CCNA IP Routing Practice Question
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?
⚠ Common exam trap
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.
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
✓
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.
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
192.168.0.0/16 does match the destination 192.168.100.77, but it is less specific than 192.168.100.0/24 because its prefix length is only 16 bits versus 24 bits. The forwarding decision uses the longest prefix match, so the /24 route wins. The /16 route would be selected only if the /24 route did not exist, or if the destination fell outside the /24 but still within the /16.
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
The route 192.168.100.0/24 is selected because it has a longer prefix length (24 bits) than 192.168.0.0/16, and routers use the most specific matching prefix (longest prefix match) to forward traffic. For destination 192.168.100.77, the /24 route provides a more precise match, satisfying the constraint of optimal path selection based on subnet mask length.
- ✗
Both routes are discarded because they overlap.
Why it's wrong here
Overlapping routes are not discarded; Cisco IOS and other routing platforms store both entries in the RIB and FIB. The existence of overlapping prefixes is expected when route summarization or discontiguous subnetting is used. Traffic is forwarded using the longest prefix match, and the shorter /16 route remains available for destinations not covered by the /24. Discarding either route would create avoidable routing black holes for other subnets within 192.168.0.0/16.
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
The default route (0.0.0.0/0) is the least specific route in the routing table, matching every destination. It is used only when no other route has a longer prefix length that matches the destination IP. For traffic to 192.168.100.77, the /24 route is more specific than the default, so the /24 is always preferred. The default route never takes precedence over a more specific matching 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
The route 192.168.100.0/24 is selected because it has a longer prefix length (24 bits) than 192.168.0.0/16, and routers use the most specific matching prefix (longest prefix match) to forward traffic. For destination 192.168.100.77, the /24 route provides a more precise match, satisfying the constraint of optimal path selection based on subnet mask length.
✗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?”
Visual reference
Go deeper
Related to this question
Learn chapter
Interpreting HSRP and VRRP Operational Status
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.
About these practice questions
Courseiva writes every 200-301 question from scratch — 1,389 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
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.