An IPv4 Flowlabel Option
draft-dreibholz-ipv4-flowlabel-30

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Network Working Group                                       T. Dreibholz
Internet-Draft                                                 SimulaMet
Intended status: Standards Track                      September 10, 2019
Expires: March 13, 2020

                        An IPv4 Flowlabel Option
                   draft-dreibholz-ipv4-flowlabel-30

Abstract

   This draft defines an IPv4 option containing a flowlabel that is
   compatible to IPv6.  It is required for simplified usage of IntServ
   and interoperability with IPv6.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 13, 2020.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   2
     1.3.  Conventions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  A Flow Label Option for IPv4  . . . . . . . . . . . . . . . .   3
     2.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   3
       2.1.1.  The Flow Label Field of IPv6  . . . . . . . . . . . .   3
       2.1.2.  The Limitations of IntServ via IPv4 . . . . . . . . .   4
     2.2.  Definition of the Flow Label Option . . . . . . . . . . .   5
   3.  Translation between IPv6 and IPv4 . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

1.1.  Terminology

   This document uses the following terms:

   o  IntServ (Integrated Services): Reservation of network resources
      (bandwidth) on a per-flow basis.  See [RFC1633], [RFC2205],
      [RFC2208], [RFC2209], [RFC2210], [RFC2211] and [RFC2212] for
      details.

   o  Flow: An IntServ reservation between two endpoints.

   o  Flow Label: The Flow Label field of the IPv6 header and the IPv4
      option header defined in this draft.  It is used for marking a
      packet to use a specific IntServ reservation.  See [RFC6437],
      [RFC6436] for detailed descriptions.

1.2.  Abbreviations

   o  RSVP: ReSource Reservation Protocol

   o  SCTP: Stream Control Transmission Protocol

   o  TCP: Transmission Control Protocol

   o  QoS: Quality of Service

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   o  UDP: User Datagram Protocol

1.3.  Conventions

   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.

2.  A Flow Label Option for IPv4

2.1.  Motivation

   This section describes the motivation to add a flow label option to
   the IPv4 protocol.

2.1.1.  The Flow Label Field of IPv6

   The Flow Label field (see [RFC6436] and [RFC6437]) of the IPv6 header
   (see [RFC2460]) is a 20-bit number.  All packets from the same source
   address having the same flow label MUST contain the same destination
   address.  Therefore, the flow label combined with the source address
   is a network- unique identification for a specific packet flow.  The
   idea behind the flow label is marking specific flows for IntServ.
   That is, the routers on the path from source to destination keep e.g.
   reservation states for the flows.  The flow label provides easy
   identification and utilizes efficient lookup, e.g. using a hash
   function on the 3-tuple (source address, destination address, flow
   label).

   Using the IPv6 flow label, packets can be mapped easily to specific
   flows, with the following features:

   o  Transport Layer Protocol Independence: Since the mapping is
      directly specified in the IP header, all possible layer 4
      protocols are supported, even protocols to be specified in a far
      future.

   o  Support for Network Layer Encryption: The mapping is independent
      of payload encryption (e.g. by IPsec).

   o  Support for Fragmentation: If fragmentation of a large IP packet
      is necessary, all fragments contain the same flow label.
      Therefore, fragmentation does not cause any flow-marking problem.

   o  Flow Sharing: By marking packets with a flow label, it is possible
      to share a single flow (IntServ reservation) with several

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      communication associations from host A to host B.  For example, a
      video stream via UDP and a HTTP download via TCP could share a
      single reservation.  For the user, flow sharing has the advantage
      that if one of its communication associations temporarily requires
      lower bandwidth than expected, other associations sharing the same
      flow may use the remaining bandwidth.  That is, his possibly
      expensive reservation is fully utilized.  Flow sharing also helps
      keeping the total number of reservations a router has to handle
      small, reducing their CPU and memory requirements and therefore
      cost.

   o  Multi-Flow Connections: One communication association can divide
      up its packets to several flows, simply by marking packets with
      different flow labels.  This technique can be used for layered
      transmission.  That is, a stream (e.g. a video) is divided up into
      several parts (called layers).  For example, the first layer (base
      layer) of a video contains a low-quality version, the second (1st
      enhancement layer) the data to generate a higher-quality version,
      etc.. Now, the first layer can be mapped to a high-quality
      reservation (guaranteed bandwidth, low loss rate) at higher cost,
      but the following layers can be mapped to lower-quality
      reservations (e.g. higher loss rate) or even best effort at lower
      cost.  Research shows that the total transmission cost can be
      highly reduced using layered transmission (see [Dre2001],
      [IJMUE2009] for details).

2.1.2.  The Limitations of IntServ via IPv4

   Using IntServ with IPv4, there are several problems that can only be
   solved with high management effort:

   o  No Transport Layer Protocol Independence: It is necessary to mark
      the packets within the layer 4 protocol header.  For example, the
      TCP, UDP or SCTP port numbers can be used to mark flows (with
      limitations, see below).  But for new protocols (e.g.
      experimental, new standards, proprietary), software updates for
      *all* IntServ routers are necessary to recognize the packet flow!

   o  No Support for Network Layer Encryption: Since it is necessary to
      read fields of the layer 4 protocol header, it may not be
      encrypted.  Therefore, e.g. the usage of IPsec is impossible.

   o  Support for Fragmentation: Only the first fragment of a large
      packet contains the layer 4 header necessary to map the packet to
      a flow.  Mapping other fragments would require the hops to
      remember packet identities and try to map fragments to packet
      identities.  Due to the management effort and memory requirements,
      this is not realistic for high-bandwidth backbone routers;

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      especially when packet reordering must be considered.
      Furthermore, load sharing or traffic distribution would be
      impossible.

   o  No Flow Sharing: It is usually impossible for two different
      communication associations to share the same flow, e.g. if TCP
      flows are recognized using port numbers.  This makes it necessary
      to reserve an IntServ flow for each communication association.
      This implies an increased number of flow states for routers to
      keep and maintain.  Furthermore, if one association temporarily
      uses a lower bandwidth, the free bandwidth of its flow cannot
      easily be borrowed to another association.

   o  No Multi-Flow Connections: To use layered transmission, e.g. a
      video via UDP, the transmission of every layer would require own
      port numbers.  In the case of connection-oriented transmission
      protocols (e.g.  TCP, SCTP), every layer would even require its
      own connection setup and management.  Depending on the transport
      protocol, the number of communication associations and the number
      of flows, much more work is necessary compared to IPv6 using flow
      labels.

   All in all, using IntServ flows with IPv4 requires much more work
   compared to IPv6, where simply the flow label can be used.  It is
   therefore useful to add such a field to IPv4, too.  An appropriate
   place to add such a field is an IPv4 option header.

2.2.  Definition of the Flow Label Option

   IPv4 (see [RFC0791]) already defines an option header for a 16-bit
   SATNET stream identifier.  Since this identifier would be
   incompatible to the 20-bit IPv6 flow label, reuse of this existing
   option header is inappropriate.  Therefore, a new one is defined as
   follows.

   Flow Label Option

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |0 0 0 0 0 0 0 0|0 0 0 0 0 0 0 0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0 0 0 0 0 0 0 0|0 0 0 0|              Flow Label               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: 143

   o  Length: 8 octets

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   o  Flow Label: The 20-bit flow label.  All definitions of [RFC6437]
      and [RFC6436] for the IPv6 flow label are also valid for this
      field.  A value of zero denotes that no flow label is used.  In
      this case, the flow label option is in fact unnecessary.

   The Flow Label option SHOULD be copied on fragmentation.  It MUST be
   the first option of the IP header and therefore MUST NOT appear more
   than once per IPv4 packet.  The Router Alert option SHOULD NOT be
   used to mark the necessity for routers to examine the options.
   Placing the Flow Label option as first option allows for easy
   processing in hardware.

3.  Translation between IPv6 and IPv4

   Since the new IPv4 flow label is fully compatible to the IPv6 flow
   label, the field MAY be translated in the other protocol's one during
   protocol translation.  That is, a router can translate an IPv6 packet
   set from an IPv6-only host to an IPv4-mapped address of an IPv4-only
   host and the flow label may simply be copied.  The same may also be
   applied in the backwards direction.

   Note, that copying the flow label during protocol translation is not
   mandatory.  There may be IntServ reservation reasons for not copying
   but setting the flow label to zero.  But a router MUST NOT set the
   flow label to another value than the copy or 0, since the source is
   responsible to ensure that the source address combined with the flow
   label is network-unique.

4.  Security Considerations

   Security considerations are similar to the IPv6 flow label, see
   [RFC6437].

5.  IANA Considerations

   This document introduces no additional considerations for IANA.

6.  Acknowledgments

   The author would like to thank Brian E.  Carpenter, Wes George, Perry
   Lorier, Christoph Reichert and Michael Tuexen for their comments.

7.  References

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7.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [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>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [RFC2210]  Wroclawski, J., "The Use of RSVP with IETF Integrated
              Services", RFC 2210, DOI 10.17487/RFC2210, September 1997,
              <https://www.rfc-editor.org/info/rfc2210>.

   [RFC2211]  Wroclawski, J., "Specification of the Controlled-Load
              Network Element Service", RFC 2211, DOI 10.17487/RFC2211,
              September 1997, <https://www.rfc-editor.org/info/rfc2211>.

   [RFC2212]  Shenker, S., Partridge, C., and R. Guerin, "Specification
              of Guaranteed Quality of Service", RFC 2212,
              DOI 10.17487/RFC2212, September 1997,
              <https://www.rfc-editor.org/info/rfc2212>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <https://www.rfc-editor.org/info/rfc6437>.

   [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>.

7.2.  Informative References

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   [Dre2001]  Dreibholz, T., "Management of Layered Variable Bitrate
              Multimedia Streams over DiffServ with Apriori
              Knowledge",  Masters Thesis, February 2001,
              <https://duepublico.uni-duisburg-
              essen.de/servlets/DerivateServlet/Derivate-29936/
              Dre2001.pdf>.

   [IJMUE2009]
              Zhu, W., Dreibholz, T., Rathgeb, E., and X. Zhou, "A
              Scalable QoS Device for Broadband Access to Multimedia
              Services", SERSC International Journal of Multimedia and
              Ubiquitous Engineering (IJMUE) Number 2, Volume 4, Pages
              157-172, ISSN 1975-0080, May 2009,
              <http://www.sersc.org/journals/IJMUE/
              vol4_no2_2009/14.pdf>.

   [RFC1633]  Braden, R., Clark, D., and S. Shenker, "Integrated
              Services in the Internet Architecture: an Overview",
              RFC 1633, DOI 10.17487/RFC1633, June 1994,
              <https://www.rfc-editor.org/info/rfc1633>.

   [RFC2208]  Mankin, A., Ed., Baker, F., Braden, B., Bradner, S.,
              O'Dell, M., Romanow, A., Weinrib, A., and L. Zhang,
              "Resource ReSerVation Protocol (RSVP) -- Version 1
              Applicability Statement Some Guidelines on Deployment",
              RFC 2208, DOI 10.17487/RFC2208, September 1997,
              <https://www.rfc-editor.org/info/rfc2208>.

   [RFC2209]  Braden, R. and L. Zhang, "Resource ReSerVation Protocol
              (RSVP) -- Version 1 Message Processing Rules", RFC 2209,
              DOI 10.17487/RFC2209, September 1997,
              <https://www.rfc-editor.org/info/rfc2209>.

   [RFC6436]  Amante, S., Carpenter, B., and S. Jiang, "Rationale for
              Update to the IPv6 Flow Label Specification", RFC 6436,
              DOI 10.17487/RFC6436, November 2011,
              <https://www.rfc-editor.org/info/rfc6436>.

Author's Address

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   Thomas Dreibholz
   Simula Metropolitan Centre for Digital Engineering
   Pilestredet 52
   0167 Oslo, Oslo
   Norway

   Phone: +47-6782-8200
   Fax:   +47-6782-8201
   Email: dreibh@simula.no
   URI:   https://www.simula.no/people/dreibh

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