Subnetting with Binary

• A byte is eight bits 0000 0000.
• A nibble is four bits 0000.
• A bit is on or off.

Powers of 2: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048

These are the groups.

Start with a /24, eight bits, or values from 0 to 256.

0000 0000

100 Hosts

A subnet needs 100 hosts, to represent that in binary, we’d need at least 7 bits, or 128.

A /24 would be too large, (256 IPs), remove a bit, and we get a /25.

10.0.0.0/25.

Borrowing One Bit

0000 0000

1000 0000

20 Hosts

We already spent the first portion of the address space, from 0 to 127.

0b0000 0000 is 0.

0b1000 0000 is 128.

How many bits to represent 20 hosts? at least 5, or 32.

So we start with 128, and use at least five bits.

0b1000 1000