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The Multicast Application Port
draft-karstens-multicast-application-port-00

Document Type Active Internet-Draft (individual)
Authors Nathan Karstens , Stuart Cheshire , Mike McBride
Last updated 2025-01-14
Replaces draft-karstens-pim-multicast-application-ports
RFC stream (None)
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IESG IESG state I-D Exists
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draft-karstens-multicast-application-port-00
Network Working Group                                        N. Karstens
Internet-Draft                                      Garmin International
Intended status: Standards Track                             S. Cheshire
Expires: 18 July 2025                                         Apple Inc.
                                                              M. McBride
                                                               Futurewei
                                                         14 January 2025

                     The Multicast Application Port
              draft-karstens-multicast-application-port-00

Abstract

   This document discusses the drawbacks of the current practice of
   assigning a UDP port to each multicast application.  Such assignments
   are redundant because the multicast address already uniquely
   identifies the data.  The document proposes assigning a UDP port
   specifically for use with multicast applications and lists
   requirements for using this port.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 18 July 2025.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components

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   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Assignment  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Host Requirements . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Application Requirements  . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Internet community has recognized the need to be judicious when
   assigning port numbers (see [RFC7605], Section 6).  With unicast
   applications, the need for explicit port assignment has been reduced
   by techniques such as locally assigning a dynamic port, combined with
   some mechanism for advertising that port (see [RFC7605],
   Section 7.1).  Dynamic assignment does not work with multicast
   applications because it is impossible to guarantee that the port
   remains unused by all hosts that may want to join a given multicast
   group.  The result is that each multicast application-layer protocol
   has had to have its own dedicated port assignment.  Even worse, each
   different use of that multicast application-layer protocol has had to
   have a different unique port assigned.

   In the TCP/IP model, the port number in the transport layer
   multiplexes applications within a host (see [RFC1122], Section 4.1.1
   and [RFC7605], Section 5).  With Any-Source Multicast, the use of a
   port number to multiplex applications is unnecessary because the
   destination multicast address already provides a unique identifier
   for the application.  The same applies to Source-Specific Multicast
   if both source address and destination multicast address are
   considered.

   Because of the desire to conserve port numbers and the fact that a
   port is not necessary to multiplex multicast applications, this
   document assigns a UDP port that may be used with multicast
   applications.

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   Use of this port is optional because there may be circumstances where
   assigning a port is preferred, such as when participants cannot meet
   the requirements in Section 3 and Section 4.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Assignment

   This document REQUESTS assignment of UDP port 49149 and gives it the
   service name "Multicast Application Port".  This port is near the end
   of the range of User ports [RFC6335], Section 6 to differentiate it
   from other port assignments.

   The REQUESTED port may be used as a source port if the application
   exclusively uses multicast messages.  If any application messages are
   unicast, then a dynamic port should be used as the source port.  This
   allows receivers to know which port to send replies to.

3.  Host Requirements

   Hosts shall require applications using this port to use it non-
   exclusively.  In practice, this means hosts using POSIX-like socket
   APIs would require applications to set the SO_REUSEADDR and/or
   SO_REUSEPORT socket options before binding the socket [POSIX].  This
   ensures that applications developed on a conformant host will also
   work on a non-conformant host.

   Hosts shall discard all incoming, non-multicast packets that use this
   destination port.

4.  Application Requirements

   Applications running on non-conformant hosts can ensure compatibility
   with conformant hosts by meeting the requirements in this section.

   Applications running on a non-conformant host shall not prevent other
   applications from using this port.  In practice, this means that
   applications using POSIX-like socket APIs would enable the
   SO_REUSEADDR and/or SO_REUSEPORT socket options before binding the
   socket [POSIX].

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   Applications running on a non-conformant host shall discard all
   datagrams that do not have the multicast address used by the
   application.

5.  Security Considerations

   Applications running on non-conformant hosts are vulnerable to a
   denial of service attack if another application claims exclusive
   access to the port.

   Systems that use POSIX-like socket APIs typically have restrictions
   on binding multiple sockets to the same port.  This can serve as a
   rudimentary security mechanism in that other local applications
   cannot eavesdrop on the multicast stream.  A necessary side-effect of
   using the Multicast Application Port is that applications can no
   longer rely on these security mechanisms.  These applications may
   want to incorporate additional security measures into their protocol.
   Note that the problem of local eavesdropping is typically no worse
   than eavesdropping in-flight, so it is likely that both attack
   vectors can be resolved by the same security measure.

6.  IANA Considerations

   IANA is REQUESTED to assign the following port:

  Service Name        Multicast Application Port
  Transport Protocol  UDP
  Assignee            IESG <iesg@ietf.org>
  Contact             IETF Chair <chair@ietf.org>
  Description         Multicast data where the application is identified
                      by the multicast address
  Reference           This document
  Port Number         49149

   IANA is requested to update its "Application for Service Names and
   User Port Numbers" [IANA-APP] to reference this document, ask if a
   Multicast Application Port may be used, and require an explanation if
   not.

7.  Acknowledgement

   Special thanks to the National Marine Electronics Association for
   their contributions in developing marine industry standards and their
   support for this research.

   Thanks also to the members of the PIM and INT-AREA working groups for
   their review of this draft and to Dr. Joe Touch for consulting on
   port assignment.

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8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [IANA-APP] Internet Assigned Numbers Authority, "Application for
              Service Names and User Port Numbers",
              <https://www.iana.org/form/ports-services>.

   [POSIX]    The Open Group, ""The Open Group Base Specifications",
              Issue 7, 2018 edition", December 2001,
              <https://pubs.opengroup.org/onlinepubs/9699919799/>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <https://www.rfc-editor.org/info/rfc1122>.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <https://www.rfc-editor.org/info/rfc6335>.

   [RFC7605]  Touch, J., "Recommendations on Using Assigned Transport
              Port Numbers", BCP 165, RFC 7605, DOI 10.17487/RFC7605,
              August 2015, <https://www.rfc-editor.org/info/rfc7605>.

Authors' Addresses

   Nate Karstens
   Garmin International
   Email: nate.karstens@gmail.com

   Stuart Cheshire
   Apple Inc.

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   Email: cheshire@apple.com

   Mike McBride
   Futurewei
   Email: michael.mcbride@futurewei.com

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