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rfc:rfc4405

Network Working Group E. Allman Request for Comments: 4405 Sendmail, Inc. Category: Experimental H. Katz

                                                       Microsoft Corp.
                                                            April 2006
                     SMTP Service Extension for
     Indicating the Responsible Submitter of an E-Mail Message

Status of This Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard of any kind.
 Discussion and suggestions for improvement are requested.
 Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

IESG Note

 The following documents  (RFC 4405, RFC 4406, RFC 4407, and RFC 4408)
 are published simultaneously as Experimental RFCs, although there is
 no general technical consensus and efforts to reconcile the two
 approaches have failed.  As such, these documents have not received
 full IETF review and are published "AS-IS" to document the different
 approaches as they were considered in the MARID working group.
 The IESG takes no position about which approach is to be preferred
 and cautions the reader that there are serious open issues for each
 approach and concerns about using them in tandem.  The IESG believes
 that documenting the different approaches does less harm than not
 documenting them.
 Note that the Sender ID experiment may use DNS records that may have
 been created for the current SPF experiment or earlier versions in
 this set of experiments.  Depending on the content of the record,
 this may mean that Sender-ID heuristics would be applied incorrectly
 to a message.  Depending on the actions associated by the recipient
 with those heuristics, the message may not be delivered or may be
 discarded on receipt.
 Participants relying on Sender ID experiment DNS records are warned
 that they may lose valid messages in this set of circumstances.
 Participants publishing SPF experiment DNS records should consider

Allman & Katz Experimental [Page 1] RFC 4405 SMTP Responsible Submitter Extension April 2006

 the advice given in section 3.4 of RFC 4406 and may wish to publish
 both v=spf1 and spf2.0 records to avoid the conflict.
 Participants in the Sender-ID experiment need to be aware that the
 way Resent-* header fields are used will result in failure to receive
 legitimate email when interacting with standards-compliant systems
 (specifically automatic forwarders which comply with the standards by
 not adding Resent-* headers, and systems which comply with RFC 822
 but have not yet implemented RFC 2822 Resent-* semantics).  It would
 be inappropriate to advance Sender-ID on the standards track without
 resolving this interoperability problem.
 The community is invited to observe the success or failure of the two
 approaches during the two years following publication, in order that
 a community consensus can be reached in the future.

Abstract

 This memo defines an extension to the Simple Mail Transfer Protocol
 (SMTP) service that allows an SMTP client to specify the responsible
 submitter of an e-mail message.  The responsible submitter is the
 e-mail address of the entity most recently responsible for
 introducing a message into the transport stream.  This extension
 helps receiving e-mail servers efficiently determine whether the SMTP
 client is authorized to transmit mail on behalf of the responsible
 submitter's domain.

Table of Contents

 1. Introduction ....................................................3
    1.1. Conventions Used in This Document ..........................4
 2. The SUBMITTER Service Extension .................................4
 3. The SUBMITTER Keyword of the EHLO Command .......................5
 4. The SUBMITTER Parameter of the MAIL Command .....................5
    4.1. Setting the SUBMITTER Parameter Value ......................5
    4.2. Processing the SUBMITTER Parameter .........................5
    4.3. Transmitting to a Non-SUBMITTER-Aware SMTP Server ..........6
 5. Examples ........................................................6
    5.1. Mail Submission ............................................7
    5.2. Mail Forwarding ............................................7
    5.3. Mobile User ................................................8
    5.4. Guest E-Mail Service .......................................9
    5.5. SUBMITTER Used on a Non-Delivery Report ...................11
 6. Security Considerations ........................................11
 7. Acknowledgements ...............................................12
 8. IANA Considerations ............................................12
 9. References .....................................................12
    9.1. Normative References ......................................12

Allman & Katz Experimental [Page 2] RFC 4405 SMTP Responsible Submitter Extension April 2006

1. Introduction

 The practice of falsifying the identity of the sender of an e-mail
 message, commonly called "spoofing", is a prevalent tactic used by
 senders of unsolicited commercial e-mail, or "spam".  This form of
 abuse has highlighted the need to improve identification of the
 "responsible submitter" of an e-mail message.
 In this specification, the responsible submitter is the entity most
 recently responsible for injecting a message into the e-mail
 transport stream.  The e-mail address of the responsible submitter
 will be referred to as the Purported Responsible Address (PRA) of the
 message.  The Purported Responsible Domain (PRD) is the domain
 portion of that address.
 This specification codifies rules for encoding the purported
 responsible address into the SMTP transport protocol.  This will
 permit receiving SMTP servers to efficiently validate whether or not
 the SMTP client is authorized to transmit mail on behalf of the
 responsible submitter's domain.
 Broadly speaking, there are two possible approaches for determining
 the purported responsible address: either from RFC 2821 [SMTP]
 protocol data or from RFC 2822 [MSG-FORMAT] message headers.  Each
 approach has certain advantages and disadvantages.
 Deriving the purported responsible domain from RFC 2821 data has the
 advantage that validation can be performed before the SMTP client has
 transmitted the message body.  If spoofing is detected, then the SMTP
 server has the opportunity, depending upon local policy, to reject
 the message before it is ever transmitted.  The disadvantage of this
 approach is the risk of false positives, that is, incorrectly
 concluding that the sender's e-mail address has been spoofed.  There
 are today legitimate reasons why the Internet domain names used in
 RFC 2821 commands may be different from those of the sender of an e-
 mail message.
 Deriving the purported responsible domain from RFC 2822 headers has
 the advantage that validation can usually be based on an identity
 that is displayed to recipients by existing Mail User Agents (MUAs)
 as the sender's identity.  This aids in detection of a particularly
 noxious form of spoofing known as "phishing" in which a malicious
 sender attempts to fool a recipient into believing that a message
 originates from an entity well known to the recipient.  This approach
 carries a lower risk of false positives since there are fewer
 legitimate reasons for RFC 2822 headers to differ from the true
 sender of the message.  The disadvantage of this approach is that it
 does require parsing and analysis of message headers.  In practice,

Allman & Katz Experimental [Page 3] RFC 4405 SMTP Responsible Submitter Extension April 2006

 much if not all the message body is also transmitted since the SMTP
 protocol described in RFC 2821 provides no mechanism to interrupt
 message transmission after the DATA command has been issued.
 It is desirable to unify these two approaches in a way that combines
 the benefits of both while minimizing their respective disadvantages.
 This specification describes just such a unified approach.  It uses
 the mechanism described in [SMTP] to describe an extension to the
 SMTP protocol.  Using this extension, an SMTP client can specify the
 e-mail address of the entity most recently responsible for submitting
 the message to the SMTP client in a new SUBMITTER parameter of the
 SMTP MAIL command.  SMTP servers can use this information to validate
 that the SMTP client is authorized to transmit e-mail on behalf of
 the Internet domain contained in the SUBMITTER parameter.

1.1. Conventions Used in This Document

 In examples, "C:" and "S:" indicate lines sent by the client and
 server, respectively.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [KEYWORDS].

2. The SUBMITTER Service Extension

 The following SMTP service extension is hereby defined:
 (1)  The name of this SMTP service extension is "Responsible
      Submitter";
 (2)  The EHLO keyword value associated with this extension is
      "SUBMITTER";
 (3)  The SUBMITTER keyword has no parameters;
 (4)  No additional SMTP verbs are defined by this extension;
 (5)  An optional parameter is added to the MAIL command using the
      esmtp-keyword "SUBMITTER", and is used to specify the e-mail
      address of the entity responsible for submitting the message for
      delivery;
 (6)  This extension is appropriate for the submission protocol
      [SUBMIT].

Allman & Katz Experimental [Page 4] RFC 4405 SMTP Responsible Submitter Extension April 2006

3. The SUBMITTER Keyword of the EHLO Command

 An SMTP server includes the SUBMITTER keyword in its EHLO response to
 tell the SMTP client that the SUBMITTER service extension is
 supported.
 The SUBMITTER keyword has no parameters.

4. The SUBMITTER Parameter of the MAIL Command

 The syntax of the SUBMITTER parameter is
    "SUBMITTER=" Mailbox
 where Mailbox is the Augmented Backus-Naur Form (ABNF) [ABNF]
 production defined in Section 4.1.2 of [SMTP].  Characters such as
 SP, "+", and "=" that may occur in Mailbox but are not permitted in
 ESMTP parameter values MUST be encoded as "xtext" as described in
 Section 4 of [DSN].

4.1. Setting the SUBMITTER Parameter Value

 The purpose of the SUBMITTER parameter is to allow the SMTP client to
 indicate to the server the purported responsible address of the
 message directly in the RFC 2821 protocol.
 Therefore, SMTP clients that support the Responsible Submitter
 extension MUST include the SUBMITTER parameter on all messages.  This
 includes messages containing a null reverse-path in the MAIL command.
 SMTP clients MUST set the SUBMITTER parameter value to the purported
 responsible address of the message as defined in [PRA].  This also
 applies to messages containing a null reverse-path.
 In some circumstances, described in Section 7 of [SENDER-ID], SMTP
 clients may need to add RFC 2822 headers to the message in order to
 ensure that the correct SUBMITTER parameter value can be set.

4.2. Processing the SUBMITTER Parameter

 Receivers of e-mail messages sent with the SUBMITTER parameter SHOULD
 select the domain part of the SUBMITTER address value as the
 purported responsible domain of the message, and SHOULD perform such
 tests, including those defined in [SENDER-ID], as are deemed
 necessary to determine whether the connecting SMTP client is
 authorized to transmit e-mail messages on behalf of that domain.

Allman & Katz Experimental [Page 5] RFC 4405 SMTP Responsible Submitter Extension April 2006

 If these tests indicate that the connecting SMTP client is not
 authorized to transmit e-mail messages on behalf of the SUBMITTER
 domain, the receiving SMTP server SHOULD reject the message and when
 rejecting MUST use "550 5.7.1 Submitter not allowed."
 If the receiving SMTP server allows the connecting SMTP client to
 transmit message data, then the server SHOULD determine the purported
 responsible address of the message by examining the RFC 2822 message
 headers as described in [PRA].  If this purported responsible address
 does not match the address appearing in the SUBMITTER parameter, the
 receiving SMTP server MUST reject the message and when rejecting MUST
 use "550 5.7.1 Submitter does not match header."
 If no purported responsible address is found according to the
 procedure defined in [PRA], the SMTP server SHOULD reject the message
 and when rejecting MUST use "554 5.7.7 Cannot verify submitter
 address."
 Verifying Mail Transfer Agents (MTAs) are strongly urged to validate
 the SUBMITTER parameter against the RFC 2822 headers; otherwise, an
 attacker can trivially defeat the algorithm.
 Note that the presence of the SUBMITTER parameter on the MAIL command
 MUST NOT change the effective reverse-path of a message.  Any
 delivery status notifications must be sent to the reverse-path, if
 one exists, as per Section 3.7 of [SMTP] regardless of the presence
 of a SUBMITTER parameter.  If the reverse-path is null, delivery
 status notifications MUST NOT be sent to the SUBMITTER address.
 Likewise, the SUBMITTER parameter MUST NOT change the effective reply
 address of a message.  Replies MUST be sent to the From address or
 the Reply-To address, if present, as described in Section 3.6.2 of
 [MSG-FORMAT] regardless of the presence of a SUBMITTER parameter.

4.3. Transmitting to a Non-SUBMITTER-Aware SMTP Server

 Notwithstanding the provisions of Section 4.1 above, when an MTA
 transmits a message to another MTA that does not support the
 SUBMITTER extension, the forwarding MTA MUST transmit the message
 without the SUBMITTER parameter.  This should involve no information
 loss, since the SUBMITTER parameter is required to contain
 information derived from the message headers.

5. Examples

 This section provides examples of how the SUBMITTER parameter would
 be used.  The following dramatis personae appear in the examples:

Allman & Katz Experimental [Page 6] RFC 4405 SMTP Responsible Submitter Extension April 2006

 alice@example.com: the original sender of each e-mail message.
 bob@company.com.example: the final recipient of each e-mail.
 bob@almamater.edu.example: an e-mail address used by Bob that he has
 configured to forward mail to his office account at
 bob@company.com.example.
 alice@mobile.net.example: an e-mail account provided to Alice by her
 mobile e-mail network carrier.

5.1. Mail Submission

 Under normal circumstances, Alice would configure her MUA to submit
 her message to the mail system using the SUBMIT protocol [SUBMIT].
 The MUA would transmit the message without the SUBMITTER parameter.
 The SUBMIT server would validate that the MUA is allowed to submit a
 message through some external scheme, perhaps SMTP Authentication
 [SMTPAUTH].  Under most circumstances, this would look like a normal,
 authenticated SMTP transaction.  The SUBMIT server would extract her
 name from the RFC 2822 headers for use in the SUBMITTER parameters of
 subsequent transmissions of the message.

5.2. Mail Forwarding

 When Alice sends a message to Bob at his almamater.edu.example
 account, the SMTP session from her SUBMIT server might look something
 like this:
    S: 220 almamater.edu.example ESMTP server ready
    C: EHLO example.com
    S: 250-almamater.edu.example
    S: 250-DSN
    S: 250-AUTH
    S: 250-SUBMITTER
    S: 250 SIZE
    C: MAIL FROM:<alice@example.com> SUBMITTER=alice@example.com
    S: 250 <alice@example.com> sender ok
    C: RCPT TO:<bob@almamater.edu.example>
    S: 250 <bob@almamater.edu.example> recipient ok
    C: DATA
    S: 354 okay, send message
    C: (message body goes here)
    C: .
    S: 250 message accepted
    C: QUIT
    S: 221 goodbye

Allman & Katz Experimental [Page 7] RFC 4405 SMTP Responsible Submitter Extension April 2006

 The almamater.edu.example MTA must now forward this message to
 bob@company.com.example.  Although the original sender of the message
 is alice@example.com, Alice is not responsible for this most recent
 retransmission of the message.  That role is filled by
 bob@almamater.edu.example, who established the forwarding of mail to
 bob@company.com.example.  Therefore, the almamater.edu.example MTA
 determines a new purported responsible address for the message,
 namely, bob@almamater.edu.example, and sets the SUBMITTER parameter
 accordingly.  The forwarding MTA also inserts a Resent-From header in
 the message body to ensure the purported responsible address derived
 from the RFC 2822 headers matches the SUBMITTER address.
    S: 220 company.com.example ESMTP server ready
    C: EHLO almamater.edu.example
    S: 250-company.com.example
    S: 250-DSN
    S: 250-AUTH
    S: 250-SUBMITTER
    S: 250 SIZE
    C: MAIL FROM:<alice@example.com>
            SUBMITTER=bob@almamater.edu.example
    S: 250 <alice@example.com> sender ok
    C: RCPT TO:<bob@company.com.example>
    S: 250 <bob@company.com.example> recipient ok
    C: DATA
    S: 354 okay, send message
    C: Resent-From: bob@almamater.edu.example
    C: Received By: ...
    C: (message body goes here)
    C: .
    S: 250 message accepted
    C: QUIT
    S: 221 goodbye

5.3. Mobile User

 Alice is at the airport and uses her mobile e-mail device to send a
 message to Bob.  The message travels through the carrier network
 provided by mobile.net.example, but Alice uses her example.com
 address on the From line of all her messages so that replies go to
 her office mailbox.

Allman & Katz Experimental [Page 8] RFC 4405 SMTP Responsible Submitter Extension April 2006

 Here is an example of the SMTP session between the MTAs at
 mobile.net.example and almamater.edu.example.
    S: 220 almamater.edu.example ESMTP server ready
    C: EHLO mobile.net.example
    S: 250-almamater.edu.example
    S: 250-DSN
    S: 250-AUTH
    S: 250-SUBMITTER
    S: 250 SIZE
    C: MAIL FROM:<alice@example.com>
            SUBMITTER=alice@mobile.net.example
    S: 250 <alice@example.com> sender ok
    C: RCPT TO:<bob@almamater.edu.example>
    S: 250 <bob@almamater.edu.example> recipient ok
    C: DATA
    S: 354 okay, send message
    C: Sender: alice@mobile.net.example
    C: Received By: ...
    C: (message body goes here)
    C: .
    S: 250 message accepted
    C: QUIT
    S: 221 goodbye
 Note that mobile.net.example uses the SUBMITTER parameter to
 designate alice@mobile.net.example as the responsible submitter for
 this message.  Further, this MTA also inserts a Sender header to
 ensure the purported responsible address derived from the RFC 2822
 headers matches the SUBMITTER address.
 Likewise, conventional ISPs may also choose to use the SUBMITTER
 parameter to designate as the responsible submitter the user's
 address on the ISP's network if that address is different from the
 MAIL FROM address.  This may be especially useful for ISPs that host
 multiple domains or otherwise share MTAs among multiple domains.
 When the message is subsequently forwarded by the
 almamater.edu.example MTA, that MTA will replace the SUBMITTER
 parameter with bob@almamater.edu.example as in Section 5.2 and add
 its own Resent-From header.

5.4. Guest E-Mail Service

 While on a business trip, Alice uses the broadband access facilities
 provided by the Exemplar Hotel to connect to the Internet and send
 e-mail.  The hotel routes all outbound e-mail through its own SMTP
 server, email.hotel.com.example.

Allman & Katz Experimental [Page 9] RFC 4405 SMTP Responsible Submitter Extension April 2006

 The SMTP session for Alice's message to Bob from the Exemplar Hotel
 would look like this:
    S: 220 almamater.edu.example ESMTP server ready
    C: EHLO email.hotel.com.example
    S: 250-almamater.edu.example
    S: 250-DSN
    S: 250-AUTH
    S: 250-SUBMITTER
    S: 250 SIZE
    C: MAIL FROM:<alice@example.com>
            SUBMITTER=guest.services@email.hotel.com.example
    S: 250 <alice@example.com> sender ok
    C: RCPT TO:<bob@almamater.edu.example>
    S: 250 <bob@almamater.edu.example> recipient ok
    C: DATA
    S: 354 okay, send message
    C: Resent-From: guest.services@email.hotel.com.example
    C: Received By: ...
    C: (message body goes here)
    C: .
    S: 250 message accepted
    C: QUIT
    S: 221 goodbye
 Note that email.hotel.com.example uses the SUBMITTER parameter to
 designate a generic account guest.services@email.hotel.com.example as
 the responsible submitter address for this message.  A generic
 account is used since Alice herself does not have an account at that
 domain.  Furthermore, this client also inserts a Resent-From header
 to ensure the purported responsible address derived from the RFC 2822
 headers with the SUBMITTER address.
 As before, when the message is subsequently forwarded by the
 almamater.edu.example MTA, that MTA will replace the SUBMITTER
 parameter with bob@almamater.edu.example as in Section 5.2 and add
 its own Resent-From header.

Allman & Katz Experimental [Page 10] RFC 4405 SMTP Responsible Submitter Extension April 2006

5.5. SUBMITTER Used on a Non-Delivery Report

 Alice sends an incorrectly addressed e-mail message and receives a
 non-delivery report from a SUBMITTER-compliant server.
    S: 220 example.com ESMTP server ready
    C: EHLO almamater.edu.example
    S: 250-example.com
    S: 250-DSN
    S: 250-AUTH
    S: 250-SUBMITTER
    S: 250 SIZE
    C: MAIL FROM:<> SUBMITTER=mailer-daemon@almamater.edu.example
    S: 250 OK
    C: RCPT TO:<alice@example.com>
    S: 250 OK
    C: DATA
    S: 354 OK, send message
    C: (message body goes here)
    C: .
    S: 250 message accepted
    C: QUIT
    S: 221 goodbye

6. Security Considerations

 This extension provides an optimization to allow an SMTP client to
 identify the responsible submitter of an e-mail message in the SMTP
 protocol, and to enable SMTP servers to perform efficient validation
 of that identity before the message contents are transmitted.
 It is, however, quite possible for an attacker to forge the value of
 the SUBMITTER parameter.  Furthermore, it is possible for an attacker
 to transmit an e-mail message whose SUBMITTER parameter does not
 match the purported responsible address of the message as derived
 from the RFC 2822 headers.  Therefore, the presence of the SUBMITTER
 parameter provides, by itself, no assurance of the authenticity of
 the message or the responsible submitter.  Rather, the SUBMITTER
 parameter is intended to provide additional information to receiving
 e-mail systems to enable them to efficiently determine the validity
 of the responsible submitter, and specifically, whether the SMTP
 client is authorized to transmit e-mail on behalf of the purported
 responsible submitter's domain.  Section 4.2 describes how receiving
 e-mail systems should process the SUBMITTER parameter.

Allman & Katz Experimental [Page 11] RFC 4405 SMTP Responsible Submitter Extension April 2006

7. Acknowledgements

 The idea of an ESMTP extension to convey the identity of the
 responsible sender of an e-mail message has many progenitors.  Nick
 Shelness suggested the idea in a private conversation with one of the
 authors.  Pete Resnick suggested a variant on the MARID mailing list.
 The idea was also discussed on the Anti-Spam Research Group (ASRG)
 mailing list.
 The authors would also like to thank the participants of the MARID
 working group and the following individuals for their comments and
 suggestions, which greatly improved this document:
    Robert Atkinson, Simon Attwell, Roy Badami, Greg Connor, Dave
    Crocker, Matthew Elvey, Tony Finch, Ned Freed, Mark Lentczner, Jim
    Lyon, Bruce McMillan, Sam Neely, Daryl Odnert, Margaret Olson,
    Pete Resnick, Hector Santos, Nick Shelness, Rand Wacker, and Meng
    Weng Wong.

8. IANA Considerations

    The IANA has registered the SUBMITTER SMTP service extension.

9. References

9.1. Normative References

 [ABNF]       Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 4234, October 2005.
 [DSN]        Moore, K., "Simple Mail Transfer Protocol (SMTP) Service
              Extension for Delivery Status Notifications (DSNs)", RFC
              3461, January 2003.
 [KEYWORDS]   Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
 [MSG-FORMAT] Resnick, P., "Internet Message Format", RFC 2822, April
              2001.
 [PRA]        Lyon, J., "Purported Responsible Address in E-Mail
              Messages", RFC 4407, April 2006.
 [SENDER-ID]  Lyon, J. and M. Wong, "Sender ID: Authenticating E-
              Mail", RFC 4406, April 2006.
 [SUBMIT]     Gellens, R. and J. Klensin, "Message Submission for
              Mail", RFC 4409, April 2006.

Allman & Katz Experimental [Page 12] RFC 4405 SMTP Responsible Submitter Extension April 2006

 [SMTP]       Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April 2001.
 [SMTPAUTH]   Myers, J., "SMTP Service Extension for Authentication",
              RFC 2554, March 1999.

Authors' Addresses

 Eric Allman
 Sendmail, Inc.
 6425 Christie Ave, Suite 400
 Emeryville, CA 94608
 USA
 EMail: eric@sendmail.com
 Harry Katz
 Microsoft Corp.
 1 Microsoft Way
 Redmond, WA 98052
 USA
 EMail: hkatz@microsoft.com

Allman & Katz Experimental [Page 13] RFC 4405 SMTP Responsible Submitter Extension April 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
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 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
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 The IETF invites any interested party to bring to its attention any
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 this standard.  Please address the information to the IETF at
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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Allman & Katz Experimental [Page 14]

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