- A
Administrative distance: A measure of the trustworthiness of a routing protocol.
This is correct because the longest prefix match rule ensures that the most specific route (with the longest subnet mask) is chosen for forwarding traffic, which is fundamental to IP routing.
- B
Metric: A value used by a routing protocol to determine the best path.
This is incorrect because administrative distance (AD) is used to rank the reliability of routing protocols, not to select the most specific route. AD is a trustworthiness value assigned to each route source.
- C
Prefix length: The number of bits in the subnet mask that defines the network portion.
This is incorrect because a metric is a value used by a routing protocol to choose the best path among routes learned from the same protocol, not to determine the most specific route. Metrics include hop count, bandwidth, delay, etc.
- D
Longest prefix match: The routing decision that selects the most specific route.
This is incorrect because equal-cost multipath (ECMP) is a feature that allows load balancing across multiple routes with the same metric and prefix length, not a method for selecting the most specific route.
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.. 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.
Match each route-selection concept to its most accurate meaning.
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
Administrative distance: A measure of the trustworthiness of a routing protocol.
Administrative distance indicates the trustworthiness of a routing protocol or static route, with lower values preferred. Metric is a protocol-specific cost used to compare routes from the same source. The longest-prefix match selects the route with the most specific (longest) subnet mask. A floating static route serves as a backup by using a higher administrative distance than the primary route.
Key principle: Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Administrative distance: A measure of the trustworthiness of a routing protocol.
Why this is correct
This is correct because the longest prefix match rule ensures that the most specific route (with the longest subnet mask) is chosen for forwarding traffic, which is fundamental to IP routing.
Related concept
Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
- ✓
Metric: A value used by a routing protocol to determine the best path.
Why this is correct
This is incorrect because administrative distance (AD) is used to rank the reliability of routing protocols, not to select the most specific route. AD is a trustworthiness value assigned to each route source.
Related concept
Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
- ✓
Prefix length: The number of bits in the subnet mask that defines the network portion.
Why this is correct
This is incorrect because a metric is a value used by a routing protocol to choose the best path among routes learned from the same protocol, not to determine the most specific route. Metrics include hop count, bandwidth, delay, etc.
Related concept
Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
- ✓
Longest prefix match: The routing decision that selects the most specific route.
Why this is correct
This is incorrect because equal-cost multipath (ECMP) is a feature that allows load balancing across multiple routes with the same metric and prefix length, not a method for selecting the most specific route.
Related concept
Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Be careful not to confuse administrative distance with prefix length. AD is about protocol preference, not route specificity. Also, remember that longest prefix match is always evaluated before metric comparison.
Detailed technical explanation
How to think about this question
Longest-prefix match is the fundamental routing principle where the router selects the route with the most specific subnet mask that matches the destination IP address. This means that if multiple routes match, the one with the longest subnet mask (most bits set) is chosen because it precisely targets the destination network. This concept is critical in Cisco routing as it ensures traffic is forwarded along the most exact path available. After longest-prefix match narrows down candidate routes, administrative distance (AD) is used to rank routes learned from different sources or routing protocols. AD is a numeric value that represents the trustworthiness of a route source; lower AD values are preferred. For example, directly connected interfaces have an AD of 0, static routes default to 1, EIGRP routes have 90, and OSPF routes have 110. This ranking ensures that if multiple protocols provide routes to the same destination, the router installs the most reliable one. Metrics come into play when multiple routes to the same destination exist within the same routing protocol. Each protocol uses its own metric calculation method: EIGRP uses bandwidth and delay, OSPF uses cost based on interface bandwidth, and RIP uses hop count. The route with the lowest metric is preferred. Floating static routes are static routes configured with a higher administrative distance than the primary route, so they remain inactive until the primary route fails. This design prevents routing conflicts and provides a reliable backup path, a common practice in Cisco network failover strategies.
KKey Concepts to Remember
- Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
- Administrative distance ranks routing sources by trustworthiness, with lower values preferred to determine which routing protocol's route is installed in the routing table.
- Metric compares multiple paths within the same routing protocol to select the best route based on protocol-specific criteria like bandwidth or hop count.
- A floating static route is configured with a higher administrative distance than the primary route to act as a backup that only activates if the primary route fails.
- Routing tables use longest-prefix match first to find candidate routes, then administrative distance to choose between different protocols, and finally metric to select the best path within a protocol.
- Administrative distance values are fixed per routing protocol in Cisco devices, such as 0 for connected routes, 1 for static routes, 90 for EIGRP, and 110 for OSPF.
- Metrics vary by routing protocol: EIGRP uses bandwidth and delay, OSPF uses cost based on interface bandwidth, and RIP uses hop count.
- Floating static routes help ensure network resilience by providing a failover path without interfering with the primary routing decisions under normal conditions.
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
Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
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.
What to study next
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FAQ
Questions learners often ask
What does this 200-301 question test?
IP Routing — This question tests IP Routing — Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask..
What is the correct answer to this question?
The correct answer is: Administrative distance: A measure of the trustworthiness of a routing protocol. — Administrative distance indicates the trustworthiness of a routing protocol or static route, with lower values preferred. Metric is a protocol-specific cost used to compare routes from the same source. The longest-prefix match selects the route with the most specific (longest) subnet mask. A floating static route serves as a backup by using a higher administrative distance than the primary route.
What should I do if I get this 200-301 question wrong?
Review longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Longest-prefix match selects the most specific route by choosing the destination IP address with the greatest number of matching bits in the subnet mask.
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Last reviewed: Apr 12, 2026
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