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-
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- J. Postel
- IEN 115 ISI
- August 1979
-
-
-
- ADDRESS MAPPINGS
- ----------------
-
-
-
- Internet Address
- ----------------
-
- 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, divided into an 8 bit
- network number and a 24 bit local address as shown below.
-
- +--------+--------+--------+--------+
- | Net | Local Address |
- +--------+--------+--------+--------+
-
- The local address carries information to address a host in the
- network identified by the network number. Since each network has a
- 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:
-
- ARPANET
- -------
-
- The ARPANET (with 96 bit leaders) has 24 bit addresses. The 24
- bits are assigned to host, logical host, and IMP fields as
- illustrated below. These 24 bit addresses are used directly
- for the 24 bit local address of the internet address.
-
- The network number of the ARPANET is 10.
-
- +--------+--------+--------+
- | HOST | LH | IMP |
- +--------+--------+--------+
- 8 8 8
-
-
-
- Postel [Page 1]
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-
- August 1979
- IEN 115 Address Mappings
-
-
-
- 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.
-
- +--------+----------------+
- | ZERO | HOST |
- +--------+----------------+
- 8 16
-
- 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
- SF-PR-1 2
- SILL-PR 5
- SF-PR-2 6
- BRAGG-PR 9
- DC-PR 20
-
- +--------+----------------+
- | ZERO | HOST |
- +--------+----------------+
- 8 16
-
- LCSNET
- ------
-
- The LCS NET at MIT's Laboratory for Computer Science uses 32
- bit addresses of several formats. Please see [2] 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.
-
-
-
- Postel [Page 2]
-
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- August 1979
- IEN 115 Address Mappings
-
-
-
- The network number of the LCS NET is 18.
-
- +--------+--------+--------+
- | SUB |RESERVED| HOST |
- | NET | | |
- +--------+--------+--------+
- 8 8 8
-
- EDN
- ---
-
- The Experimental Data Network at the Defense Communication
- Engineering Center (DCEC) uses the old 1822 32 bit leader, and
- so has 8 bit addresses. These 8 bit EDN addresses are located
- in the 24 bit internet local address as shown below.
-
- The network number of the EDN is 21.
-
- +------+--+----------+------+
- | | H| | |
- | ZERO | O| ZERO | IMP |
- | | S| | |
- | | T| | |
- +------+--+----------+------+
- 6 2 10 6
-
- DCNs
- ----
-
- The 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 CONSAT-DCN is 29, and of the UCL-DCN
- is 30.
-
- +--------+--------+--------+
- | ZERO | HID | PID |
- +--------+--------+--------+
- 8 8 8
-
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- Postel [Page 3]
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- August 1979
- IEN 115 Address Mappings
-
-
-
- References
- ----------
-
- [1] Jonathan B. Postel, "Internet Protocol," USC/Information
- Sciences Institute, IEN 111, August 1979.
-
- [2] 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 4]
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