Level 3 addresses: IPv4

Definition: An IPv4 address is a sequence of 4 numbers separated by a dot, called : dotted decimals.

Ex: 192.168.10.1 -- xxx = 1 byte = 8 bits An IPv4 address is encoded on 4 bytes The size of an IP address is 32 bits.

Anatonmie of an IPv4 address :

IPv4 addresses are divided into classes: There are 5 IPv4 classes:

Example:

Subnet mask

The subnet mask is an IPv4 address whose first octet must be 255.

It separates the network and machine parts of an IPv4 address.

Default subnet masks

Network part: NetID -- Network Identification

This is the network part of an IPv4 address, enabling you to identify the network to which a machine belongs.

Machine part: HostID

This is the machine/host part of an IPv4 address, used to identify a machine on the network.

Calculating the number of available addresses :

To calculate the number of available addresses:

2^n - 2 = available addresses

n = number of 0s in the subnet mask in binary.

Private IP addresses

A private IP address is used to communicate on a local area network (LAN).

A public IP address enables communication on the public network (WAN).

Network subdivision

We subdivide a network to obtain distinct sub-networks.

Example: Specification: The network is given: 192.168.10.1 | 255.255.255.0

We ask that this network be divided into 4 distinct subnetworks.

Step 1

Find the number of bits to freeze:

2^n >= Number of subnetworks to create

n is the number of bits to freeze.

In our case:

2² = 4

The number of bits to freeze is 2.

Step 2

Convert IP address and mask to binary

192.168.10.1 = 11000000.10101000.00001010.00000001
255.255.255.0 = 11111111.11111111.11111111.00000000

Reminder of the truth table for the ET logical operator:

Step 3:

Perform the logical “AND” operation bit by bit between the IP address and the subnet mask.

11000000.10101000.00001010.00000001
11111111.11111111.11111111.00000000

11000000.10101000.00001010.00000000

11000000.10101000.00001010.00000000 will be the address of the router, the subnetwork

@router = 192.168.10.0 | 255.255.255.0

Subdivision into subnetworks :

Reminder:

2^n >= Number of subnetworks

2² = 4

Count to 4 in binary with 2 bits :

Subnet 0 :

192.168.10.0000 00000

The bolded bits are the freezed bits, 00 for subnet 0, we start counting from 0. The aim is to set all non-freezed bits to 1 to have the broadcast address.

INFO: The broadcast address makes it possible to communicate with all hosts on the network.

First usable address = Subnet address + 0.0.0.1

Last usable address = Broadcast address - 0.0.0.1

Subnet 0 summary :

Subnet 1 :

Subnet address = 192.168.10.0100 0000

Subnet address = 192.168.10.64

Broadcast address = 192.168.10.0111 1111

Broadcast address = 192.168.10.127

Subnet 1 summary

Subnet 2 :

Subnet address = 192.168.10.1000 0000

Subnet address = 192.168.10.128

Broadcast address = 192.168.10.1011 1111

Broadcast address = 192.168.10.191

Subnet 2 summary

Subnet 3 :

Subnet address = 192.168.10.1100 0000

Subnet address = 192.168.10.192

Broadcast address = 192.168.10.1111 1111

Broadcast address = 192.168.10.255

Subnet 3 summary

CIDR notation :

CIDR notation (Classless Interdomain Routing) is a notation that associates its IP address with its subnet mask.

We thus have: <@IP>/Number of bits in subnet.

Example: @IP : 192.168.10.1 | 255.255.255.0

255.255.255.0 => 11111111.11111111.11111111.00000000

8+8+8 = 24 192.168.10.1/24