IPv4

IPv4 has been defined 1981 in the RFC 791. It is the first version, which has been used worldwide to connect far away computers and was a main factor of the development of the “internet“.

The IPv4 address consists of 32 bits which allows a maximum of 4.294.967.296 (232) unique addresses.

Network- and Host devision

An IP address consists of 2 parts – a Network and a Host part.
The devision is defined via the so called “subnet mask”.

Example: 24-Bit network

Subnet=11111111.11111111.11111111.00000000(255.255.255.0)
Network part=11000000.10101000.00000000(192.168.0)
Network address=11000000.10101000.00000000.00000000(192.168.0.0)
First address=11000000.10101000.00000000.00000001(192.168.0.1)
Last address=11000000.10101000.00000000.11111110(192.168.0.254)
Broadcast=11000000.10101000.00000000.11111111(192.168.0.255)

Amount of available addresses: 28 − 2 = 254

It is 28, because the whole IP address has 32 bit and 24-Bit have been “occupied” by the subnet. Thats why we only have 8 bit left.

The network address (192.168.0.0) and the broadcast address (192.168.0.255) are always subtracted from the maximal amount of available addresses because these 2 shouldn’t be used as client addresses.

Example: 16-Bit network

Subnet=11111111.11111111.00000000.00000000(255.255.0.0)
Network part=11000000.10101000(192.168)
Network address=11000000.10101000.00000000.00000000(192.168.0.0)
First address=11000000.10101000.00000000.00000001(192.168.0.1)
Last address=11000000.10101000.11111111.11111110(192.168.255.254)
Broadcast=11000000.10101000.11111111.11111111(192.168.255.255)

Amount of available addresses: 216 − 2 = 65,534

Reserved IP address spaces

Not everything of the maximum 232 available IP addresses have the same “functionality”. Instead some areas have a special cause. The most import are:

Address space (Prefix)UsageReferenz
0.0.0.0/8Current networkRFC 1122
10.0.0.0/81 private 8-Bit networkRFC 1918
127.0.0.0/8Loopback (Local computer)RFC 1122
169.254.0.0/16Private network (link local), APIPARFC 3927
172.16.0.0/1216 private 16-Bit networksRFC 1918
192.168.0.0/16256 private 24-Bit networksRFC 1918
255.255.255.255/32Limited BroadcastRFC 919RFC 922

Most of the here mentioned IP address spaces are only used for private usage and therefore for the “LAN” space.

Through this and other predefined IP address spaces the maximum amount of usable IPv4 addresses is decreased significantly.

Source: https://en.wikipedia.org/wiki/IPv4

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