INTERNET-DRAFT X.Wei Intended Status: Standards Track C.Xiong Expires: January 1, 2015 Huawei Technologies June 30, 2014 MPTCP proxy mechanisms draft-wei-mptcp-proxy-mechanism-00 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. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright and License Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. X.Wei Expires November 20, 2014 [Page 1] INTERNET DRAFT MPTCP proxy June 30, 2014 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 carefully, as they describe your rights and restrictions with respect to this document. 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Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1 Mechanisms for on-path MPTCP proxy . . . . . . . . . . . . 5 3.2 Mechanisms for off-path MPTCP proxy . . . . . . . . . . . . 8 4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Security Considerations . . . . . . . . . . . . . . . . . . . . 11 6 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 11 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1 Normative References . . . . . . . . . . . . . . . . . . . 11 7.2 Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 X.Wei Expires November 20, 2014 [Page 2] INTERNET DRAFT MPTCP proxy June 30, 2014 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 one cellular network interface and one 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]. But there are still some barriers existing for the promotion of MPTCP, and one of them is that now all most all of the ICP 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. 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. To support MPTCP capable mobile devices, to use MPTCP to communicate with traditional ICP servers through mobile network, a new entity named MPTCP proxy (or proxy for abbreviation) is introduced into mobile network and the deployment models of proxy are discussed in [Deng]. This document goes more detail into the mechanisms of the proxy mentioned in [Deng], and in the following sections we mainly discuss how proxy could be implemented to support the a common scenario that the communication is between MPTCP capable host (e.g. mobile device) and non-MPTCP capable host (e.g. ICP server), and other scenarios such as CPE scenario in [Deng] will be discussed in the latter version. 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 RFC 2119 [RFC2119]. MPTCP proxy (proxy): An entity used to support MPTCP session between MPTCP capable host and non-MPTCP capable host. UE: User Equipment. ICP: Internet Content Provider. X.Wei Expires November 20, 2014 [Page 3] INTERNET DRAFT MPTCP proxy June 30, 2014 3 Solutions As discussed in [Deng], MPTCP proxy is introduced to provide supports for MPTCP capable host to communicate using MPTCP with non-MPTCP capable host. There are mainly two models of proxy for different network 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, 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, shown in Figure 2. _.---.. ,' `. .' 3GPP +--| Cellular|-------+ | `. ,' | +--------+ | `.._,,,' +-|-+ +--------+ +--------------+ |UE(A) |--+ |PGW|---|MPTCP |----|ICP Server(B) | |(MPTCP) |--+ ,--'''--. +- -+ |Proxy(P)| |(TCP) | +--------+ | ,' `. | +--------+ +--------------+ +-- WLAN ---------+ ' `.._ _,,' `'' Figure 1: Scenario of on-path proxy deployment For the scenario shown in Figure 1, MPTCP capable UE communicates with non-MPTCP capable ICP server locating on Internet. The 3GPP cellular network and WLAN network are deployed by single network operator, and the MPTCP capable UE supports both 3GPP cellular network interface and WLAN network interface, in this case operator could locate the proxy on the path shared by both 3GPP cellular network traffic and WLAN network traffic. X.Wei Expires November 20, 2014 [Page 4] INTERNET DRAFT MPTCP proxy June 30, 2014 _.---.. ,' `. .' 3GPP +--| Cellular|-------+ | `. ,' | +--------+ | `.._,,,' +-|-+ +--------+ +-------------+ |UE(A) |--+ |PGW|---|MPTCP |----|ICP Server(B)| |(MPTCP) |--+ ,--'''--. +- -+ |Proxy(P)| |(TCP) | +--------+ | ,' `. +--|-----+ +-------------+ +-- WLAN . | ------------------+ `.._ _,,' `'' Figure 2: Scenario of off-path proxy deployment For the scenario shown in Figure 2, only the 3GPP cellular network is deployed by a mobile network operator, and the WLAN network is deployed by other operator, e.g. another fixed-line operator. In this case, the mobile network operator could only locate the proxy on the direct routing path 3GPP cellular network traffic. The following sub-sections will discuss the detailed mechanisms of on- path proxy and off-path proxy as introduced above. 3.1 Mechanisms for on-path MPTCP proxy When the direct routing path of all the sub-flows of a MPTCP capable UE pass through the same proxy, the proxy will act as on-path proxy, and the on-path proxy is transparent to UE, i.e. UE itself knows nothing about the existence of the proxy. X.Wei Expires November 20, 2014 [Page 5] INTERNET DRAFT MPTCP proxy June 30, 2014 +-------+ +--------------+ +--------------+ |UE(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 UE 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, as shown in Figure 3. The following clauses focus on the description of each sub- function. (1) Supporting for initial MPTCP capability negotiation The MPTCP capable UE starts a connection establishment procedure by sending the first handshake packet with MP_CAPABLE option, including UE's Key-A, to ICP server; proxy inspects the packet and creates a temporary entry consisting of UE IP, Server IP, UE port number and Server port number for the connection, then the proxy forwards the X.Wei Expires November 20, 2014 [Page 6] INTERNET DRAFT MPTCP proxy June 30, 2014 packet to ICP server. UE IP, server IP, UE port number and server port number are used by proxy to match SYN/ACK response from ICP server. Proxy inspects the second handshake SYN/ACK packet from ICP server, if MP_CAPABLE option is included in SYN/ACK packet, then it means the ICP server is MPTCP capable and the proxy doesn't need to act as proxy for the connection and the temporary entry for the connection will be removed; 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 UE and the temporary entry will be sustained for the connection to record all of the sub-flows belonging to the connection, the token as described in [MPTCP Protocol] is used to identify the entry. An example of the entry is shown in Table 1. In table 1, the server's IP addresses and port numberes for different sub-flows could be the same. +------------+----------------------------------------+ | ID | token | |------------+----------------------------------------| | sub-flow#1 |UE IP1,UE port1,server IP1,server port1 | |------------+----------------------------------------| | sub-flow#2 |UE IP2,UE port2,server IP2,server port2 | +------------+----------------------------------------+ Table 1: An example of entry for connection (2)Supporting for sub-flow establishment After the initial MPTCP connection established, UE could choose to start a new MPTCP sub-flow. Because UE is unaware of the existence of proxy, so UE 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 and add UE IP, Server IP, UE port number and Server port number to the entry for the connection; otherwise proxy will not taken any action on the establishment of sub-flow. (3)Data mapping Proxy implements two separate kind 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. X.Wei Expires November 20, 2014 [Page 7] INTERNET DRAFT MPTCP proxy June 30, 2014 +-----------------------+ MPTCP | Mapping | TCP +--+ | +-----+ +---+ | +----------+ |UE|<====|>|MPTCP|<<<<>>>>|TCP|<-+-->|ICP server| +--+ | +-----+ +---+ | +----------+ |proxy | +-----------------------+ Figure 4: 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. Because the IP addresses in packet of both MPTCP session and TCP session are not proxy's IP address, so proxy needs to inspect the packet to decide whether the packet belongs to the connection between UE and ICP server. 3.2 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 will 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 explicitly steer sub-flows to proxy, and MPTCP capable UE is aware of the existence of proxy. UE will start new sub- flow with proxy, but not with ICP server. X.Wei Expires November 20, 2014 [Page 8] INTERNET DRAFT MPTCP proxy June 30, 2014 +-------+ +--------------+ +--------------+ |UE(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 UE 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. (1) Supporting for initial MPTCP capability negotiation The MPTCP capable UE 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 consisting of UE IP, Server IP, UE port number, and Server port number,for the connection, then the proxy forwards the packet to ICP server. UE IP, server IP, UE port number and server port number are used by proxy to match SYN/ACK response from ICP server. X.Wei Expires November 20, 2014 [Page 9] INTERNET DRAFT MPTCP proxy June 30, 2014 Proxy inspects the second handshake SYN/ACK packet from ICP server, if MP_CAPABLE option is included in SYN/ACK packet, then it means the ICP server is MPTCP capable and the proxy doesn't need to act as proxy for the connection and the temporary entry for the connection will be removed; 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 UE and the temporary entry will be sustained for the connection to record all of the sub-flows belonging to the connection, the token as described in [MPTCP Protocol] is used to identify the entry. To avoid UE starts the establishment of sub-flow with ICP server's IP address, proxy notifies UE the existence of itself through sending a P flag in MP_CAPABLE option in SYN/ACK packet. When UE 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. (2)Supporting for sub-flow establishment In off-path model, after MPTCP capable UE 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 UE, and then UE 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. X.Wei Expires November 20, 2014 [Page 10] INTERNET DRAFT MPTCP proxy June 30, 2014 4 Conclusion This document provides two kinds of proxy modes, which could be used to support MPTCP capable UE 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 the MPTCP capable host needs to support a new defined P flag. 5 Security Considerations The introduction of implicit proxies and anchors does not add new principal vulnerabilities. 6 IANA Considerations A new flag 'P' in MPTCP MP_CAPABLE option 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. 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) | | | +---------------------------------------------------------------+ 7 References 7.1 Normative References [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [MPTCP Protocol]Ford, A., Raiciu, C., Handley, M., and O. Bonaventure, "TCP Extensions for Multipath Operation with Multiple Addresses", RFC 6824, January 2013. 7.2 Informative References [Deng] L.Deng, D.Liu, T.Sun. "draft-deng-mptcp-mobile-network-proxy- 01", April 18, 2014 X.Wei Expires November 20, 2014 [Page 11] INTERNET DRAFT MPTCP proxy June 30, 2014 Authors' Addresses Xinpeng Wei EMail: weixinpeng@huawei.com Chunshan Xiong EMail: sam.xiongchunshan@huawei.com X.Wei Expires November 20, 2014 [Page 12]