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Versions: 00

TCP Maintenance and Minor Extensions                        J. Kang, Ed.
Internet-Draft                                                  Q. Liang
Intended status: Informational                                    Huawei
Expires: 10 August 2021                                  6 February 2021


           Subtype Capability Exchange During MPTCP Handshake
             draft-kang-tcpm-subtype-capability-exchange-00

Abstract

   Multipath TCP provides the ability to simultaneously use multiple
   paths between peers.  MPTCP protocol defines seven subtypes in MPTCP
   v0 [RFC6824] and ten subtypes in MPTCP v1 [RFC8684] to differentiate
   message types and implement some additional functions during a
   session.

   This draft proposes an enhancement to support Subtype Capability
   Exchange during MPTCP connection establishment in order to improve
   elastic scalability of MPTCP protocol.  It includes: 1) requirements
   for which this kind of capability exchange during handshake is
   important for a MPTCP session; 2) a typical flow for Subtype
   Capability Exchange between peers; 3) a feasible solution on protocol
   design is suggested.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on 10 August 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     1.2.  Background  . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  One Typical Flow  . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Implementation . . . . . . . . . . . . . . . . . . .   5
     3.1.  Carrying Subtype Capabilities in MP_CAPABLE Option  . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].

1.2.  Background

   Table 1 lists all subtypes that have been specified in current MPTCP
   versions.  Besides version negotiation, MPTCP peers can not interact
   with each other on the granularity of subtype capability.  This
   feature may cause inflexible protocol extension.  For example, if a
   new message type A is added in future extension, a higher version
   should be released to import it and a new subtype may need to be
   allocated.  Another case is that if a sender does not know the
   subtypes supported by a receiver in a MPTCP session, as a result,
   invalid data packets may been sent from the sender during data
   transmission and the receiver will discard it which causes system
   overhead on receiver side.






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    +=======+=================+===============+===========+===========+
    | Value | Symbol          | Name          | MPTCPv0   | MPTCPv1   |
    +=======+=================+===============+===========+===========+
    | 0x0   | MP_CAPABLE      | Multipath     | Supported | Supported |
    |       |                 | Capable       |           |           |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x1   | MP_JOIN         | Join          | Supported | Supported |
    |       |                 | Connection    |           |           |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x2   | DSS             | Data Sequence | Supported | Supported |
    |       |                 | Signal (Data  |           |           |
    |       |                 | ACK and Data  |           |           |
    |       |                 | Sequence      |           |           |
    |       |                 | Mapping)      |           |           |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x3   | ADD_ADDR        | Add Address   | Supported | Supported |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x4   | REMOVE_ADDR     | Remove        | Supported | Supported |
    |       |                 | Address       |           |           |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x5   | MP_PRIO         | Change        | Supported | Supported |
    |       |                 | Subflow       |           |           |
    |       |                 | Priority      |           |           |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x6   | MP_FAIL         | Fallback      | Supported | Supported |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x7   | MP_FASTCLOSE    | Fast Close    | Supported | Supported |
    +-------+-----------------+---------------+-----------+-----------+
    | 0x8   | MP_TCPRST       | Subflow Reset | /         | Supported |
    +-------+-----------------+---------------+-----------+-----------+
    | 0xf   | MP_EXPERIMENTAL | Reserved for  | /         | Supported |
    |       |                 | Private Use   |           |           |
    +-------+-----------------+---------------+-----------+-----------+

                      Table 1: Overview MPTCP Subtypes

   This document suggests a new function of Subtype Capability Exchange
   during MPTCP handshake in the scenario that MPTCP peers in a session
   support same MPTCP protocol version but with different subtype sets.

2.  One Typical Flow

   Figure 1 illustrates a typical flow for this Subtype Capability
   Exchange during MPTCP connection setup.  The field of Subtype
   Capability is used to indicate whether these subtypes are supported
   by the sender, for example, Host A Subtype Capabilities indicates the
   status of the subtypes on Host A and Host B Subtype Capabilities
   indicates that on Host B.  Through the transmission of this



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   information between both parties, a sender can determine whether a
   message can be properly processed by its receiver and only send the
   message that can be supported by the receiver during data
   transmission.

               Host A                                  Host B
        ------------------------                       ----------
        Address A1    Address A2                       Address B1
        ----------    ----------                       ----------
            |             |                                |
            |        SYN + Host A Subtype Capability       |
            |--------------------------------------------->|
            |                                        Determine and
            |                                    Cache the capabilities
            |                                          of Host A
            |<---------------------------------------------|
            |      SYN/ACK + Host B Subtype Capability     |
   Determine and Cache the                                 |
    capabilities of Host B                                 |
            |                         ACK                  |
            |--------------------------------------------->|
            |             |                                |
            |             |        SYN + MP_JOIN           |
            |             |------------------------------->|
            |             |<-------------------------------|
            |             |      SYN/ACK + MP_JOIN         |
            |             |                                |
            |             |        ACK + MP_JOIN           |
            |             |------------------------------->|
            |             |<-------------------------------|
            |             |             ACK                |
            |             |                                |
            |   Data Transmission(with subtype messages)   |
            |<-------------------------------------------->|
            |             |                                |
            |             | Data Transmission(with subtype |
            |             |<------------------------------>|
            |             |             messages)          |
            |             |                                |

                Figure 1: MPTCP Subtype Capability Exchange










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   In practice, another possible implementation is as follows: after
   receiving the subtype capability information sent by Host A, Host B
   determines the common subtype sets supported by both parties, and
   returns this common subtype sets in the reponse.  Host A caches this
   common subtype sets locally.  In data transmission phase, Host A
   sends the specified subtype messages to Host B that are included in
   the common subtype sets.  As an alternative solution, its protocol
   design on MPTCP will be considered and updated in later versions.

3.  Protocol Implementation

   This document describes one solution on the modifications to MPTCP
   protocol to support this mechanism.In this solution, MP_CAPABLE
   option is used and extended to add bits to carry subtype capabilities
   information.  There should be other possible solutions that can be
   defined in subsequent discussions.

3.1.  Carrying Subtype Capabilities in MP_CAPABLE Option

   In Figure 2, a 32-bit "OptionSupported" is added to MP_CAPABLE option
   to indicate whether the subtypes are supported by the sender.

                          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
     +---------------+---------------+-------+-------+---------------+
     |     Kind      |    Length     |Subtype|Version|A|B|C|D|E|F|G|H|
     +---------------+---------------+-------+-------+---------------+
     |                   Option Sender's Key (64 bits)               |
     |                      (if option Length > 4)                |
     |                                                               |
     +---------------------------------------------------------------+
     |                  Option Receiver's Key (64 bits)              |
     |                      (if option Length > 12)               |
     |                                                               |
     +-------------------------------+-------------------------------+
     |                    OptionSupported (32 bits)                  |
     +-------------------------------+-------------------------------+
     |  Data-Level Length (16 bits)  |  Checksum (16 bits, optional) |
     +-------------------------------+-------------------------------+

                      Figure 2: OptionSupported Format

   For MPTCP v1, ten subtypes has been defined and applied in practice.
   So the first 10-bits in OptionSupported field is used for indicating
   whether these subtypes is supported by sender.  The order is listed
   below:

   0: MP_CAPABLE



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   1: MP_JOIN

   2: DSS

   3: ADD_ADDR

   4: REMOVE_ADDR

   5: MP_PRIO

   6: MP_FAIL

   7: MP_FASTCLOSE

   9: MP_TCPRST

   10: MP_EXPERIMENTAL

   11~31: Reserved for Future Use

   Two values, that is 0 and 1, can be set to these bits in
   OptionSupported field.  The value of 0 indicates that the sender does
   not support this subtype.  The value of 1 indicates that the sender
   supports this subtype.

4.  Security Considerations

   To be added.

5.  IANA Considerations

   To be added.

6.  References

6.1.  Normative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [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>.






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   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
              <https://www.rfc-editor.org/info/rfc6824>.

   [RFC8684]  Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
              Paasch, "TCP Extensions for Multipath Operation with
              Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
              2020, <https://www.rfc-editor.org/info/rfc8684>.

6.2.  Informative References

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              DOI 10.17487/RFC2629, June 1999,
              <https://www.rfc-editor.org/info/rfc2629>.

Authors' Addresses

   Jiao Kang (editor)
   Huawei
   D2-03,Huawei Industrial Base
   Shenzhen
   China

   Email: kangjiao@huawei.com


   Qiandeng Liang
   Huawei
   No. 207, Jiufeng 3rd Road, East Lake High-tech Development Zone
   Wuhan
   China

   Email: liangqiandeng@huawei.com

















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