This 200-301 practice question tests your understanding of ip routing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: a router uses the longest prefix match rule to select the most specific route that matches the destination IP address.. 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 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?
172.20.0.0/16
Why wrong: This is wrong because it is less specific than the matching /24 and /26 routes.
172.20.10.0/24
Why wrong: This is wrong because it is less specific than the matching /26 route.
172.20.10.64/26
This is correct because .70 falls within the 172.20.10.64/26 range.
The default route
Why wrong: This is wrong because multiple more specific routes already match the destination.
Answer choices
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.
Key principle: A router uses the longest prefix match rule to select the most specific route that matches the destination IP address.
Answer analysis
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
This is wrong because it is less specific than the matching /24 and /26 routes.
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.
Related concept
A router uses the longest prefix match rule to select the most specific route that matches the destination IP address.
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
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.
Why this is correct
This is correct because .70 falls within the 172.20.10.64/26 range.
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.
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.
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?”
Common exam traps
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.
Detailed technical explanation
Routing in IP networks relies on the longest prefix match rule, where the router selects the route with the most specific subnet mask that matches the destination IP address. In this scenario, the router has three routes: 172.20.0.0/16, 172.20.10.0/24, and 172.20.10.64/26. Each route covers a progressively smaller range of IP addresses, with the /26 subnet being the most specific. The IP address 172.20.10.70 falls within the 172.20.10.64/26 subnet, which ranges from 172.20.10.64 to 172.20.10.127, making it the best match for routing decisions. The router uses the longest prefix match algorithm to determine the best route. This means it compares the destination IP against all available routes and selects the one with the longest subnet mask that still includes the destination address. Even though the /16 and /24 routes also cover 172.20.10.70, the /26 route is preferred because it is more specific. This behavior ensures traffic is routed efficiently and accurately to the intended subnet, minimizing unnecessary hops or routing ambiguity. A common exam trap is to assume that broader routes like /16 or /24 are sufficient or preferred simply because they are listed first or cover more addresses. However, Cisco routers always prioritize the most specific route due to longest prefix matching. In practical networks, this behavior allows for hierarchical subnetting and route summarization, improving scalability and performance. Understanding this principle is critical for troubleshooting routing issues and designing efficient IP addressing schemes.
Key takeaway
A router uses the longest prefix match rule to select the most specific route that matches the destination IP address.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
IP Routing — This question tests IP Routing — A router uses the longest prefix match rule to select the most specific route that matches the destination IP address..
The correct answer is: 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.
Review a router uses the longest prefix match rule to select the most specific route that matches the destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
A router uses the longest prefix match rule to select the most specific route that matches the destination IP address.
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Last reviewed: May 17, 2026
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