Network Working Group M. Boucadair
Internet-Draft C. Jacquenet
Intended status: Experimental Orange
Expires: May 28, 2017 November 24, 2016
Negotiating the Maximum Number of Multipath TCP (MPTCP) Subflows
draft-boucadair-mptcp-max-subflow-03
Abstract
This document specifies an experimental Multipath TCP (MPTCP) option
that is meant to negotiate the maximum number of subflows that can be
established and maintained for a given MPTCP connection. The purpose
is to minimize any possible performance degradation that can be
induced by a possibly large number of establishment requests for
additional subflows if the remote endpoint is not appropriately
dimensioned to handle such requests.
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].
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 May 28, 2017.
Copyright Notice
Copyright (c) 2016 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. Experiment Goals . . . . . . . . . . . . . . . . . . . . 3
2. Maximum Subflows MPTCP Option (MP_MAXSUBFLOW) . . . . . . . . 3
3. Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
This document specifies a Multipath TCP (MPTCP) [RFC6824] option that
is meant to indicate to a remote peer the maximum number of subflows
that can be established within a single MPTCP connection. If the
remote peer honors the indication provided in this option, any
performance degradation induced by a possibly abusive setup of
additional subflows that exceed the said maximum becomes unlikely.
This option mainly targets MPTCP deployments within a single
administrative domain such as those MPTCP designs meant to achieve
load-balancing, for example. The use of this option contributes to
the harmonization of node configuration within an administrative
domain, so that an optimal number of subflows is maintained by
involved nodes independently of their actual performance
capabilities. This option can be used in other deployment scenarios.
It is out of scope of this document to identify what are such
scenarios.
Section 3.4 of [I-D.ietf-mptcp-experience] includes a discussion on
the MPTCP session manager issues. That document states that creating
subflows between multihomed clients and servers may sometimes lead to
operational issues. The present document targets to soften these
issues.
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1.1. Experiment Goals
Experiments based upon the MPTCP option described in this document
are meant to help operators optimize their MPTCP design and
operational procedures, by tweaking some MPTCP parameters such as the
number of subflows to be associated with a given MPTCP connection.
Experimenting with this MPTCP option should also help assess whether
this option can be used to propagate MPTCP-related optimization
parameters (derived from the number of concurrent subflows associated
to each MPTCP connection) that can be configured in a node that is
responsible for aggregating MPTCP connections established with
upstream nodes.
2. Maximum Subflows MPTCP Option (MP_MAXSUBFLOW)
The MP_MAXSUBFLOW option (Figure 1) follows the shared experimental
format defined in [I-D.ietf-mptcp-rfc6824bis].
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| Flags | Experiment Id |
+---------------+---------------+-------+-------+---------------+
| Maximum Subflows |
+---------------+-----------------------------------------------+
Figure 1: Option Format
The meaning of "Kind", "Length", "Subtype", and "Flags" (especially
'S' and 'U' flags) are exactly the same as defined in Section 3.7 of
[I-D.ietf-mptcp-rfc6824bis].
Experiment ID MUST be set to 0xAA (see Section 5).
The "Maximum Subflows" field indicates the maximum number of
concurrent subflows that can be maintained by a given MPTCP endpoint
for each MPTCP connection established by or with this endpoint. The
value of this field MUST be strictly greater than zero.
3. Behavior
The MP_MAXSUBFLOW option may be used by a TCP endpoint to indicate to
its corresponding peer the maximum number of subflows that it can
maintain per MPTCP connection.
How an MPTCP endpoint determines the maximum number of concurrent
subflows it supports (i.e., the value it indicates in an
MP_MAXSUBFLOW option) is implementation-specific. For example, an
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implementation may support a configuration parameter and/or use a
default value.
If two peers (T1 and T2) indicate the maximum number of concurrent
subflows per connection they can maintain, then they MUST NOT
maintain more than "MIN(MAX_SUBFLOW(T1), MAX_SUBFLOW(T2))" concurrent
subflows.
The absence of the MP_MAXSUBFLOW option in an MPTCP control message
issued by a MPTCP endpoint is an indication that this endpoint can
instantiate any number of subflows per MPTCP connection.
4. Security Considerations
MPTCP-related security considerations are documented in [RFC6824] and
[RFC7430].
Establishing a large number of subflows may exhaust the resources of
an MPTCP implementation (especially, MPTCP servers). MPTCP
implementations SHOULD rate-limit the number of concurrent subflows
per MPTCP connection. This policy is meant to prevent DoS attacks
that would result in creating additional subflows to exhaust the
remote peer resources (typically, an MPTCP server).
5. IANA Considerations
This document uses the experiment Id (0xAA). This Id is not
registered yet given that no registry is maintained by IANA for this
purpose.
6. References
6.1. Normative References
[I-D.ietf-mptcp-rfc6824bis]
Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", draft-ietf-mptcp-rfc6824bis-07 (work
in progress), October 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://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,
<http://www.rfc-editor.org/info/rfc6824>.
6.2. Informative References
[I-D.ietf-mptcp-experience]
Bonaventure, O., Paasch, C., and G. Detal, "Use Cases and
Operational Experience with Multipath TCP", draft-ietf-
mptcp-experience-07 (work in progress), October 2016.
[RFC7430] Bagnulo, M., Paasch, C., Gont, F., Bonaventure, O., and C.
Raiciu, "Analysis of Residual Threats and Possible Fixes
for Multipath TCP (MPTCP)", RFC 7430,
DOI 10.17487/RFC7430, July 2015,
<http://www.rfc-editor.org/info/rfc7430>.
Authors' Addresses
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Christian Jacquenet
Orange
Rennes 35000
France
Email: christian.jacquenet@orange.com
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