Network Working Group R. Colella (NIST)
INTERNET DRAFT R. Callon (DEC)
February 12, 1991
OSI NSAP Address Format For Use In The Internet
Status of This Memo
This draft document will be submitted to the RFC editor
as a protocol specification. Distribution of this document
is unlimited. Comments should be sent to Richard Colella
(``colella@osi3.ncsl.nist.gov'').
Abstract
The Internet is moving towards a multi-protocol environment
that includes OSI. To support OSI, it is necessary to address
network layer entities and network service users. The basic
principles of OSI Network Layer addressing and Network
Service Access Points (NSAPs) are defined in Addendum 2 to
the OSI Network service definition. This internet draft
recommends a structure for the Domain Specific Part of NSAP
addresses for use in the Internet that is consistent with
these principles.
INTERNET-DRAFT OSI NSAP Address Format For Use In The Internet February 12, 1991
NOTE
This document is aligned with U.S. GOSIP Version 2 [3]. The
final text of the technical specification is available as of
January 1991.
An errata to GOSIP Version 1 [4] became effective in August
1990 mandating use of the GOSIP Version 2 NSAP format with
Version 1. The errata is an official part of the GOSIP
Version 1 FIPS; it is published as a section within GOSIP
Version 2.
This document is also aligned with the current work in ANSI
X3S3.3 on the DSP structure for NSAP addresses under the U.S.
Data Country Code.
1 Introduction
The Internet is moving towards a multi-protocol environment
that includes OSI. To support OSI, it is necessary to
address network layer entities and network service users. The
basic principles of OSI Network Layer addressing and Network
Service Access Points (NSAPs) are defined in Addendum 2 to the
Network service definition [5]. These principles include NSAP
address administration based upon the concept of hierarchical
addressing domains and international standardization of
the topmost levels of global NSAP addressing domain. The
Initial Domain Part (IDP) of an NSAP address identifies the
authority responsible for the structure and assignment of
the remainder of the address, the Domain Specific Part (DSP)
(see Figure 1). For example, an IDP may identify a country's
ISO Member Body, such as ANSI in the U.S. or BSI in the UK,
or an organization of international standing, such as the
U.S. National Institute of Standards and Technology (NIST).
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______________
!_____IDP______!_________________________________
!__AFI__!_IDI__!______________DSP________________!
IDP Initial Domain Part
AFI Authority and Format Identifier
IDI Initial Domain Identifier
DSP Domain Specific Part
Figure 1: ISO/CCITT NSAP address structure.
While [5] ensures coordination of the format and assignment
of IDPs, it places no constraint on the structure of DSPs,
leaving such decisions to those who implement and deploy
OSI. To support OSI in the Internet requires that a choice
be made as to the appropriate DSP format.
The manner in which NSAPs are assigned is strongly related
to the ability to aggregate address information at the
boundaries of routing domains and confederations of domains.
The ability to achieve address aggregation at these
boundaries is important to allow efficient routing in very
large internets. The relationship between address assignment,
address aggregation, and routing efficiency is beyond the
scope of this document. Detailed discussion of these issues
is the subject of a forthcoming document [2].
2 Recommended DSP Format
NSAP addresses for use within the U.S. portion of the
Internet are expected to be based primarily on two address
prefixes: the IDP format administered for NIST by GSA and
the DCC format administered by ANSI.
The recommended DSP format for use in the U.S. portion of the
Internet which is addressed under the IDP with AFI=47 and
IDI=0005 is that specified in Section 5.1.1 of GOSIP
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Version 2 ** (this section is reproduced for reference as Appendix
A). There are primarily three reasons for recommending this
format:
* it is consistent with the emerging OSI intra-domain
routing protocol in DIS 10589 [6],
* it will encourage a uniform addressing scheme throughout
the Internet (both government and non-government), and,
* its alignment with GOSIP Version 2 means that it is likely
to be supported in vendor products.
For the part of the U.S. Internet which is addressed based
on the ANSI-regulated U.S. DCC (Data Country Code) prefix,
the precise format is outside of the scope of this standard.
There is a proposal in ANSI X3S3.3 [1] to create an American
National Standard (ANS) for the DSP structure under the
U.S. DCC. This will provide a structure for the DSP which
is similar to that specified within GOSIP Version 2. This
document is in technical alignment with the current ANSI
proposal. For more information, contact the chair of X3S3.3.
For the part of the Internet which is outside the U.S., again
the precise format is outside the scope of this standard.
However, it is recommended that the DSP portion of the
address be structured similarly to that specified within
GOSIP Version 2.
A Appendix: Extract from GOSIP Version 2
[This appendix contains a copy of Section 5.1.1 from
GOSIP Version 2, which describes the GOSIP Version 2
________________________________
** GSA will accept requests from non-U.S. government
organizations for NSAP addressing authority under the GOSIP
Version 2 NSAP structure. See [2] for more information.
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NSAP structure.
Addendum 2 to the Network layer service definition
[5] defines two representations for NSAP addresses.
The abstract syntax is a descriptive device used
for people to discuss and write NSAP addresses; it
dictates the form taken on paper.
The encoding is how the NSAP addresses are
represented in protocol data units. The encoding is a
mapping from the abstract syntax to the octets carried
in a protocol.
The AFI, IDI, and DFI values in the GOSIP excerpt
are presented in their abstract syntax:
_Field____Abstract_Syntax__________Value_____
AFI decimal 47
IDI decimal 0005
DFI binary 1000 0000
Note that CLNP encodes NSAP addresses using the
preferred binary encoding, as defined in [5].]
5.1.1 NSAP Address Administration, Routing Structures and
NSAP Address Structure
Network Service Access Point (NSAP) addresses specify the
points where the communication capability of the Network
Layer (i.e., the Network Service) is made available to
its users. In effect they address the direct users of the
Network Service, normally transport entities. The semantics
of NSAP addresses are encoded into Network Protocol Address
Information (NPAI) and conveyed in the appropriate protocol
data units (PDUs) between protocol entities providing the
Network Service.
The basic principles of Network Layer addressing, as defined
in Addendum 2 to the Network service definition [ISO 5],
include:
* NSAP address administration is based on the concept of
hierarchical Addressing Domains. An Addressing Domain
is a set of addresses interrelated by virtue of being
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administered by a common authority. The term authority
refers to the entity that specifies the structure and
ensures the uniqueness of identifiers in the associated
domain. In practice the structure of NSAP addresses
reflects this administrative hierarchy in that, at any
level of the hierarchy, an initial part of the address
unambiguously identifies the Addressing (sub) Domain.
* The first three levels of the NSAP addressing domain are
standardized and result in the NSAP address structure
in Figure 5.1.1. The Initial Domain Part (IDP) of the
address consists of two parts, the Authority and Format
Identifier (AFI) and the Initial Domain Identifier (IDI).
The AFI specifies the format of the IDI, the authority
that is responsible for allocating IDI values, and the
syntax used to represent the Domain Specific Part (DSP).
The IDI is interpreted according to the value of the AFI
and its value identifies the authority responsible for
the structure and assignment of DSP values. The DSP is
allocated and assigned by the authority specified by the
IDP part.
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______________
!_____IDP______!_________________________________
ISO/CCITT NSAP ADDRESS !_AFI__!_IDI___!______________DSP________________!
Figure 5.1.1 NSAP Address Structure
The National Institute of Standards and Technology (NIST)
has been designated as the authority to administer the
addressing domain identified by IDI value 0005 under AFI
47. The AFI value of decimal 47 specifies that the IDI part
is interpreted as a four decimal digit International Code
Designator (ICD) and that the DSP has a binary abstract
syntax. ICDs are allocated and assigned by ISO [ISO 27] and
identify international organizations that are the authorities
for address administration for an addressing subdomain.
The addressing domain identified by ICD 0005 shall be
available for use by all of the Federal Government. The
NIST shall specify the structure and semantics of the
DSP associated with ICD 0005 and delegate the task of
administering the assignment of DSP values to the General
Services Administration (GSA). This is summarized in Figure
5.1.2.
_______________
!_____IDP_______!_________________________________
ISO/CCITT NSAP Address !__AFI__!__IDI__!____________DSP__________________!
Fed.Govt.NSAP Address !___47__!_0005__!_structure__specified__by__GOSIP_!
Figure 5.1.2 The NIST ICD Addressing Domain
NSAP addresses, encoded as NPAI in appropriate NPDUs, serve
as the primary input to the routing and relaying functions
of protocol entities providing the Network Service. As such,
the semantics of NSAP addresses must convey information
required for routing as well as address administration.
The basic principles of Network Layer routing, as defined in
the OSI Routing Framework [ISO 48], include:
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* The global OSI environment will consist of a number of
Administrative Domains. An Administrative Domain consists
of a collection of End Systems (ESs) and Intermediate
Systems (ISs), and subnetworks operated by a single
entity or Administrative Authority. The Administrative
Authority is responsible for the organization of ESs and
ISs into Routing Domains; the further structuring and
assignment of NSAP addresses; the policies that govern
the information that is collected and disseminated both
internally and externally to the Administrative Domain;
and, the establishment of subdomains and the corresponding
delegation of responsibilities.
* A Routing Domain is a set of ESs and ISs which operate
according to the same routing procedures and which is
wholly contained within a single Administrative Domain.
An Administrative Authority may delegate to the entity
responsible for a Routing Domain the responsibilities
to further structure and assign NSAP addresses. The
hierarchical decomposition of Routing Domains into
subdomains may greatly reduce the resources required
in the maintenance, computation and storage of routing
information.
This GOSIP makes provisions for the establishment of
Administrative Domains, Routing Domains and one level of
routing subdomains (called Areas). This decomposition of the
routing environment allows, where appropriate, administrative
entities to request the delegation of responsibility for
the organization and administration of their systems and
subnetworks. The provision of two levels of routing structures
within an Administrative Domain will allow Administrative
Authorities to engineer routing configurations that best
serve their individual needs.
Figure 5.1.3 depicts the GOSIP NSAP address structure. This
structure is mandatory for addresses allocated from the ICD
0005 addressing domain.
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_________
!___IDP___!____________________________________________________________________
!AFI_!IDI_!__________________________________DSP_______________________________!
!_47_!0005!DFI!_Admin_Author.!_Reserved_!_Routing_Domain_!_Area_!_System_!_NSel!
!_1__!_2__!_1_!_______3______!_____2____!_______2________!__2___!___6____!__1__!
(octets)
Figure 5.1.3 GOSIP NSAP Address Structure
The DSP Format Identifier (DFI) specifies the structure,
semantics and administration requirements associated with
the remainder of the DSP. This field provides for graceful
support of future DSP structures should the need arise.
Currently, only one DSP format (DFI=10000000) is defined
under ICD 0005. The remainder of this section describes this
DSP format.
The Administrative Authority field identifies the entity
that is responsible for the organization of ISs and ESs into
Routing Domains and Areas; the allocation and assignment
of the remaining portion of the DSP; and the policies that
govern the dissemination of information within and external
to the Administrative Domain. Note that it is unlikely that
a large number of Federal Government organizations will
establish their own Administrative Domains. Instead, it is
more likely that Administrative Domains will be established
for collective organizations that autonomously operate
large inter-networks and that individual organizations would
correspondingly be delegated authority for Routing Domains
or Areas.
The Reserved field is positioned to be available for encoding
higher level routing structures above those of the routing
domain or to be used to expand either the Administrative
Authority or the Routing Domain fields in future DSP formats
should the need arise.
The Routing Domain field identifies a unique Routing Domain
within an Administrative Domain.
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The Area field identifies a unique subdomain of the Routing
Domain.
The System field identifies a unique system (ES or IS) within
an Area. The format, value, structure and meaning of this
field is left to the discretion of its administrator.
The NSAP Selector field identifies a direct user of the
Network Layer service, usually a Transport entity. (The
NSAP Selector may also identify other direct users of the
Network Service if required by the Acquisition Authority.)
GOSIP allows a system administrator to configure NSAP
Selector-to-Transport entity mappings because, for example,
several transport entities may co-exist in some systems.
References
[1] Lyman Chapin. Proposed ANS for the Structure of the
DSP Part of the NSAP Address When the ISO DCC IDI
Format is used with the ISO DCC Code '840'. Technical
Report 1990-26, ANSI X3S3.3, (forthcoming).
[2] Richard Colella, Ella Gardner, and Ross Callon.
Guidelines for OSI NSAP Allocation in the Internet.
Technical Report, (Pending Publication).
[3] GOSIP Advanced Requirements Group. Government Open
Systems Interconnection Profile (GOSIP) Version 2 [Final
Text]. Federal Information Processing Standard, U.S.
Department of Commerce, National Institute of Standards
and Technology, Gaithersburg, MD, (Pending Publication).
[4] GOSIP Advanced Requirements Group. Government Open
Systems Interconnection Profile (GOSIP) Version 1.
Federal Information Processing Standard 146, U.S.
Department of Commerce, National Institute of Standards
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and Technology, National Technical Information Service,
Springfield, VA, August 1988.
[5] ISO/IEC. Information Processing Systems -- Data
Communications -- Network Service Definition
Addendum 2: Network Layer Addressing. International
Standard 8348/Addendum 2, ISO/IEC JTC 1, Switzerland,
1988.
[6] ISO/IEC. Intermediate System to Intermediate System
Intra-Domain Routeing Exchange Protocol for use in
Conjunction with the Protocol for Providing the
Connectionless-mode Network Service (ISO 8473). Draft
International Standard 10589, ISO/IEC JTC 1, Switzerland,
November 1990.
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