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 selects the route with the longest prefix match when multiple routes match a 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 these routes in its routing table:
O 172.16.0.0/16 O 172.16.20.0/24 S 172.16.20.128/25
A packet destined for 172.16.20.200 arrives. Which route will the router use?
172.16.0.0/16
Why wrong: The /16 route matches, but it is less specific than the /25.
172.16.20.0/24
Why wrong: The /24 route also matches, but the /25 is more specific.
172.16.20.128/25
Correct. Longest prefix match takes precedence over route source and less specific entries.
The default route
Why wrong: A default route is only used when no more specific route matches.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
172.16.20.128/25
Routers choose the most specific matching route. The destination 172.16.20.200 falls within 172.16.20.128/25, so that static route is used even though broader matches also exist.
Key principle: A router selects the route with the longest prefix match when multiple routes match a destination IP address.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
172.16.0.0/16
Why it's wrong here
The /16 route matches, but it is less specific than the /25.
When this WOULD be correct
In a different scenario where the routing table only contains the route 172.16.0.0/16 and no more specific routes for the destination 172.16.20.200, this option would be correct as it would be the only available route.
172.16.20.0/24
Why it's wrong here
The /24 route also matches, but the /25 is more specific.
When this WOULD be correct
In a different scenario where the routing table only contains the routes 172.16.0.0/16 and 172.16.20.0/24, and the packet is destined for 172.16.20.10, option B would be correct as it would be the most specific match available.
172.16.20.128/25
Why this is correct
Correct. Longest prefix match takes precedence over route source and less specific entries.
Related concept
A router selects the route with the longest prefix match when multiple routes match a destination IP address.
The default route
Why it's wrong here
A default route is only used when no more specific route matches.
When this WOULD be correct
If the question stated that the router had no specific routes for the 172.16.20.200 destination and only a default route configured, then the default route would be the correct answer. This scenario would require that all other routes be either inactive or not applicable.
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
Correct. Longest prefix match takes precedence over route source and less specific entries.
Why this is wrong here
This option is wrong because the route 172.16.0.0/16 is less specific than the other routes, and the router uses the most specific route available for packet forwarding.
★ When this WOULD be the correct answer
In a different scenario where the routing table only contains the route 172.16.0.0/16 and no more specific routes for the destination 172.16.20.200, this option would be correct as it would be the only available route.
Why candidates choose this
Candidates may choose this option due to the recognition that 172.16.0.0/16 encompasses the destination IP, leading to a misconception that it could be the correct choice despite being less specific.
Why this is wrong here
Option B is incorrect because the packet's destination IP address, 172.16.20.200, matches the more specific route 172.16.20.128/25, which has a higher priority in routing decisions due to its longer prefix length.
★ When this WOULD be the correct answer
In a different scenario where the routing table only contains the routes 172.16.0.0/16 and 172.16.20.0/24, and the packet is destined for 172.16.20.10, option B would be correct as it would be the most specific match available.
Why candidates choose this
Candidates might choose option B because it appears to be a more specific route than the broader 172.16.0.0/16, leading to confusion about the importance of prefix length in routing decisions.
Why this is wrong here
The default route is used when no specific route matches the destination address. In this case, the destination 172.16.20.200 matches the more specific route 172.16.20.0/24, making the default route irrelevant.
★ When this WOULD be the correct answer
If the question stated that the router had no specific routes for the 172.16.20.200 destination and only a default route configured, then the default route would be the correct answer. This scenario would require that all other routes be either inactive or not applicable.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of routing priorities, thinking that a default route is a catch-all solution for any unmatched destination, without recognizing the importance of more specific routes.
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 frequent exam trap is to select the route with the lowest administrative distance or the route learned via OSPF simply because it is dynamic. Candidates often overlook that the router first applies the longest prefix match rule before considering administrative distance. In this question, the static route 172.16.20.128/25 is more specific than the OSPF routes, so it is chosen despite static routes typically having a lower administrative distance. Misunderstanding this can lead to incorrect answers, especially when multiple routes overlap in the routing table.
Detailed technical explanation
Routing tables store multiple routes to the same destination network, each with different subnet masks and administrative distances. The core concept in routing is the longest prefix match, where the router selects the route with the most specific subnet mask that matches the destination IP address. This ensures packets are forwarded along the most precise path available. When a packet arrives, the router compares the destination IP against all routes in its routing table. It chooses the route with the longest subnet mask that includes the destination IP, regardless of whether the route is learned via OSPF (denoted by 'O') or configured statically (denoted by 'S'). In this question, the static route 172.16.20.128/25 is the most specific match for 172.16.20.200, so it is selected over the broader OSPF routes. A common exam trap is to assume that dynamic routing protocols like OSPF always take precedence over static routes or that the route with the lowest administrative distance is always chosen first. However, the longest prefix match rule supersedes administrative distance when multiple routes match the destination. Practically, this means network engineers must carefully design subnetting and route entries to ensure traffic follows the intended path.
Key takeaway
A router selects the route with the longest prefix match when multiple routes match a 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 selects the route with the longest prefix match when multiple routes match a destination IP address..
The correct answer is: 172.16.20.128/25 — Routers choose the most specific matching route. The destination 172.16.20.200 falls within 172.16.20.128/25, so that static route is used even though broader matches also exist.
Review a router selects the route with the longest prefix match when multiple routes match a destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
A router selects the route with the longest prefix match when multiple routes match a destination IP address.
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Last reviewed: May 17, 2026
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