Quick Answer
The answer is 10.50.10.128/25, because the router applies the longest prefix match rule, selecting the most specific route that contains the destination address. For traffic to 10.50.10.140, the /25 prefix matches exactly the upper half of the 10.50.10.0/24 block, while the /24 and /16 also match but are less specific—the router always prefers the narrowest, most precise prefix. On the CCNA 200-301 v2 exam, this concept tests your understanding of how routers make forwarding decisions when multiple routes overlap; a common trap is assuming the route with the lowest administrative distance or metric wins, but longest prefix match takes priority first. Remember the memory tip: “The longer the mask, the more specific the task”—a /25 is longer than a /24, so it wins every time.
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: cisco routers use longest-prefix match to select the route with the most specific subnet mask 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 10.50.0.0/16, 10.50.10.0/24, and 10.50.10.128/25. Which route is used for traffic to 10.50.10.140?
10.50.0.0/16
Why wrong: This is wrong because the /16 is less specific than the matching /24 and /25 routes.
10.50.10.0/24
Why wrong: This is wrong because the /24 is less specific than the matching /25.
10.50.10.128/25
This is correct because .140 falls inside the 10.50.10.128/25 range.
The default route
Why wrong: This is wrong because more specific matching routes exist.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
10.50.10.128/25
The /25 route is used because it is the most specific matching prefix. In practical terms, 10.50.10.140 belongs to the upper half of the 10.50.10.0/24 space, which is exactly what 10.50.10.128/25 describes. Even though the /24 and /16 also match, longest-prefix match prefers the narrowest route. This is a direct route-selection question. It reinforces that the router chooses the route that describes the destination most precisely.
Key principle: Cisco routers use longest-prefix match to select the route with the most specific subnet mask 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.
10.50.0.0/16
Why it's wrong here
This is wrong because the /16 is less specific than the matching /24 and /25 routes.
When this WOULD be correct
In a different scenario where the router only has the route 10.50.0.0/16 available and no more specific routes exist for the 10.50.10.0 subnet, traffic to 10.50.10.140 would use this route due to its broader coverage.
10.50.10.0/24
Why it's wrong here
This is wrong because the /24 is less specific than the matching /25.
When this WOULD be correct
In a different scenario where the question specifies that the router only has the routes 10.50.0.0/16 and 10.50.10.0/24, and traffic to 10.50.10.140 is being routed without any more specific routes, option B would be correct as it would be the best match available.
10.50.10.128/25
Why this is correct
This is correct because .140 falls inside the 10.50.10.128/25 range.
Related concept
Cisco routers use longest-prefix match to select the route with the most specific subnet mask that matches the destination IP address.
The default route
Why it's wrong here
This is wrong because more specific matching routes exist.
When this WOULD be correct
If the question specified that the router had no specific routes for the 10.50.10.140 address and only had a default route configured, then the correct answer would be the default route. For example, 'What route will be used if the only available route is the default route?'
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 .140 falls inside the 10.50.10.128/25 range.
Why this is wrong here
The route 10.50.0.0/16 has a prefix length of 16, which is less specific than the /24 and /25 routes. Since 10.50.10.140 falls within the more specific /24 and /25 ranges, the router will use the longest prefix match, not the /16.
★ When this WOULD be the correct answer
In a different scenario where the router only has the route 10.50.0.0/16 available and no more specific routes exist for the 10.50.10.0 subnet, traffic to 10.50.10.140 would use this route due to its broader coverage.
Why candidates choose this
Students might think that because 10.50.10.140 is within the 10.50.0.0/16 range, the /16 route would be used. However, they forget that routers always prefer the most specific (longest prefix) match.
Why this is wrong here
The route 10.50.10.0/24 has a prefix length of 24, which is less specific than the /25 route. Since 10.50.10.140 falls within the 10.50.10.128/25 range, the /25 route is more specific and will be preferred.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that the router only has the routes 10.50.0.0/16 and 10.50.10.0/24, and traffic to 10.50.10.140 is being routed without any more specific routes, option B would be correct as it would be the best match available.
Why candidates choose this
Students may see that 10.50.10.140 is within the 10.50.10.0/24 range and assume the /24 route is the best match, overlooking the existence of a more specific /25 route that also matches.
Why this is wrong here
A default route (0.0.0.0/0) is only used when no other more specific route matches the destination. Since there are matching routes (10.50.10.0/24 and 10.50.10.128/25) for 10.50.10.140, the default route is not considered.
★ When this WOULD be the correct answer
If the question specified that the router had no specific routes for the 10.50.10.140 address and only had a default route configured, then the correct answer would be the default route. For example, 'What route will be used if the only available route is the default route?'
Why candidates choose this
Students might think that if a destination is not explicitly listed, the default route is used. However, here there are explicit matching routes, so the default route is not applicable.
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 choosing a less specific route such as 10.50.0.0/16 or 10.50.10.0/24 because they also include the destination IP address. Candidates might overlook the importance of the subnet mask length and assume any matching route is acceptable. This mistake ignores the longest-prefix match rule, which always prefers the route with the most bits matching the destination IP. Selecting a broader route leads to incorrect routing decisions and fails to reflect Cisco’s routing behavior.
Detailed technical explanation
Routing tables in Cisco routers use prefix matching to determine the best path for forwarding packets. Each route in the table has a network prefix and a subnet mask, which together define the range of IP addresses covered. When a packet arrives, the router compares the destination IP address against all routes and selects the one with the longest matching prefix, meaning the most specific subnet mask. This process is known as longest-prefix match and ensures traffic is routed as precisely as possible. In the given scenario, the router has three routes: 10.50.0.0/16, 10.50.10.0/24, and 10.50.10.128/25. The destination IP 10.50.10.140 falls within all three ranges, but the /25 subnet mask is the most specific because it covers fewer addresses and matches more bits of the destination IP. Therefore, the router chooses the 10.50.10.128/25 route to forward the traffic, following the longest-prefix match rule that Cisco routers strictly enforce. A common exam trap is to select a less specific route like the /16 or /24 because they also include the destination IP. However, Cisco routers always prefer the most specific route, even if broader routes exist. Practically, this behavior allows network administrators to create hierarchical and overlapping subnets, where more specific routes override general ones. Understanding this helps avoid misconfigurations and ensures efficient routing in complex networks.
Key takeaway
Cisco routers use longest-prefix match to select the route with the most specific subnet mask 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
Review cisco routers use longest-prefix match to select the route with the most specific subnet mask that matches the destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
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FAQ
IP Routing — This question tests IP Routing — Cisco routers use longest-prefix match to select the route with the most specific subnet mask that matches the destination IP address..
The correct answer is: 10.50.10.128/25 — The /25 route is used because it is the most specific matching prefix. In practical terms, 10.50.10.140 belongs to the upper half of the 10.50.10.0/24 space, which is exactly what 10.50.10.128/25 describes. Even though the /24 and /16 also match, longest-prefix match prefers the narrowest route. This is a direct route-selection question. It reinforces that the router chooses the route that describes the destination most precisely.
Review cisco routers use longest-prefix match to select the route with the most specific subnet mask that matches the destination IP address., then practise related 200-301 questions on the same topic to reinforce the concept.
Cisco routers use longest-prefix match to select the route with the most specific subnet mask that matches the destination IP address.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A router has routes to 192.168.0.0/16 and 192.168.100.0/24. Which route is used for traffic to 192.168.100.77?
hardWhy B: The route to 192.168.100.0/24 is used because it is more specific. In plain language, even though the /16 route covers a large address range that includes the destination, the /24 route describes the destination network more precisely. Longest-prefix match therefore prefers the /24. This is a basic but critical routing-table concept. The router does not choose the broader route when a narrower one matches the same destination.
Variation 2. A router has routes to 192.168.100.0/24 and 192.168.100.128/25. Which route is used for traffic to 192.168.100.140?
hardWhy B: The /25 route is used because it is the most specific matching prefix. In practical terms, 192.168.100.140 falls inside the upper half of the /24, which is exactly what the 192.168.100.128/25 route describes. Even though the /24 also matches, the router always prefers the narrower route when both are valid. This is a direct longest-prefix-match question. It reinforces that specificity is checked before broader route-source preferences matter.
Variation 3. 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?
hardWhy C: 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.
Variation 4. A router has routes to 192.168.0.0/16 and 192.168.50.0/24. Which route is used for traffic to 192.168.50.99?
hardWhy B: The 192.168.50.0/24 route is used because it is more specific. In practical terms, even though the /16 also matches, the router always prefers the route that describes the destination more narrowly. Since 192.168.50.99 falls inside the /24, longest-prefix match chooses that entry. This is a basic but essential routing rule. The broader /16 still matters for other destinations in 192.168.0.0/16, but not for this one.
Last reviewed: May 17, 2026
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