Network Working Group C. Malamud
Internet-Draft Memory Palace Press
Expires: August 8, 2005 February 4, 2005
Attaching Meaning to Solicitation Class Keywords
draft-malamud-keyword-discovery-01.txt
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This Internet-Draft proposes a mechanism for finding information
about solicitation class keywords which are defined in RFC 3865, the
No Soliciting SMTP Service Extension. The mechanism uses a DNS NAPTR
Resource Record to associate a URI with a solicitation class keyword.
Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, [RFC2119].
Table of Contents
1. Solicitation Class Keywords . . . . . . . . . . . . . . . . . 3
2. The No-Solicit NAPTR Application . . . . . . . . . . . . . . . 3
3. Example(Non-Normative) . . . . . . . . . . . . . . . . . . . . 4
4. DDDS Application Specification . . . . . . . . . . . . . . . . 7
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1 Normative References . . . . . . . . . . . . . . . . . . . 8
8.2 Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 9
A. Intended Status and Discussion (TO BE REMOVED UPON
PUBLICATION) . . . . . . . . . . . . . . . . . . . . . . . . . 9
B. Changes From Previous Draft (TO BE REMOVED UPON
PUBLICATION) . . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 11
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1. Solicitation Class Keywords
[RFC3865] defines the concept of a "solicitation class keyword",
which is an arbitrary string or label which can be associated with an
electronic mail message and transported by the ESMTP mail service as
defined in [RFC2821] and related documents. Solicitation class
keywords are formatted like domain names, but reversed. For example,
the registrant of "example.com" might specify a particular
solicitation class keyword such as "com.example.adv" that could be
inserted in a "No-Solicit:" header or in a trace field. [RFC3865]
explicitly placed discovery of the meaning of a solicitation class
keywords as outside of the scope of the basic ESMTP service
extension.
If that standard becomes widely deployed, a mail message might
contain a large number of solicitation class keywords. The
"No-Solicit:" header has keywords inserted by the sender of the
message, which might include the sender's own keywords, as well as
those mandated by regulatory authorities or recommended by voluntary
industry associations. Likewise, the "received:" trace fields might
contain a large number of keywords produced by message transfer
agents (MTAs), filtering software, forwarding software in the message
user agent (MUA), or any other system in the chain of delivery.
As the number of keywords employed grows, it will be important to
find a method for discovering the meaning behind the various labels.
This draft specifies such a mechanism using the DNS NAPTR Resource
Record, which is defined in [RFC3403]. An explicit design goal is to
keep the system as simple as possible. Approaches such as defining
an XML-based structure that would contain keyword meta-data or other
approaches that define the format of the explanation were ruled out.
Instead, the goal is to associate a solicitation class keyword with a
URI, which in turn contains an explanation of the keyword.
2. The No-Solicit NAPTR Application
The DDDS framework of [RFC3401] and related documents provides a
powerful set of mechanisms that can yield sophisticated applications
such as ENUM.[RFC3761] There is a simplification of the DDDS
framework called the Straightforward-NAPTR (S-NAPTR) application
[RFC3958]. Unfortunately, S-NAPTR does not permit the use of the "U"
flag for terminal lookups and does not support the regular expression
field of the NAPTR RR. Since a replacement field in a NAPTR record
must contain only a domain name, and our goal is to find a URI, this
draft does not use the S-NAPTR mechanism.
This draft uses the NAPTR RR to do a single lookup from solicitation
class keyword to URI. The fields of the NAPTR RR are used as
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follows:
o The "ORDER" and "PREFERENCE" fields are to be processed as
specified in [RFC3403]: if multiple records are returned, the
one(s) with the lowest "ORDER" value that have a matching
"SERVICE" field MUST be used. Of those with the lowest ORDER
value, those with the lowest "PREFERENCE" SHOULD be used.
o The "FLAGS" field MUST contain the character "U".
o The "SERVICES" field MUST contain only the string "no-solicit".
o The "REGEXP" field MUST contain a valid URI as further specified
in this section.
o The "REPLACEMENT" field MUST be empty.
The "REGEXP" field is defined in [RFC3402] as consisting of a
"delim-character", a POSIX Extended Regular Expression, another
"delim-character", a replacement value, and a final
"delim-character". For this application the following rules apply:
o The "delim-character" MAY be any valid character as defined in
section 3.2 of [RFC3402].
o The extended regular expression MUST be empty.
o The replacement value MUST contain a valid URI as specified in
[RFC2396].
o The replacement value SHOULD contain a URI limited to the "ftp",
"http", and "https" schemes as specified in [RFC2396] and
[RFC2660].
o The document that is retrieved at the URI SHOULD conform to
[W3C.REC-html401-19991224], including the Accessibility Guidelines
contained therein.
3. Example(Non-Normative)
A set of NAPTR records have been installed in the "simians.net"
subdomain and can be retrieved using "dig" or other DNS utilities:
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[carl@example.com]% dig 2795.simians.net naptr
; <<>> DiG 9.2.3 <<>> 2795.simians.net naptr
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY,
status: NOERROR, id: 43494
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 5,
AUTHORITY: 2, ADDITIONAL: 1
;; QUESTION SECTION:
;2795.simians.net. IN NAPTR
;; ANSWER SECTION:
2795.simians.net. 86400 IN
NAPTR 1 1 "U" "iam+invalid"
"!!http://invalid.simians.net/contact.html!" .
2795.simians.net. 86400 IN
NAPTR 1 1 "U" "sip+invalid"
"!!http://invalid.simians.net/contact.html!" .
2795.simians.net. 86400 IN
NAPTR 1 2 "U" "no-solicit"
"!!http://infinite.simians.net/keywordinfo.html!" .
2795.simians.net. 86400 IN
NAPTR 2 1 "U" "no-solicit"
"!!http://infinite.simians.net/keywordinfo.html!" .
2795.simians.net. 86400 IN
NAPTR 1 1 "U" "no-solicit"
"!!http://infinite.simians.net/keywordinfo.html!" .
A simple utility written in PERL accepts a lookup key and returns a
URL using the specifications in this document:
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#!/usr/bin/perl
# This program accepts a solicitation class keyword and
# returns a URL on success. It dies quietly on failure.
use strict;
# http://www.net-dns.org/
use Net::DNS;
# reverse the label to create a domain name
my $target = join( ".", reverse( split( /\./, $ARGV[0]) ) );
# create a resolver
my $res = Net::DNS::Resolver->new;
# find all naptr records
my $query = $res->query( "$target", "NAPTR" ) || exit ;
# Do your DNSSEC checks here, throw away all invalid RRs
# get the answers, strip out non-matching services,
# sort by order, preference
my @rr =
sort {
# sort records numerically by order, preference
$a->order <=> $b->order
|| $a->preference <=> $b->preference
}
grep { $_->service =~ /no-solicit/ } $query->answer;
# print the first qualifying record, strip out the
# regexp markers
my $op = substr( my $answer = $rr[0]->regexp , 0, 1 )
|| exit ;
print split ( $op, $answer ) ; exit ;
Running the code gives the following results:
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[carl@example.com]% lynx -source `./discover.pl net.simians.2795`
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>About Our Solicitation Class Keyword</title>
</head>
<body>
<center>
<a href="monkey.mp3">
<img alt="bouncy monkey logo"
src="images/monkey_fpo.gif" border="0" />
<br />
</a>
<br />
About net.simians.2795:<br />
It has been determined that the content of this
mail message<br />
conforms to the spirit of RFC 2795.
Congratulations?
</center>
</body>
</html>
4. DDDS Application Specification
The following definitions apply to this application:
o Application Unique String: The application unique string is a
Solicitation Class Keyword as defined in [RFC3865].
o First Well Known Rule: The Solicitation Class Keyword is reversed
in order to produce a valid domain name. For example,
"com.example.adv" would become "adv.example.com".
o Valid Databases: The DNS _is_ the database.
o Expected Output: A URI.
o The "SERVICE" field MUST contain the string "no-solicit", the
"FLAGS" field MUST contain the string "U", the "REPLACEMENT" field
MUST be empty, and the "REGEXP" field MUST be formatted as
specified in Section 2.
Wildcards are appropriate for this application, allowing multiple
solicitation class keywords that share a common prefix to all point
to the same URI.
5. Acknowledgments
The author would like to thank the following for their helpful
suggestions and reviews of this draft: Leslie Daigle, Arnt
Gulbrandsen, Michael Mealling, and Ted Hardie.
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6. Security Considerations
Use of a URI with the "https:" scheme without the use of DNSSEC makes
an unwarranted illusion of authenticity and the possibility of active
attacks a serious concern.
7. IANA Considerations
There does not appear to be a central registry maintained by the IANA
of values that might appear in a "SERVICE" field of a NAPTR resource
record. Thus, no direct IANA actions are required.
However, the IANA does maintain an Application Service Tag Registry,
which is used to support the S-NAPTR DDDS application defined in
[RFC3958]. The IANA is advised that the "no-solicit" value for the
SERVICE field is in use per this draft and thus should not be used in
the Application Service Tag Registry for other applications.
8. References
8.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[RFC2660] Rescorla, E. and A. Schiffman, "The Secure HyperText
Transfer Protocol", RFC 2660, August 1999.
[RFC3402] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Two: The Algorithm", RFC 3402, October 2002.
[RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Three: The Domain Name System (DNS) Database",
RFC 3403, October 2002.
[RFC3865] Malamud, C., "A No Soliciting Simple Mail Transfer
Protocol (SMTP) Service Extension", RFC 3865, September
2004.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[W3C.REC-html401-19991224]
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Hors, A., Jacobs, I. and D. Raggett, "HTML 4.01
Specification", W3C REC REC-html401-19991224, December
1999.
8.2 Informative References
[RFC2795] Christey, S., "The Infinite Monkey Protocol Suite (IMPS)",
RFC 2795, April 2000.
[RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[RFC3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part One: The Comprehensive DDDS", RFC 3401, October 2002.
[RFC3761] Faltstrom, P. and M. Mealling, "The E.164 to Uniform
Resource Identifiers (URI) Dynamic Delegation Discovery
System (DDDS) Application (ENUM)", RFC 3761, April 2004.
Author's Address
Carl Malamud
Memory Palace Press
PO Box 300
Sixes, OR 97476
US
Email: carl@media.org
Appendix A. Intended Status and Discussion (TO BE REMOVED UPON
PUBLICATION)
This draft is being submitted to the RFC Editor as an individual
submission with an intended publication as a Proposed Standard.
Discussion of this draft should take place on the
<mailto:namedroppers@ops.ietf.org> mailing list
(<mailto:namedroppers-request@ops.ietf.org> to subscribe). The
source and alternative transformations for this draft may be found at
<http://trusted.resource.org/no-solicit/>.
Appendix B. Changes From Previous Draft (TO BE REMOVED UPON
PUBLICATION)
From draft-malamud-keyword-discovery-00 to
draft-malamud-keyword-discovery-01:
o Moved the example from the appendix to the main text.
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o Added a brief note on use of wildcards to the DDDS application
definition.
o Minor re-arranging to conform to RFC Editor requirements.
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except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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