    Internet Engineering Task Force (IETF)                    A. Morton, Ed.
    Request for Comments: 8545                                     AT&T Labs
    Updates: 4656, 5357                                       G. Mirsky, Ed.
    Category: Standards Track                                      ZTE Corp.
    ISSN: 2070-1721                                               March 2019

                        Well-Known Port Assignments for
              the One-Way Active Measurement Protocol (OWAMP) and
                the Two-Way Active Measurement Protocol (TWAMP)

    Abstract

       This memo explains the motivation and describes the reassignment of
       well-known ports for the One-Way Active Measurement Protocol (OWAMP)
       and the Two-Way Active Measurement Protocol (TWAMP) for control and
       measurement.  It also clarifies the meaning and composition of these
       Standards Track protocol names for the industry.

       This memo updates RFCs 4656 and 5357, in terms of the UDP well-known
       port assignments, and it clarifies the complete OWAMP and TWAMP
       protocol composition for the industry.

    Status of This Memo

       This is an Internet Standards Track document.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Further information on
       Internet Standards is available in Section 2 of RFC 7841.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       https://www.rfc-editor.org/info/rfc8545.

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    Copyright Notice

       Copyright (c) 2019 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
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       include Simplified BSD License text as described in Section 4.e of
       the Trust Legal Provisions and are provided without warranty as
       described in the Simplified BSD License.

    Table of Contents

       1. Introduction ....................................................3
       2. Requirements Language ...........................................3
       3. Scope ...........................................................3
       4. Definitions and Background ......................................3
       5. New Well-Known Ports ............................................5
          5.1. Impact on TWAMP-Control Protocol ...........................5
          5.2. Impact on OWAMP-Control Protocol ...........................6
          5.3. Impact on OWAMP-Test/TWAMP-Test Protocols ..................6
       6. Security Considerations .........................................7
       7. IANA Considerations .............................................8
       8. References ......................................................8
          8.1. Normative References .......................................8
          8.2. Informative References .....................................9
       Appendix A. Background on TWAMP Light .............................10
       Acknowledgements ..................................................11
       Contributors ......................................................11
       Authors' Addresses ................................................11

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    1.  Introduction

       The IETF IP Performance Metrics (IPPM) Working Group first developed
       the One-Way Active Measurement Protocol (OWAMP), as specified in
       [RFC4656].  Further protocol development to support testing resulted
       in the Two-Way Active Measurement Protocol (TWAMP), as specified in
       [RFC5357].

       Both OWAMP and TWAMP require the implementation of a control and mode
       negotiation protocol (OWAMP-Control and TWAMP-Control) that employs
       the reliable transport services of TCP (including security
       configuration and key derivation).  The control protocols arrange for
       the configuration and management of test sessions using the
       associated test protocol (OWAMP-Test or TWAMP-Test) on UDP transport.

       The IETF recognizes the value of assigning a well-known UDP port to
       the OWAMP-Test and TWAMP-Test protocols and also recognizes that this
       goal can be easily arranged through port reassignments.

    2.  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.

    3.  Scope

       The scope of this memo is twofold: (1) to reallocate the well-known
       ports for the UDP test protocols that compose necessary parts of
       their respective Standards Track protocols (OWAMP and TWAMP) and
       (2) to clarify the meaning and composition of these Standards Track
       protocol names for the industry.

       This memo updates [RFC4656] and [RFC5357], in terms of the UDP
       well-known port assignments.

    4.  Definitions and Background

       This section defines key terms and clarifies the required composition
       of the OWAMP and TWAMP Standards Track protocols.

       "OWAMP-Control" is the protocol defined in Section 3 of [RFC4656].

       "OWAMP-Test" is the protocol defined in Section 4 of [RFC4656].

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       OWAMP is described in this direct quote from Section 1.1 of
       [RFC4656]: "OWAMP actually consists of two inter-related protocols:
       OWAMP-Control and OWAMP-Test."  A similar sentence appears in
       Section 2 of [RFC4656].  For avoidance of doubt, the implementation
       of both OWAMP-Control and OWAMP-Test is REQUIRED for Standards Track
       OWAMP as specified in [RFC4656] (applying the consensus of many
       dictionary definitions of "consist").

       "TWAMP-Control" is the protocol defined in Section 3 of [RFC5357].

       "TWAMP-Test" is the protocol defined in Section 4 of [RFC5357].

       TWAMP is described in this direct quote from Section 1.1 of
       [RFC5357]: "Similar to OWAMP [RFC4656], TWAMP consists of two
       inter-related protocols: TWAMP-Control and TWAMP-Test."  For
       avoidance of doubt, the implementation of both TWAMP-Control and
       TWAMP-Test is REQUIRED for Standards Track TWAMP as specified in
       [RFC5357] (applying the consensus of many dictionary definitions of
       "consist").

       "TWAMP Light" is an idea described in Appendix I ("TWAMP Light
       (Informative)") of [RFC5357]; TWAMP Light includes an unspecified
       control protocol combined with the TWAMP-Test protocol.  In
       [RFC5357], the TWAMP Light idea was relegated to Appendix I because
       TWAMP Light failed to meet the requirements for IETF protocols (there
       are no specifications for negotiating this form of operation and no
       specifications for mandatory-to-implement security features), as
       described in Appendix A of this memo.  See also [LarsAD] and
       [TimDISCUSS].

       Since the idea of TWAMP Light clearly includes the TWAMP-Test
       component of TWAMP, it is considered reasonable for future systems to
       use the TWAMP-Test well-known UDP port (whose reallocated assignment
       is specified in this document).  Clearly, the TWAMP Light idea
       envisions many components and communication capabilities beyond
       TWAMP-Test (implementing the security requirements, for example);
       otherwise, Appendix I of [RFC5357] would be one sentence long
       (equating TWAMP Light with TWAMP-Test only).

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    5.  New Well-Known Ports

       Originally, both TCP and UDP well-known ports were assigned to the
       control protocols that are essential components of Standards Track
       OWAMP and TWAMP.

       Since OWAMP-Control and TWAMP-Control require TCP transport, they
       cannot make use of the UDP ports that were originally assigned.
       However, test sessions using OWAMP-Test or TWAMP-Test operate on UDP
       transport.

       Per this memo, IANA has reassigned the UDP well-known port from the
       control protocol to the test protocol (see Section 7 ("IANA
       Considerations")).  The use of this UDP port is OPTIONAL in Standards
       Track OWAMP and TWAMP.  It may simplify some operations to have a
       well-known port available for the test protocols or for future
       specifications involving TWAMP-Test to use this port as a default
       port.  For example, [TR-390] is a specification for testing at the
       customer edge of IP networks, and conforming implementations will
       benefit from reallocation of the well-known UDP port to the test
       protocol.

    5.1.  Impact on TWAMP-Control Protocol

       Section 3.5 of [RFC5357] describes the detailed process of
       negotiating the Receiver Port number, on which the TWAMP
       Session-Reflector will send and receive TWAMP-Test packets; see the
       quoted text below.  The Control-Client, acting on behalf of the
       Session-Sender, proposes the Receiver Port number from the Dynamic
       Ports range [RFC6335]:

          The Receiver Port is the desired UDP port to which TWAMP-Test
          packets will be sent by the Session-Sender (the port where the
          Session-Reflector is asked to receive test packets).  The Receiver
          Port is also the UDP port from which TWAMP-Test packets will be
          sent by the Session-Reflector (the Session-Reflector will use the
          same UDP port to send and receive packets).

       It is possible that the proposed Receiver Port may not be available,
       e.g., the port is in use by another test session or another
       application.  In this case, we update the last paragraph of
       Section 3.5 of [RFC5357] per Erratum ID 1587 (see
       <https://www.rfc-editor.org/errata/eid1587>) as follows:

          ... the Server at the Session-Reflector MAY suggest an alternate
          and available port for this session in the Port field.  The
          Control-Client either accepts the alternate port or composes a new
          Session-Request message with suitable parameters.  Otherwise, the

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          Server uses the Accept field to convey other forms of session
          rejection or failure to the Control-Client and MUST NOT suggest an
          alternate port; in this case, the Port field MUST be set to zero.

       A Control-Client that supports the use of the allocated TWAMP-Test
       Receiver Port (Section 7) MAY request to use that port number in the
       Request-TW-Session command.  If the Server does not support the
       allocated TWAMP-Test Receiver Port, then it sends an alternate port
       number in the Accept-Session message with Accept field = 0.  Thus,
       the deployment of the allocated TWAMP Receiver Port number is
       backward compatible with existing TWAMP-Control solutions that are
       based on [RFC5357].  Of course, using a UDP port number chosen from
       the Dynamic Ports range [RFC6335] will help avoid the situation where
       the Control-Client or Server finds that the proposed port is already
       in use.

    5.2.  Impact on OWAMP-Control Protocol

       As described above, an OWAMP-Control client that supports the use of
       the allocated OWAMP-Test Receiver Port (Section 7) MAY request to use
       that port number in the Request-Session command.  If the Server does
       not support the allocated OWAMP-Test Receiver Port (or does not have
       the port available), then it sends an alternate port number in the
       Accept-Session message with Accept field = 0.  Further exchanges
       proceed as already specified.

    5.3.  Impact on OWAMP-Test/TWAMP-Test Protocols

       OWAMP-Test/TWAMP-Test may be used to measure IP performance metrics
       in an Equal-Cost Multipath (ECMP) environment.  Though algorithms to
       balance IP flows among available paths have not been standardized,
       the most common is the five-tuple that uses destination IP address,
       source IP address, protocol type, destination port number, and source
       port number.  When attempting to monitor different paths in an ECMP
       network, it is sufficient to vary only one of five parameters, e.g.,
       the source port number.  Thus, there will be no negative impact on
       the ability to arrange concurrent OWAMP/TWAMP test sessions between
       the same test points to monitor different paths in the ECMP network
       when using the reallocated UDP port number as the Receiver Port, as
       using the port is optional.

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    6.  Security Considerations

       The security considerations that apply to any active measurement of
       live paths are relevant here as well (see [RFC4656] and [RFC5357]).

       When considering the privacy of those involved in measurement or
       those whose traffic is measured, the sensitive information available
       to potential observers is greatly reduced when using active
       techniques that are within this scope of work.  Passive observations
       of user traffic for measurement purposes raise many privacy issues.
       We refer the reader to the security and privacy considerations
       described in the Large-Scale Measurement of Broadband Performance
       (LMAP) framework [RFC7594], which covers both active and passive
       techniques.

       The registered UDP port as the Receiver Port for OWAMP-Test/
       TWAMP-Test could become a target of denial of service (DoS) or could
       be used to aid man-in-the-middle (MITM) attacks.  To improve
       protection against DoS, the following methods are recommended:

       o  filtering access to the OWAMP/TWAMP Receiver Port via an
          access list.

       o  using a non-globally routable IP address for the OWAMP/TWAMP
          Session-Reflector address.

       A MITM attacker may try to modify the contents of the OWAMP-Test/
       TWAMP-Test packets in order to alter the measurement results.
       However, an implementation can use authenticated mode to detect
       modification of data.  In addition, an implementation can use
       encrypted mode to prevent eavesdropping and undetected modification
       of the OWAMP-Test/TWAMP-Test packets.

       There is also the risk of a network under test giving special
       treatment to flows involving the well-known UDP port, with or without
       knowing source and destination addresses of measurement systems, and
       thus biasing the results through preferential or detrimental
       processing.

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    7.  IANA Considerations

       IANA has reallocated two UDP port numbers from the System Ports range
       of the "Service Name and Transport Protocol Port Number Registry"
       [RFC6335].  Specifically, IANA has reallocated UDP ports 861 and 862
       as shown below, leaving the TCP port assignments as is.  IANA has
       also updated the Assignee and Contact for these ports (both UDP and
       TCP) to be the IESG and the IETF Chair, respectively.

       +---------------+--------+-----------+------------------+-----------+
       | Service       | Port   | Transport | Description      | Reference |
       | Name          | Number | Protocol  |                  |           |
       +---------------+--------+-----------+------------------+-----------+
       | owamp-control | 861    | tcp       | OWAMP-Control    | RFC 4656  |
       | owamp-test    | 861    | udp       | OWAMP-Test       | RFC 8545  |
       |               |        |           |    Receiver Port |           |
       |               |        |           |                  |           |
       | twamp-control | 862    | tcp       | TWAMP-Control    | RFC 5357  |
       | twamp-test    | 862    | udp       | TWAMP-Test       | RFC 8545  |
       |               |        |           |    Receiver Port |           |
       +---------------+--------+-----------+------------------+-----------+

    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>.

       [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and
                  M. Zekauskas, "A One-way Active Measurement Protocol
                  (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
                  <https://www.rfc-editor.org/info/rfc4656>.

       [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and
                  J. Babiarz, "A Two-Way Active Measurement Protocol
                  (TWAMP)", RFC 5357, DOI 10.17487/RFC5357, October 2008,
                  <https://www.rfc-editor.org/info/rfc5357>.

       [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>.

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       [RFC7594]  Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
                  Aitken, P., and A. Akhter, "A Framework for Large-Scale
                  Measurement of Broadband Performance (LMAP)", RFC 7594,
                  DOI 10.17487/RFC7594, September 2015,
                  <https://www.rfc-editor.org/info/rfc7594>.

       [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

       [IPPM-TWAMP-06]
                  Hedayat, K., Krzanowski, R., Yum, K., Morton, A., and
                  J. Babiarz, "A Two-way Active Measurement Protocol
                  (TWAMP)", Work in Progress, draft-ietf-ippm-twamp-06,
                  December 2007.

       [LarsAD]   Eggert, L., "Subject: [ippm] AD review:
                  draft-ietf-ippm-twamp-06.txt", message to the ippm mailing
                  list, April 2008, <https://mailarchive.ietf.org/
                  rch/msg/ippm/LzcTPYhPhWhbb5-ncR046XKpnzo>.

       [TimDISCUSS]
                  "Tim Polk's Ballot discuss", July 2008,
                  <https://datatracker.ietf.org/doc/rfc5357/history>.

       [TR-390]   Broadband Forum, "TR-390: Performance Measurement from IP
                  Edge to Customer Equipment using TWAMP Light", Issue: 1,
                  May 2017, <https://www.broadband-forum.org/technical/
                  download/TR-390.pdf>.

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    Appendix A.  Background on TWAMP Light

       This informative appendix provides the background on the decision to
       move the TWAMP Light idea to an informative appendix in [RFC5357].

       As also noted in Section 4, the TWAMP Light idea was relegated to
       Appendix I of [RFC5357] because it failed to meet the requirements
       for IETF protocols (there are no specifications for negotiating this
       form of operation and no specifications for mandatory-to-implement
       security features), as described in the references cited below:

       o  Lars Eggert's Area Director review [LarsAD], where he pointed out
          that having two variants of TWAMP (TWAMP Light and Complete TWAMP)
          requires a protocol mechanism to negotiate which variant will be
          used.  Note that "Complete TWAMP" is called "Standards Track
          TWAMP" in this document.  See Lars's "Section 5.2, paragraph 0"
          comment on [LarsAD], which refers to a section in [IPPM-TWAMP-06].
          The working group consensus was to place the TWAMP Light
          description in Appendix I and to refer to that appendix only as an
          "incremental path to adopting TWAMP, by implementing the
          TWAMP-Test protocol first."

       o  Tim Polk's "Ballot discuss" of 2008-07-16 [TimDISCUSS], which
          points out that TWAMP Light was an incomplete specification
          because the key required for authenticated and encrypted modes
          depended on the TWAMP-Control Session key.  Additional requirement
          statements were added in Appendix I to address Tim's Ballot
          discuss (see the last three paragraphs of Appendix I in
          [RFC5357]).

       Since the idea of TWAMP Light clearly includes the TWAMP-Test
       protocol and other undefined facilities, Appendix I of [RFC5357]
       simply describes ideas for how TWAMP-Test might be used outside of
       the context of Standards Track TWAMP.

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    Acknowledgements

       The authors thank the IPPM Working Group for their rapid review;
       thanks also to Muthu Arul Mozhi Perumal and Luay Jalil for their
       participation and suggestions.

    Contributors

       Richard Foote and Luis M. Contreras made notable contributions on
       this topic.

    Authors' Addresses

       Al Morton (editor)
       AT&T Labs
       200 Laurel Avenue South
       Middletown, NJ  07748
       United States of America

       Phone: +1 732 420 1571
       Fax:   +1 732 368 1192
       Email: acmorton@att.com

       Greg Mirsky (editor)
       ZTE Corp.

       Email: gregimirsky@gmail.com

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