RFC 4548
Internet Code Point (ICP) Assignments for NSAP Addresses
RFC 4548: Internet Code Point (ICP) Assignments for NSAP Addresses 💖
okay bestie, so this is RFC 4548 🎀 from the Network Working Group. It's a Standards Track doc dated May 2006 ✨. The authors are E. Gray and J. Rutemiller (both at Ericsson) and G. Swallow (Cisco Systems, Inc.) 🫶. It updates RFC 1888 and RFC 4048 🦋.
Status of This Memo 🌸
so this doc is an Internet standards track protocol for the whole Internet community, and it's literally asking people to discuss it and send suggestions to make it better 🧚. for the official standardization state and status, go check the current edition of "Internet Official Protocol Standards" (STD 1) 💅. distribution of this memo is unlimited, so share away ✨.
Copyright Notice 🎀
Copyright (C) The Internet Society (2006).
Abstract 💜
this doc has two super connected jobs 🔥. first, it sets up an "initial" Internet Code Point (ICP) assignment for IPv4 and IPv6 address encoding inside Network Service Access Point (NSAP) Addresses. second, it recommends an IANA assignment policy for ICP values that aren't assigned yet. for job one, it's a partial replacement for RFC 1888, especially section 6 of RFC 1888. for job two, it pulls in wording and specs from ITU-T Recommendation X.213 and further recommends that IANA use the "IETF consensus" assignment policy for future ICP assignments 👑.
Table of Contents 🧚
1. Introduction ....................................................2
1.1. Conventions ................................................2
1.2. Acronyms and Terminology ...................................3
2. IANA Considerations .............................................3
3. Initial Allocations and Uses ....................................4
3.1. IPv4 Address Encoding in an NSAPA ..........................4
3.2. IPv6 Address Encoding in an NSAPA ..........................5
4. Security Considerations .........................................6
5. References ......................................................7
5.1. Normative References .......................................7
5.2. Informative References .....................................71. Introduction ✨
okay so back in the day 🌈, section 6 of RFC 1888 [1888] set aside the initial Internet Code Point (ICP) value '0' for encoding an IPv6 address in a Network Service Access (or Attachment) Point [NSAP] address. RFC 1888 also defined multiple means for restricted encoding of an NSAP address in an IPv6 address.
the means RFC 1888 defined for encoding NSAP addresses in IPv6 address format were heavily annotated with warnings and limitations that apply should this encoding be used 🙈. possibly as a result, these encodings aren't used, and they appear never to have been used in any IPv6 deployment. section 6 also has minor errors. because of all this, RFC 1888 [1888] has been obsoleted and declared Historic by RFC 4048 [4048] 💀.
the authors think the errors in section 6 of RFC 1888 happened, at least partly, because the ITU-T specification [X.213] that originally assigned Authority and Format Identifier (AFI) '35' to IANA wasn't freely publicized. it also wasn't incorporated or explained the way the IETF usually does things, with an RFC 📝.
so explaining that is part of this doc's purpose 💅.
plus, other docs refer to the IPv6 ICP assignment in RFC 1888, so the errors in section 6 of RFC 1888 need to be corrected no matter what the RFC's ultimate status ends up being 🫶.
finally, no previous RFC (including RFC 1888) has ever formalized an assignment of an IPv4 ICP 😭. this may partly be because there was no formal definition of an IANA assignment policy for ICP values under the IANA-allocated AFI ('35').
this document replaces section 6 of RFC 1888 in defining the ICP for IPv6 address encoding in an NSAP address, and it formalizes the ICP assignment for IPv4 address encoding in an NSAP address 🦋.
1.1. Conventions 🎀
quick vibe check on the key words 💖:
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [2119].
1.2. Acronyms and Terminology 🍓
AFI - Authority and Format Identifier
BCD - Binary Coded Decimal
DSP - Domain Specific Part
IANA - Internet Assigned Numbers Authority
ICP - Internet Code Point
IDI - Initial Domain Identifier
IDP - Initial Domain Part
IETF - Internet Engineering Task Force
ISO - International Organization for Standardization
NSAP - Network Service Access (or Attachment) Point (often NSAPA)
NSAPA - NSAP Address; 20-Octet Address Format
OSI - Open Systems Interconnection
RFC - Request For Comments
WIP - Work In Progress2. IANA Considerations 🌈
an ITU-T Recommendation [X.213] has allocated two AFIs that designate IANA as the assignment authority 👑. one of these two AFIs ('34') is allocated for assignment of NSAPA in Decimal Numeric Format. this document doesn't address allocation for this AFI, since it isn't clear what use (if any) can be made of this encoding format at this time 🤷♀️. the other AFI ('35') is to be used for binary encoding, except as noted below.
the NSAPA format is made of an Initial Domain Part (IDP) and a Domain Specific Part (DSP) 🧚. the IDP is made of an Authority and Format Identifier (AFI) and an Initial Domain Identifier (IDI). the AFI is defined to be a binary octet, and the IDI is defined to be a four decimal digit number encoded in two octets using Binary Coded Decimal format. each nibble of the IDI represents a decimal digit, using binary values '0000' through '1001' ✨.
when AFI '35' gets allocated to IANA, the ITU-T Recommendation [X.213] specifies that the two-octet IDI holds an Internet Code Point (ICP). because of the decimal encoding, that ICP MUST be in the decimal range from '0' to '9999' 🔢.
the ITU-T recommendation assumes ICP '0' (zero) is assigned for IPv6 address encoding in a Network Service Access Point Address (NSAPA, or often NSAP) 💜. ITU-T also assumed that IANA would assign an ICP for IPv4 address encoding in an NSAPA, and X.213 assumed that the ICP value for this purpose would be '1' 🦋.
in an NSAPA, the DSP is the remaining octets after the IDP. for AFI '35', that's 17 octets, with a format defined by IANA or by another party and published with IANA consent 🌸.
IANA, as the authority responsible for AFI '35', SHOULD NOT assign an ICP unless there is a corresponding defined and published format at the time of the code point assignment 🙅♀️.
the IANA has assigned the following ICP values 💅:
ICP Value Address Encoding Format Definition
---------- ----------------- ----------------------------
'0' IPv6 RFC 4548, section 3.2
'1' IPv4 RFC 4548, section 3.1the remaining decimal values '2' through '9999' MUST be assigned on an IETF consensus basis [2434] 🫶.
3. Initial Allocations and Uses 🦋
this document continues the ICP assignment and format definition from RFC 1888. it also formalizes the allocation of ICP value '1' for IPv4 encoding, plus the format to be used 💖. the sections below describe the specific IPv4 and IPv6 address encoding formats 🎀.
3.1. IPv4 Address Encoding in an NSAPA 🌈
if it is required, for whatever reason, to embed an IPv4 address inside a 20-octet NSAP address, then the following format MUST be used 🔥. note: alignment is an artifact of existing NSAPA usage.
a specific possible use of this embedding is to express an IP address within the ATM Forum address format ✨. another possible use would be to let Connectionless Network Protocol (CLNP) packets that encapsulate IPv4 packets get routed in a CLNP network using the IPv4 address architecture 🧚. several leading octets of the IPv4 address could be used as a CLNP routing prefix 💜.
an NSAPA with an AFI value of '35' and an ICP value of '1' (one) encodes a 4-octet IPv4 address in the first 4 octets of the DSP. the last 13 octets of the DSP are unspecified in this document. to keep compatibility with both NSAP format and IPv4 addressing, these octets MUST be present, but they have no intrinsic significance for IPv4 🙈. the default value for the unspecified octets is zero 🍓.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0-3 | AFI = 0x35 | ICP = 0001 | IPv4 (octet 0)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4-7 | IPv4 (octets 1-3) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8-11 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12-15| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16-19| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+an NSAPA with the IANA AFI code and ICP set to '1' (one) gets converted to an IPv4 address by stripping off the first 3 and the last 13 octets 🌸. if the NSAP-addressed contents are passed up to a higher layer, the last 13 octets SHOULD be presented to the higher layer as well 🎀.
if an NSAP address using this encoding is used for routing in an IPv4 routing architecture, only the 4-octet IPv4 address MAY be considered 👀.
3.2. IPv6 Address Encoding in an NSAPA ✨
okay so what if you need to shove an IPv6 address inside a 20-octet NSAP address? 🫣 for whatever reason, the following format MUST be used. the alignment is basically a leftover from how NSAPAs were already being used, so don't stress about it 🙈
a super specific use is expressing an IP address inside the ATM Forum address format 🦋 another possible use is letting CLNP packets that carry IPv6 packets get routed through a CLNP network using the IPv6 address architecture. several leading octets of the IPv6 address could work as a CLNP routing prefix 💜
an NSAPA with an AFI value of '35' and an ICP value of '0' (zero) encodes a 16-octet IPv6 address in the first 16 octets of the DSP. the last octet of the DSP is a selector. to stay compatible with both NSAP format and IPv6 addressing, this octet MUST be present, but it has no intrinsic significance for IPv6 🙃 its default value is zero, but other values may be used as specified for any specific application. for example, this octet may be used to specify one of 255 possible port numbers 🔥
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0-3 | AFI = 0x35 | ICP = 0000 | IPv6 (octet 0)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4-7 | IPv6 (octets 1-4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8-11| IPv6 (octets 5-8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12-15| IPv6 (octets 9-12) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16-19| IPv6 (octets 13-15) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+an NSAPA with the IANA AFI code and ICP set to '0' (zero) gets converted to an IPv6 address by stripping off the first 3 octets and the 20th octet 🧚 if the NSAP-addressed contents get passed up to a higher layer, the last octet SHOULD be presented to that higher layer as well 💅
if an NSAP address using this encoding is used for routing in an IPv6 routing architecture, only the 16-octet IPv6 address MAY be considered 👑
4. Security Considerations 🔐
okay this part is actually so good 😭 the NSAP encoding of IPv4 and IPv6 addresses is compatible with the corresponding security mechanisms of RFC 4301 [4301], so this document introduces no new security exposure in the Internet 🫶 no new drama, bestie 🌈
5. References
5.1. Normative References
[4301] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[NSAP] International Organization for Standardization, "Information
technology - Open Systems Interconnection - Network service
Definition", ISO/IEC 8348:2002, 2002.
[X.213] ITU-T Recommendation X.213, X-Series Recommendations, Data
Networks and Open Systems Communications, October, 2001.
[2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.5.2. Informative References
[1888] Bound, J., Carpenter, B., Harrington, D., Houldsworth, J.,
and A. Lloyd, "OSI NSAPs and IPv6", RFC 1888, August 1996.
[4048] Carpenter, B., "RFC 1888 Is Obsolete", RFC 4048, April 2005.Authors' Addresses 🎀
the squad behind this one 💖
Eric Gray
Ericsson
900 Chelmsford Street
Lowell, MA, 01851
EMail: Eric.Gray@Marconi.com
John Rutemiller
Ericsson
3000 Marconi Drive
Warrendale, PA, 15086-7502
EMail: John.Rutemiller@Marconi.com
George Swallow
Cisco Systems, Inc.
1414 Massachusetts Avenue
Boxborough, MA, 01719
EMail: swallow@cisco.comFull Copyright Statement ⭐
the legal bits, kept word-for-word so nothing gets lost in translation 🧾
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Administrative Support Activity (IASA).📦 where this page comes from
- ietf: rfc4548 2006-05
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