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+
+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
+
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+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).
+
+ +--------+--------+--------+
+ | HOST | ZERO | IMP | ARPANET
+ +--------+--------+--------+
+ 8 8 8
+
+ +--------+--------+--------+--------+
+ | 10 | HOST | LH | IMP | IP
+ +--------+--------+--------+--------+
+ 8 8 8 8
+
+ DCNs
+ ----
+
+ The Distributed Computing Networks (DCNs) at COMSAT and UCL use
+ 16 bit addresses divided into an 8 bit host identifier (HID),
+ and an 8 bit process identifier (PID). The format locates
+ these 16 bits in the low order 16 bits of the 24 bit internet
+ address, as shown below.
+
+ The network number of the COMSAT-DCN is 29 (Class A), and of
+ the UCL-DCN is 30 (Class A).
+
+ +--------+--------+
+ | HID | PID | DCN
+ +--------+--------+
+ 8 8
+
+ +--------+--------+--------+--------+
+ | 18 | ZERO | HID | PID | IP
+ +--------+--------+--------+--------+
+ 8 8 8 8
+
+
+
+
+
+
+Postel [Page 3]
+
+
+ September 1981
+RFC 796 Address Mappings
+
+
+
+ EDN
+ ---
+
+ The Experimental Data Network at the Defense Communication
+ Engineering Center (DCEC) uses the same type of addresses as
+ the ARPANET (with 96 bit leaders) and 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 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 EDN is 21 (Class A).
+
+ +--------+--------+--------+
+ | HOST | ZERO | IMP | EDN
+ +--------+--------+--------+
+ 8 8 8
+
+ +--------+--------+--------+--------+
+ | 21 | HOST | LH | IMP | IP
+ +--------+--------+--------+--------+
+ 8 8 8 8
+
+ LCSNET
+ ------
+
+ The LCS NET at MIT's Laboratory for Computer Science uses 32
+ bit addresses of several formats. Please see [3] for more
+ details. The most common format locates the low order 24 bits
+ of the 32 bit LCS NET address in the 24 bit internet local
+ address, as shown below.
+
+ The network number of the LCS NET is 18 (Class A).
+
+ +--------+--------+--------+
+ | SUBNET |RESERVED| HOST | LCSNET
+ +--------+--------+--------+
+ 8 8 8
+
+ +--------+--------+--------+--------+
+ | 18 | SUBNET |RESERVED| HOST | IP
+ +--------+--------+--------+--------+
+ 8 8 8 8
+
+
+
+
+
+Postel [Page 4]
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+
+ September 1981
+RFC 796 Address Mappings
+
+
+
+ PRNET
+ -----
+
+ The Packet Radio networks use 16 bit addresses. These are
+ independent of location (indeed the hosts may be mobile). The
+ 16 bit PRNET addresses are located in the 24 bit internet local
+ address as shown below.
+
+ The network numbers of the PRNETs are:
+
+ BBN-PR 1 (Class A)
+ SF-PR-1 2 (Class A)
+ SILL-PR 5 (Class A)
+ SF-PR-2 6 (Class A)
+ BRAGG-PR 9 (Class A)
+ DC-PR 20 (Class A)
+
+ +--------+--------+
+ | HOST | PRNET
+ +--------+--------+
+ 16
+
+ +--------+--------+--------+--------+
+ | net | ZERO | HOST | IP
+ +--------+--------+--------+--------+
+ 8 8 16
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+Postel [Page 5]
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+ September 1981
+RFC 796 Address Mappings
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+ SATNET
+ ------
+
+ The Atlantic Satellite Packet Network has 16 bit addresses for
+ hosts. These addresses may be assigned independent of location
+ (i.e., ground station). It is also possible to assign several
+ addresses to one physical host, so the addresses are logical
+ addresses. The 16 bit SATNET address is located in the 24 bit
+ internet local address as shown below.
+
+ The network number of the SATNET is 4 (Class A).
+
+ +--------+--------+
+ | HOST | SATNET
+ +--------+--------+
+ 16
+
+ +--------+--------+--------+--------+
+ | 4 | ZERO | HOST | IP
+ +--------+--------+--------+--------+
+ 8 8 16
+
+ WBCNET
+ ------
+
+ The Wideband Communication Satellite Packet Network (WBCNET)
+ Host Access Protocol (HAP) has 16 bit addresses for hosts. It
+ is possible to assign several addresses to one physical host,
+ so the addresses are logical addresses. The 16 bit WBCNET
+ address is divided into a HAP Number field and a Local Address
+ field, and is located in the 24 bit internet local address as
+ shown below. Please see [2] for more details.
+
+ The network number of the WBCNET is 28 (Class A).
+
+ +--------+--------+
+ | HAP NUM| LCL ADD| WBCNET
+ +--------+--------+
+ 8 8
+
+ +--------+--------+--------+--------+
+ | 28 | HAP NUM| ZERO | LCL ADD| IP
+ +--------+--------+--------+--------+
+ 8 8 8 8
+
+
+
+
+
+
+Postel [Page 6]
+
+
+ September 1981
+RFC 796 Address Mappings
+
+
+
+References
+----------
+
+ [1] Postel, J. (ed.), "Internet Protocol - DARPA Internet Program
+ Protocol Specification," RFC 791, USC/Information Sciences
+ Institute, September 1981.
+
+ [2] Pershing J., "Addressing Revisited," Bolt Beranek and Newman
+ Inc., W Note 27, May 1981.
+
+ [3] Noel Chiappa, David Clark, David Reed, "LCS Net Address
+ Format," M.I.T. Laboratory for Computer Science Network
+ Implementation, Note No.5, IEN 82, February 1979.
+
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+Postel [Page 7]
+