Guidelines for the use of Internet-IP addresses in the ISO Connectionless-Mode Network Protocol
A June 1986 working draft that shows how to build ISO CLNP addresses out of existing Internet IP addresses.
Callon, R. and H.W. Braun, "Guidelines for the use of Internet-IP addresses in the ISO Connectionless-Mode Network Protocol", RFC 986, DOI 10.17487/RFC0986, June 1986, <https://www.rfc-editor.org/info/rfc986>.
@misc{rfc986,
series = {Request for Comments},
number = 986,
howpublished = {RFC 986},
publisher = {RFC Editor},
doi = {10.17487/RFC0986},
url = {https://www.rfc-editor.org/info/rfc986},
author = {R. Callon and H.W. Braun},
title = {{Guidelines for the use of Internet-IP addresses in the ISO Connectionless-Mode Network Protocol}},
pagetotal = 7,
year = 1986,
month = jun,
} RFC text
Contents
Network Working Group Ross Callon (BBN)
Request for Comments: 986 Hans-Werner Braun (UMich)
June 1986
WORKING DRAFT
Guidelines for the use of Internet-IP addresses in the
ISO Connectionless-Mode Network Protocol
Status of This Memo
This RFC suggests a method to allow the existing IP addressing,
including the IP protocol field, to be used for the ISO
Connectionless Network Protocol (CLNP). This is a draft solution to
one of the problems inherent in the use of "ISO-grams" in the DOD
Internet. Related issues will be discussed in subsequent RFCs. This
RFC suggests a proposed protocol for the ARPA-Internet community, and
requests discussion and suggestions for improvements. Distribution
of this memo is unlimited.
1. Introduction
The CLNP is documented in [1], but for matters of completeness the
following illustration of the CLNP header is included here as
Figure 1.
The addressing part of the header is the subject of this RFC, i.e.,
the source and the destination address, respectively. These
addresses are generally discussed in [2] and [3], with this document
presenting a specific method for addressing in the DOD Internetwork
environment, consistent with the international standardized NSAP
addresses.
DOD IP Addresses in ISO CLNP
Octet
+--------------------------------------+ +--------
| Network Layer Protocol Identifier | 1 :
|--------------------------------------| :
| Length Indicator | 2 :
|--------------------------------------| :
| Version/Protocol Id Extension | 3 : Fixed
|--------------------------------------| :
| Lifetime | 4 : Part
|--------------------------------------| :
|SP|MS|E/R| Type | 5 :
|--------------------------------------| :
| Segment Length | 6,7 :
|--------------------------------------| :
| Checksum | 8,9 :
|--------------------------------------| +--------
| Destination Address Length Indicator | 10 :
|--------------------------------------| :
| Destination Address | 11 through m-1 : Address
|--------------------------------------| :
| Source Address Length Indicator | m : Part
|--------------------------------------| :
| Source Address | m+1 through n-1 :
|--------------------------------------| +--------
| Data Unit Identifier | n,n+1 :
|--------------------------------------| : Segment
| Segment Offset | n+2,n+3 : ation
|--------------------------------------| :
| Total Length | n+4,n+5 : Part
|--------------------------------------| +--------
| Options | n+6 through p : Options
Part
|--------------------------------------| +--------
| Data | p+1 through z : Data
+--------------------------------------+ +--------
Figure 1: PDU Header Format
DOD IP Addresses in ISO CLNP
2. Addresses for Use in the Internet
This section describes the primary addresses used to address NSAPs in
the Internet. A later section will describe a separate address
format for end systems and individual simple LANs that are attached
to the Internet only through intervening Public Data Networks.
The appropriate Authority and Format Identifier (AFI) is one octet in
length.
"The AFI consists of an integer with a value between 0 and 99 with
an abstract syntax of two decimal digits" [3], that is, the AFI
codes are binary coded decimal (BCD).
It specifies an ISO-6523-ICD assignment, and also that the Domain
Specific Part (DSP) of the address is based on binary. The AFI octet
uses the value "47". The ISO-6523-ICD format is used to emphasize
that this is an administrative assignment. The usage of an ISO DCC
(Data Country Code) would be possible, but could be misleading due to
the fairly far spread geographical extent of the Internet-IP.
As required by the ISO addressing standard, the next two octets of
the address, in this case, specify the Initial Domain Identifier.
This two octet value is the International Code Designator (ICD)
assigned to the DOD Internet, "0006".
The remainder of the NSAP address is the Domain Specific Part (DSP).
This is assigned by the Internet administration, which is considered
to be an addressing domain. The remainder of the address specifies a
one byte version number, the four byte Internet Protocol address and
a one byte IP user protocol field. The version number allows for
future extensions. The IP address used is the same as the current
four octet IP address. The user protocol field is the same as the
user protocol field in the current IP header. This is necessary
because the ISO protocol considers identification of the user
protocol to be an addressing issue, and therefore does not allow for
the user protocol to be specified in the protocol header
independently from the address.
DOD IP Addresses in ISO CLNP
Therefore a source or destination address within the ISO
Connectionless Protocol, when used in the DOD Internet, looks as
follows:
Octet
+------------------------+
| AFI | 1
+------------------------+
| IDI / ICD | 2
+-- --+
|(specifies DOD Internet)| 3
+------------------------+
| Version Number | 4
+------------------------+
| | 5
+--- four byte ---+
| | 6
+--- Internet ---+
| | 7
+--- Address (IP) ---+
| | 8
+------------------------+
| IP User Protocol ID | 9
+------------------------+
Figure 2: ISO IP address structure
The Authority and Format Identifier (AFI) is "47" (BCD). The Initial
Domain Identifier (IDI) consists of the International Code Designator
(ICD) assigned to the Internet, and must contain the value "0006".
The Version Number must contain the value "01". The Current IP
addresses and IP user protocol numbers can be found in [4].
3. Devices Attached to PDNs
Otherwise isolated end systems, which are attached to the Internet
only indirectly via public data networks, and simple LANs which are
similarly attached only via Public Data Networks, will make use of a
separate address format based on their X.121 address.
Figure 3 specifies the address for use by end systems attached to
PDNs. Here the AFI specifies an ISO-X.121 address format, with the
DSP based on binary. The AFI occupies a single octet, and must take
the value "37" (hexadecimal). The IDI contains the X.121 addresses
DOD IP Addresses in ISO CLNP
encoded in binary (using BCD), padded at the end if necessary with
all ones (binary "1111") to make up 7 full octets. Finally, the DSP
contains a single octet, which specifies the user protocol.
Octet
+------------------------+
| AFI | 1
+------------------------+
| IDI | 2
+-- --+
| (specifies X.121 | 3
+-- --+
| address, padded to | 4
+-- --+
| 7 octets) | 5
+-- --+
| | 6
+-- --+
| | 7
+-- --+
| | 8
+------------------------+
| IP User Protocol ID | 9
+------------------------+
Figure 3: ISO IP address structure for isolated end systems
Figure 4 specifies the address for use by simple LANs attached to
PDNs. This address is the same as the address used for end systems
directly attached to PDNs, except for the addition of the (variable
length) local address as used on the LAN. Whether the address is of
the form shown in figure 3, or of the form shown in figure 4, is
determined by looking at the length of the address.
DOD IP Addresses in ISO CLNP
Octet
+------------------------+
| AFI | 1
+------------------------+
| IDI | 2
+-- --+
| (specifies X.121 | 3
+-- --+
| address, padded to | 4
+-- --+
| 7 octets) | 5
+-- --+
| | 6
+-- --+
| | 7
+-- --+
| | 8
+------------------------+
| | 9
+-- local net --+
| |
+-- address --+
| |
+--- --+ (variable
| | sized)
+------------------------+
| IP User Protocol ID |
+------------------------+
Figure 4: ISO IP address structure for isolated LANs
DOD IP Addresses in ISO CLNP
References
[1] ISO, "Protocol for Providing the Connectionless-Mode Network
Services", RFC-926, ISO, December 1984.
[2] ANSI, "Guidelines for the Specification of the Structure of the
Domain Specific Part (DSP) of the ISO Standard NSAP Address",
RFC-982, ANSI Working Document X3S3.3/85-258, April 1986.
[3] ISO, Draft International Standard 8348/DAD2, "Information
Processing Systems -- Data Communications -- Network Service
Definition, Addendum 2 Covering Network Layer Addressing",
RFC-941, April 1985.
[4] Reynolds, J. and J. Postel, "Assigned Numbers", RFC-960, USC
Information Sciences Institute, December 1985.
AI ELI5
On this page
§1Introduction
RFC 986 suggests a method for using the existing IP addressing, including the IP protocol field, with the ISO Connectionless Network Protocol (CLNP). It calls this a draft solution to one of the problems of carrying "ISO-grams" in the DOD Internet, says related issues will be discussed in later RFCs, and asks for discussion and suggestions.
The memo reproduces the CLNP header only for completeness. The address part of that header, the destination and source addresses, is what the memo is about. It presents a specific way to address in the DOD Internetwork environment that stays consistent with the international standardized NSAP addresses.
The memo is about the address label on a packet, not the rest of the packet. It explains how to write an Internet address in the label format the ISO world expects.
§2Addresses for Use in the Internet
An NSAP address in the Internet starts with a one-octet Authority and Format Identifier (AFI) with the value 47, written in binary coded decimal. That value specifies an ISO-6523-ICD assignment and says the rest of the address is based on binary. The ICD format was chosen to emphasize that this is an administrative assignment. A Data Country Code would be possible but could be misleading, given the wide geographic spread of the Internet.
The next two octets are the Initial Domain Identifier, which holds the International Code Designator assigned to the DOD Internet. It must contain 0006. The rest is the Domain Specific Part, assigned by the Internet administration as an addressing domain. It has a one-byte version number, which must contain 01 and allows for future extensions, then the four-byte IP address, then the one-byte IP user protocol field.
The new address is built like a nesting doll: first a code saying which kind of address it is, then a code for the Internet as a whole, then a version number, then the ordinary Internet address and a note about which program should get the packet.
| Octet | Field | Value |
|---|---|---|
| 1 | AFI | 47 (BCD) |
| 2 to 3 | IDI / ICD (DOD Internet) | 0006 |
| 4 | Version number | 01 |
| 5 to 8 | Four-byte Internet (IP) address | The current IP address |
| 9 | IP user protocol ID | As in the IP header |
§3Why the User Protocol Is in the Address
The IP address used inside the ISO address is the same four-octet IP address in use at the time, and the user protocol field is the same as the user protocol field in the current IP header. The memo says it is necessary to include it because the ISO protocol treats identification of the user protocol as an addressing issue. It therefore does not allow the user protocol to be specified in the protocol header independently of the address.
Current IP addresses and user protocol numbers are to be found in the Assigned Numbers document, RFC 960.
In the ISO system, the note saying which program should get the packet has to be written on the address label itself, so the memo copies it there.
§4Devices Attached to Public Data Networks
Otherwise isolated end systems, and simple LANs that are attached to the Internet only through public data networks (PDNs), use a separate address format based on their X.121 address. Here the AFI specifies an ISO-X.121 address format with a binary Domain Specific Part. The AFI is a single octet that must take the value 37 (hexadecimal). The IDI contains the X.121 address encoded in binary (using BCD), padded at the end if necessary with all ones to make up 7 full octets. The DSP then holds a single octet naming the user protocol.
Simple LANs attached to PDNs use the same address with a variable-length local address added for the LAN. Whether an address is the end-system form or the LAN form is determined by looking at its length.
Computers that only reach the Internet through a phone-company network use their phone-style number instead. A small local network adds its own extra room number at the end.