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INTERNET-DRAFT                                                     X.Wei
Intended Status: Standards Track                                 C.Xiong
Expires: January 2, 2016                             Huawei Technologies
                                                                E. Lopez
                                                                Fortinet
                                                            July 1, 2015


                        MPTCP proxy mechanisms
                   draft-wei-mptcp-proxy-mechanism-02


Abstract

   Multipath TCP provides the ability to simultaneously use multiple
   paths between peers for a TCP/IP session, and it could improve
   resource usage within the network and, thus, improve user experience
   through higher throughput and improved resilience to network failure.
   This document discusses the mechanism of a new network entity, named
   MPTCP proxy, which is aimed to assist MPTCP capable peer to use MPTCP
   session in case of one of the peers not being MPTCP capable or to act
   as an aggregation point for sublfows.


Status of this Memo

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

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Copyright and License Notice




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   Copyright (c) 2015 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
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   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  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3  MPTCP Proxy models  . . . . . . . . . . . . . . . . . . . . . .  4
   4  MPTCP Proxy Solutions . . . . . . . . . . . . . . . . . . . . .  5
     4.1  Mechanisms for on-path MPTCP proxy  . . . . . . . . . . . .  5
     4.2  Mechanisms for off-path MPTCP proxy . . . . . . . . . . . .  7
   5  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6  Security Considerations . . . . . . . . . . . . . . . . . . . . 10
   7  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
   8  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1  Normative References  . . . . . . . . . . . . . . . . . . . 10
     8.2  Informative References  . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11





















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1  Introduction

   Nowadays, the volume of mobile devices, e.g. smart phone, has
   increased greatly, and most of these devices have more than one
   interface for network communication, for example it's very common for
   a smart phone to have a cellular network interface and a WLAN
   interface; at the same time, multi-homing scenarios have been more
   and more common. All these situations provide a good pre-condition
   for the implementation of MPTCP [MPTCP Protocol]. Some network
   operators also show interests in MPTCP, they want to utilize MPTCP's
   multipath feature to realize optimization of their network
   performances, such as resource pooling, network mobility etc.

   But there are still some barriers existing for the promotion of
   MPTCP, and one of them is that now almost all of the ICP (Internet
   Content Provider) servers on the Internet are traditional TCP servers
   and there seems no motivation for these traditional servers to embed
   MPTCP into their protocol stack, this situation leads to the fact
   that when communicating with these servers the MPTCP capable devices
   have to fall back to traditional TCP and cannot fully utilize their
   MPTCP capability.

   Besides, the multipath feature of MPTCP protocol brings impacts on
   the performances of some kinds of network middleboxes which are
   deployed to enhance network performance or to provide traffic
   optimization for network traffic. For example, middleboxes, such as
   HTTP proxy, video/audio optimizer and firewall are deployed enroute
   by network operators to provide performance enhancements, and all of
   these middleboxes need to have knowledge about the entire content of
   the traffic flow in order to function properly on the flow. But for
   MPTCP traffic, it is likely that only a part of subflows traverse the
   middlebox, and leads these middleboxes to be blind about the traffic,
   and the result would be that the endhost could not benefit from
   performance enhancement service or the traffic from endhost could be
   blocked by firewall because the firewall cannot trust the traffic. A
   more detailed description of MPTCP's impacts on middleboxes can be
   found in [Lopez]. For all the middlebox scenarios, we can conclude a
   basic requirement that the MPTCP traffic should be able to aggregate
   at middlebox.

   To support the use of MPTCP session between a MPTCP host and a TCP
   host, and to make MPTCP traffic get benefits from network middlebox
   that providing performance enhancement, this document defines a new
   entity named MPTCP proxy (or proxy for abbreviation).

2  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",



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   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   MPTCP proxy (proxy): An entity used to support MPTCP session between
                  MPTCP capable host and non-MPTCP capable host.

   ICP: Internet Content Provider.


3  MPTCP Proxy models

To support the use of MPTCP session between MPTCP host and TCP host, or
to help to aggregate MPTCP subflows, there are mainly two models of
proxy for different  scenarios: the first one is that the proxy is
deployed on the common direct routing path of traffic from different
access network, and this kind of proxy is referred as on-path proxy, an
example is shown in Figure 1; the second one is that the proxy locates
only on the direct routing path of traffic from one of the access
networks the MPTCP capable host attached to, and this kind of proxy is
referred as off-path proxy, an example is shown in Figure 2.

                   _.---..
                 ,'       `.
                .' Access
             +--|  Network 1|-------+
             |   `.        ,'       |
 +--------+  |     `.._,,,'         |     +--------+    +--------------+
 |Host (A)|--+                      +-----|MPTCP   |----|Host(B)       |
 |(MPTCP) |--+   ,--'''--.          +-----|Proxy(P)|    |(TCP)         |
 +--------+  | ,' Access  `.        |     +--------+    +--------------+
             +--  Network 2---------+
                          '
                `.._   _,,'
                    `''

        Figure 1: Scenario of on-path proxy deployment

For the scenario shown in Figure 1, the MPTCP capable host A has two
network interfaces and connects to two access networks simultaneously
through the two interfaces. In this case, the proxy is located on the
path shared by the two access networks' traffic, for example, the proxy
could be deployed by Host B (e.g. OTT server) side.









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                  _.---..
                ,'       `.
               .' Access             +--------+    +--------------+
            +--|  Network 1|---------|MPTCP   |----|Host(B)       |
            |   `.        ,'         |Proxy(P)|    |              |
+--------+  |     `.._,,,'           +--|-----+    +--------------+
|Host(A) |--+                           |
|        |--+   ,--'''--.               |
+--------+  | ,' Access  `.             |
            +--  Network 2.             |
                         --------------+
               `.._   _,,'
                   `''

        Figure 2: Scenario of off-path proxy deployment

For the scenario shown in Figure 2, MPTCP proxy is located only on the
direct routing path of traffic from one of the access networks the MPTCP
capable host attached to, for example, the proxy could be located at
aggregation point such as firewall. As shown in Figure 2, the MPTCP
proxy is located on the natural routing path of traffic from access
network 1, but not on the natural routing path of traffic from access
network 2, which means when host A communicates using MPTCP with host B,
the subflow through access network 2 will not be naturally routed to
MPTCP proxy.

The MPTCP communication in this scenario could occur between a MPTCP
host and a TCP host, or two MPTCP hosts.

The following sections will discuss the detailed mechanisms of on-path
proxy and off-path proxy as introduced above.

4  MPTCP Proxy Solutions

4.1  Mechanisms for on-path MPTCP proxy

When the direct routing path of all the sub-flows of a MPTCP capable
host pass through the same proxy, the proxy will act as on-path proxy,
and the on-path proxy could be transparent to the end host, i.e. end
host itself knows nothing about the existence of the proxy.











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+-------+               +--------------+            +--------------+
|Host(A)|               |MPTCP Proxy(P)|            |ICP Server(B) |
|(MPTCP)|               +--------|-----+            |(TCP)         |
+-|-----+                        |                  +-------|------+
  |-----SYN+MP_CAPABLE(Key-A)--->|--SYN+MP_CAPABLE(Key-A)-->|
  |              +---------------------------------+        |
  |              |create temp. entry for connection|        |
  |              +---------------------------------+        |
  |                              |<--------SYN+ACK ---------|
  |                       +------------+                    |
  |                       |create Key-P|                    |
  |                       +------|-----+                    |
  <--SYN+ACK+MP_CAPABLE(Key-P)---|                          |
  |                              |                          |
  -ACK+MP_CAPABLE(Key-A,Key-P)--->                          |
  |                              |---------ACK-------------->
  |                       +------------+                    |
  |<------Data----------->|Data Mapping|<----Data---------->|
  |                       +------|-----+                    |
  |                           +--|------+                   |
  |---------SYN+MP_JOIN------->         |                   |
  |                           | inspect |                   |
  <-----SYN+ACK+MP_JOIN-------- MPTCP   |                   |
  |                           | signal  |                   |
  |--- -----ACK+MP_JOIN------->  and    |                   |
  |                           |establish|                   |
  <---------ACK --------------|sub-flow |                   |
  |                           +--|------+                   |
  |                       +------------+                    |
  |<======Data===========>|Data Mapping|<----Data---------->|
  |                       +------|-----+                    |

Figure 3: On-path proxy for connection between MPTCP Host and TCP Server


The function of on-path proxy could mainly be divided into three sub-
functions: supporting for initial MPTCP capability negotiation,
supporting for sub-flow establishment and data mapping.  Figure 3 shows
an example signal flow for on-path proxy. The following clauses focus on
the description of each sub-function.

(1) Supporting for initial MPTCP capability negotiation

The MPTCP capable host starts a connection establishment procedure by
sending the first handshake packet with MP_CAPABLE option, including
Host's Key-A, to ICP server; proxy inspects the packet and creates a
temporary entry, which will be used to match SYN/ACK response from ICP
server, for the connection, then the proxy forwards the packet to ICP



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server.

(2)Supporting for sub-flow establishment

After the initial MPTCP connection established, Host could choose to
start a new MPTCP sub-flow. Because Host is unaware of the existence of
proxy, so Host will start the new sub-flow with ICP server, i.e. the
destination IP address of SYN/MP_JOIN packet is ICP server's IP address.

The proxy inspects sub-flow establishment signal packet, i.e.
SYN/MP_JOIN, and decides whether it has provided proxy function for the
MPTCP session through the token included in MP_JOIN. If proxy has
provided proxy function for the MPTCP session, then it will provide
proxy function for the sub-flow; otherwise proxy will not take any
action on the establishment of sub-flow.

(3)Data mapping

Proxy implements two separate kinds of data mapping: forward mapping and
reverse mapping. Forward mapping means mapping data from MPTCP session
to TCP session; reverse mapping means mapping data from TCP session to
MPTCP session. Figure 4 shows the data mapping function of proxy. In
forward mapping, proxy maps data from all sub-flows belonging to MPTCP
session to a single TCP flow in TCP session.

         +-----------------------+
   MPTCP |         Mapping       | TCP
+--+     | +-----+        +---+  |   +----------+
|Host|<===|>|MPTCP|<<<<>>>>|TCP|<-+-->|ICP server|
+--+     | +-----+        +---+  |   +----------+
         |proxy                  |
         +-----------------------+
Figure 4: Data mapping function of proxy

4.2  Mechanisms for off-path MPTCP proxy

When proxy locates on the initial sub-flow's direct routing path, but
some other sub-flow's direct routing path might not go through the same
proxy, then proxy could act in off-path model. The main difference
between on-path model proxy and off-path model proxy is that in off-path
model proxy needs to steer sub-flows to proxy, and Host will start new
sub-flow with proxy, but not with its peer host.









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+-------+               +--------------+            +--------------+
|Host(A)|               |MPTCP Proxy(P)|            |ICP Server(B) |
|(MPTCP)|               +--------|-----+            |(TCP)         |
+-|-----+                        |                  +-------|------+
  |-----SYN+MP_CAPABLE(Key-A)--->|--SYN+MP_CAPABLE(Key-A) ->|
  |              +---------------------------------+        |
  |              |create temp. entry for connection|        |
  |              +---------------------------------+        |
  |                              |<--------SYN+ACK ---------|
  |                       +------------+                    |
  |                       |create Key-P|                    |
  |                       +------|-----+                    |
  <--SYN+ACK+MP_CAPABLE(Key-P,P)-|                          |
  |                              |                          |
  -ACK+MP_CAPABLE(Key-A,Key-P)--->---------ACK-------------->
  |                       +------------+                    |
  |<------Data----------->|Data Mapping|<----Data---------->|
  |                       +------|-----+                    |
  |<------ADD_ADDR(proxy IP)-----|                          |
  |                           +--|------+                   |
  |------SYN+MP_JOIN---------->         |                   |
  |                           | inspect |                   |
  <-----SYN+ACK+MP_JOIN-------- MPTCP   |                   |
  |                           | signal  |                   |
  |------ACK+MP_JOIN---------->  and    |                   |
  |                           |establish|                   |
  <---------ACK --------------|sub-flow |                   |
  |                           +--|------+                   |
  |                       +------------+                    |
  |<======Data===========>|Data Mapping|<----Data---------->|
  |                       +------|-----+                    |

Figure 5:Off-path proxy for connection between MPTCP Host and TCP Server

Similar to on-path model proxy, the function of off-path proxy could
also be divided into three sub-functions: supporting for initial MPTCP
capability negotiation, supporting for sub-flow establishment and data
mapping. Figure 5 shows an example signal flow for on-path proxy.

(1) Supporting for initial MPTCP capability negotiation

The MPTCP capable Host starts a connection establishment procedure by
sending the first handshake packet with MP_CAPABLE option, including
Key-A, to ICP server; proxy inspects the packet and creates a temporary
entry, which is used by proxy to match SYN/ACK response from ICP server,
then the proxy forwards the packet to ICP server.

Proxy inspects the second handshake SYN/ACK packet from ICP server, if



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MP_CAPABLE option is included in SYN/ACK packet, then it means the ICP
server is MPTCP capable and the proxy could choose whether to act as
proxy or not for the connection, for example if the proxy wants to act
as an aggregation point for MPTCP subflow traffics then it could choose
to act proxy function for the MPTCP session; but if the purpose of proxy
is just provide MPTCP support for communication between MPTCP host and
legacy TCP host, then it could choose not to act proxy function; if no
MP_CAPABLE option is included in SYN/ACK, the proxy will generate Key-P
on behalf of ICP server to finish MPTCP connection with Host.

To avoid Host starts the establishment of sub-flow with ICP server's IP
address, proxy notifies Host the existence of itself through sending a P
flag in MP_CAPABLE option in SYN/ACK packet. When Host receives this P
flag it SHOULD NOT start the new sub-flow with ICP server's IP address
any more, but chooses to establish sub-flow with proxy after obtaining
proxy's IP address.

There are reasons why a new P flag needs to be defined for explicit
indication the existence of proxy, instead of implicitly inject the
proxy into MPTCP session using existing MPTCP signaling , e.g. using
ADD_ADDR/ADDR_JOIN to inform MPTCP host of proxy's IP address, and using
 REMOVE_ADDR to disable initial subflow between MPTCP host and its peer
host:When a new subflow is to be established, the subflow management
strategy should be considered. As stated in [MPTCP Experience], "The
subflows are created immediately after the creation of the initial
subflow", so MPTCP host might have started a new subflow before a
REMOVE_ADDR is received, due to message delay or lost of REMOVE_ADDR, in
that case the new subflow might be established between MPTCP host and
its peer host but not between MPTCP host and proxy.

(2)Supporting for sub-flow establishment

In off-path model, after MPTCP capable Host has established the initial
sub-flow in MPTCP session with the assistance of proxy, proxy could
advertise its own IP address in ADD_ADDR option to Host, and then Host
could establish new sub-flow with proxy.

(3)Data mapping

The data mapping function for off-path proxy is the same as the function
described in on-path model.

5  Conclusion

This document provides two kinds of proxy modes, which could be used to
support MPTCP capable Host in two different scenarios. For the first on-
path MPTCP proxy, there is no need to modify the current MPTCP stack
implementation of the host; for the off-path MPTCP proxy, it requires



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the MPTCP capable host needs to support a new defined P flag.

6  Security Considerations

The P flag provides a method for explicitly interpose a proxy function
in MPTCP session, but this does not bring more security risks than MPTCP
protocol itself, because even without P flag, an on-path middlebox could
still interpose it in MPTCP session using existing MPTCP protocol
signaling.


7  IANA Considerations

A new flag 'P' in MPTCP MP_CAPABLE option [MPTCP Protocol] needs to be
defined refer to RFC 6824, Section 3.1. This flag is used by proxy to
inform MPTCP capable host the existence of proxy, besides the 'P' flag
could also be used to inform other potential MPTCP proxy its presence.


                           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|P|C|D|E|F|G|H|
      +---------------+---------------+-------+-------+---------------+
      |                   Option Sender's Key (64 bits)               |
      |                                                               |
      |                                                               |
      +---------------------------------------------------------------+
      |                  Option Receiver's Key (64 bits)              |
      |                     (if option Length == 20)                  |
      |                                                               |
      +---------------------------------------------------------------+



8  References

8.1  Normative References

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

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




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8.2  Informative References

   [Deng] L.Deng, D.Liu, T.Sun. "draft-deng-mptcp-mobile-network-proxy-
              01", April 18, 2014
   [Lopez] E. Lopez. "draft-lopez-mptcp-middlebox-00", November 11, 2014
   [MPTCP Experience] O. Bonaventure et al. "draft-ietf-mptcp-
              experience-00". September 16, 2014


Authors' Addresses


   Xinpeng Wei
   Huawei Technoligies
   Beijing, China
   EMail: weixinpeng@huawei.com

   Chunshan Xiong
   Huawei Technoligies
   Beijing, China
   EMail: sam.xiongchunshan@huawei.com

   Edward Lopez
   Fortinet
   899 Kifer Road
   Sunnyvale, CA 94086
   EMail: elopez@fortinet.com
























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