IP Address allocation

Out of the 126 usable Class A networks (1-126):

• 125 are designated for public use (networks 1-9 and 11-126)

• 1 is reserved for private use (network 10)

Reserved/Special Use Networks:

• 10.0.0.0/8 - Reserved for private use (RFC 1918)

• 127.0.0.0/8 - Loopback addresses (though this is technically outside the 1-126 range)

Early Internet Assignments: Many Class A networks were assigned in the early days of the internet to large organizations, universities, and government entities. Some notable examples:

• MIT, Stanford, IBM, General Electric, AT&T, and other major institutions received entire Class A blocks

• The U.S. Department of Defense received several Class A networks

Current Reality:

• Some originally assigned Class A networks have been returned to IANA for redistribution

• Others have been subdivided using CIDR (Classless Inter-Domain Routing) rather than being used as single massive networks

• The rigid Class A/B/C system has been largely replaced by CIDR, which allows for more flexible network sizing

IPv4 Exhaustion: Since IPv4 addresses are now exhausted (the last blocks were allocated in 2011), the focus has shifted to IPv6 deployment rather than trying to utilize every possible Class A network.

The RFC 1918 private IP address ranges are:

Class A:

• 10.0.0.0/8 (10.0.0.0 to 10.255.255.255) - Only one Class A private range

Class B:

• 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) - 16 Class B private ranges

Class C:

• 192.168.0.0/16 (192.168.0.0 to 192.168.255.255) - 256 Class C private ranges

The technical definition of "10.0.0.0/8" would be:

"Network 10.0.0.0 with an 8-bit subnet mask" or "Network 10.0.0.0 with a /8 prefix length"