Lossless and overhead free DCCP - UDP header conversion (U-DCCP)
draft-amend-tsvwg-dccp-udp-header-conversion-01

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Transport Area Working Group                                    M. Amend
Internet-Draft                                          Deutsche Telekom
Intended status: Experimental                               A. Brunstrom
Expires: January 9, 2020                                      A. Kassler
                                                     Karlstad University
                                                            V. Rakocevic
                                               City University of London
                                                           July 08, 2019

    Lossless and overhead free DCCP - UDP header conversion (U-DCCP)
            draft-amend-tsvwg-dccp-udp-header-conversion-01

Abstract

   The Datagram Congestion Control Protocol (DCCP) is a transport-layer
   protocol that provides upper layers with the ability to use non-
   reliable congestion-controlled flows.  DCCP is not widely deployed in
   the Internet, and the reason for that can be defined as a typical
   example of a chicken-egg problem.  Even if an application developer
   decided to use DCCP, the middle-boxes like firewalls and NATs would
   prevent DCCP end-to-end since they lack support for DCCP.  Moreover,
   as long as the protocol penetration of DCCP does not increase, the
   middle-boxes will not handle DCCP properly.  To overcome this
   challenge, NAT/NATP traversal and UDP encapsulation for DCCP is
   already defined.  However, the former requires special middle-box
   support and the latter introduces overhead.  The recent proposal of a
   multipath extension for DCCP further underlines the challenge of
   efficient middle-box passing as its main goal is to be applied over
   the Internet, traversing numerous uncontrolled middle-boxes.  This
   document introduces a new solution which disguises DCCP during
   transmission as UDP without requiring middle-box modification or
   introducing any overhead.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 9, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  U-DCCP  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  The DCCP Generic header . . . . . . . . . . . . . . . . .   4
     3.3.  UDP header  . . . . . . . . . . . . . . . . . . . . . . .   5
     3.4.  U-DCCP conversion considerations  . . . . . . . . . . . .   6
     3.5.  U-DCCP header . . . . . . . . . . . . . . . . . . . . . .   6
     3.6.  Implementation  . . . . . . . . . . . . . . . . . . . . .   7
     3.7.  Pseudo-code DCCP to U-DCCP conversion . . . . . . . . . .   7
     3.8.  Pseudo-code U-DCCP to DCCP restoration  . . . . . . . . .   8
     3.9.  U-DCCP negotiation (required????) . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Datagram Congestion Control Protocol (DCCP) [RFC4340] is a
   transport-layer protocol that provides upper layers with the ability
   to use non-reliable congestion-controlled flows.  The current
   specification for DCCP [RFC4340] specifies a direct native
   encapsulation in IPv4 or IPv6 packets.

   DCCP support has been specified for devices that use Network Address
   Translation (NAT) or Network Address and Port Translation (NAPT)

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   [RFC5597].  However, there is a significant installed base of NAT/
   NAPT devices that do not support [RFC5597].  An UDP encapsulation for
   DCCP [RFC6773] circumvents such limitations and makes DCCP compatible
   with any UDP [RFC0768] compliant device that supports [RFC4787] but
   does not support [RFC5597].  For convenience, the standard
   encapsulation for DCCP [RFC4340] (including [RFC5596] and [RFC5597]
   as required) is referred to as DCCP-STD, whereas the UDP
   encapsulation for DCCP [RFC6773] is referred to as DCCP-UDP.

   It can be stated that DCCP-STD and DCCP-UDP are techniques which
   increase the success rate of DCCP transmissions significantly.
   However, DCCP-STD fails on devices that block DCCP for any reasons.
   On the other hand, DCCP-UDP uses the well-accepted UDP to let devices
   assume they are handling the UDP protocol, but at the cost of a
   reduced goodput/throughput ratio.

   To compensate for the inefficiency of DCCP-STD (device blocking) and
   DCCP-UDP (overhead), this document proposes a beneficial modification
   scheme relying on UDP (like DCCP-UDP), but with no overhead.  This
   goal is reached by re-arranging DCCP's extended header to make it
   look like UDP, without losing critical information.  This solution is
   referred to as U-DCCP.

   U-DCCP is limited to DCCP's extended header, requiring X is set to 1.
   Otherwise U-DCCP relies on the NAT/NATP functionalities specified for
   UDP in [RFC4787], [RFC6888] and [RFC7857].

2.  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 [RFC2119].

3.  U-DCCP

3.1.  Overview

   The basic approach of U-DCCP is to modify the extended header of a
   DCCP packet so that it appears like UDP [RFC0768].  In particular,
   this takes place without losing any header information, but requires
   a U-DCCP termination before the packet is delivered to the DCCP end
   system .  This method does not change the 4-tuple of IP and port
   addressing, however it changes the protocol carried over IP from DCCP
   to UDP.  As a consequence, the length of the packet remains unchanged
   and behaves like DCCP-STD.  The solution is not a tunneling approach.
   It requires that the same port used by DCCP can be used by UDP.

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   The method is designed to support use when the IP addresses are
   modified by a device that implements NAT/NAPT.  A NAT translates the
   IP addresses, which impacts the transport-layer checksum.  A NAPT
   device may also translate the port values (usually the source port).
   In both cases, the outer transport header that includes these values
   would need to be updated by the NAT/NAPT.

   U-DCCP supports IPv4 and IPv6.

   The basic format of a U-DCCP packet is:

   +-----------------------------------+
   |     IP Header (IPv4 or IPv6)      |  Variable length
   +-----------------------------------+
   |UDP like arranged DCCP ext. Header |  8 bytes \
   +-----------------------------------+           ) U-DCCP header
   |Rest of rearranged DCCP ext. Header|  8 bytes /
   +-----------------------------------+
   | Additional (type-specific) Fields |  Variable length (could be 0)
   +-----------------------------------+
   |           DCCP Options            |  Variable length (could be 0)
   +-----------------------------------+
   |      Application Data Area        |  Variable length (could be 0)
   +-----------------------------------+

                     Figure 1: Format of U-DCCP packet

   The U-DCCP header is described in Section 3.4 after introducing the
   traditional DCCP header in Section 3.1 and its target appearance of a
   UDP header in Section 3.2.  Section 3.3 discusses considerations for
   building the U-DCCP header upfront.

3.2.  The DCCP Generic header

   The DCCP Generic Header [RFC4340] takes two forms: one with long
   sequence numbers (48 bits) and the other with short sequence numbers
   (24 bits).  The short one is not part of U-DCCP's modification.

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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Source Port          |           Dest Port           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Data Offset  | CCVal | CsCov |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     |       |X|               |                               .
     | Res | Type  |=|   Reserved    |  Sequence Number (high bits)  .
     |     |       |1|               |                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                  Sequence Number (low bits)                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 2: The extended DCCP Header with Long Sequence Numbers
                                 [RFC4340]

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Source Port          |           Dest Port           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Data Offset  | CCVal | CsCov |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     |       |X|                                               |
     | Res | Type  |=|   Sequence Number (low bits)                  |
     |     |       |0|                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 3: The short DCCP Header with Short Sequence Numbers [RFC4340]

   All generic header fields have the meaning specified in [RFC4340],
   updated by [RFC5596].

3.3.  UDP header

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Source Port          |           Dest Port           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             Length            |           Checksum            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 4: The UDP Header [RFC768]

   All header fields have the meaning specified in [RFC0768].

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3.4.  U-DCCP conversion considerations

   The U-DCCP header has the goal to merge the information of DCCP's
   extended header (Section 3.1) and imitates in the first 64 bits the
   UDP header (Section 3.2).  Information required to restore a DCCP
   header from any conversion, which must not be lost, includes: source
   and destination port, Data Offset, CCVal, CsCov, Checksum, Type, X
   and the Sequence Number.

   Compared with the UDP header, the DCCP extented header shows
   similarities in source and destination port and checksum.  The length
   field of UDP (bits 33-48) is not part of the DCCP header and contains
   in case of DCCP the fields Data Offset, CCVal and CsCov.

   For the goal of imitating UDP, the checksum must cover the whole
   datagram, which renders any limitation by CsCov useless.  The
   checksum itself is required to re-calculate after conversion anyway.

   If the conversion is limited to DCCP'S extended header only, X is
   always "1".

   Thus, Data Offset, CCVal, Type and Sequence Number must be re-
   arranged in a way that the Length field of UDP can be applied.

3.5.  U-DCCP header

   The considerations of Section 3.3 leads to the following header,
   denoted as U-DCCP header.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   U  |          Source Port          |           Dest Port           |
   D  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   P  |          Length               |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type  | CCVal |  Data Offset  |  Sequence Number (high bits)  .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                  Sequence Number (low bits)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 5: The U-DCCDP Header

   The first 8 bytes of the U-DCCP header corresponds to [RFC0768] and
   the fields are interpreted as follows:

   Source and Dest(ination) Ports: 16 bits each

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   These fields identify the UDP ports used by the source and
   destination (respectively) of the packet to listen for incoming UDP
   packets.  The UDP port values identify the DCCP source and
   destination ports.

   Length: 16 bits

   This field is the length of the UDP datagram, including the UDP
   header and the payload (for U-DCCP, the payload comprises the payload
   of the original DCCP datagram and part of its header).

   Checksum: 16 bits

   This field is the Internet checksum of a network-layer pseudoheader
   and Length bytes of the UDP packet [RFC0768].  The UDP checksum MUST
   NOT be zero for a U-DCCP packet.

   The remaining 8 bytes of the U-DCCP header contains:

   Type, CCVal, Data Offset, Seq. Number: As specified in [RFC4340]

   In case U-DCCP is applied, the IP layer must be instructed to carry
   an UDP datagram and its checksum must be re-calculated.  For detailed
   information see Section 3.7.

3.6.  Implementation

   The process of applying U-DCCP is defined as follows:

   DCCP generation -> U-DCCP conversion -> UDP transmission -> U-DCCP
   reception and restoration -> DCCP reception

   The conversion can be integrated into DCCP endpoints directly or as
   an additional component on the way along the transmission route.
   Depending on the degree of integration, especially the process of
   checksum calculation and validation can be optimized.  Section 3.7
   and Section 3.8 provide a possible pseudo-code for the conversion
   without any optimized integration into the sender's network stack or
   into the receiver's network stack.  The pseudo-code assumes explicit
   knowledge on which U-DCCP flows need conversion between the sender
   and the receiver.

3.7.  Pseudo-code DCCP to U-DCCP conversion

   A possible processing of an already generated DCCP datagram for
   U-DCCP conversion:

   1.   Receive DCCP datagram.

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   2.   Check eligibility for conversion; otherwise bypass conversion.

   3.   Verify consistency, e.g. checksum; otherwise drop.

   4.   Shift Type and CCVal field to the ninth octet.

   5.   Shift Data Offset field to the tenth octet.

   6.   Place a length information at octet 5+6 corresponding to
        [RFC0768].

   7.   Modify the IP header's encapsulated protocol from DCCP to UDP.

   8.   Re-calculate IP header checksum.

   9.   Reset DCCP checksum field: octet 7+8 = 0.

   10.  Generate new checksum at octet 7+8 as described in [RFC0768].

   11.  Forward to destination based on the unmodified 4-tuple of IP-
        addresses and ports.

3.8.  Pseudo-code U-DCCP to DCCP restoration

   A possible processing of an already converted U-DCCP datagram for
   DCCP restoration:

   1.   Receive UDP datagram.

   2.   Check eligibility for restoration; otherwise bypass restoration

   3.   Validate UDP checksum; otherwise drop.

   4.   Restore Data Offset field according to [RFC4340].

   5.   Restore CCVal field according to [RFC4340].

   6.   Set CsCov field according to [RFC4340] to "0".

   7.   Restore Type field according to [RFC4340].

   8.   Set Reserved bits according to [RFC4340] to "0".

   9.   Set X according to [RFC4340] to "1".

   10.  Modify the IP header's encapsulated protocol from UDP to DCCP.

   11.  Re-calculate IP header checksum.

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   12.  Reset DCCP checksum field: octet 7+8 = 0.

   13.  Generate new checksum at octet 7+8 as described in [RFC0768].

   14.  Forward to destination based on the unmodified 4-tuple of IP-
        addresses and ports.

3.9.  U-DCCP negotiation (required????)

   Tbd later if required.  Otherwise assumes explicit knowledge about
   the U-DCCP conversion between sender and receiver.

4.  Security Considerations

   TBD.

5.  IANA Considerations

6.  Notes

   This document is inspired by [RFC6773] and some text passages for the
   -00 version are copied unmodified.

7.  Acknowledgments

8.  Informative References

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

   [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>.

   [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
              Congestion Control Protocol (DCCP)", RFC 4340,
              DOI 10.17487/RFC4340, March 2006,
              <https://www.rfc-editor.org/info/rfc4340>.

   [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <https://www.rfc-editor.org/info/rfc4787>.

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   [RFC5596]  Fairhurst, G., "Datagram Congestion Control Protocol
              (DCCP) Simultaneous-Open Technique to Facilitate NAT/
              Middlebox Traversal", RFC 5596, DOI 10.17487/RFC5596,
              September 2009, <https://www.rfc-editor.org/info/rfc5596>.

   [RFC5597]  Denis-Courmont, R., "Network Address Translation (NAT)
              Behavioral Requirements for the Datagram Congestion
              Control Protocol", BCP 150, RFC 5597,
              DOI 10.17487/RFC5597, September 2009,
              <https://www.rfc-editor.org/info/rfc5597>.

   [RFC6773]  Phelan, T., Fairhurst, G., and C. Perkins, "DCCP-UDP: A
              Datagram Congestion Control Protocol UDP Encapsulation for
              NAT Traversal", RFC 6773, DOI 10.17487/RFC6773, November
              2012, <https://www.rfc-editor.org/info/rfc6773>.

   [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
              A., and H. Ashida, "Common Requirements for Carrier-Grade
              NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
              April 2013, <https://www.rfc-editor.org/info/rfc6888>.

   [RFC7857]  Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar,
              S., and K. Naito, "Updates to Network Address Translation
              (NAT) Behavioral Requirements", BCP 127, RFC 7857,
              DOI 10.17487/RFC7857, April 2016,
              <https://www.rfc-editor.org/info/rfc7857>.

Authors' Addresses

   Markus Amend
   Deutsche Telekom
   Deutsche-Telekom-Allee 7
   64295 Darmstadt
   Germany

   Email: Markus.Amend@telekom.de

   Anna Brunstrom
   Karlstad University
   Universitetsgatan 2
   651 88 Karlstad
   Sweden

   Email: anna.brunstrom@kau.se

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   Andreas Kassler
   Karlstad University
   Universitetsgatan 2
   651 88 Karlstad
   Sweden

   Email: andreas.kassler@kau.se

   Veselin Rakocevic
   City University of London
   Northampton Square
   London
   United Kingdom

   Email: veselin.rakocevic.1@city.ac.uk

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