ANDing Network Address Calculator

About this interactive

With a classful mask the network address is easy to read off, but with a custom mask a device works it out by ANDing: it lines up its IP address and its subnet mask in binary and compares them bit by bit. The result bit is 1 only where both bits are 1; 1 AND 0, 0 AND 1 and 0 AND 0 all give 0. Because the mask is ones and then zeros, the network bits of the address come through unchanged and every host bit is cleared, which is exactly the network address. You only need binary for one octet. Where the mask octet is 255 the address octet copies across, and where it is 0 the result is 0. Take 192.168.0.88 with mask 255.255.255.192: the first three octets copy, and in the last, 88 is 01011000 and 192 is 11000000, so the AND is 01000000, which is 64. The network address is 192.168.0.64. The line can fall in any octet: 10.100.111.5/19 has mask 255.255.224.0, so the third octet does the work (111 AND 224 is 96), the last becomes 0, and the network is 10.100.96.0. Type the network address in dotted decimal. Anything you miss shows the answer and the AND that gives it. Seven of the twenty questions are drawn each run.

What you'll learn

Apply a bitwise AND between an IPv4 address and its subnet mask to find the network address
Find the network address for a mask whose boundary falls inside the second, third or fourth octet

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.
Binary: The base-2 number system that uses only the digits 0 and 1; the native language of digital computers, which store and process data as electrical on/off states.
Prefix Length: The number of consecutive 1-bits in a subnet mask, written after a slash (e.g., /24), that defines how many bits of an IP address represent the network portion versus the host portion. A /24 prefix means the first 24 bits identify the network, leaving 8 bits for host addresses.

Topics

Anding Network Address Subnet Mask Interactive Calculation

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