The issue is that R2 is advertising its loopback interface (10.0.0.1/32) as a /24 network (10.0.0.0/24) into the routing protocol. R1 receives this /24 route and installs it in its routing table, but when it tries to reach 10.0.0.1, it performs a longest-prefix match. Since R1 has a more specific /32 route for 10.0.0.1 via a different next-hop (or no /32 route at all), it does not use the /24 route to reach the loopback, causing the ping to fail.
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 loopback interface on R2 is administratively down.
Why it's wrong here
If the interface were down, R2 would not advertise any route for 10.0.0.0/24, but R1 shows a /24 route via EIGRP, so the interface is up.
✓
R2 is advertising the loopback as a /24 network, not a /32 host route.
Why this is correct
The loopback address 10.0.0.1/32 is typically advertised as a /32. If R2's loopback is configured with a /24 mask, it advertises 10.0.0.0/24. R1 then has a /24 route but no /32 route, so when trying to reach 10.0.0.1, the longest-prefix match fails, and the router drops the packet.
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.
✗
R1 has a route for 10.0.0.0/24 via a different next-hop, causing a routing loop.
Why it's wrong here
While R1 has two routes for 10.0.0.0/24 (one connected, one via EIGRP), the connected route is more specific (directly connected) but still a /24. The issue is not a loop but the lack of a /32 route.
✗
The EIGRP metric for the /24 route is too high, so R1 prefers the connected route.
Why it's wrong here
The EIGRPmetric is 30720, which is normal, and the connected route has a lower administrative distance (0 vs 90), so R1 uses the connected route for 10.0.0.0/24. However, neither route is a /32, so the problem remains.
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.
✓R2 is advertising the loopback as a /24 network, not a /32 host route.Correct answer▾
Why this is correct
The loopback address 10.0.0.1/32 is typically advertised as a /32. If R2's loopback is configured with a /24 mask, it advertises 10.0.0.0/24. R1 then has a /24 route but no /32 route, so when trying to reach 10.0.0.1, the longest-prefix match fails, and the router drops the packet.
✗The loopback interface on R2 is administratively down.Wrong answer — click to see why▾
Why this is wrong here
If the loopback interface were administratively down, R2 would not advertise any route for 10.0.0.0/24 via EIGRP. However, R1's routing table shows a /24 route via EIGRP, indicating the interface is up and the route is being advertised.
Why candidates choose this
Students may think that a down interface is the most common cause of connectivity failure, but the presence of a /24 route in R1's table contradicts this assumption.
✗R1 has a route for 10.0.0.0/24 via a different next-hop, causing a routing loop.Wrong answer — click to see why▾
Why this is wrong here
A routing loop would require packets to be forwarded back and forth between routers. In this scenario, R1 has a connected route for 10.0.0.0/24 and an EIGRP route for the same prefix, but it will use the connected route due to lower administrative distance. There is no loop because the next-hop for the connected route is directly connected, and packets are not sent to another router.
Why candidates choose this
Students may confuse the presence of two routes for the same prefix with a routing loop, but a loop requires packets to be forwarded in a cycle, which is not happening here.
✗The EIGRP metric for the /24 route is too high, so R1 prefers the connected route.Wrong answer — click to see why▾
Why this is wrong here
The EIGRP metric of 30720 is normal for a loopback route, and the connected route is preferred due to its lower administrative distance (0 vs 90), not because of a high metric. Even if the metric were lower, the connected route would still be preferred. The core issue is the missing /32 route, not the metric.
Why candidates choose this
Students may think that a high metric could cause a route to be ignored, but in this case, the EIGRP route is present in the table. The real problem is the subnet mask mismatch, not the metric.
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 a routing protocol may advertise a loopback interface with a different prefix length than configured, and candidates mistakenly think the issue is a routing loop or metric problem rather than a prefix-length mismatch.
Trap categories for this question
Command / output trap
If the interface were down, R2 would not advertise any route for 10.0.0.0/24, but R1 shows a /24 route via EIGRP, so the interface is up.
Detailed technical explanation
How to think about this question
In routing protocols like OSPF or EIGRP, loopback interfaces are often advertised as host routes (/32) by default unless explicitly configured with a network statement that matches a broader prefix. The longest-prefix match rule dictates that a /32 route is more specific than a /24, so if R1 has a /32 route for 10.0.0.1 via another path (or none), it will not use the /24 route. This is a common misconfiguration when redistributing or advertising loopbacks without proper network statements or using the 'ip ospf network point-to-point' command to force a /32 advertisement.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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: R2 is advertising the loopback as a /24 network, not a /32 host route. — The issue is that R2 is advertising its loopback interface (10.0.0.1/32) as a /24 network (10.0.0.0/24) into the routing protocol. R1 receives this /24 route and installs it in its routing table, but when it tries to reach 10.0.0.1, it performs a longest-prefix match. Since R1 has a more specific /32 route for 10.0.0.1 via a different next-hop (or no /32 route at all), it does not use the /24 route to reach the loopback, causing the ping to fail.
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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