Network Working Group                                        Tal Mizrahi
Internet Draft                                                   Marvell
Intended status: Informational
Expires: November 2013                                      May 28, 2013

                  UDP Checksum Trailer in OWAMP and TWAMP
             draft-mizrahi-owamp-twamp-checksum-trailer-00.txt


Abstract

   The One-Way Active Measurement Protocol (OWAMP) and the Two-Way
   Active Measurement Protocol (TWAMP) are used for performance
   monitoring in IP networks. Delay measurement is performed in these
   protocols by using timestamped test packets. Some implementations use
   hardware-based timestamping engines that integrate the accurate
   transmission timestamp into every outgoing OWAMP/TWAMP test packet
   during transmission.  Since these packets are transported over UDP,
   the UDP checksum field is then updated to reflect this modification.
   This document proposes to use the last 2 octets of every test packet
   as a Checksum Trailer, allowing timestamping engines to reflect the
   checksum modification in the last 2 octets rather than in the UDP
   checksum field. The behavior defined in this document is completely
   interoperable with existing OWAMP/TWAMP implementations.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on October 28, 2013.




Mizrahi, T.           Expires November 28, 2013               [Page 1]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


Copyright Notice

   Copyright (c) 2013 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.

Table of Contents

   1. Introduction ................................................. 2
   2. Conventions used in this document ............................ 4
      2.1. Terminology ............................................. 4
      2.2. Abbreviations ........................................... 4
   3. Using the UDP Checksum Trailer in OWAMP and TWAMP ............ 5
      3.1. Overview ................................................ 5
      3.2. OWAMP / TWAMP Test Packets with Checksum Trailer ........ 5
         3.2.1. Transmission of OWAMP/TWAMP with Checksum Trailer .. 8
         3.2.2. Intermediate Updates of OWAMP/TWAMP with Checksum
         Trailer ................................................... 8
         3.2.3. Reception of OWAMP/TWAMP with Checksum Trailer ..... 8
      3.3. Interoperability with Existing Implementations........... 8
      3.4. Using the Checksum Trailer with or without Authentication 8
   4. Security Considerations ...................................... 9
   5. IANA Considerations .......................................... 9
   6. Acknowledgments .............................................. 9
   7. References ................................................... 9
      7.1. Normative References .................................... 9
      7.2. Informative References ................................. 10

1. Introduction

   The One-Way Active Measurement Protocol ([OWAMP]) and the Two-Way
   Active Measurement Protocol ([TWAMP]) are used for performance
   monitoring in IP networks.

   Delay and delay variation are two of the metrics that OWAMP/TWAMP can
   measure. This measurement is performed using timestamped test
   packets.



Mizrahi, T.           Expires November 28, 2013               [Page 2]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


   The accuracy of delay measurements relies on the timestamping method
   and its implementation. In order to facilitate accurate timestamping,
   an implementation MAY use a hardware based timestamping engine, as
   shown in Figure 1. In such cases, the OWAMP/TWMAP packets are sent
   and received by a software layer, whereas the timestamping engine
   modifies every outgoing test packet by incorporating its accurate
   transmission time into the <Timestamp> field in the packet.

                      OWAMP/TWAMP-enabled Node
                        +-------------------+
                        |                   |
                        |   +-----------+   |
       Software         |   |OWAMP/TWAMP|   |
                        |   | protocol  |   |
                        |   +-----+-----+   |
                        |         |         |
                        |   +-----+-----+   |
                        |   | Accurate  |   |
       ASIC/FPGA        |   | Timestamp |   |
                        |   |  engine   |   |
                        |   +-----------+   |
                        |         |         |
                        +---------+---------+
                                  |
                                  |test packets
                                  |
                              ___ v _
                             /   \_/ \__
                            /           \_
                           /     IP      /
                           \_  Network  /
                            /           \
                            \__/\_   ___/
                                  \_/

               Figure 1 Accurate Timestamping in OWAMP/TWAMP

   OWAMP/TWAMP test packets are transported over UDP. When the UDP
   payload is changed by an intermediate entity such as the timestamping
   engine, the UDP Checksum field must be updated to reflect the new
   payload. When using UDP over IPv4 ([UDP]), an intermediate entity
   that cannot update the value of the UDP checksum can assign a value
   of zero to the checksum field, causing the receiver to ignore the


Mizrahi, T.           Expires November 28, 2013               [Page 3]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


   checksum field. UDP over IPv6, as defined in [IPv6], does not allow a
   zero checksum, and requires the UDP checksum field to contain a
   correct checksum of the UDP payload.

   Since an intermediate entity only modifies a specific field in the
   packet, i.e. the timestamp field, the UDP checksum update can be
   performed incrementally, using the concepts presented in [Checksum].

   A similar problem is addressed in Annex E of [IEEE1588]. When the
   Precision Time Protocol (PTP) is transported over IPv6, two octets
   are appended to the end of the PTP payload for UDP checksum updates.
   The value of these two octets can be updated by an intermediate
   entity, causing the value of the UDP checksum field to remain
   correct.

   This document defines a similar concept for [OWAMP] and [TWAMP],
   allowing intermediate entities to update OWAMP/TWAMP test packets and
   maintain the correctness of the UDP checksum by modifying the last 2
   octests of the packet.

   The term Checksum Trailer is used throughout this document and refers
   to the 2 octets at the end of the UDP payload, used for updating the
   UDP checksum by intermediate entities.

   The usage of the Checksum Trailer can in some cases simplify the
   implementation, since if the packet data is processed in a serial
   order, it is simpler to first update the timestamp field, and then
   update the Checksum Trailer rather than to update the timestamp and
   then update the UDP checksum, residing at the UDP header.

2. Conventions used in this document

2.1. Terminology

   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 [KEYWORDS].

2.2. Abbreviations

   NTP      Network Time Protocol

   OWAMP    One-Way Active Measurement Protocol

   PTP      Precision Time Protocol

   TWAMP    Two-Way Active Measurement Protocol


Mizrahi, T.           Expires November 28, 2013               [Page 4]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


   UDP      User Datagram Protocol

3. Using the UDP Checksum Trailer in OWAMP and TWAMP

3.1. Overview

   The UDP Checksum Trailer is a two-octet trailer that is piggybacked
   at the end of the test packet. It resides in the last 2 octests of
   the UDP payload.

                    +--------------------------------+
                    |      IPv4 / IPv6 Header        |
                    +--------------------------------+
                    |           UDP Header           |
                    +--------------------------------+
            ^       |                                |
            |       |         OWAMP / TWAMP          |
           UDP      |            packet              |
          Payload   +--------------------------------+
            |       |UDP Checksum Trailer (2 octets) |
            v       +--------------------------------+

            Figure 2 Checksum Trailer in OWAMP/TWAMP Test Packet

3.2. OWAMP / TWAMP Test Packets with Checksum Trailer

   The One-Way Active Measurement Protocol [OWAMP], and the Two-Way
   Active Measurement Protocol [TWAMP] both make use of timestamped test
   packets. The formats of these packets are defined in [OWAMP] and in
   [TWAMP].

   OWAMP/TWAMP test packets are transported over UDP, either over IPv4
   or over IPv6. This document applies to both OWAMP/TWAMP over IPv4 and
   over IPv6.

   OWAMP/TWAMP test packets contain a Packet Padding field. This
   document proposes to use the last 2 octests of the Packet Padding
   field as the Checksum Trailer. In this case the Checksum Trailer is
   always the last 2 octets of the UDP payload, and thus the trailer is
   located UDP Length - 2 octets after the beginning of the UDP header.

   Figure 3 illustrates the OWAMP test packet format including the UDP
   checksum trailer.




Mizrahi, T.           Expires November 28, 2013               [Page 5]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


    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         |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   .                         Packet Padding                        .
   .                                                               .
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |       Checksum Trailer        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 3 Checksum Trailer in OWAMP Test Packets

   Figure 4 illustrates the TWAMP test packet format including the UDP
   checksum trailer.


























Mizrahi, T.           Expires November 28, 2013               [Page 6]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013



   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   |                                               |
   +-+-+-+-+-+-+-+-+                                               +
   |                                                               |
   .                                                               .
   .                         Packet Padding                        .
   .                                                               .
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |       Checksum Trailer        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 4 Checksum Trailer in TWAMP Test Packets

   The length of the Packet Padding field in test packets is announced
   during the session initiation through the "Padding Length" field in
   the Request-Session message [OWAMP], or in the Request-TW-Session
   [TWAMP].

   When a Checksum Trailer is included, the "Padding Length" MUST
   include the Checksum Trailer.






Mizrahi, T.           Expires November 28, 2013               [Page 7]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


3.2.1. Transmission of OWAMP/TWAMP with Checksum Trailer

   The transmitter of an OWAMP/TWAMP test packet MAY include a Checksum
   Trailer field, incorporated in the last 2 octets of the Packet
   Padding.

   A transmitter that includes a Checksum Trailer in its outgoing test
   packets MUST include a Packet Padding in these packets, the length of
   which is at least 2 octets.

3.2.2. Intermediate Updates of OWAMP/TWAMP with Checksum Trailer

   An intermediate entity that receives and alters an OWAMP/TWAMP test
   packet MAY alter the Checksum Trailer field in order to maintain the
   correctness of the UDP checksum value.

3.2.3. Reception of OWAMP/TWAMP with Checksum Trailer

   This document does not impose new requirements on the receiving end
   of an OWAMP/TWAMP test packet.

   The UDP layer at the receiving end verifies the UDP Checksum of
   received test packets, and the OWAMP/TWAMP layer SHOULD treat the
   Checksum Trailer as part of the Packet Padding.

3.3. Interoperability with Existing Implementations

   The behavior defined in this document does not impose new
   requirements on the reception behavior of an OWAMP receiver or a
   TWAMP reflector, since the existence of the checksum trailer is
   transparent from the perspective of the receiver/reflector. Thus, the
   functionality described in this document allows interoperability with
   existing implementations that comply to [OWAMP] or [TWAMP].

3.4. Using the Checksum Trailer with or without Authentication

   When message authentication is used, intermediate entities that alter
   test packets must also re-compute the Message Authentication Code
   (MAC) accordingly. The MAC update typically requires the intermediate
   entity to store the packet, re-compute its MAC, and then forward it.

   While a Checksum Trailer MAY be used when authentication is enabled,
   in practice the Checksum Trailer is more useful in unauthenticated
   mode, allowing the intermediate entity to perform serial processing
   of the packet without storing-and-forwarding it.




Mizrahi, T.           Expires November 28, 2013               [Page 8]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


4. Security Considerations

   This document describes how the last two octests of a test packet can
   be used for updating the checksum. This concept is logically similar
   to an intermediate node that directly modifies the UDP Checksum
   field, and thus does not present any new security implications.

   As described in Section 3.4. , the concept described in this document
   is especially useful for unauthenticated mode. However, this document
   does not make a statement about the circumstances in which
   authentication should or should not be used.

5. IANA Considerations

   There are no IANA actions required by this document.

   RFC Editor: please delete this section before publication.

6. Acknowledgments

   This document was prepared using 2-Word-v2.0.template.dot.

7. References

7.1. Normative References

   [KEYWORDS]    Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

   [IPv6]        Deering, S., Hinden, R., "Internet Protocol, Version 6
                 (IPv6) Specification", RFC 2460, December 1998.

   [Checksum]    Rijsinghani, A., "Computation of the Internet Checksum
                 via Incremental Update", RFC 1624, May 1994.

   [UDP]         Postel, J., "User Datagram Protocol", RFC 768, August
                 1980.

   [OWAMP]       Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and
                 Zekauskas, M., "A One-way Active Measurement Protocol
                 (OWAMP)", RFC 4656, September 2006.

   [TWAMP]       Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and
                 Babiarz, J., "A Two-Way Active Measurement Protocol
                 (TWAMP)", RFC 5357, October 2008.




Mizrahi, T.           Expires November 28, 2013               [Page 9]

Internet-Draft    OWAMP and TWAMP Checksum Trailer            May 2013


7.2. Informative References

   [IEEE1588]    IEEE TC 9 Instrumentation and Measurement Society,
                 "1588 IEEE Standard for a Precision Clock
                 Synchronization Protocol for Networked Measurement and
                 Control Systems Version 2", IEEE Standard, 2008.



Authors' Addresses

   Tal Mizrahi
   Marvell
   6 Hamada St.
   Yokneam, 20692 Israel

   Email: talmi@marvell.com































Mizrahi, T.           Expires November 28, 2013              [Page 10]