Subnetting

Binary Basics

• Binary uses only two values: 0 or 1
• Each bit represents a single binary value (0 or 1)

Bit and Byte

• 1 bit = 0 or 1
• 1 byte = 8 bits
• 1 octet = 1 byte = 8 bits

In networking, we usually say octet instead of byte because an IPv4 address always uses 8-bit groupings.

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IPv4 Addresses and Decimal vs Binary

An IPv4 address is: 192.168.1.165

• 32 bits total
• Written as 4 octets
• Each octet = 8 bits
• Each octet is shown in decimal (base 10), but computers work in binary (base 2)

To truly understand an IP address, we convert each decimal octet into binary.

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Decimal to Binary Conversion (One Octet)

Each octet uses 8 binary place values:

128	64	32	16	8	4	2	1

You determine whether each value is used (1) or not used (0).

Rule:

• Put 1 if you use that value
• Put 0 if you don’t
• The values you choose must add up to the decimal number

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Convert Each Octet to Binary

1) Convert 192 to Binary

192 = 128 + 64

128	64	32	16	8	4	2	1
1	1	0	0	0	0	0	0

192 = 11000000

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2) Convert 168 to Binary

168 = 128 + 32 + 8

128	64	32	16	8	4	2	1
1	0	1	0	1	0	0	0

168 = 10101000

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3) Convert 1 to Binary

1 = 1

128	64	32	16	8	4	2	1
0	0	0	0	0	0	0	1

1 = 00000001

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4) Convert 165 to Binary

165 = 128 + 32 + 4 + 1

128	64	32	16	8	4	2	1
1	0	1	0	0	1	0	1

165 = 10100101

Final Answer (Full IPv4 in Binary):

11000000.	10101000.	00000001.	10100101
192.	168.	1.	165

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Key Notes

• Each octet is 8 bits, so it has 256 possible values
• That’s why each octet ranges from:
  • 0 to 255 (because 2^8 = 256 values)

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Host Bits	Total Addresses	Usable Devices
1	2	0
2	4	2