Network Address Worksheet Audit

About this interactive

A device finds the network it is on by ANDing its IP address with its subnet mask, bit by bit: the result is 1 only where both bits are 1. Because a mask is ones and then zeros, every network bit of the address comes through unchanged and every host bit becomes 0. That result is the network address. You only need binary in one octet. Where the mask octet is 255 the address octet copies across, and where it is 0 the result is 0. In the octet where the mask is neither, AND the two in binary. Take 10.5.83.20/21: the mask is 255.255.248.0, so the third octet does the work. 83 is 01010011 and 248 is 11111000, so the AND is 01010000, which is 80, and the network address is 10.5.80.0. The prefix and the dotted mask are the same thing written two ways: count the ones in the mask (8 + 8 + 5 = 21) and you have the prefix. Checking someone else's work is the same AND, done for every row, plus one more check: that the prefix and the dotted mask agree. Flag every wrong row, then submit. Every wrong row is then explained, with the fix.

What you'll learn

Check a network address worked out by ANDing a host address with its subnet mask, with the mask boundary in the second, third or fourth octet
Check that a subnet mask written in dotted decimal and its CIDR prefix describe the same mask

Aligned to

CompTIA Network+

1.7 Given a scenario, use appropriate IPv4 network addressing.

Cisco CCNA

1.6 Configure and verify IPv4 addressing and subnetting

Cisco CCST Networking

2.2 Identify IPv4 addresses and subnet formats

Key terms

ANDing: A bitwise operation used to calculate a network address by comparing each bit of an IP address with the corresponding bit of a subnet mask, returning 1 only when both bits are 1.
Network Address: The first address in an IP network range that identifies the network itself and cannot be assigned to a host. It is formed when all host bits are set to zero.
Subnet Mask: A 32-bit number that divides an IP address into network and host portions.
Host Bits: The portion of an IPv4 address that identifies individual devices within a network segment, as determined by the subnet mask.
Classless Inter-Domain Routing: A method for allocating IP addresses and expressing routing prefixes that replaces the older classful addressing scheme by using variable-length prefix notation (e.g., /24). CIDR enables more efficient use of IPv4 address space and reduces the size of internet routing tables through route aggregation.

Topics

Subnetting Anding Network Address Subnet Mask Interactive Spot The Error

About TechKnowSurge

TechKnowSurge builds IT and cybersecurity professionals through hands-on, concept-first training built around real understanding — not memorization. Free interactive tools, structured programs, and 25+ years of real-world experience, all in one place.

Explore free tools and programs →