CCNA IP Routing Practice Question
A router has routes to 172.20.0.0/16, 172.20.10.0/24, and 172.20.10.64/26. Which route is used for traffic to 172.20.10.70?
⚠ Common exam trap
A common exam trap is to select a less specific route such as 172.20.0.0/16 or 172.20.10.0/24 because they appear to cover the destination IP 172.20.10.70. Candidates may overlook that the router always prefers the most specific route, which in this case is the /26 subnet. Choosing a broader subnet ignores the longest prefix match principle and leads to incorrect routing decisions. This trap tests your understanding of how subnet masks influence route selection and the importance of prefix length in Cisco routing tables.
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
✓
172.20.10.64/26
The /26 route is used because it is the most specific matching prefix. In practical terms, 172.20.10.70 falls inside the 172.20.10.64/26 range, so that route narrows the destination more precisely than the broader /24 and /16 routes. Longest-prefix match therefore selects the /26 entry. This question is designed to reinforce that specificity comes first in route lookup. Broader routes remain useful, but they lose when a more exact route matches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
172.20.0.0/16
Why it's wrong here
The /16 prefix is too broad, as the router selects the longest prefix match; 172.20.10.70 falls within 172.20.10.64/26, which offers a more specific 26-bit mask. This option is tempting because it summarises the entire 172.20.0.0 block and would be correct for any destination outside the more specific subnets, but it fails here because the /26 route is a better match.
When this WOULD be correct
In a scenario where the question asks which route would be used for traffic to any IP address within the 172.20.0.0/16 network, such as 172.20.5.10, then the option 172.20.0.0/16 would be correct as it encompasses all addresses in that range.
- ✗
172.20.10.0/24
Why it's wrong here
This is wrong because it is less specific than the matching /26 route.
When this WOULD be correct
In a different question, if the router only had routes to 172.20.0.0/16 and 172.20.10.0/24 without the more specific 172.20.10.64/26, then traffic to 172.20.10.70 would be routed using 172.20.10.0/24 as the most specific match available.
- ✓
172.20.10.64/26
Why this is correct
This is correct because .70 falls within the 172.20.10.64/26 range.
- ✗
The default route
Why it's wrong here
This is wrong because multiple more specific routes already match the destination.
When this WOULD be correct
In a different scenario where the router has no specific routes for the 172.20.10.70 destination and only a default route configured (e.g., 0.0.0.0/0), the default route would be used to forward traffic to that IP address.
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.
✓172.20.10.64/26Correct answer▾
Why this is correct
This is correct because .70 falls within the 172.20.10.64/26 range.
✗172.20.0.0/16Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because the route 172.20.0.0/16 is a broader match and does not specifically target the subnet that includes the IP address 172.20.10.70, which falls under the more specific route 172.20.10.64/26.
★ When this WOULD be the correct answer
In a scenario where the question asks which route would be used for traffic to any IP address within the 172.20.0.0/16 network, such as 172.20.5.10, then the option 172.20.0.0/16 would be correct as it encompasses all addresses in that range.
Why candidates choose this
Candidates may choose this option because they recognize 172.20.0.0/16 as a valid route and mistakenly assume that broader routes are always preferred, overlooking the importance of specific subnet matches.
✗172.20.10.0/24Wrong answer — click to see why▾
Why this is wrong here
Option B is wrong because the subnet 172.20.10.0/24 encompasses addresses from 172.20.10.0 to 172.20.10.255, but the more specific route 172.20.10.64/26 takes precedence for the address 172.20.10.70.
★ When this WOULD be the correct answer
In a different question, if the router only had routes to 172.20.0.0/16 and 172.20.10.0/24 without the more specific 172.20.10.64/26, then traffic to 172.20.10.70 would be routed using 172.20.10.0/24 as the most specific match available.
Why candidates choose this
Candidates may choose this option because they recognize that 172.20.10.0/24 includes the target address, leading to the assumption that it would be the best match without considering the specificity of the other routes.
✗The default routeWrong answer — click to see why▾
Why this is wrong here
The default route is not used for specific traffic to 172.20.10.70 since there are more specific routes available in the routing table that match this destination. The default route is only utilized when no other routes are applicable.
★ When this WOULD be the correct answer
In a different scenario where the router has no specific routes for the 172.20.10.70 destination and only a default route configured (e.g., 0.0.0.0/0), the default route would be used to forward traffic to that IP address.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of routing principles, thinking that the default route serves as a catch-all for any unmatched traffic, especially in complex routing environments.
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?”
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Key term
Router
A router is a networking device that connects different networks together and directs data traffic between them by choosing the best path for data to travel.
Key term
Route
A route is a path that data takes through a network from one device or network to another, determined by routing protocols and configured rules.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.