RFC 986
Guidelines for the use of Internet-IP addresses in the ISO Connectionless-Mode Network Protocol
RFC 986: Guidelines for the use of Internet-IP addresses in the ISO Connectionless-Mode Network Protocol ✨
- Authors: Ross Callon (BBN) and Hans-Werner Braun (UMich)
- Stream: Network Working Group, Request for Comments: 986
- Date: June 1986
- Status: WORKING DRAFT
- Obsoletes / Updates: The title block doesn't list anything this RFC obsoletes or updates. 🫶
Status of This Memo 🎀
okay so this RFC suggests a way to let the existing IP addressing, including the IP protocol field, get used for the ISO Connectionless Network Protocol (CLNP) 🦋 it's a draft fix for one of the problems you run into when you use "ISO-grams" on the DOD Internet. more on related issues is coming in later RFCs. it's a proposed protocol for the ARPA-Internet community, and it's literally asking people to talk about it and suggest improvements 🗣️ distribution of this memo is unlimited, so share it with everyone 💅
1. Introduction ✨
the CLNP is documented in [1], but just so everything's complete, figure 1 below shows the CLNP header again 🧚
the addressing part of the header is what this RFC is about, meaning the source address and the destination address 💜 these get talked about in [2] and [3], and this doc shows one specific way to do addressing in the DOD Internetwork environment that still matches the international standardized NSAP addresses 🌸
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 🌈
2. Addresses for Use in the Internet 🌷
this section covers the main addresses used to address NSAPs on the Internet 💖 a later section covers a separate address format for end systems and individual simple LANs that only hook up to the Internet through Public Data Networks in between 🧚
the Authority and Format Identifier (AFI) is one octet long 🎀
"The AFI consists of an integer with a value between 0 and 99 with an abstract syntax of two decimal digits" [3]
so basically the AFI codes are binary coded decimal (BCD) 🔢
it specifies an ISO-6523-ICD assignment, and it also says that the Domain Specific Part (DSP) of the address is based on binary 💅 the AFI octet uses the value 47. ISO-6523-ICD is the format that really shows this is an administrative assignment 🫶 using an ISO DCC (Data Country Code) would've been possible, but it could be misleading because the Internet-IP is spread out pretty far geographically 🌍
as the ISO addressing standard requires, the next two octets specify the Initial Domain Identifier 👑 this two octet value is the International Code Designator (ICD) assigned to the DOD Internet, which is 0006 💜
the rest of the NSAP address is the Domain Specific Part (DSP) 🦋 the Internet administration assigns this, and it's treated as an addressing domain. the remainder of the address has a one byte version number, the four byte Internet Protocol address, and a one byte IP user protocol field 🌸 the version number is there so future extensions are possible ✨ the IP address is the same as the current four octet IP address, and the user protocol field is the same as the user protocol field in the current IP header 💖 this is needed because the ISO protocol treats identifying the user protocol as an addressing issue, so it doesn't let the user protocol be specified in the protocol header separately from the address 🙈
so a source or destination address inside the ISO Connectionless Protocol, when it's used on the DOD Internet, looks like this:
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) is the International Code Designator (ICD) assigned to the Internet, and it 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 🌈
okay so this part is for end systems that are only connected to the Internet indirectly through public data networks, plus simple LANs that connect the same way 💜 they use their own address format, which is based on their X.121 address 🦋
figure 3 shows the address that end systems attached to PDNs use 💖 here the AFI points to an ISO-X.121 address format, with the DSP based on binary 🔥 the AFI is a single octet and must take the value 37 (hexadecimal) ✨ the IDI holds the X.121 address encoded in binary (using BCD), padded at the end if needed with all ones (binary 1111) so it fills up 7 full octets 🌸 finally, the DSP is a single octet that 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 shows the address for simple LANs attached to PDNs 🎀 it's the same as the address for end systems directly attached to PDNs, except it adds the (variable length) local address that's used on the LAN 💖 whether an address looks like figure 3 or figure 4 depends on the length of the address 💅
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 🦋
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.
📦 where this page comes from
- ietf: rfc986 1986-06
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