Some large blocks of IPv4 addresses, the former Class A network blocks, are assigned in whole to single organizations or related groups of organizations, either by the Internet Corporation for Assigned Names and Numbers (ICANN), through the Internet Assigned Numbers Authority (IANA), or a regional Internet registry.
Each block contains 256 = 2 = 16,777,216 addresses, which covers the whole range of the last three delimited segments of an IP address. This means that 256 /8 address blocks fit into the entire IPv4 space.
As IPv4 address exhaustion has advanced to its final stages, some organizations, such as Stanford University, formerly using , have returned their allocated blocks (in this case to APNIC) to assist in the delay of the exhaustion date.
List of reserved /8 blocks
Block Organization IANA date RIR date Notes 0.0.0.0/8 IANALocal Identification 1981-09 Originally IANAReserved 1981-09. 0.0.0.0/8 reserved for self-identification. 10.0.0.0/8 IANAPrivate Use 1995-06 Reserved for Private Networks. Formerly ARPANET. 127.0.0.0/8 IANALoopback 1981-09 127.0.0.0/8 is reserved for loopback. 224.0.0.0/8–239.0.0.0/8 Multicast 1981-09 1991-05-22 Multicast (formerly "Class D") registered in multicast addresses 240.0.0.0/8–255.0.0.0/8 Future Use 1981-09 Reserved for future use (formerly "Class E"). 255.255.255.255 is reserved for "limited broadcast" destination address.
List of /8 blocks assigned to commercial organizations Block Organization IANA date RIR date Notes 12.0.0.0/8 AT&T Services 1995-06 1983-08-23 Originally AT&T Bell Laboratories, but retained by AT&T when Bell Labs was spun off to Lucent Technologies in 1996. Assignment administered by ARIN (Legacy space). 17.0.0.0/8 Apple Inc. 1992-07 1990-04-16 Assignment administered by ARIN (Legacy space) 19.0.0.0/8 Ford Motor Company 1995-05 1988-06-15 Assignment administered by ARIN (Legacy space) 38.0.0.0/8 Cogent Communications 1994-09 1991-04-16 Formerly PSINet. As of 2025, portions of this range are leased to local ISPs. Assignment administered by ARIN (Legacy space)53.0.0.0/8Mercedes-Benz Group AG1993-10Assignment administered by RIPE (Legacy space) 73.0.0.0/8 Comcast Corporation N/A 2005-04-19 Assignment administered by ARIN
List of /8 blocks assigned to the United States Department of Defense Block Organization IANA date RIR date Notes 6.0.0.0/8 Army Information Systems Center 1994-02 1994-02-01 Headquarters, USAISC 7.0.0.0/8 DoD Network Information Center 1995-04 1997-11-24 Formerly IANAReserved 1995-04.Entirely assigned to DoD Network Information Center (DNIC) 1997-11-24.Updated to Administered by ARIN not before 2007. 11.0.0.0/8 DoD Intel Information Systems 1993-05 1984-01-19 21.0.0.0/8 DDN-RVN 1991-07 1991-07-01 DoD Network Information Center (DNIC) 22.0.0.0/8 Defense Information Systems Agency 1993-05 1989-06-26 DoD Network Information Center (DNIC) 26.0.0.0/8 Defense Information Systems Agency 1995-05 1995-05-01 DoD Network Information Center (DNIC) 28.0.0.0/8 DSI-North 1992-07 DoD Network Information Center (DNIC) 29.0.0.0/8 Defense Information Systems Agency 1991-07 1991-07-01 DoD Network Information Center (DNIC) 30.0.0.0/8 Defense Information Systems Agency 1991-07 1991-07-01 DoD Network Information Center (DNIC) 33.0.0.0/8 DLA Systems Automation Center 1991-01 1991-01-01 DoD Network Information Center (DNIC) 55.0.0.0/8 DoD Network Information Center 1995-04 1996-10-26 Headquarters, USAISC. Formerly Boeing Computer Services 1995-04.Updated to DoD Network Information Center in 2007-02. 214.0.0.0/8 US-DOD 1998-03 1998-03-27 DoD Network Information Center (DNIC) 215.0.0.0/8 US-DOD 1998-03 1998-06-05 DoD Network Information Center (DNIC)
List of /8 blocks assigned to the regional Internet registries
The regional Internet registries (RIRs) allocate IPs within a particular region of the world.