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 the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length.. 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 192.168.0.0/16 and 192.168.100.0/24. Which route is used for traffic to 192.168.100.77?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
192.168.100.0/24
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.
Key principle: Cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
192.168.0.0/16
Why it's wrong here
This is wrong because the /16 is less specific than the matching /24.
When this WOULD be correct
In a scenario where the question specifies that the router is configured to prefer the less specific route for some reason, such as a policy-based routing configuration that prioritizes broader networks, then 192.168.0.0/16 could be the correct answer.
✓
192.168.100.0/24
Why this is correct
This is correct because it is the more specific matching prefix.
Related concept
Cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length.
✗
Both routes are discarded because they overlap.
Why it's wrong here
This is wrong because overlapping prefixes are normal and route specificity resolves the choice.
When this WOULD be correct
In a scenario where a router has conflicting routes to the same destination but with different subnet masks, and the router is configured to discard overlapping routes due to administrative policies, this option would be correct. For example, if a question stated that both routes were configured with the same administrative distance and the router was set to ignore overlapping routes, then this answer would apply.
✗
The default route is preferred if present.
Why it's wrong here
This is wrong because more specific matching routes are preferred before the default route.
When this WOULD be correct
In a different scenario where the router has no specific routes for the destination IP and only a default route is configured, the default route would be used for traffic to 192.168.100.77, making this option correct.
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.
✓192.168.100.0/24Correct answer▾
Why this is correct
This is correct because it is the more specific matching prefix.
✗192.168.0.0/16Wrong answer — click to see why▾
Why this is wrong here
The route 192.168.0.0/16 is less specific (larger subnet) than the matching /24 route. The router always prefers the most specific matching prefix (longest prefix match) for forwarding decisions.
★ When this WOULD be the correct answer
In a scenario where the question specifies that the router is configured to prefer the less specific route for some reason, such as a policy-based routing configuration that prioritizes broader networks, then 192.168.0.0/16 could be the correct answer.
Why candidates choose this
Students might think that because 192.168.100.77 falls within the 192.168.0.0/16 range, this route would be used. However, they overlook the principle of longest prefix match, which gives priority to the more specific /24 route.
✗Both routes are discarded because they overlap.Wrong answer — click to see why▾
Why this is wrong here
Overlapping routes are common in routing tables and are not discarded. The router uses the longest prefix match to select the most specific route among overlapping entries.
★ When this WOULD be the correct answer
In a scenario where a router has conflicting routes to the same destination but with different subnet masks, and the router is configured to discard overlapping routes due to administrative policies, this option would be correct. For example, if a question stated that both routes were configured with the same administrative distance and the router was set to ignore overlapping routes, then this answer would apply.
Why candidates choose this
Some students may incorrectly believe that overlapping prefixes cause conflicts or errors, leading to route discarding. In reality, routers handle overlapping routes gracefully by preferring the most specific one.
✗The default route is preferred if present.Wrong answer — click to see why▾
Why this is wrong here
The default route (0.0.0.0/0) is only used when no other more specific route matches the destination. Since a matching route (192.168.100.0/24) exists, the default route is not considered.
★ When this WOULD be the correct answer
In a different scenario where the router has no specific routes for the destination IP and only a default route is configured, the default route would be used for traffic to 192.168.100.77, making this option correct.
Why candidates choose this
Students might think that the default route is always preferred or that it overrides specific routes. In fact, the default route has the lowest priority and is only a last resort.
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
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is to select the broader route 192.168.0.0/16 because it seems to cover more addresses, including the destination. Candidates may mistakenly think that a larger subnet mask means a better route or that overlapping routes cause the router to discard both. However, Cisco routers always prefer the most specific route based on the longest-prefix match rule. Overlapping routes are normal and do not cause discarding; instead, the router uses the route with the longest subnet mask. Misunderstanding this can lead to incorrect answers and confusion about routing behavior.
Detailed technical explanation
How to think about this question
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 by that route. 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 that fits the destination address.
The longest-prefix match rule means that if multiple routes cover the destination IP, the router prefers the route with the smallest subnet (largest mask). In this question, 192.168.0.0/16 covers all addresses from 192.168.0.0 to 192.168.255.255, while 192.168.100.0/24 covers only 192.168.100.0 to 192.168.100.255. Since 192.168.100.77 falls within both ranges, the router chooses the /24 route because it is more specific and thus a better match.
A common exam trap is to assume that the broader route (192.168.0.0/16) is preferred because it covers a larger address space. However, Cisco routers always use the longest-prefix match rule first, regardless of route size or administrative distance unless no more specific route exists. This behavior ensures precise routing and prevents routing ambiguity in overlapping subnets, which is critical for efficient network operation and troubleshooting.
KKey Concepts to Remember
Cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length.
A route with a smaller subnet (larger mask) is preferred over a broader route when both cover the destination IP address.
Overlapping routes in a routing table are normal and do not cause routes to be discarded; the router chooses the best match.
The router compares destination IP addresses against all routes and selects the one with the longest matching prefix first.
Default routes are only used when no more specific matching route exists in the routing table.
Routing decisions in Cisco devices prioritize prefix specificity before considering administrative distance or metrics.
The presence of multiple routes to overlapping subnets requires understanding subnetting and prefix lengths for correct route selection.
Misinterpreting route specificity can lead to incorrect routing decisions and exam mistakes in CCNA routing questions.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length.
Real-world example
How this comes up in practice
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — Cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length..
What is the correct answer to this question?
The correct answer is: 192.168.100.0/24 — 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.
What should I do if I get this 200-301 question wrong?
Review cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length.
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