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Address mappings (RFC0796)

IP.com Disclosure Number: IPCOM000003845D
Original Publication Date: 1981-Sep-01
Included in the Prior Art Database: 2019-Feb-14
Document File: 7 page(s) / 7K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J. Postel: AUTHOR

Related Documents

10.17487/RFC0796: DOI

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 39% of the total text.

Network Working Group J. Postel Request for Comments: 796 ISI Replaces: IEN 115 September 1981 ADDRESS MAPPINGS ----------------

Internet Addresses ------------------

This memo describes the relationship between address fields used in the Internet Protocol (IP) [1] and several specific networks.

An internet address is a 32 bit quantity, with several codings as shown below.

The first type (or class a) of address has a 7-bit network number and a 24-bit local address.

1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| NETWORK | Local Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Class A Address

The second type (or class b) of address has a 14-bit network number and a 16-bit local address.

1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 0| NETWORK | Local Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Class B Address

The third type (or class c) of address has a 21-bit network number and a 8-bit local address.

1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 1 0| NETWORK | Local Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Class C Address

The local address carries information to address a host in the network identified by the network number. Since each network has a

Postel [Page 1]

September 1981 RFC 796 Address Mappings

particular address format and length, the following section describes the mapping between internet local addresses and the actual address format used in the particular network.

Internet to Local Net Address Mappings --------------------------------------

The following transformations are used to convert internet addresses to local net addresses and vice versa:

AUTODIN II ----------

The AUTODIN II has 16 bit subscriber addresses which identify either a host or a terminal. These addresses may be assigned independent of location. The 16 bit AUTODIN II address is located in the 24 bit internet local address as shown below.

The network number of the AUTODIN II is 26 (Class A).

+----------------+ | HOST/TERMINAL | AUTODIN II +----------------+ 16

+--------+--------+--------+--------+ | 26 | ZERO | HOST/TERMINAL | IP +--------+--------+--------+--------+ 8 8 16

Postel [Page 2]

September 1981 RFC 796 Address Mappings

ARPANET -------

The ARPANET (with 96 bit leaders) has 24 bit addresses. The 24 bits are assigned to host, logical host, and IMP leader fields as illustrated below. These 24 bit addresses are used directly for the 24 bit local address of the internet address. However, the ARPANET IMPs do not yet support this form of logical addressing so the logical host field is set to zero in the leader.

The network number of the ARPANET is 10 (Class A).

+--------+--------+--------+ | HOS...

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