Manning & Colella [Page 1]
RFC 1706 DNS NSAP RRs October 1994
OSI lower layer protocols, comprising the connectionless network
protocol (CLNP) [5] and supporting routing protocols, are deployed in
some parts of the global Internet. Maintenance and debugging of CLNP
connectivity is greatly aided by support in the Domain Name System
(DNS) [7] [8] for mapping between names and NSAP (network service
access point) addresses [6] [Note: NSAP and NSAP address are used
interchangeably throughout this memo].
This document defines the format of one new Resource Record (RR) for
the DNS for domain name-to-NSAP mapping. The RR may be used with any
NSAP-to-name translation is accomplished through use of the PTR RR
(see RFC 1035 for a description of the PTR RR). This paper describes
how PTR RRs are used to support this translation.
This memo assumes that the reader is familiar with the DNS. Some
familiarity with NSAPs is useful; see [1] or Annex A of [6] for
The reason for defining DNS mappings for NSAPs is to support the
existing CLNP deployment in the Internet. Debugging with CLNP ping
and traceroute has become more difficult with only numeric NSAPs as
the scale of deployment has increased. Current debugging is supported
by maintaining and exchanging a configuration file with
name/NSAP mappings similar in function to
hosts.txt. This suffers from the lack
of a central coordinator for this file and also from the perspective
of scaling. The former describes the most serious short-term
term scaling difficiencies.
The methods defined in this paper are applicable to all NSAP formats.
As a point of reference, there is a distinction between registration
and publication of addresses. For IP addresses, the IANA is the root
registration authority and the DNS a publication method. For NSAPs,
Annex A of the network service definition, ISO8348 [6], describes the
root registration authority and this memo defines how the DNS is used
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RFC 1706 DNS NSAP RRs October 1994
NSAPs are hierarchically structured to allow distributed
administration and efficient routing. Distributed administration
permits subdelegated addressing authorities to, as allowed by the
delegator, further structure the portion of the NSAP space under
their delegated control. Accomodating this distributed authority
requires that there be little or no a priori knowledge of the
structure of NSAPs built into DNS resolvers and servers.
For the purposes of this memo, NSAPs can be thought of as a tree of
identifiers. The root of the tree is ISO8348 [6], and has as its
immediately registered subordinates the one-octet Authority and
Format Identifiers (AFIs) defined there. The size of subsequently-
defined fields depends on which branch of the tree is taken. The
depth of the tree varies according to the authority responsible for
defining subsequent fields.
An example is the authority under which
U.S. GOSIP defines NSAPs [2].
Under the AFI of 47, NIST (National Institute of Standards and
Technology) obtained a value of 0005 (the AFI of 47 defines the next
field as being two octets consisting of four BCD digits from the
International Code Designator space [3]). NIST defined the subsequent
fields in [2], as shown in Figure 1. The field immediately following
0005 is a format identifier for the rest of the
U.S. GOSIP NSAP
structure, with a hex value of 80. Following this is the three-octet
field, values for which are allocated to network operators; the
registration authority for this field is delegated to GSA (General
Services Administration).
The last octet of the NSAP is the NSelector (NSel). In practice, the
NSAP minus the NSel identifies the CLNP protocol machine on a given
system, and the NSel identifies the CLNP user. Since there can be
more than one CLNP user (meaning multiple NSel values for a given
"base" NSAP), the representation of the NSAP should be CLNP-user
independent. To achieve this, an NSel value of zero shall be used
with all NSAP values stored in the DNS. An NSAP with NSel=0
identifies the network layer itself. It is left to the application
retrieving the NSAP to determine the appropriate value to use in that
instance of communication.
When CLNP is used to support TCP and UDP services, the NSel value
used is the appropriate IP PROTO value as registered with the IANA.
For "standard" OSI, the selection of NSel values is left as a matter
of local administration. Administrators of systems that support the
OSI transport protocol [4] in addition to
TCP/UDP must select NSels
for use by OSI Transport that do not conflict with the IP PROTO
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RFC 1706 DNS NSAP RRs October 1994
|--------------|-------------------------------------|
| AFI | IDI | <-- DSP --> |
|-----|--------|-------------------------------------|
| 47 | 0005 | DFI | AA |Rsvd | RD |Area | ID |Sel |
|-----|--------|-----|----|-----|----|-----|----|----|
octets | 1 | 2 | 1 | 3 | 2 | 2 | 2 | 6 | 1 |
|-----|--------|-----|----|-----|----|-----|----|----|
AFI Authority and Format Identifier
IDI Initial Domain Identifier
DFI DSP Format Identifier
AA Administrative Authority
RD Routing Domain Identifier
Figure 1: GOSIP Version 2 NSAP structure.
In the NSAP RRs in Master Files and in the printed text in this memo,
NSAPs are often represented as a string of "."-separated hex values.
The values correspond to convenient divisions of the NSAP to make it
more readable. For example, the "."-separated fields might correspond
to the NSAP fields as defined by the appropriate authority (RARE,
U.S. GOSIP, ANSI, etc.). The use of this notation is strictly for
readability. The "."s do not appear in DNS packets and DNS servers
can ignore them when reading Master Files. For example, a printable
representation of the first four fields of a
U.S. GOSIP NSAP might
and a full
U.S. GOSIP NSAP might appear as
47.0005.80.005a00.0000.1000.0020.00800a123456.00.
Other NSAP formats have different lengths and different
administratively defined field widths to accomodate different
requirements. For more information on NSAP formats in use see RFC
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RFC 1706 DNS NSAP RRs October 1994
The NSAP RR is defined with mnemonic "NSAP" and TYPE code 22
(decimal) and is used to map from domain names to NSAPs. Name-to-NSAP
mapping in the DNS using the NSAP RR operates analogously to IP
address lookup. A query is generated by the resolver requesting an
NSAP RR for a provided domain name.
NSAP RRs conform to the top level RR format and semantics as defined
in Section 3.2.1 of RFC 1035.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
* NAME: an owner name,
i.e., the name of the node to which this
resource record pertains.
* TYPE: two octets containing the NSAP RR TYPE code of 22 (decimal).
* CLASS: two octets containing the RR IN CLASS code of 1.
* TTL: a 32 bit signed integer that specifies the time interval in
seconds that the resource record may be cached before the source
of the information should again be consulted. Zero values are
interpreted to mean that the RR can only be used for the
transaction in progress, and should not be cached. For example,
SOA records are always distributed with a zero TTL to prohibit
caching. Zero values can also be used for extremely volatile data.
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RFC 1706 DNS NSAP RRs October 1994
* RDLENGTH: an unsigned 16 bit integer that specifies the length in
octets of the RDATA field.
* RDATA: a variable length string of octets containing the NSAP.
The value is the binary encoding of the NSAP as it would appear in
the CLNP source or destination address field. A typical example of
such an NSAP (in hex) is shown below. For this NSAP, RDLENGTH is
20 (decimal); "."s have been omitted to emphasize that they don't
appear in the DNS packets.
39840f80005a0000000001e13708002010726e00
NSAP RRs cause no additional section processing.
6. NSAP-to-name Mapping Using the PTR RR
The PTR RR is defined in RFC 1035. This RR is typically used under
the "
IN-ADDR.ARPA" domain to map from IPv4 addresses to domain names.
Similarly, the PTR RR is used to map from NSAPs to domain names under
the "
NSAP.INT" domain. A domain name is generated from the NSAP
according to the rules described below. A query is sent by the
resolver requesting a PTR RR for the provided domain name.
A domain name is generated from an NSAP by reversing the hex nibbles
of the NSAP, treating each nibble as a separate subdomain, and
appending the top-level subdomain name "
NSAP.INT" to it. For example,
the domain name used in the reverse lookup for the NSAP
[Implementation note: For sanity's sake user interfaces should be
designed to allow users to enter NSAPs using their natural order,
i.e., as they are typically written on paper. Also, arbitrary "."s
should be allowed (and ignored) on input.]
The format of NSAP RRs (and NSAP-related PTR RRs) in Master Files
conforms to Section 5, "Master Files," of RFC 1035. Below are
examples of the use of these RRs in Master Files to support name-to-
NSAP and NSAP-to-name mapping.
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RFC 1706 DNS NSAP RRs October 1994
The NSAP RR introduces a new hex string format for the RDATA field.
The format is "0x" (
i.e., a zero followed by an 'x' character)
followed by a variable length string of hex characters (0 to 9, a to
f). The hex string is case-insensitive. "."s (
i.e., periods) may be
inserted in the hex string anywhere after the "0x" for readability.
The "."s have no significance other than for readability and are not
propagated in the protocol (
e.g., queries or zone transfers).
1994041800 ; Serial - date
1800 ; Refresh - 30 minutes
3600 ) ; Minimum - 1 hour
IN HINFO PC/486 BSDi1.0(TUBA)
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RFC 1706 DNS NSAP RRs October 1994
;;;;;; Master File for reverse mapping of NSAPs under the
1994041800 ; Serial - date
1800 ; Refresh - 30 minutes
3600 ) ; Minimum - 1 hour
8. Security Considerations
Security issues are not discussed in this memo.
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RFC 1706 DNS NSAP RRs October 1994
Marina del Rey, CA. 90292
National Institute of Standards and Technology
[1] Colella, R., Gardner, E., Callon, R., and Y. Rekhter, "Guidelines
for OSI NSAP Allocation inh the Internet", RFC 1629, NIST,
Wellfleet, Mitre,
T.J. Watson Research Center, IBM Corp., May
[2] GOSIP Advanced Requirements Group. Government Open Systems
Interconnection Profile (GOSIP) Version 2. Federal Information
Processing Standard 146-1,
U.S. Department of Commerce, National
Institute of Standards and Technology, Gaithersburg, MD, April
[3]
ISO/IEC. Data interchange - structures for the identification of
organization. International Standard 6523,
ISO/IEC JTC 1,
[4]
ISO/IEC. Connection oriented transport protocol specification.
International Standard 8073,
ISO/IEC JTC 1, Switzerland, 1986.
[5]
ISO/IEC. Protocol for Providing the Connectionless-mode Network
Service. International Standard 8473,
ISO/IEC JTC 1,
Manning & Colella [Page 9]
RFC 1706 DNS NSAP RRs October 1994
[6]
ISO/IEC. Information Processing Systems -- Data Communications --
Network Service Definition. International Standard 8348,
ISO/IEC JTC 1, Switzerland, 1993.
[7] Mockapetris, P., "Domain Names -- Concepts and Facilities", STD
[8] Mockapetris, P., "Domain Names -- Implementation and
Institute, November 1987.
Manning & Colella [Page 10]