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Versions: (draft-mizrahi-owamp-twamp-checksum-trailer) 00 01 02 draft-ietf-ippm-checksum-trailer

Network Working Group                                         T. Mizrahi
Internet Draft                                                   Marvell
Intended status: Informational
Expires: June 2015                                     December 15, 2014

                  UDP Checksum Trailer in OWAMP and TWAMP
                draft-mizrahi-ippm-checksum-trailer-02.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
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   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 June 15, 2015.




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Copyright Notice

   Copyright (c) 2014 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 ................................................... 9
         3.2.3. Reception of OWAMP/TWAMP with Checksum Trailer ..... 9
      3.3. Interoperability with Existing Implementations........... 9
      3.4. Using the Checksum Trailer with or without Authentication 9
   4. Security Considerations ..................................... 10
   5. IANA Considerations ......................................... 10
   6. Acknowledgments ............................................. 10
   7. References .................................................. 10
      7.1. Normative References ................................... 10
      7.2. Informative References ................................. 11

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.



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   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


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   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
   octets 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

   OWAMP    One-Way Active Measurement Protocol

   PTP      Precision Time Protocol

   TWAMP    Two-Way Active Measurement Protocol

   UDP      User Datagram Protocol


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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 octets 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 octets 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.






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    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.


























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   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 be
   sufficiently long to include the Checksum Trailer:

   o In OWAMP the padding length is at least 2 octets, allowing the
      sender to incorporate the checksum trailer in the last 2 octets of
      the padding.


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   o In TWAMP the padding length is at least 29 octets. The additional
      padding is required since the header of reflector test packets is
      27 octets longer than the header of sender test packets. Thus, the
      padding in reflector test packets is 27 octets shorter than in
      sender packet. Using 29 octets of padding in sender test packets
      allows both the sender and the reflector to use a 2-octet checksum
      trailer.
      Note: the 27-octet difference between the sender packet and the
      reflector packet is specifically in unauthenticated mode, whereas
      in authenticated mode the difference between the sender and
      receiver packets is 56 octets. As specified in Section 3.4. , the
      checksum trailer should only be used in unauthenticated mode.

   o Two optional TWAMP features are defined in [RFC6038]: octet
      reflection and symmetrical size. When at least one of these
      features is enabled, the Request-TW-Session includes the <Padding
      Length> field, as well as a <Length of padding to reflect> field.
      In this case both fields must be sufficiently long to allow at
      least 2 octets of padding in both sender test packets and
      reflector test packets.
      Specifically, when octet reflection is enabled, the two length
      fields must be defined such that the padding expands at least 2
      octets beyond the end of the reflected octets.

   As described in Section 1. , the extensions described in this
   document are implemented by two logical layers, a protocol layer and
   a timestamping layer. It is assumed that the two layers are
   synchronized about whether the usage of the Checksum Trailer is
   enabled or not; since both logical layers reside in the same network
   device, it is assumed there is no need for a protocol that
   synchronizes this information between the two layers. When Checksum
   Trailer usage is enabled, the protocol layer must take care to verify
   that test packets include the necessary padding, and avoiding the
   need for the timestamping layer to verify that en-route test packets
   include the necessary padding.

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 MUST be sufficient to include the checksum trailer. The length
   of the padding field is negotiated during session initiation, as
   described in Section 3.2.


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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

   Both OWAMP and TWAMP may use authentication, as defined in [OWAMP] or
   [TWAMP]. A Checksum Trailer SHOULD NOT be used when authentication is
   enabled. The Checksum Trailer is effective in unauthenticated mode,
   allowing the intermediate entity to perform serial processing of the
   packet without storing-and-forwarding it.

   On the other hand, when message authentication is used, an
   intermediate entity that alters 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. Thus, the benefit of the
   checksum trailer is effectively irrelevant when a MAC is used.

   Note: while [OWAMP] and [TWAMP] include an inherent security
   mechanism, these protocols can be secured by other measures, e.g.,
   [IPPMIPsec]. For similar reasons as described above, a Checksum
   Trailer SHOULD NOT be used in this case.






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4. Security Considerations

   This document describes how a Checksum Trailer extension can be used
   for maintaining the correctness of the UDP checksum.

   The purpose of this extension is to ease the implementation of
   accurate timestamping engines, as described in Figure 1. The
   extension is intended to be used internally in an OWAMP/TWAMP enabled
   node, and not intended to be used by intermediate switches and
   routers that reside between the sender and the receiver/reflector.
   Any modification of a test packet by intermediate switches or routers
   should be considered a malicious MITM attack.

   It is important to emphasize that the scheme described in this
   document does not increase the protocol's vulnerability to MITM
   attacks; a MITM who maliciously modifies a packet and its checksum
   trailer is logically equivalent to a MITM attacker who modifies a
   packet and its UDP Checksum field.

   The concept described in this document is intended to be used only in
   unauthenticated mode. As described in Section 3.4. , the benefits of
   the Checksum Trailer do not apply when authentication is enabled.

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.




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   [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.

   [RFC6038]     Morton, A., Ciavattone, L., "Two-Way Active
                 Measurement Protocol (TWAMP) Reflect Octets and
                 Symmetrical Size Features", RFC 6038, October 2010.

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.

   [IPPMIPsec]   Pentikousis, K., Cui, Y., Zhang, E., "Network
                 Performance Measurement for IPsec", draft-ietf-ippm-
                 ipsec (work in progress), September 2014.



Authors' Addresses

   Tal Mizrahi
   Marvell
   6 Hamada St.
   Yokneam, 20692 Israel

   Email: talmi@marvell.com












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