CCNA Network Services and Security Practice Question
R1 has the following routes installed:
O 10.10.10.0/24 via 192.0.2.2 S 10.10.10.128/25 via 198.51.100.2
S* 0.0.0.0/0 via 203.0.113.1
A packet destined for 10.10.10.200 arrives at R1. Which route is used?
⚠ Common exam trap
A common exam trap is assuming that the router will always prefer OSPF routes over static routes because OSPF is a dynamic routing protocol. Candidates may also mistakenly believe that overlapping routes are invalid or cause routing conflicts. In reality, Cisco routers allow overlapping routes and use the longest prefix match rule first, regardless of the routing protocol or administrative distance. This leads to confusion when a static route with a longer prefix exists alongside an OSPF route with a shorter prefix. Misunderstanding this can cause incorrect answers about which route will be used for forwarding packets.
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
✓
The static route to 10.10.10.128/25 via 198.51.100.2
Routers forward using longest prefix match first. Even though the OSPF /24 exists, the static /25 is more specific and covers 10.10.10.200, so the packet is sent via 198.51.100.2. The default route is used only when nothing more specific matches.
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 route to 10.10.10.0/24 via 192.0.2.2
Why it's wrong here
The OSPF route to 10.10.10.0/24 does match the destination, since 10.10.10.200 lies within that subnet. However, a /24 prefix is shorter than the /25 provided by the static route to 10.10.10.128/25. The router will therefore prefer the longer /25 prefix, making the OSPF route the less-specific match and not the one used for forwarding.
When this WOULD be correct
If the question stated that the packet was destined for an IP address within the 10.10.10.0/24 subnet, such as 10.10.10.50, then the OSPF route would be the correct answer as it matches the destination IP.
- ✓
The static route to 10.10.10.128/25 via 198.51.100.2
Why this is correct
Routers prioritise routes based on the longest prefix match principle. For the destination 10.10.10.200, all three listed routes are potential matches. However, the static route to 10.10.10.128/25 offers a 25-bit prefix, which is longer and therefore more specific than the 24-bit prefix of 10.10.10.0/24 or the 0-bit prefix of the default route. This ensures the packet is forwarded via 198.51.100.2, satisfying the requirement for the most precise route.
- ✗
The default route via 203.0.113.1
Why it's wrong here
The default route has a prefix length of /0, making it the least specific match for any destination. Although it is a valid candidate, the router's longest-prefix-match algorithm will always prefer the static /25 route and even the OSPF /24 route over the default route for 10.10.10.200. Therefore, the default route's next hop of 203.0.113.1 is never selected.
When this WOULD be correct
This option would be correct if the question specified that there were no more specific routes available for the destination address, making the default route the only viable option for routing the packet.
- ✗
The packet is dropped because OSPF routes cannot overlap with static routes.
Why it's wrong here
OSPF and static routes can coexist in the same routing table even when their prefixes overlap; this is entirely valid. The router's forwarding decision is based on the longest prefix match, not on protocol precedence or any prohibition against overlapping routes. For the destination 10.10.10.200, the static /25 route is the most specific, so the packet is forwarded normally and never dropped.
When this WOULD be correct
In a scenario where the question specifies that OSPF routes are configured to prevent overlapping with static routes, and the routing table is set to drop packets if such overlap occurs, this option would be 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.
✓The static route to 10.10.10.128/25 via 198.51.100.2Correct answer▾
Why this is correct
Routers prioritise routes based on the longest prefix match principle. For the destination 10.10.10.200, all three listed routes are potential matches. However, the static route to 10.10.10.128/25 offers a 25-bit prefix, which is longer and therefore more specific than the 24-bit prefix of 10.10.10.0/24 or the 0-bit prefix of the default route. This ensures the packet is forwarded via 198.51.100.2, satisfying the requirement for the most precise route.
✗The OSPF route to 10.10.10.0/24 via 192.0.2.2Wrong answer — click to see why▾
Why this is wrong here
The OSPF route to 10.10.10.0/24 matches the destination 10.10.10.200, but the static route to 10.10.10.128/25 has a longer prefix length (25 vs 24), making it more specific. The router uses the longest prefix match, so the OSPF route is not selected.
★ When this WOULD be the correct answer
If the question stated that the packet was destined for an IP address within the 10.10.10.0/24 subnet, such as 10.10.10.50, then the OSPF route would be the correct answer as it matches the destination IP.
Why candidates choose this
Students may think that OSPF routes are preferred over static routes due to administrative distance, but in this case the static route has a longer prefix, which takes precedence regardless of routing protocol.
✗The default route via 203.0.113.1Wrong answer — click to see why▾
Why this is wrong here
The default route 0.0.0.0/0 matches any destination, but it is only used when no more specific route exists. Since the static route 10.10.10.128/25 is more specific, the default route is not selected.
★ When this WOULD be the correct answer
This option would be correct if the question specified that there were no more specific routes available for the destination address, making the default route the only viable option for routing the packet.
Why candidates choose this
Students may assume that a default route is always used as a last resort, but they forget that the longest prefix match rule overrides the default route when a more specific match exists.
✗The packet is dropped because OSPF routes cannot overlap with static routes.Wrong answer — click to see why▾
Why this is wrong here
Overlapping routes are allowed in a routing table; there is no rule that OSPF routes cannot overlap with static routes. The router simply selects the most specific match based on prefix length. The packet is not dropped unless no route matches at all.
★ When this WOULD be the correct answer
In a scenario where the question specifies that OSPF routes are configured to prevent overlapping with static routes, and the routing table is set to drop packets if such overlap occurs, this option would be correct.
Why candidates choose this
Some students might think that overlapping routes cause conflicts or errors, but routers handle overlapping prefixes by using the longest prefix match. The statement about OSPF and static routes being incompatible is incorrect.
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
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
RA Guard — IPv6 First-Hop Security
Key term
Packet
A packet is a small unit of data that is sent over a network, containing both the actual data and control information for delivery.
Key term
Longest prefix match
Longest prefix match is the algorithm routers use to select the most specific route from a routing table when forwarding a packet to its destination.
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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.