IP Addressing

Hosts

CIDR

(CIDR) Classless Inter-Domain Routing

Worked Example of CIDR Block Relationships

10.0.0.0/16    = 10.0.0.0    to 10.0.255.255  which is 65,536 addresses

10.0.0.0/19    = 10.0.0.0    to 10.0.31.255   which is  8,192 addresses

10.0.32.0/19   = 10.0.32.0   to 10.0.63.255   which is  8,192 addresses

10.0.128.0/20  = 10.0.128.0  to 10.0.143.255  which is  4,096 addresses

10.0.144.0/20  = 10.0.144.0  to 10.0.159.255  which is  4,096 addresses

10.0.144.7/32  = 10.0.144.7  to 10.0.144.7    which is      1 address

Private Address Space

IANA has reserved the following three blocks of the IP address space for private internets:

10.0.0.0        -   10.255.255.255  (10/8 prefix)

172.16.0.0      -   172.31.255.255  (172.16/12 prefix)

192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

Loopback / localhost

Addresses in the 127.0.0.0/8 CIDR range are reserved for connections within the same machine (i.e. they cannot be used for connecting to another machine in the way that other IP addresses can). The loopback address is most often 127.0.0.1 but, in theory, any of the other addresses in the range could be used to similar effect.

For IPv6 the loopback address is 0000:0000:0000:0000:0000:0000:0000:0001 which is equivalent to 0:0:0:0:0:0:0:1 ior ::1

Bibliography