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.
Exhibit
O 10.1.1.0/24 via 192.0.2.1
S 10.1.1.128/25 via 198.51.100.1
S* 0.0.0.0/0 via 203.0.113.1
Exhibit: A router has the following routes in its routing table:
- OSPF: 10.1.1.0/24
- Static: 10.1.1.128/25
- Default: 0.0.0.0/0
A packet is destined for 10.1.1.130. Which route does the router use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The static 10.1.1.128/25 route
Routers use longest-prefix match before they think about metrics. The /25 route for 10.1.1.128/25 is more specific than the /24 or the default route, so traffic for 10.1.1.130 follows that path.
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.
✗
The OSPF 10.1.1.0/24 route
Why it's wrong here
It matches, but there is a more specific /25 route.
When this WOULD be correct
In a scenario where the question asks which route would be used if the destination IP were 10.1.1.0, the OSPF 10.1.1.0/24 route would be the correct answer, as it matches the entire subnet and is the best match for that specific address.
✓
The static 10.1.1.128/25 route
Why this is correct
Longest-prefix match sends 10.1.1.130 to the /25.
Related concept
Cisco routers use the longest-prefix match rule to select the most specific route for forwarding packets based on subnet mask length.
✗
The default route
Why it's wrong here
The default route is used only when no more specific route exists.
When this WOULD be correct
In a scenario where the router has no specific routes for the destination address and only a default route configured (e.g., 0.0.0.0/0), a packet destined for an unknown address would use the default route. An exam question could specify that no other routes are available for the destination.
✗
The router load-balances across all three
Why it's wrong here
These routes have different prefix lengths.
When this WOULD be correct
In a different scenario where multiple equal-cost routes exist for the same destination, and the router is configured to load-balance, this option would be correct. For example, if there were multiple static routes to 10.1.1.130 with the same metric, the router would indeed load-balance traffic across them.
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.
✓The static 10.1.1.128/25 routeCorrect answer▾
Why this is correct
Longest-prefix match sends 10.1.1.130 to the /25.
✗The OSPF 10.1.1.0/24 routeWrong answer — click to see why▾
Why this is wrong here
The OSPF 10.1.1.0/24 route matches the destination 10.1.1.130, but the router uses the longest-prefix match rule. Since the static 10.1.1.128/25 route has a longer prefix length (25 vs 24), it is more specific and preferred.
★ When this WOULD be the correct answer
In a scenario where the question asks which route would be used if the destination IP were 10.1.1.0, the OSPF 10.1.1.0/24 route would be the correct answer, as it matches the entire subnet and is the best match for that specific address.
Why candidates choose this
Students may think that because the /24 route is learned via OSPF (a dynamic routing protocol) and has a lower administrative distance than a static route, it would be preferred. However, prefix length takes precedence over administrative distance in the forwarding decision.
✗The default routeWrong answer — click to see why▾
Why this is wrong here
The default route (0.0.0.0/0) is only used when no other route matches the destination. Since the destination 10.1.1.130 matches both the /24 and /25 routes, the default route is not considered.
★ When this WOULD be the correct answer
In a scenario where the router has no specific routes for the destination address and only a default route configured (e.g., 0.0.0.0/0), a packet destined for an unknown address would use the default route. An exam question could specify that no other routes are available for the destination.
Why candidates choose this
Students might think that if a default route exists, it will be used as a catch-all. However, the router always checks for more specific matches first; the default route is the last resort.
✗The router load-balances across all threeWrong answer — click to see why▾
Why this is wrong here
Load balancing only occurs when multiple routes have the same prefix length and administrative distance. Here, the routes have different prefix lengths (/24, /25, and /0), so the router selects the single best match based on longest prefix.
★ When this WOULD be the correct answer
In a different scenario where multiple equal-cost routes exist for the same destination, and the router is configured to load-balance, this option would be correct. For example, if there were multiple static routes to 10.1.1.130 with the same metric, the router would indeed load-balance traffic across them.
Why candidates choose this
Students may confuse equal-cost multipath (ECMP) load balancing with the general concept of having multiple routes. They might think that because multiple routes exist, the router will distribute traffic among them, but that only happens when routes are equally specific.
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 common exam trap is to select a route based solely on routing protocol preference or administrative distance without considering prefix length. Many candidates incorrectly choose the OSPF 10.1.1.0/24 route because OSPF is a dynamic protocol and might assume it is preferred over a static route. However, Cisco routers always apply longest-prefix match first, so the static 10.1.1.128/25 route is chosen because it is more specific. Another trap is to think the router load-balances across all routes, but load balancing only occurs among routes with equal prefix length and metric, not across different subnet sizes.
Detailed technical explanation
How to think about this question
Routing tables in Cisco routers contain multiple routes to various destinations, each with a prefix and prefix length that defines the network size. The router uses the longest-prefix match rule to select the most specific route for forwarding packets. A longer prefix length (larger subnet mask) means a more specific route, which takes precedence over less specific routes with shorter prefix lengths. This ensures packets are routed optimally to the most precise destination network.
When a packet arrives, the router compares the destination IP address against all routes in its routing table. It selects the route with the longest matching prefix. In this scenario, the destination 10.1.1.130 matches both the 10.1.1.0/24 OSPF route and the 10.1.1.128/25 static route. Since /25 is a longer prefix than /24, the static route is preferred regardless of routing protocol or administrative distance. Default routes (0.0.0.0/0) are only used if no more specific route exists.
A common exam trap is to assume routing protocol preference or administrative distance overrides longest-prefix match. However, Cisco routers always apply longest-prefix match first, then use administrative distance to break ties between routes of equal prefix length. Practically, this means a static /25 route will be chosen over an OSPF /24 route for the same destination. Understanding this behavior prevents mistakes in subnetting and routing questions, especially when multiple routes overlap in the routing table.
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 longer prefix length (e.g., /25) is preferred over a route with a shorter prefix length (e.g., /24) regardless of routing protocol.
Static routes are installed in the routing table and can override dynamic routing protocol routes if they have a more specific prefix.
Default routes (0.0.0.0/0) are only used when no other more specific route matches the destination IP address.
Routing protocols like OSPF advertise routes, but the router still applies longest-prefix match before considering administrative distance or metrics.
Administrative distance is used only to choose between routes with the same prefix length, not to override longest-prefix match.
Routers do not load-balance across routes with different prefix lengths because longest-prefix match selects a single best route.
Understanding subnetting and prefix lengths is critical to correctly interpreting routing table entries and route selection.
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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
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: The static 10.1.1.128/25 route — Routers use longest-prefix match before they think about metrics. The /25 route for 10.1.1.128/25 is more specific than the /24 or the default route, so traffic for 10.1.1.130 follows that path.
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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