IP Addressing

IP addresses are described as consisting of two groups of bits in the address:

  - the most significant part is the network address which identifies a whole network or subnet

  - and the least significant portion is the host identifier, which specifies a particular host interface on that network.

This division is used as the basis of traffic routing between IP networks and for address allocation policies.

Classful Addressing -

 - Classful network design for IPv4 sized the network address as one or more 8-bit groups, resulting in the blocks of Class A, B, or C addresses.

Class	First Byte	Network ID / Host ID (Bytes)	Theoretical IP Address Range
Class A	0xxx xxxx	1 / 3	1.0.0.0 to 126.255.255.255
Class B	10xx xxxx	2 / 2	128.0.0.0 to 191.255.255.255
Class C	110x xxxx	3 / 1	192.0.0.0 to 223.255.255.255
Class D	1110 xxxx	—	224.0.0.0 to 239.255.255.255
Class E	1111 xxxx	—	240.0.0.0 to 255.255.255.255

Classless Inter-Domain Routing -

 - CIDR allocates address space to Internet service providers and end users on any address bit boundary, instead of on 8-bit segments

 - CIDR specifies an IP address range using a combination of an IP address and its associated network mask. CIDR notation uses the following format - xxx.xxx.xxx.xxx/n, where n is the number of (leftmost) '1' bits in the mask.

 - For example, 192.168.12.0/23 applies the network mask 255.255.254.0 to the 192.168 network, starting at 192.168.12.0. This notation represents the address range 192.168.12.0 - 192.168.13.255.