This 300-410 practice question tests your understanding of route summarization. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
A network engineer runs the following command to troubleshoot a Route Summarization issue:
R1# show ip route summary
IP routing table maximum-paths limit: 32
IP routing table entry count: 15
IP routing table active entry count: 15
Number of prefixes: 15
Number of /0: 0
Number of /8: 1
Number of /16: 2
Number of /24: 12
Number of /32: 0
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The routing table contains 2 /16 summary routes, likely summarizing the 12 /24 subnets, indicating successful route summarization.
This output shows a summary of the IP routing table. The prefix length distribution indicates that there are 2 /16 routes and 12 /24 routes. This suggests that route summarization is in effect, as the /16 routes likely summarize the /24 subnets.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 routing table contains 2 /16 summary routes, likely summarizing the 12 /24 subnets, indicating successful route summarization.
Why this is correct
The presence of fewer /16 routes than /24 routes suggests summarization is working.
The routing table has no summarization, as all routes are /24 or smaller.
Why it's wrong here
There are 2 /16 routes, which are summary routes.
✗
The routing table is full and cannot accept more routes.
Why it's wrong here
The entry count is only 15, well below typical limits.
✗
The summary routes are not being used because they are inactive.
Why it's wrong here
All 15 entries are active.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.
Route Summarization — This question tests Route Summarization — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The routing table contains 2 /16 summary routes, likely summarizing the 12 /24 subnets, indicating successful route summarization. — This output shows a summary of the IP routing table. The prefix length distribution indicates that there are 2 /16 routes and 12 /24 routes. This suggests that route summarization is in effect, as the /16 routes likely summarize the /24 subnets.
What should I do if I get this 300-410 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 300-410 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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