Subnetting Answer Checker
Check calculated ranges and masks.
Subnetting Answer Checker: inputs and results
Enter an IP address, CIDR prefix, or range. Then check its first and last address below.
Calculated Boundaries & ParametersReady
Key Capabilities
- •100% Client-Side: Zero telemetry or server latency.
- •RFC Compliant: Exact 32-bit and 128-bit integer precision.
- •Quick Copy: Instant access to CIDR, mask, and range bounds.
- •Cross-Platform: Works on desktop, tablet, and mobile browsers.
Related Subnet Math & Set OperationsAll Tools
Bitwise Subnet Calculator
Show address-and-mask operations.
IP Address Offset Calculator
Add or subtract address positions.
Address Distance Calculator
Count positions between two addresses.
Subnet Boundary Checker
Check alignment to a specified prefix.
IP-in-Range Checker
Test whether an address belongs.
IP-in-Subnet Checker
Test membership within a CIDR block.
How Subnetting Answer Checker Works?
This tool works by computing the correct answer for a subnetting question and comparing it field by field with the submitted answer.
Enter the question
Type the address and prefix, such as
172.16.77.200/21.Enter the answers
Fill in network, broadcast, first host, last host, mask, and usable hosts.
Compute the correct values
The checker runs the subnet calculation for the question.
Mark each field
Each field is marked correct or wrong, and wrong fields show the expected value.
Subnetting Answer Checker Formula
The formula is Score = correct fields ÷ total fields × 100 %, with each field compared against the computed subnet value.
Network
IP AND MaskExpected network address.
Broadcast
Network OR WildcardExpected broadcast address.
Usable hosts
2^(32 − p) − 2Expected host count.
Score
correct ÷ 6 × 100 %For a 6-field question.
Worked example: 172.16.77.200/21
Block size in octet 3 = 256 − 248 = 8 77 → 72 (largest multiple of 8 ≤ 77) Network = 172.16.72.0 Broadcast = 172.16.79.255 Usable = 2^11 − 2 = 2,046
Subnetting Answer Checker Conversion Table
The table grades a sample student answer for 172.16.77.200/21, field by field.
| Field | Student Answer | Correct Answer | Result |
|---|---|---|---|
| Network address | 172.16.72.0 | 172.16.72.0 | Correct |
| Broadcast address | 172.16.79.255 | 172.16.79.255 | Correct |
| First usable host | 172.16.72.1 | 172.16.72.1 | Correct |
| Last usable host | 172.16.80.254 | 172.16.79.254 | Wrong |
| Subnet mask | 255.255.240.0 | 255.255.248.0 | Wrong |
| Usable hosts | 2,046 | 2,046 | Correct |
Score: 4 of 6 fields correct (66.7 %).
What is Subnetting Answer Checker?
The Subnetting Answer Checker is a tool that grades manual subnetting answers by comparing each field with the computed correct value.
Subnetting is a core skill in CCNA, CompTIA Network+, and university networking courses. Practice works best with fast feedback. The checker marks each field separately, so a student sees exactly which step went wrong: the block size, the mask, or the host range.
The checker accepts dotted masks and prefix lengths, and it applies RFC 3021 and host-route rules to /31 and /32 questions.
What are the uses of Subnetting Answer Checker?
There are 4 main uses of the Subnetting Answer Checker, including self-study, classroom grading, and interview practice.
Self-studying for exams
Learners solve questions on paper and check each field instantly.
Grading classroom work
Instructors grade worksheets field by field.
Practicing for interviews
Network engineering interviews include whiteboard subnetting.
Finding error patterns
Repeated wrong fields point to the step a learner needs to practice.