Classes of IP addresses
IP address belongs in the same IP network as another IP address.
It is also for establishing the host address size for any given IP address. The IP address netmask, which is so commonly associated with an IP address today, was not required as the mask length was purely a function of the IP address. Any network device could inspect the first few bits of the 32 bit IP address to see which class it belonged to.
| Class
| Start
| End
| First bits
|
| Class A
| 0.0.0.0
| 127.255.255.255
| 0000
|
| Class B
| 128.0.0.0
| 191.255.255.255
| 1000
|
| Class C
| 192.0.0.0
| 223.255.255.255
| 1100
|
| Class D (multicast)
| 224.0.0.0
| 239.255.255.255
| 1110
|
| Class E (experimental)
| 240.0.0.0
| 255.255.255.255
| 1111
|
Some addresses are reserved for special uses.
| Addresses
| Purpose
| Class
| # of addresses
|
| 0.0.0.0 - 0.255.255.254<tt>
| Zero Addresses
| A
| 16,777,214
|
| <tt> 10.0.0.0 - 10.255.255.254
| intranet
| A
| 16,777,214
|
| 127.0.0.0 - 127.255.255.254
| localhost
| A
| 16,777,214
|
| 169.254.0.0 - 169.254.255.254
| APIPA
| B
| 65,534
|
| 172.16.0.0 - 172.31.255.254
| intranet
| B
| 1,048,574
|
| 192.168.0.0 - 192.168.255.254
| intranet
| C
| 65,534
|
Early allocations of IP addresses by IANA were in some cases not made very efficiently. This resulted with some organisations receiving class A networks which has contributed to the IP address shortage. Classful networking has been replaced by Classless InterDomain Routing since 1993 to solve this problem.
