Internet DRAFT - draft-levine-additional-registered-clauses
draft-levine-additional-registered-clauses
Network Working Group J. Levine
Internet-Draft Taughannock Networks
Updates: 5321 (if approved) July 30, 2019
Intended status: Standards Track
Expires: January 31, 2020
Update to Additional Registered Clauses in SMTP Received Headers
draft-levine-additional-registered-clauses-03
Abstract
SMTP servers add Received: trace headers to mail messages to track
their progress This document updates the registration criteria for
Additional Registered Clauses in those headers to Expert Review, and
adds new clauses for Server Name Indication (SNI) and sending port
number (PORT).
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 31, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The Server Name Indication clause . . . . . . . . . . . . . . 2
3. The Port Number clause . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4.1. Guidance for Designated Expert . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 3
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Uninformative References . . . . . . . . . . . . . . . . 4
Appendix A. Change history . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
SMTP servers add Received: trace headers to mail messages to track
their progress. The syntax of those headers is defined in [RFC5321].
Each header can include optional Additional Registered Clauses that
log information related to optional SMTP features.
This document updates the registration criteria for Additional
Registered Clauses in those headers to Expert Review, and adds a new
clause for Server Name Indication (SNI). The headers can include
Additional Registered Clauses that add information about optional
SMTP features.
2. The Server Name Indication clause
Server Name Indication or SNI [RFC6066] is an optional TLS feature
that a TLS client can use to advise a server the name it expects the
server to have. When used in the initial negotiation for a STARTTLS
[RFC3207] session it enables the server to use a certificate with the
identity that the client expects, as is recommended in [RFC7817] and
is required for SMTP MTA-STS [RFC8461]. When a client presents a
name using SNI, the server can log the name using the "sni"
additional-registered-clause.
IANA is requested to add one new entry to the additional-registered-
clauses registry:
"sni" - indicates the Server Name Indication was used.
"name" - the name provided by SNI. It has the syntax of a Domain
Name.
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3. The Port Number clause
When several sending mail hosts send mail from behind a Network
Address Translator (NAT), often the only way to tell which host sent
the is to look up the sending port number in the NAT's logs. The
server can log the sending port number using the "port" additional-
registered-clause.
IANA is requested to add one new entry to the additional-registered-
clauses registry:
"port" - indicates the mail client's port number
"number" - the client's port number. It has the syntax of an
integer.
4. IANA Considerations
IANA is requested to update the Registration Procedure for the
Additional-registered-clauses registry to Expert Review. The IESG
will appoint the expert(s).
4.1. Guidance for Designated Expert
The Designated Expert is expected to check that a proposed
Additional-registered-clause has a specification that is stable and
detailed enough to implement the clause and interoperate. The Expert
should ensure that the clause name is reasonably related to the
information it represents, that the contents of the clause are well-
defined, and that any external references it depends on, e.g., a
vocabulary of keywords, are stable and well-defined.
5. Security Considerations
E-mail is subject to a vast range of threats and abuses. In a few
circumstances, a new Additional-registered-clause might disclose
information to a recipient that was otherwise unavailable. On the
other hand, better logging usually makes it easier to diagnose
failures and attacks.
If the SNI information in a STARTTLS negotiation is logged, it may
make it easier to determine the recipient(s) of the message if they
are not already logged in trace headers.
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6. References
6.1. Normative References
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207,
February 2002, <https://www.rfc-editor.org/info/rfc3207>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008,
<https://www.rfc-editor.org/info/rfc5321>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
6.2. Uninformative References
[RFC7817] Melnikov, A., "Updated Transport Layer Security (TLS)
Server Identity Check Procedure for Email-Related
Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016,
<https://www.rfc-editor.org/info/rfc7817>.
[RFC8461] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
and J. Jones, "SMTP MTA Strict Transport Security (MTA-
STS)", RFC 8461, DOI 10.17487/RFC8461, September 2018,
<https://www.rfc-editor.org/info/rfc8461>.
Appendix A. Change history
02 to 03 Add port numbers. What the heck.
01 to 02 Take out ESNI clause to prevent downref.
00 to 01 Add new ESNI clause. Fix many typos.
00 New draft
Author's Address
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John Levine
Taughannock Networks
PO Box 727
Trumansburg, NY 14886
Phone: +1 831 480 2300
Email: standards@taugh.com
URI: http://jl.ly
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