Internet DRAFT - draft-kang-tcpm-subtype-capability-exchange
draft-kang-tcpm-subtype-capability-exchange
TCP Maintenance and Minor Extensions J. Kang
Internet-Draft Q. Liang
Intended status: Informational X. Fei, Ed.
Expires: 13 July 2023 Huawei
9 January 2023
Subtype Capability Exchange During MPTCP Handshake
draft-kang-tcpm-subtype-capability-exchange-02
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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 13 July 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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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
Huawei
Email: jiao_kang2022@163.com
Qiandeng Liang
Huawei
No. 207, Jiufeng 3rd Road, East Lake High-tech Development Zone
Wuhan
China
Email: liangqiandeng@huawei.com
XinCai Fei (editor)
Huawei
No. 410, Jianghong Road, Binjiang District
Hangzhou
China
Email: feixincai1@huawei.com
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