CCNA Network Infrastructure and Connectivity Practice Question
A host address is 172.16.8.70/26. What is the network address of its subnet?
⚠ Common exam trap
A frequent exam trap is mistaking the host IP address for the network address or selecting the wrong subnet block based on the subnet mask. Candidates often pick 172.16.8.0 because it looks like a common network address or 172.16.8.128 assuming it’s the next block, but these do not contain the host 172.16.8.70 under a /26 mask. The trap arises from not calculating subnet ranges correctly or misunderstanding how subnet masks segment the address space into fixed blocks. This mistake leads to incorrect subnet identification and can cause routing or addressing errors in real networks.
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
✓
172.16.8.64
A /26 uses blocks of 64 addresses. In plain language, the fourth-octet subnet ranges are 0–63, 64–127, 128–191, and 192–255. Since the host address ends in 70, it belongs to the 64–127 block. That means the network address of the subnet is 172.16.8.64. This is a standard subnetting calculation. The key is to identify the correct block based on the prefix and then choose the first address in that block as the network address.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
172.16.8.0
Why it's wrong here
The network 172.16.8.0/26 spans addresses .0 through .63, and the host address .70 is beyond that upper boundary. Because the next /26 subnet starts at .64, the .0 network cannot include this host. Thus, 172.16.8.0 is incorrect; the block containing .70 begins at .64.
When this WOULD be correct
If the question asked for the network address of the subnet for a host address of 172.16.8.70 with a subnet mask of /24, then 172.16.8.0 would be the correct answer, as it represents the beginning of that subnet.
- ✓
172.16.8.64
Why this is correct
For a /26 prefix, the subnet mask is 255.255.255.192, which creates block sizes of 64 addresses in the fourth octet. The host address .70 lies in the range 64–127, so the network address is found by zeroing the host bits: 70 AND 192 = 64. Thus, 172.16.8.64 is the correct network address for this host.
- ✗
172.16.8.70
Why it's wrong here
172.16.8.70 is simply the host address itself, not the network address. In a /26 subnet, the low 6 bits are host bits, and 70 in binary is 01000110; clearing those host bits yields 01000000, which is 64. Therefore, .70 is a valid host address inside the 172.16.8.64/26 subnet but cannot be the network address.
When this WOULD be correct
If the question asked for the specific host address within the subnet or if it was framed to identify a host's IP address rather than the network address, then 172.16.8.70 would be the correct answer.
- ✗
172.16.8.128
Why it's wrong here
The network 172.16.8.128/26 covers addresses from .128 to .191, which is the next block after the .64 subnet. Since the host address .70 is numerically less than .128, it falls into the earlier .64–.127 range, not the .128 block. Therefore, .128 is the network address of a different subnet that does not contain host .70.
When this WOULD be correct
In a different question, if the subnet mask were changed to /25, the network address would be 172.16.8.128. For example, a question asking for the network address of the subnet containing the host 172.16.8.130 with a /25 mask would make this option correct.
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.
✓172.16.8.64Correct answer▾
Why this is correct
For a /26 prefix, the subnet mask is 255.255.255.192, which creates block sizes of 64 addresses in the fourth octet. The host address .70 lies in the range 64–127, so the network address is found by zeroing the host bits: 70 AND 192 = 64. Thus, 172.16.8.64 is the correct network address for this host.
✗172.16.8.0Wrong answer — click to see why▾
Why this is wrong here
The /26 prefix means a subnet mask of 255.255.255.192, which creates subnets with a block size of 64. The subnet ranges are 0–63, 64–127, 128–191, and 192–255. Since 70 is not in the 0–63 range, 172.16.8.0 is not the correct network address.
★ When this WOULD be the correct answer
If the question asked for the network address of the subnet for a host address of 172.16.8.70 with a subnet mask of /24, then 172.16.8.0 would be the correct answer, as it represents the beginning of that subnet.
Why candidates choose this
Students often mistakenly assume that the network address is always the first address of the entire /16 or /24 network, ignoring the subnetting. They might think 172.16.8.0 is the network address because it is the first address in the 172.16.8.0/24 range.
✗172.16.8.70Wrong answer — click to see why▾
Why this is wrong here
The network address is the first address in a subnet, where all host bits are 0. The address 172.16.8.70 has host bits that are not all zeros; it is a valid host address within the subnet 172.16.8.64/26. Therefore, it cannot be the network address.
★ When this WOULD be the correct answer
If the question asked for the specific host address within the subnet or if it was framed to identify a host's IP address rather than the network address, then 172.16.8.70 would be the correct answer.
Why candidates choose this
A student might confuse the host address with the network address, especially if they are not careful about the distinction between the two. They might think that the given IP address itself is the network address.
✗172.16.8.128Wrong answer — click to see why▾
Why this is wrong here
The subnet 172.16.8.128/26 covers addresses 128–191. Since 70 is less than 128, it does not belong to this subnet. The network address for the subnet containing 70 is 172.16.8.64, not 172.16.8.128.
★ When this WOULD be the correct answer
In a different question, if the subnet mask were changed to /25, the network address would be 172.16.8.128. For example, a question asking for the network address of the subnet containing the host 172.16.8.130 with a /25 mask would make this option correct.
Why candidates choose this
Students sometimes miscalculate the subnet boundaries, especially when the host address is near the boundary. They might incorrectly think that 70 is close to 128 and choose 172.16.8.128 without performing the proper calculation.
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
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Related to this question
Learn chapter
IPv4 Addressing and Address Classes
Key term
Subnetting
Subnetting is the process of dividing a larger IP network into smaller, more manageable subnetworks (subnets) to improve performance, security, and efficient use of IP addresses.
Key term
Classless Inter-domain Routing
Classless Inter-domain Routing (CIDR) is a method for allocating IP addresses and routing IP packets more efficiently by replacing the old class-based system with variable-length subnet masks.
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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.