GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc7750

Internet Engineering Task Force (IETF) J. Hedin Request for Comments: 7750 G. Mirsky Updates: 5357 S. Baillargeon Category: Standards Track Ericsson ISSN: 2070-1721 February 2016

Differentiated Service Code Point and Explicit Congestion Notification

   Monitoring in the Two-Way Active Measurement Protocol (TWAMP)

Abstract

 This document describes an optional extension for Two-Way Active
 Measurement Protocol (TWAMP) allowing the monitoring of the
 Differentiated Service Code Point and Explicit Congestion
 Notification fields with the TWAMP-Test protocol.

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 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7750.

Copyright Notice

 Copyright (c) 2016 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
 (http://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 extracted from this document must
 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.

Hedin, et al. Standards Track [Page 1] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
     1.1.1.  Terminology . . . . . . . . . . . . . . . . . . . . .   3
     1.1.2.  Requirements Language . . . . . . . . . . . . . . . .   3
 2.  TWAMP Extensions  . . . . . . . . . . . . . . . . . . . . . .   3
   2.1.  Setting Up Connection to Monitor DSCP and ECN . . . . . .   3
   2.2.  TWAMP-Test Extension  . . . . . . . . . . . . . . . . . .   4
     2.2.1.  Session-Reflector Packet Format for DSCP and ECN
             Monitoring  . . . . . . . . . . . . . . . . . . . . .   4
     2.2.2.  DSCP and ECN Monitoring with Extensions from RFC 6038   8
     2.2.3.  Consideration for TWAMP Light Mode  . . . . . . . . .   8
 3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
 4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
 5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   5.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
   5.2.  Informative References  . . . . . . . . . . . . . . . . .  10
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  10
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1. Introduction

 The One-Way Active Measurement Protocol (OWAMP) [RFC4656] defines the
 Type-P Descriptor field and negotiation of its value in the OWAMP-
 Control protocol.  The Two-Way Active Measurement Protocol (TWAMP)
 [RFC5357] states that only a Differentiated Services Code Point
 (DSCP) value (see [RFC2474], [RFC3168], and [RFC3260]) can be defined
 by Type-P Descriptor, and the negotiated value must be used by both
 the Session-Sender and Session-Reflector.  The TWAMP specification
 also states that the same DSCP value (found in the Session-Sender
 packet) MUST be used in the test packet reflected by the Session-
 Reflector.  However, the TWAMP-Test protocol does not specify any
 methods to determine or report when the DSCP value has changed or is
 different than expected in the forward or reverse direction.  Re-
 marking the DSCP (changing its original value) in IP networks is
 possible and often accomplished by a Differentiated Services policy
 configured on a single node along the IP path.  In many cases, a
 change of the DSCP value indicates an unintentional or erroneous
 behavior.  At best, the Session-Sender can detect a change of the
 DSCP reverse direction, assuming such a change is actually
 detectable.
 This document describes an OPTIONAL feature for TWAMP.  It is called
 DSCP and ECN Monitoring.  It allows the Session-Sender to know the
 actual DSCP value received at the Session-Reflector.  Furthermore,
 this feature tracks the Explicit Congestion Notification (ECN) value
 (see [RFC2474], [RFC3168], and [RFC3260]) received at the Session-

Hedin, et al. Standards Track [Page 2] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

 Reflector.  This is helpful to determine if the ECN is actually
 operating or if an ECN-capable node has detected congestion in the
 forward direction.

1.1. Conventions Used in This Document

1.1.1. Terminology

 DSCP: Differentiated Services Code Point
 ECN: Explicit Congestion Notification
 IPPM: IP Performance Metrics
 TWAMP: Two-Way Active Measurement Protocol
 OWAMP: One-Way Active Measurement Protocol

1.1.2. 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
 [RFC2119].

2. TWAMP Extensions

 TWAMP connection establishment follows the procedure defined in
 Section 3.1 of [RFC4656] and Section 3.1 of [RFC5357] where the Modes
 field is used to identify and select specific communication
 capabilities.  At the same time, the Modes field is recognized and
 used as an extension mechanism [RFC6038].  The new feature requires a
 new flag to identify the ability of a Session-Reflector to return the
 values of received DSCP and ECN values back to a Session-Sender, and
 to support the new Session-Reflector packet format in the TWAMP-Test
 protocol.  See Section 3 for details on the assigned bit position.

2.1. Setting Up Connection to Monitor DSCP and ECN

 The Server sets the DSCP and ECN Monitoring flag in the Modes field
 of the Server Greeting message to indicate its capabilities and
 willingness to monitor them.  If the Control-Client agrees to monitor
 DSCP and ECN on some or all test sessions invoked with this control
 connection, it MUST set the DSCP and ECN Monitoring flag in the Modes
 field in the Setup Response message.

Hedin, et al. Standards Track [Page 3] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

2.2. TWAMP-Test Extension

 Monitoring of DSCP and ECN requires support by the Session-Reflector
 and changes the test packet format in all the original modes
 (unauthenticated, authenticated, and encrypted).  Monitoring of DSCP
 and ECN does not alter the Session-Sender test packet format, but
 certain considerations must be taken when and if this mode is
 accepted in combination with Symmetrical Size mode [RFC6038].

2.2.1. Session-Reflector Packet Format for DSCP and ECN Monitoring

 When the Session-Reflector supports DSCP and ECN Monitoring, it
 constructs the Sender DSCP and ECN (S-DSCP-ECN) field, presented in
 Figure 1, for each test packet it sends to the Session-Sender
 according to the following procedure:
 o  the six (least-significant) bits of the Differentiated Service
    field MUST be copied from the received Session-Sender test packet
    into the Sender DSCP (S-DSCP) field;
 o  the two bits of the ECN field MUST be copied from the received
    Session-Sender test packet into the Sender ECN (S-ECN) field.
    0   1   2   3   4   5   6   7
  +---+---+---+---+---+---+---+---+
  |         S-DSCP        | S-ECN |
  +---+---+---+---+---+---+---+---+
              Figure 1: Sender DSCP and ECN Field Format
 Formats of the test packet transmitted by the Session-Reflector in
 unauthenticated, authenticated, and encrypted modes have been defined
 in Section 4.2.1 of [RFC5357].  For the Session-Reflector that
 supports DSCP and ECN Monitoring, these formats are displayed in
 Figures 2 and 3.

Hedin, et al. Standards Track [Page 4] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

 For unauthenticated mode:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       Sequence Number                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Timestamp                            |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Error Estimate         |             MBZ                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Receive Timestamp                         |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                  Sender Sequence Number                       |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                     Sender Timestamp                          |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Sender Error Estimate      |             MBZ               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Sender TTL    |  S-DSCP-ECN   |             MBZ               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 ~                        Packet Padding                         ~
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Figure 2: Session-Reflector Test Packet Format with DSCP and ECN
                  Monitoring in Unauthenticated Mode
 The DSCP and ECN values (part of the Type-P Descriptor [RFC4656]) can
 be provisioned through TWAMP-Control or by other means (command-line
 interface (CLI) or Central Controller).  The DSCP and ECN values are
 often copied into reflected test packets with current TWAMP
 implementations without TWAMP-Control protocol.  With the DSCP and
 ECN Monitoring extension, the Session-Reflector handles the DSCP as
 follows:
 o  the Session-Reflector MUST extract the DSCP and ECN values from
    the received packet and MUST use them to populate the S-DSCP-ECN
    field of the corresponding reflected packet;
 o  the Session-Reflector MUST transmit each reflected test packet
    with the DSCP set to the provisioned value;

Hedin, et al. Standards Track [Page 5] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

 o  if the provisioned DSCP value is not known (e.g., TWAMP Light),
    the choice of the DSCP is implementation specific.  For instance,
    the Session-Reflector MAY copy the DSCP value from the received
    test packet and set it as the DSCP in a reflected packet.
    Alternatively, the Session-Reflector MAY set the DSCP value to CS0
    (zero) [RFC2474];
 o  if the provisioned ECN value is not known, ECN SHOULD be set to
    Not-ECT codepoint value [RFC3168].  Otherwise, the provisioned ECN
    value for the session SHALL be used.
 A Session-Reflector in the DSCP and ECN Monitoring mode does not
 analyze nor act on the ECN value of the received TWAMP test packet;
 therefore, it ignores congestion indications from the network.  It is
 expected that sending rates are low enough, as TWAMP deployment
 experience had demonstrated since TWAMP base (RFC 5357) was published
 in 2008, that ignoring these congestion indications will not
 significantly contribute to network congestion.
 For authenticated and encrypted modes:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Sequence Number                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                       MBZ (12 octets)                         |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Timestamp                             |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       Error Estimate          |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 |                        MBZ (6 octets)                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Receive Timestamp                        |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       MBZ (8 octets)                          |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                   Sender Sequence Number                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                      MBZ (12 octets)                          |
 |                                                               |

Hedin, et al. Standards Track [Page 6] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      Sender Timestamp                         |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Sender Error Estimate      |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 |                         MBZ (6 octets)                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Sender TTL    |  S-DSCP-ECN   |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 |                                                               |
 |                         MBZ (14 octets)                       |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                        HMAC (16 octets)                       |
 |                                                               |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 ~                       Packet Padding                          ~
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Figure 3: Session-Reflector Test Packet Format with DSCP and ECN
            Monitoring in Authenticated or Encrypted Modes

Hedin, et al. Standards Track [Page 7] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

2.2.2. DSCP and ECN Monitoring with Extensions from RFC 6038

 [RFC6038] defined two extensions to TWAMP -- first, to ensure that
 the Session-Sender and Session-Reflector exchange TWAMP-Test packets
 of equal size; second, to specify the number of octets to be
 reflected by Session-Reflector.  If DSCP and ECN Monitoring and
 Symmetrical Size and/or Reflects Octets modes are being negotiated
 between Server and Control-Client in Unauthenticated mode, then,
 because Sender DSCP and Sender ECN increase the size of the
 unauthenticated Session-Reflector packet by 4 octets, the Padding
 Length value SHOULD be greater than or equal to 28 octets to allow
 for the truncation process that TWAMP recommends in Section 4.2.1 of
 [RFC5357].
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Sequence Number                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Timestamp                           |
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         Error Estimate        |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 |                                                               |
 |                         MBZ (28 octets)                       |
 |                                                               |
 +                             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             |                                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                                 +
 |                                                               |
 .                                                               .
 .                        Packet Padding                         .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 4: Session-Sender Test Packet Format with DSCP and ECN
    Monitoring and Symmetrical Test Packet in Unauthenticated Mode

2.2.3. Consideration for TWAMP Light Mode

 Appendix I of [RFC5357] does not explicitly state how the value of
 the Type-P Descriptor is synchronized between the Session-Sender and
 Session-Reflector and whether different values are considered as
 error conditions and should be reported.  We assume that by some
 means the Session-Sender and the Session-Reflector of the given
 TWAMP-Test session have been informed to use the same DSCP value.
 The same means, i.e., configuration, could be used to inform the

Hedin, et al. Standards Track [Page 8] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

 Session-Reflector to support DSCP and ECN Monitoring mode by copying
 data from received TWAMP test packets.  Then Session-Sender may be
 informed to use the Sender DSCP and ECN field in the reflected TWAMP
 test packet.

3. IANA Considerations

 In the TWAMP-Modes registry defined in [RFC5618], IANA has reserved a
 new DSCP and ECN Monitoring Capability as follows:
 +-----+---------------------------+---------------------+-----------+
 | Bit | Description               | Semantics           | Reference |
 | Pos |                           | Definition          |           |
 +-----+---------------------------+---------------------+-----------+
 | 8   | DSCP and ECN Monitoring   | Section 2           | RFC 7750  |
 |     | Capability                |                     |           |
 +-----+---------------------------+---------------------+-----------+
         Table 1: New Type-P Descriptor Monitoring Capability

4. Security Considerations

 Monitoring of DSCP and ECN does not appear to introduce any
 additional security threat to hosts that communicate with TWAMP as
 defined in [RFC5357] and existing extensions [RFC6038].  Sections
 such as 3.2, 4, 4.1.2, 4.2, and 4.2.1 of [RFC5357] discuss
 unauthenticated, authenticated, and encrypted modes in varying
 degrees of detail.  The security considerations that apply to any
 active measurement of live networks are relevant here as well.  See
 the Security Considerations sections in [RFC4656] and [RFC5357].

5. References

5.1. 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,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
            "Definition of the Differentiated Services Field (DS
            Field) in the IPv4 and IPv6 Headers", RFC 2474,
            DOI 10.17487/RFC2474, December 1998,
            <http://www.rfc-editor.org/info/rfc2474>.

Hedin, et al. Standards Track [Page 9] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

 [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
            of Explicit Congestion Notification (ECN) to IP",
            RFC 3168, DOI 10.17487/RFC3168, September 2001,
            <http://www.rfc-editor.org/info/rfc3168>.
 [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,
            <http://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,
            <http://www.rfc-editor.org/info/rfc5357>.
 [RFC5618]  Morton, A. and K. Hedayat, "Mixed Security Mode for the
            Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
            DOI 10.17487/RFC5618, August 2009,
            <http://www.rfc-editor.org/info/rfc5618>.
 [RFC6038]  Morton, A. and L. Ciavattone, "Two-Way Active Measurement
            Protocol (TWAMP) Reflect Octets and Symmetrical Size
            Features", RFC 6038, DOI 10.17487/RFC6038, October 2010,
            <http://www.rfc-editor.org/info/rfc6038>.

5.2. Informative References

 [RFC3260]  Grossman, D., "New Terminology and Clarifications for
            Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
            <http://www.rfc-editor.org/info/rfc3260>.

Acknowledgements

 The authors greatly appreciate thorough review and thoughtful
 comments by Bill Cerveny, Christofer Flinta, and Samita Chakrabarti.

Hedin, et al. Standards Track [Page 10] RFC 7750 DSCP and ECN Monitoring in TWAMP February 2016

Authors' Addresses

 Jonas Hedin
 Ericsson
 Email: jonas.hedin@ericsson.com
 Greg Mirsky
 Ericsson
 Email: gregory.mirsky@ericsson.com
 Steve  Baillargeon
 Ericsson
 Email: steve.baillargeon@ericsson.com

Hedin, et al. Standards Track [Page 11]

/data/webs/external/dokuwiki/data/pages/rfc/rfc7750.txt · Last modified: 2016/02/03 01:50 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki