Question 1mediummultiple choice
Full question →A router has these routes in its routing table:
O 172.16.0.0/16 O 172.16.20.0/24 S 172.16.20.128/25
A packet destined for 172.16.20.200 arrives. Which route will the router use?
mediummultiple choiceObjective-mapped
A router has these routes in its routing table:
O 172.16.0.0/16 O 172.16.20.0/24 S 172.16.20.128/25
A packet destined for 172.16.20.200 arrives. Which route will the router use?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
172.16.0.0/16
The /16 route matches, but it is less specific than the /25.
B
Distractor review
172.16.20.0/24
The /24 route also matches, but the /25 is more specific.
C
Best answer
172.16.20.128/25
Correct. Longest prefix match takes precedence over route source and less specific entries.
D
Distractor review
The default route
A default route is only used when no more specific route matches.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is to select the route with the lowest administrative distance or the route learned via OSPF simply because it is dynamic. Candidates often overlook that the router first applies the longest prefix match rule before considering administrative distance. In this question, the static route 172.16.20.128/25 is more specific than the OSPF routes, so it is chosen despite static routes typically having a lower administrative distance. Misunderstanding this can lead to incorrect answers, especially when multiple routes overlap in the routing table.
Technical deep dive
How to think about this question
Routing tables store multiple routes to the same destination network, each with different subnet masks and administrative distances. The core concept in routing is the longest prefix match, where the router selects the route with the most specific subnet mask that matches the destination IP address. This ensures packets are forwarded along the most precise path available. When a packet arrives, the router compares the destination IP against all routes in its routing table. It chooses the route with the longest subnet mask that includes the destination IP, regardless of whether the route is learned via OSPF (denoted by 'O') or configured statically (denoted by 'S'). In this question, the static route 172.16.20.128/25 is the most specific match for 172.16.20.200, so it is selected over the broader OSPF routes. A common exam trap is to assume that dynamic routing protocols like OSPF always take precedence over static routes or that the route with the lowest administrative distance is always chosen first. However, the longest prefix match rule supersedes administrative distance when multiple routes match the destination. Practically, this means network engineers must carefully design subnetting and route entries to ensure traffic follows the intended path.
KKey Concepts to Remember
- A router selects the route with the longest prefix match when multiple routes match a destination IP address.
- Static routes are preferred over dynamic routes only when they have a longer prefix match or lower administrative distance if prefix lengths are equal.
- OSPF routes are identified by 'O' and have a default administrative distance of 110 in Cisco routers.
- The router compares subnet masks of all matching routes and chooses the one with the most specific subnet mask regardless of route source.
- A default route is only used when no other more specific route matches the destination IP address.
- Administrative distance is used to break ties when multiple routes have the same prefix length but different sources.
- Subnetting determines the range of IP addresses a route covers, which directly affects route selection in the routing table.
- Longest prefix match takes precedence over route source and administrative distance in Cisco routing decisions.
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
A router selects the route with the longest prefix match when multiple routes match a destination IP address.
What is the correct answer to this question?
The correct answer is: 172.16.20.128/25 — Routers choose the most specific matching route. The destination 172.16.20.200 falls within 172.16.20.128/25, so that static route is used even though broader matches also exist.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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