Bits, Bytes, and Hex

 

⭐ PART 1 — Bits, Nibbles, Bytes (The Foundations)

Bit

• A 0 or 1

• Smallest unit of data.

Example:
1 or 0

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Nibble

• 4 bits

• Can represent values 0–15 decimal

• Hex digit maps perfectly to a nibble, which is why hex exists in networking.

Example:

Binary: 1010
Decimal: 10
Hex: A

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Byte

• 8 bits = 2 nibbles

• Can represent 0–255 decimal

Example:

Binary:   11001100
Nibbles:  1100 1100
Hex:      CC
Decimal:  204

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⭐ PART 2 — Why Networking Loves Hex

Hex is just a human-friendly way to write binary.

• 1 hex digit = 4 bits

• 2 hex digits = 1 byte (8 bits)

This makes it ideal for:

• MAC addresses (48 bits)

• IPv6 addresses (128 bits)

• TCP/IP headers (lots of 16-bit and 32-bit fields)

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⭐ PART 3 — MAC Addresses (48 bits, always hex)

A MAC address is 48 bits = 6 bytes = 12 hex digits.

Example MAC:

AA-BB-CC-11-22-33

Let’s decode the first byte:

First byte: AA

Hex	Binary
A	1010
A	1010

So AA in binary:

1010 1010

The entire MAC in binary:

AA      BB      CC      11      22      33
1010 1010 1011 1011 1100 1100 0001 0001 0010 0010 0011 0011

Important MAC-level bits:

The first byte contains two special bits:

Bit	Meaning
LSB of first byte	Unicast (0) / Multicast (1)
2nd LSB	Globally unique (0) / Locally administered (1)

Example:
AA = 10101010

• LSB = 0 → Unicast

• Next bit = 1 → Locally administered MAC

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⭐ PART 4 — IPv4 Addresses

(32 bits = 4 bytes = 8 hex digits)

Example IPv4 address:

192.168.1.10

Break into bytes:

• 192 → 11000000 → C0

• 168 → 10101000 → A8

• 1 → 00000001 → 01

• 10 → 00001010 → 0A

IPv4 in hex:

C0 A8 01 0A

IPv4 in binary (all 32 bits):

11000000 10101000 00000001 00001010

Why useful?
This is exactly how routers see IPs in memory and packet headers.

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⭐ PART 5 — IPv6 Addresses

(128 bits = 16 bytes = 32 hex digits)

Example IPv6:

2001:0db8:85a3:0000:0000:8a2e:0370:7334

Each group is 16 bits (2 bytes):

• 2001 in binary =
  0010 0000 0000 0001

IPv6 in full binary representation is a 128-bit monster, but hex makes it readable.

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⭐ PART 6 — Example: IP Header Fields in Binary/Hex

Let’s decode the first 4 bytes of an IPv4 header:

Hex dump:

45 00 00 54

Breakdown:

Byte 1 — Version + IHL

45 hex = 0100 0101 binary

• Version = 0100 = 4

• IHL = 0101 = 5 × 4 bytes = 20-byte header

Byte 2 — DSCP/ECN

00 hex = 0000 0000

• DSCP = 000000

• ECN = 00

Bytes 3–4 — Total Length

00 54 hex → 0x0054 → 84 bytes

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⭐ PART 7 — ARP Packet Example (MAC + IP in binary/hex)

Example ARP request (simplified):

Sender MAC: AA-BB-CC-11-22-33
Sender IP: 192.168.1.10

Sender IP in hex:

C0 A8 01 0A

ARP field dump (simplified):

AA BB CC 11 22 33  C0 A8 01 0A

Binary:

[48 bits MAC]        [32 bits IP]
10101010 10111011... 11000000 10101000 00000001 00001010

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⭐ PART 8 — TCP Header Example (16-bit and 32-bit fields)

TCP Source Port: 443

• Decimal: 443

• Hex: 01BB

• Binary: 0000 0001 1011 1011

Sequence number (32 bits):
Example: 0xABCD1234 → 128-bit hex notation becomes useful.

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⭐ PART 9 — Hex is Everywhere in Protocols

• VLAN tags: 0x8100

• EtherType fields:

  • IPv4 = 0x0800

  • IPv6 = 0x86DD

  • ARP = 0x0806

• TCP flags are individual bits inside a byte

• STP BPDUs have fields like:

  • Root Priority: 0x8000

  • Bridge ID uses MAC + priority (combination of hex + binary)

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⭐ PART 10 — Quick Conversion Table (for your brain)

Hex → Binary

Hex	Binary
0	0000
1	0001
2	0010
3	0011
4	0100
5	0101
6	0110
7	0111
8	1000
9	1001
A	1010
B	1011
C	1100
D	1101
E	1110
F	1111