Ariel@RELAY.PRIME.COM (Robert Ullmann) (07/31/90)
Hi,
The following is a draft of a proposed RFC on DNS records for
domain name to X.25 and ISDN bindings, submitted for your comments,
criticisms, and flames.
The intent is to define the syntax, and first level semantics; then
to experiment with use of the bindings.
The unpublished document on TP/IX is available only in PostScript
at this time; send me mail if you would like a copy; feel free to
redistribute it, but only in its entirety.
With apologies to those subscribers to both NAMEDROPPERS (aka
comp.protocols.tcp-ip.domains) and TCP-ISDN ...
Best Regards,
Robert Ullmann
Prime Computer, Inc.
+1 508 879 2960 ext 1736
Ariel@Relay.Prime.COM
Network Working Group R. Ullmann
Request for Comments: DRAFT Prime Computer, Inc.
July 1990
Domain Name System Records for X.25 and ISDN
1. Status of this Memo
This [DRAFT] memo describes an experimental representation of PSDN and
ISDN addresses, in the DNS, as well as a route binding method for very
large scale networks.
This [DRAFT] memo specifies the Internet standard for the definition of
DNS RR types 25, 26, and 27 in the Internet class.
[The use of codes 25 to 27 has NOT been approved by Paul Mockapetris as
of the date of this DRAFT, 30 July 1990]
Distribution of this memo is unlimited.
2. Introduction
This memo specifies new RR types defined for use in the IN (Internet)
class of the DNS [6, 7]. These include addresses for PSDN and ISDN
service, and a new route-binding RR analogous to the MX RR for mail
routing.
There are several possible uses, all experimental at this time. First,
the RRs provide simple documentation of the correct address(es) to use
in static configurations of IP/X.25 [5] and SMTP/X.25 [8].
The RRs could also be used automatically by an internet network-layer
router, typically IP. The procedure would be to map IP address to domain
name, then name to canonical name if needed, then following RT records,
and finally attempting an IP/X.25 call to the address found.
Alternately, configured domain names could be resolved to identify IP to
X.25/ISDN bindings for a static but periodically refreshed routing
table.
This provides a function similar to ARP for wide area non-broadcast
networks that will scale well to a network with hundreds of millions of
hosts.
Also, a standard address binding reference will facilitate other
experiments in the use of X.25 and ISDN, especially in serious
inter-operability testing. (The author knows from experience that the
majority of work in such a test is establishing the n-squared entries in
static tables.)
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RFC DRAFT Domain Name System Records for X.25 and ISDN July 1990
Finally, the RRs are intended for use in a proposal [9] by the author
for a possible next-generation internet.
3. The X25 resource record
The X25 record identifies the PSDN address in the X.121 [4] numbering
plan for the domain name. The address is represented as a string of
decimal digits, beginning with the 4 digit DNIC (Data Network
Identification Code).
For example:
Relay.Prime.COM. IN X25 311061700956
The encoded form is the ASCII representation of the decimal digits, as a
<character-string>. Type X25 is 25.
4. The ISDN resource record
The ISDN (Integrated Services Digital Network) record identifies the
PSTN (Public Switched Telephone Network) number of the host, together
with any DDI (Direct Dial In) and subaddress (SA) as defined by
E.164 [2] and E.163 [1], the ISDN and PSTN numbering plans.
The number is represented as a string of decimal digits, beginning with
the E.163 country code and ending with the DDI if any. If a SA is
present, it is represented as another string.
For example:
Relay.Prime.COM. IN ISDN 150887929603217
sh.Prime.COM. IN ISDN 150887929603217 004
The RR data is the ASCII representation of the decimal digits. It is
encoded as one or two <character-string>s, i.e. count followed by
characters. Type ISDN is 26.
CCITT recommendation E.166 [3] defines escape codes for the
representation of ISDN addresses in X.121, and PSDN addresses in E.164.
It specifies that the exact codes are a "national matter", i.e.
different on different networks. An ISDN host may be able to use both
the X25 and ISDN addresses, with local information added, but the
addresses must be distinct in the DNS.
5. The RT resource record
The RT resource record provides a route-through binding for hosts that
do not have their own direct wide area network addresses. It is used in
much the same way as the MX RR.
The format is one (usually small) integer, representing the preference
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RFC DRAFT Domain Name System Records for X.25 and ISDN July 1990
of the route. Smaller numbers indicate more preferred routes. This is
followed by the domain name of the host to route through, which is
expected to have at least one A, X25, or ISDN record.
For example,
sh.prime.com. IN RT 2 Relay.Prime.COM.
IN RT 10 NET.Prime.COM.
*.prime.com. IN RT 90 Relay.Prime.COM.
When a host is looking up DNS records to attempt to route a datagram, it
first looks for RT records for the destination host, which point to
hosts with address records (A, X25, ISDN) compatible with the wide area
networks available to the host. If it is itself in the set of RT
records, it discards any RTs with preferences higher or equal to its
own. If there are no (remaining) RTs, it can then use address records
of the destination itself.
Wild-card RTs are used exactly as are wild-card MXs.
The concrete encoding is identical to the MX RR. Type RT is 27.
References
[1] International Telegraph and Telephone Consultative Committee.
Numbering Plan for the International Telephone Service.
In CCITT Recommendations E.163. IXth Plenary Assembly, Melbourne,
1988.
Fascicle II.2 ("Blue Book").
[2] International Telegraph and Telephone Consultative Committee.
Numbering Plan for the ISDN Era.
In CCITT Recommendations E.164. IXth Plenary Assembly, Melbourne,
1988.
Fascicle II.2 ("Blue Book").
[3] International Telegraph and Telephone Consultative Committee.
Numbering Plan Interworking in the ISDN Era.
In CCITT Recommendations E.166. IXth Plenary Assembly, Melbourne,
1988.
Fascicle II.2 ("Blue Book").
[4] International Telegraph and Telephone Consultative Committee.
International Numbering Plan for the Public Data Networks.
In CCITT Recommendations X.121. IXth Plenary Assembly, Melbourne,
1988.
Fascicle VIII.3 ("Blue Book"); provisional, Geneva, 1978; amended,
Geneva, 1980, Malaga-Torremolinos, 1984 and Melborne, 1988.
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RFC DRAFT Domain Name System Records for X.25 and ISDN July 1990
[5] J. T. Korb.
Standard for the transmission of IP datagrams over public data
networks.
RFC 877, Purdue University, September, 1983.
[6] P. Mockapetris.
Domain Names -- Concepts and Facilities.
RFC 1034, ISI, November, 1987.
[7] P. Mockapetris.
Domain Names -- Implementation and Specification.
RFC 1035, ISI, November, 1987.
[8] Robert L. Ullmann.
SMTP on X.25.
RFC 1090, Prime Computer, February, 1989.
[9] Robert L. Ullmann.
TP/IX: The Next Internet.
July, 90.
Prime Computer, Inc. (unpublished).
Author's Address
Robert Ullmann 10-30
Prime Computer, Inc.
500 Old Connecticut Path
Framingham, MA 01701
Phone: +1 508 879 2960 x1736
Email: Ariel@Relay.Prime.COM
Ullmann [Page 4]smart@mel.dit.csiro.au (Robert Smart) (08/08/90)
I think the general idea of the proposed draft RFC is excellent. I would like to quibble at some details. 1) The RT records are to be used by the network layer. Like all network activity this should work without reference to domain names. It seems more correct to make this an extension of the in-addr.arpa domain 17.128.in-addr.arpa. IN RT 10 sh.prime.com. is a route to a whole class B network (128.17). Alternatively 17.18.19.20.in-addr.arpa. IN RT 30 relay.prime.com. is a route to a specific host. The names on the right here are used to choose X25 or ISDN or other routes -- their IN A records are irrelevant in this context. 2) The X25 and ISDN types should be network types parallel to IN not parts of the IN network info. E.g. Relay.prime.com. X25 A 311061700956 ISDN A 150887929603217 003 Records of the form 31106700956.x25-addr.arpa. IN X25 x.y.edu should mean that host x.y.edu will accept X25-over-IP calls for X.25 address 31106700956 using some to-be-defined protocol for running X.25 over IP. I would point out that CISCO have such a protocol and might release it (my guess: they would release it if there was a threat of some other protocol becoming a standard). Similarly for IN ISDN. Yes ISDN over IP could be used to provide telephone/fax/whatever connectivity to workstations with IP connectivity. It may not be as clearly desirable as IP over ISDN but it is possible and whatever the theoretical difficulties I suspect it would work fine in practice in many situations. 3) It is possible to imagine access to X25 and ISDN A records from boxes which don't run IP. So it would be nice to define a protocol for accessing the DNS over raw X.25 and raw ISDN networks. Since the DNS can be accessed by UDP and TCP this shouldn't be hard. Bob Smart <smart@mel.dit.csiro.au>