CCNA Network Infrastructure and Connectivity Practice Question
Which prefix length corresponds to the subnet mask 255.255.255.192?
⚠ Common exam trap
Be careful not to confuse similar subnet masks or miscount the number of bits in the binary representation.
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
✓
/26
The mask 255.255.255.192 corresponds to /26. In practical terms, the first three octets contribute 24 network bits, and 192 in binary is 11000000, which contributes 2 more network bits. That totals 26 network bits. This is a standard conversion skill that matters in subnetting, ACL design, and route interpretation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
/25
Why it's wrong here
Choosing /25 would imply a subnet mask of 255.255.255.128, where the last octet is 10000000 and only seven host bits remain. That configuration allows 128 addresses per subnet, which is double the address space of 255.255.255.192, indicating a larger subnet. The given mask's last octet is 11000000, so it requires 26 network bits, not the 25 bits of /25.
When this WOULD be correct
In a different question, if the exam asked for the prefix length of a subnet mask of 255.255.255.128, then option A: /25 would be the correct answer, as it accurately reflects that subnet mask.
- ✓
/26
Why this is correct
The subnet mask 255.255.255.192 has a binary pattern of 11111111.11111111.11111111.11000000, which places two additional network bits in the fourth octet beyond the standard /24. Adding those two bits to the 24 bits of the first three octets yields 26 network bits, so the only correct prefix length is /26. This mask provides 64 total addresses per subnet and 62 usable host addresses.
- ✗
/27
Why it's wrong here
A /27 prefix means 27 network bits, which translates to a subnet mask of 255.255.255.224 (the last octet being 11100000 in binary). This mask creates subnets of 32 addresses each, leaving only five host bits, and is too specific because it subdivides the network further than 255.255.255.192. The mask in question has 26 network bits, not 27, so /27 does not correspond to 255.255.255.192.
When this WOULD be correct
If the question asked for the prefix length for a subnet mask of 255.255.255.224, then option C: /27 would be the correct answer, as it accurately represents that subnet mask.
- ✗
/28
Why it's wrong here
With 28 network bits, the subnet mask becomes 255.255.255.240, as the final octet is 11110000. Such a mask yields only 16 addresses per subnet and 14 usable hosts, making it a much smaller subnet than the one defined by 255.255.255.192. Since 255.255.255.192 has exactly 26 consecutive ones, /28 cannot be the matching prefix length.
When this WOULD be correct
If the exam question asked for the prefix length corresponding to the subnet mask 255.255.255.240, then option D: /28 would be the correct answer, as it accurately represents that subnet mask.
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.
✓/26Correct answer▾
Why this is correct
The subnet mask 255.255.255.192 has a binary pattern of 11111111.11111111.11111111.11000000, which places two additional network bits in the fourth octet beyond the standard /24. Adding those two bits to the 24 bits of the first three octets yields 26 network bits, so the only correct prefix length is /26. This mask provides 64 total addresses per subnet and 62 usable host addresses.
✗/25Wrong answer — click to see why▾
Why this is wrong here
The /25 prefix length corresponds to subnet mask 255.255.255.128, not 255.255.255.192. The mask 255.255.255.128 has 128 in the last octet, while 255.255.255.192 has 192, indicating a different number of host bits.
★ When this WOULD be the correct answer
In a different question, if the exam asked for the prefix length of a subnet mask of 255.255.255.128, then option A: /25 would be the correct answer, as it accurately reflects that subnet mask.
Why candidates choose this
Students often confuse /25 and /26 because both are common subnet masks used for subnetting a /24 network. The difference of one bit can be overlooked, especially when quickly calculating subnet boundaries.
✗/27Wrong answer — click to see why▾
Why this is wrong here
The /27 prefix length corresponds to subnet mask 255.255.255.224, not 255.255.255.192. The mask 255.255.255.224 has 224 in the last octet, which provides 30 usable hosts per subnet, whereas 255.255.255.192 provides 62 usable hosts.
★ When this WOULD be the correct answer
If the question asked for the prefix length for a subnet mask of 255.255.255.224, then option C: /27 would be the correct answer, as it accurately represents that subnet mask.
Why candidates choose this
Students may mistakenly think that /27 is the next logical step after /26, but the actual progression is /25, /26, /27, /28. The value 192 in the mask can be misremembered as 224 due to similar numeric patterns.
✗/28Wrong answer — click to see why▾
Why this is wrong here
The /28 prefix length corresponds to subnet mask 255.255.255.240, not 255.255.255.192. The mask 255.255.255.240 has 240 in the last octet, which supports 14 usable hosts, while 255.255.255.192 supports 62 usable hosts.
★ When this WOULD be the correct answer
If the exam question asked for the prefix length corresponding to the subnet mask 255.255.255.240, then option D: /28 would be the correct answer, as it accurately represents that subnet mask.
Why candidates choose this
Students might confuse the decimal value 192 with 240 because both are common subnet mask values. Additionally, /28 is a frequently used prefix for small subnets, leading to a hasty association with any mask ending in a non-zero octet.
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
Subnetting and VLSM
Key term
ACL
An Access Control List is a set of rules that determines who or what can access specific network resources or data.
Key term
Subnet mask
A subnet mask is a 32-bit number that helps a computer or network device determine which part of an IP address identifies the network and which part identifies the host device on that network.
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JA
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.