Question 144 of 2,152

Administrative Distance →easyMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the RIP route is preferred because the connected route exists for a different subnet mask, not for the exact prefix 10.0.0.0/8. Connected routes have an administrative distance of 0, which is the lowest possible value and should always be chosen over any dynamic protocol like RIP with its default AD of 120. However, a connected route is only installed for the exact subnet mask configured on the interface; if R3’s directly connected interface uses a different mask, such as /16 or /24, then no connected route for 10.0.0.0/8 exists, leaving the RIP-learned route as the only entry in the routing table. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that AD comparison only matters when comparing routes to the exact same prefix and mask—a common trap is assuming AD alone decides the winner. Remember the memory tip: “AD decides ties, but only if the masks match—different masks mean different routes entirely.”

300-410 Administrative Distance Practice Question

This 300-410 practice question tests your understanding of administrative distance. 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.

A network engineer is troubleshooting a connectivity issue between two sites. R1 learns the prefix 10.0.0.0/8 via RIP (AD 120) from R2, and also via a directly connected interface on R3. The engineer notices that R1 uses the RIP route instead of the connected route. 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 1easymultiple choice

Review the full routing breakdown →

A
The connected interface on R3 has a higher metric than the RIP route.
Why wrong: Connected routes have AD 0, so they are always preferred regardless of metric.
B
The RIP route has an AD of 120, but the connected route is for a different subnet mask.
If the connected route is for 10.0.0.0/16 and the RIP route is for 10.0.0.0/8, they are different prefixes; the router will use the most specific match, but if the connected route is not for the exact prefix, RIP may be the only route.
C
The distance rip 0 command was applied under RIP, making RIP routes have AD 0.
Why wrong: If RIP AD were set to 0, it would tie with the connected route, but the router would still prefer the connected route due to route type preference (connected is directly attached).
D
The connected interface is administratively down.
Why wrong: If the interface is down, the connected route is removed, so RIP would be the only route, but the question states the connected route is learned from R3, implying it exists.

Full breakdown with real-world context →

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 RIP route has an AD of 120, but the connected route is for a different subnet mask.

Connected routes have an AD of 0, which is always preferred over any dynamic routing protocol. If the connected route is not used, it likely does not exist for that exact prefix, or the interface is down. However, if the prefix is learned via RIP with AD 120, the connected route should take precedence. The only way RIP is preferred is if the connected route is not present for that prefix.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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 connected interface on R3 has a higher metric than the RIP route.
Why it's wrong here
Connected routes have AD 0, so they are always preferred regardless of metric.
✓
The RIP route has an AD of 120, but the connected route is for a different subnet mask.
Why this is correct
If the connected route is for 10.0.0.0/16 and the RIP route is for 10.0.0.0/8, they are different prefixes; the router will use the most specific match, but if the connected route is not for the exact prefix, RIP may be the only route.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
The distance rip 0 command was applied under RIP, making RIP routes have AD 0.
Why it's wrong here
If RIP AD were set to 0, it would tie with the connected route, but the router would still prefer the connected route due to route type preference (connected is directly attached).
✗
The connected interface is administratively down.
Why it's wrong here
If the interface is down, the connected route is removed, so RIP would be the only route, but the question states the connected route is learned from R3, implying it exists.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Real-world example

How this comes up in practice

A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.

What to study next

Got this wrong? Here's your next step.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this 300-410 question test?

Administrative Distance — This question tests Administrative Distance — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The RIP route has an AD of 120, but the connected route is for a different subnet mask. — Connected routes have an AD of 0, which is always preferred over any dynamic routing protocol. If the connected route is not used, it likely does not exist for that exact prefix, or the interface is down. However, if the prefix is learned via RIP with AD 120, the connected route should take precedence. The only way RIP is preferred is if the connected route is not present for that prefix.

What should I do if I get this 300-410 question wrong?

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?

CIDR notation defines the prefix length.

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