Internet Engineering Task Force R. Winter Internet-Draft A. Ripke Intended status: Informational NEC Laboratories Europe Expires: September 8, 2011 March 7, 2011 Multipath TCP Support for Single-homed End-systems draft-wr-mptcp-single-homed-00 Abstract Multipath TCP relies on the existence of multiple paths at the end- systems. While this scenario is certainly becoming increasingly a reality (e.g. mobile devices), currently most end-systems are single- homed (e.g. residential broadband customers). This memo describes mechanisms to make multiple paths available to multipath TCP that are not available at the end-systems but somewhere within the network. This can be thought of as a form of proxy multi-homing. 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 http://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 September 8, 2011. Copyright Notice Copyright (c) 2011 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 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 Winter & Ripke Expires September 8, 2011 [Page 1] Internet-Draft single-homed MPTCP March 2011 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. General Operation . . . . . . . . . . . . . . . . . . . . . . . 4 3. Other scenarios and extensions . . . . . . . . . . . . . . . . 5 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Winter & Ripke Expires September 8, 2011 [Page 2] Internet-Draft single-homed MPTCP March 2011 1. Introduction The IETF is specifying a multipath TCP (MPTCP) architecture and protocol where end-systems operate a modified standard TCP stack which allows packets of the same TCP connection to be sent via different paths to a MPTCP-capable destination ([I-D.ietf-mptcp-multiaddressed], [I-D.ietf-mptcp-architecture]). Using multiple paths has a number of benefits such as an increased reliability of the transport connection and an effect known as resource pooling [resource_pooling]. Most end-systems today do not have multiple paths available in order to make use of multipath TCP, however further within the network multiple paths are the norm rather than the exception. This memo therefore describes a way how a network element that is multi-homed can somehow "extend" this multi- homing to end-systems and act as a kind of multi-homing proxy for the end-system, providing the multipath TCP benefits starting at that network element. In order to illustrate the general mechanism we make use of a simple reference scenario shown in Figure 1. +-------+ | DHCP | +-------+ +----------+ Server| | | | | | | Host +------+ +-------+ | | | +-------+ ISP 1 +-------+ +------+ |---------- | Gatew.| | |---------- +-------+ ISP 2 Figure 1: Reference Scenario The scenario in Figure 1 depicts e.g. a possible SOHO or enterprise setup where a gateway/router is connected to two ISPs and a DHCP server gives out leases to hosts connected to the local network. Both, the gateway and the DHCP server could be on the same device (similar to current home gateway implementations). The host is running a multipath-capable IP stack, however it only has a single interface. The method described in the following sections is to let the host make use of the gateway's two interfaces without requiring modifications to the MPTCP implementation. Winter & Ripke Expires September 8, 2011 [Page 3] Internet-Draft single-homed MPTCP March 2011 2. General Operation Multipath TCP distinguishes paths by their source and destination IP addresses. Assuming a certain level of path diversity in the Internet, using different source and destination IP addresses for a given subflow of a multipath TCP connection will, with a certain probability, result in different paths taken by packets of different subflows. Even in case subflows share a common bottleneck, the proposed multipath congestion control algorithm will make sure that multipath TCP will play nicely with regular TCP flows. In order to not impact the TCP implementation, we keep the above assumptions multipath TCP makes, i.e. working with different IP addresses to use different paths. Since the end-system is single- homed, all IP addresses are bound to the same physical interface. In our reference scenario in Figure 1, the host would receive more than one RFC1918 [RFC1918] private IP address from the DHCP server. Host Gateway +-----------------+ ISP1 +--------+ | src. | | virt. | 10.1.2.5 | 10.1.0.0/16 __.+---------- | +---+ | __.--' | | phys. | | | __.--' N | | +----------+.:_ A | | | 10.2.2.6 | `-.._ T | +--------+ | src. `-.._ | ISP2 | 10.2.0.0/16 `-..+---------- | | +-----------------+ | Figure 2: Gateway internals The gateway in the figure has received two IP addresses, one from each ISP. The NAT that the gateway is implementing needs to map each private IP address of the host consistently to a one of the addresses, each private IP to a different public IP. The way the gateway funtions is depicted in more detail in Figure 2. This way, depending on the source address of the host, the packets will either go through ISP 1 or ISP 2 and TCP will balance the traffic across those two links using its built-in congestion control mechanism. The way the gateway has received it's public IP addresses is not relevant. It could be via via DHCP, IPCP or static configuration. In order to configure the host via DHCP, we propose two new DHCP options. The first option "mp-proxy-avail" will be sent by single- homed multipath TCP-enabled clients in the "Parameter Request List". Winter & Ripke Expires September 8, 2011 [Page 4] Internet-Draft single-homed MPTCP March 2011 This will show the DHCP server that the client is multipath-capable. The DHCP server will answer with "mp-proxy-avail" and the option value is set to the number of additional interfaces the gateway can offer to the client (in our reference scenario that value would be 1; see Figure 3). client server | request mp-proxy-avail | |--------------------------------------------------- >| | mp-proxy-avail 1 + other config | |< ---------------------------------------------------| | | |------+ | | | configure physical and | | | create virtual interface | | | | |< ----+ | | | | virt. interf. 1 | | | send mp-range 1 | | |-------------------------------------------- >| | | virt. interface config | | |< --------------------------------------------| | | | | | | Figure 3: DHCP Sequence Diagram Upon receipt of the "mp-proxy-avail" option from the server, the client can create up to n virtual interfaces, where n is the option value. Each virtual interface will contact the DHCP server and will include the "mp-range" option. The option value will tell the DHCP server that the client is requesting an IP out of an IP range that the gateway will be forwarding through a different interface. The above has been implemented using the ISC DHCP server and client version 4.2.1 and the multipath TCP kernel patch 0.5 and a 2.6.36 Linux kernel. 3. Other scenarios and extensions The reference scenario is only one conceivable setting. Other scenarios such as DSL broadband customers or mobile phones are conceivable as well. As an example, take the DSL scenario. The home gateway could be provided with multiple IP addresses using extensions to IPCP. The home gateway in turn can then implement the DHCP server Winter & Ripke Expires September 8, 2011 [Page 5] Internet-Draft single-homed MPTCP March 2011 and gateway functionality as described before. These scenarios will be described in future versions of this document. 4. Acknowledgements The authors are supported by Trilogy (http://www.trilogy-project.org), a research project (ICT-216372) partially funded by the European Community under its Seventh Framework Program. The views expressed here are those of the author(s) only. The European Commission is not liable for any use that may be made of the information in this document. 5. IANA Considerations Two new DHCP options are required by this version of this document. 6. Security Considerations TBD. 7. References 7.1. Normative References [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. 7.2. Informative References [I-D.ietf-mptcp-architecture] Ford, A., Raiciu, C., Handley, M., Barre, S., and J. Iyengar, "Architectural Guidelines for Multipath TCP Development", draft-ietf-mptcp-architecture-05 (work in progress), January 2011. [I-D.ietf-mptcp-multiaddressed] Ford, A., Raiciu, C., and M. Handley, "TCP Extensions for Multipath Operation with Multiple Addresses", draft-ietf-mptcp-multiaddressed-02 (work in progress), October 2010. [resource_pooling] Wischik, D., Handley, M., and M. Bagnulo Braun, "The Winter & Ripke Expires September 8, 2011 [Page 6] Internet-Draft single-homed MPTCP March 2011 Resource Pooling Principle", October 2008, . Authors' Addresses Rolf Winter NEC Laboratories Europe Kurfuersten-Anlage 36 Heidelberg 69115 Germany Email: rolf.winter@neclab.eu Andreas Ripke NEC Laboratories Europe Kurfuersten-Anlage 36 Heidelberg 69115 Germany Email: andreas.ripke@neclab.eu Winter & Ripke Expires September 8, 2011 [Page 7]