Question 1hardmultiple choice
Full question →Which summary route best represents these four networks?
10.20.0.0/24 10.20.1.0/24 10.20.2.0/24 10.20.3.0/24
hardmultiple choiceObjective-mapped
Which summary route best represents these four networks?
10.20.0.0/24 10.20.1.0/24 10.20.2.0/24 10.20.3.0/24
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
Best answer
10.20.0.0/22
Correct. /22 is the smallest summary that covers exactly those four /24 networks.
B
Distractor review
10.20.0.0/23
/23 would cover only two /24 networks at a time.
C
Distractor review
10.20.0.0/24
/24 covers only one of the listed networks.
D
Distractor review
10.20.0.0/21
/21 would also include additional networks and is less precise than needed.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent mistake is selecting a summary route with a mask that is either too specific or too broad. For instance, 10.20.0.0/23 covers only two of the four /24 networks, leading to incomplete summarization and routing table fragmentation. Conversely, 10.20.0.0/21 includes additional networks beyond the four intended, potentially causing routing inaccuracies and unnecessary traffic forwarding. This trap arises from not carefully analyzing the binary boundaries of the networks to find the smallest mask that covers all target subnets precisely.
Technical deep dive
How to think about this question
Subnet summarization is a critical concept in IP routing that reduces the size of routing tables by aggregating multiple contiguous networks into a single summary route. This process improves routing efficiency and conserves router resources by advertising fewer routes. In Cisco networking, summarization is often applied to contiguous subnets that share the same higher-order bits in their network addresses. To determine the correct summary route for multiple /24 networks, you analyze the binary representation of their network addresses to find the smallest subnet mask that encompasses all the given networks without including unrelated addresses. For the networks 10.20.0.0/24 through 10.20.3.0/24, the first 22 bits are common, making 10.20.0.0/22 the precise summary. This /22 mask covers exactly the IP range from 10.20.0.0 to 10.20.3.255, including all four /24 networks. A common exam trap is selecting a summary route that is either too narrow or too broad. For example, choosing 10.20.0.0/23 only covers two /24 networks, missing half the range, while 10.20.0.0/21 covers eight /24 networks, including four not listed, which can cause routing inefficiencies or incorrect traffic forwarding. Understanding how to calculate the correct summary mask ensures accurate and efficient routing in Cisco environments.
KKey Concepts to Remember
- Subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency.
- Cisco routers use the longest common prefix of network addresses to determine the smallest subnet mask for summarization.
- A summary route must cover all specified subnets without including unrelated networks to avoid routing errors.
- The /22 mask covers four contiguous /24 networks by encompassing all IP addresses from 10.20.0.0 to 10.20.3.255.
- Choosing a summary mask that is too narrow excludes some networks, causing incomplete routing information.
- Choosing a summary mask that is too broad includes extra networks, leading to inefficient routing and potential traffic misdirection.
- Binary analysis of network addresses is essential to accurately calculate summary routes in Cisco routing configurations.
- Proper summarization reduces routing overhead and improves convergence times in dynamic routing protocols.
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.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
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?
Subnet summarization aggregates multiple contiguous networks into a single route to reduce routing table size and improve efficiency.
What is the correct answer to this question?
The correct answer is: 10.20.0.0/22 — Four contiguous /24 networks starting at 10.20.0.0 summarize cleanly into 10.20.0.0/22. That block covers 10.20.0.0 through 10.20.3.255.
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.
Discussion
Loading comments…
Sign in to join the discussion.