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IP Addressing Fundamentals

What is IP?

IP (Internet Protocol) is used to identify a device on a network or the internet.

There are two versions of IP:

IPv4

  • 32 bits
  • Decimal format
  • Example: 192.168.1.1
  • Total addresses: 2³² = 4.29 billion

IPv6

  • 128 bits

  • Hexadecimal format

  • Example: 2001:0db8::1

  • Total addresses: 2¹²⁸ ≈ 3.4 × 10³⁸

    IPv6 has about 7.9 × 10²⁸ times more addresses than IPv4

IPv4 Address

IPv4 is a 32-bit address.

These 32 bits are divided into 4 portions (octets).

Each octet:

  • Contains 8 bits
  • Range: 0 – 255

Format:

n.n.n.n

Example:

192.168.10.1

Minimum value:

00000000 = 0

Maximum value:

11111111 = 255

Network Part and Host Part

Each IPv4 address has two parts:

Network Part

  • Identifies network
  • Same for all devices in network
  • Defined by subnet mask
  • Contains 1s in subnet mask

Host Part

  • Identifies device
  • Must be unique
  • Contains 0s in subnet mask

Example:

IP:

192.168.20.12

Subnet mask:

255.255.255.0

Network part:

192.168.20

Host part:

12

Subnet Mask

Subnet mask is used to identify network and host part.

Example:

IP address:

192.168.20.12

Subnet mask:

255.255.255.0

Subnet Mask Notations

Subnet mask can be written in three ways

Binary

11111111.00000000.00000000.00000000

Decimal

255.0.0.0

Slash notation (CIDR)

/8

IPv4 Classes

Class A

Range:

1 – 127

Subnet mask:

255.0.0.0

CIDR:

/8

Network bits: 8 Host bits: 24

Number of networks:

126

Hosts per network:

2^24 - 2 = 16,777,214

-2 is for:

  • Network ID
  • Broadcast address

Example:

Network ID:

120.0.0.0

Broadcast:

120.255.255.255

Class B

Range:

128 – 191

Subnet mask:

255.255.0.0

CIDR:

/16

Number of networks:

2^14 = 16384

Hosts per network:

2^16 - 2 = 65534

Class C

Range:

192 – 223

Subnet mask:

255.255.255.0

CIDR:

/24

Number of networks:

2^21 = 2,097,152

Hosts per network:

2^8 - 2 = 254

Class D

Range:

224 – 239

Used for:

Multicast

Class D is used for multicast, not host addressing

Class E

Range:

240 – 255

Used for:

  • Experimental purposes
  • Research
  • Not public use

Reserved by:

IETF

Loopback IP Address

Loopback IPv4:

127.0.0.0/8

Common loopback:

127.0.0.1

IPv6 loopback:

::1

Used for:

  • Testing TCP/IP
  • Testing network card
  • Testing local machine

Also called:

localhost

IP Configuration

IP can be assigned in two ways

1. Static IP (Manual)

Assigned manually.

Steps (Windows):

Run → ncpa.cpl
Ethernet → Properties
IPv4 → Properties
Uncheck "Obtain IP automatically"

Check IP:

ipconfig

Detailed:

ipconfig /all

Default Gateway

Default gateway is the IP address of router used to access:

  • Other networks
  • Internet

Example:

192.168.1.1

DNS Server

DNS = Domain Name System

DNS translates:

Domain → IP
IP → Domain

Example:

google.com → 8.8.8.8

Dynamic IP Configuration (DHCP)

DHCP server automatically assigns:

  • IP address
  • Subnet mask
  • Default gateway
  • DNS server

Steps:

Run → ncpa.cpl
Ethernet → Properties
IPv4 → Properties
Check "Obtain IP automatically"

APIPA

APIPA = Automatic Private IP Addressing

When DHCP fails:

  • Computer assigns IP to itself

Range:

169.254.0.0 – 169.254.255.255

Characteristics:

  • Temporary
  • No internet access
  • DHCP problem indicator
  • Local communication only

Private IP Addresses

Used inside LAN networks.

Reserved by IANA

Class A:

10.0.0.0 – 10.255.255.255

Class B:

172.16.0.0 – 172.31.255.255

Class C:

192.168.0.0 – 192.168.255.255

Used with:

NAT

Public IP Addresses

Used on:

  • Internet
  • WAN networks

Characteristics:

  • Globally unique
  • Assigned by ISP
  • Must be purchased

Everything outside private ranges is public.

Why IPv4 Still Used

  • Easy to understand
  • Compatible with old systems
  • Widely deployed
  • Supported everywhere

IPv4 shortage solved by:

  • NAT
  • Subnetting

NAT

Converts:

Private IP ↔ Public IP

Subnetting

Divides:

Large network → Small networks