IPv6 Destination Option for Conex
draft-ietf-conex-destopt-01

conex Working Group                                          S. Krishnan
Internet-Draft                                                  Ericsson
Intended status: Standards Track                           M. Kuehlewind
Expires: May 2, 2012                         IKR University of Stuttgart
                                                               C. Ucendo
                                                              Telefonica
                                                        October 30, 2011

                   IPv6 Destination Option for Conex
                      draft-ietf-conex-destopt-01

Abstract

   Conex is a mechanism by which senders inform the network about the
   congestion encountered by packets earlier in the same flow.  This
   document specifies an IPv6 destination option that is capable of
   carrying conex markings in IPv6 datagrams.

Status of this Memo

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   This Internet-Draft will expire on May 2, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Conventions used in this document . . . . . . . . . . . . . . . 3
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Conex Destination Option (CDO)  . . . . . . . . . . . . . . . . 4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6

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1.  Introduction

   Conex [CAM] is a mechanism by which senders inform the network about
   the congestion encountered by packets earlier in the same flow.  This
   document specifies an IPv6 destination option [RFC2460] that can be
   used for performing conex markings in IPv6 datagrams.

2.  Conventions used in this document

   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 [RFC2119].

3.  Background

   The Conex working group came up with a list of requirements that had
   to be met by any marking mechanism.  It then considered several
   alternative mechanisms and evaluated their suitability for conex
   marking.  There were no mechanisms found that were completely
   suitable, but the only mechanism that came close to meeting the
   requirements was IPv6 destination options.  The analysis of the
   different alternatives can be found in [draft-krishnan-conex-ipv6].

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4.  Conex Destination Option (CDO)

   The Conex Destination Option (CDO) is a destination option that can
   be included in IPv6 datagrams that are sent by conex-aware senders in
   order to inform conex-aware nodes on the path about the CDO has an
   alignment requirement of (none).

    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
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |  Option Type  | Option Length |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |X|L|E|C|                       Reserved                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: Conex Destination Option Layout

   Option Type

      8-bit identifier of the type of option. The option identifier
      for the conex destination option will be allocated by the IANA.

   Option Length

      8-bit unsigned integer.  The length of the option (excluding
      the Option Type and Option Length fields). This field MUST be
      set to the value 4.

   X Bit
      When this bit is set, the transport sender is using ConEx with
      this packet. If it is reset, the sender is not using ConEx.

   L Bit

      When this bit is set, the transport sender has experienced a loss.
      If it is reset, the sender has not experienced a loss.

   E Bit

      When this bit is set, the transport sender has experienced
      ECN-signaled congestion. If it is reset, the sender has not
      experienced ECN-signaled congestion.

   C Bit

      When this bit is set, the transport sender is building up
      congestion credit. Otherwise it is not.

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   All packets of a ConEx-capable connection MUST carry the CDO.

   If the X bit is the zero all other three bits MUST be zero as well.
   If the X bit is zero that means that the connection is ConEx-capable
   but this packet SHOULD NOT be accounted to determine ConEx
   information in an audit function.  This can be the case for e.g. pure
   control packets not carrying any user data.  As an example in TCP
   pure ACKs are usually not ECN-capable and TCP does not have an
   mechanism to announce the lost of a pure ACK to the sender.  Thus
   congestion information about the ACKs are not available at the
   sender.  An audit function MUST be aware of this possibility and
   SHOULD ensure that not a large amount of data is sent as not-ConEx
   capable with a ConEx capable connection.

   If the X bit is set, all three other bit (L, E, C) MAY be set.  When
   ever one if this bits is set, the number of bytes carried by this IP
   packet (incl.  IP header) SHOULD be accounted when determining
   congestion or credit information.  In IPv6 the length ca easily be
   calculated by the value given in the Payload Length header field
   (payload length + option space) plus a fixed value of 40 Bytes for
   the IP header itself.

   In principle all of these three bits (L, E, C) MAY be set in the same
   packet.  In this case the packet size MUST be accounted more than
   once for each respective ConEx information counter.  In practice loss
   and ECN marks can not occur at the same time, so there should usually
   be a way to signal the respective ConEx information in different
   packets.  In many cases if congestion occurs the sender will not sent
   additional credit bit, but if e.g. a sender assumes losses because of
   an audit function or needs to maintain a certain sending rate to make
   an application layer service work, the occurrence of credit bits (c)
   in parallel to congestion exposure bit (L, E) is reasonable.

   If a network node extracts the ConEx information from a connection,
   this node is usually supposed to hold this information byte-wise,
   e.g. comparing the total number of bytes sent with the number of
   bytes sent with ConEx congestion mark (L, E) to determine the current
   whole path congestion level.  When equally sized packets can be
   assumed accounting the number of packets (and comparing the total
   number to marked once) should deliver the same result.  But a network
   node MUST be aware that this estimation can be quite wrong and thus
   is not reliable if e.g. different sized packed are send.

5.  Acknowledgements

   The authors would like to thank Marcelo Bagnulo, Bob Briscoe, Ingemar
   Johansson, Joel Halpern and John Leslie for the discussions that led

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   to this document.

6.  Security Considerations

   This document does not bring up any new security issues.

7.  IANA Considerations

   This document defines a new IPv6 destination option for carrying
   conex markings.  IANA is requested to assign a new destination option
   type in the Destination Options registry maintained at
   http://www.iana.org/assignments/ipv6-parameters <TBA1> Conex
   Destination Option [RFCXXXX] The act bits for this option need to be
   10 and the chg bit needs to be 0.

8.  Normative References

   [CAM]      Briscoe, B., "Congestion Exposure (ConEx) Concepts and
              Abstract Mechanism", draft-ietf-conex-abstract-mech-01
              (work in progress), March 2011.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

Authors' Addresses

   Suresh Krishnan
   Ericsson
   8400 Blvd Decarie
   Town of Mount Royal, Quebec
   Canada

   Email: suresh.krishnan@ericsson.com

   Mirja Kuehlewind
   IKR University of Stuttgart

   Email: mirja.kuehlewind@ikr.uni-stuttgart.de

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   Carlos Ralli Ucendo
   Telefonica

   Email: ralli@tid.es

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