IETF P. McCann, Ed. Internet-Draft J. Kaippallimalil Intended status: Informational Huawei Expires: September 8, 2015 March 7, 2015 Communicating Prefix Cost to Mobile Nodes draft-mccann-dmm-prefixcost-00 Abstract In a network implementing Distributed Mobility Management, it has been agreed that Mobile Nodes (MNs) should exhibit agility in their use of IP addresses. For example, an MN might use an old address for ongoing socket connections but use a new, locally assigned address for new socket connections. Determining when to assign a new address, and when to release old addresses, is currently an open problem. Making an optimal decision about address assignment and release must involve a tradeoff in the amount of signaling used to allocate the new addresses, the amount of utility that applications are deriving from the use of a previously assigned address, and the cost of maintaining an address that was assigned at a previous point of attachment. As the MN moves farther and farther from the initial point where an address was assigned, more and more resources are used to redirect packets destined for that IP address to its current location. The MN currently does not know the amount of resources used as this depends on mobility path and internal routing topology of the network(s) which are known only to the network operator. This document provides a mechanism to communicate to the MN the cost of maintaining a given prefix at the MN's current point of attachment so that the MN can make better decisions about when to release old addresses and assign new ones. 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." McCann & Kaippallimalil Expires September 8, 2015 [Page 1] Internet-Draft Prefix Cost March 2015 This Internet-Draft will expire on September 8, 2015. Copyright Notice 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 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4 2. Prefix Cost Sub-option . . . . . . . . . . . . . . . . . . . 4 3. Host Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 6.1. Normative References . . . . . . . . . . . . . . . . . . 5 6.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction Previous discussions on address agility in distributed mobility management have focused on "coloring" prefixes with one of a small number of categories, such as Fixed, Sustained, or Nomadic. The assumption here is that the MN should use a permanent home address for sessions that need a persistent IP address, and a local, ephemeral address for short-lived sessions such as browsing. However, a small set of address categories lacks expressive power and leads to false promises being made to mobile nodes. For example, the concept that a home address can be maintained permanently and offered as an on-link prefix by any access router to which the MN may be attached in future is simply not attainable in the real world. There will always exist some access routers that do not have arrangements in place with the home network to re-route (via tunneling or other mechanisms) the home prefix to the current point of attachment. McCann & Kaippallimalil Expires September 8, 2015 [Page 2] Internet-Draft Prefix Cost March 2015 Conversely, the assumption that a Nomadic prefix will never be available to an MN after it changes its current point of attachment is too limiting. There is no reason why an MN should not be able to keep a prefix that was assigned by a first network after it moves to a second network, provided that measures are put in place to re-route such prefixes to the new attachment point. Rather, this document argues that there is in reality a continuum of cost associated with an address as the MN moves from one attachment point to another or from one network to another. The sources of the cost are the increased latency, network bandwidth, and network state being maintained by a network-based mobility management scheme to route packets destined to the prefix to the MN's current point of attachment. By communicating this cost to the MN every time its attachment point changes, the MN can make intelligent decisions about when to release old addresses and when to acquire new ones. The cost should be communicated to the MN because of several constraints inherent in the problem: (1) The MN is the entity that must make decisions about allocating new addresses and releasing old ones. This is because only the MN has the information about which addresses are still in use by applications or have been registered with other entities such as DNS servers. (2) Only the network has information about the cost of maintaining the prefix in a network-based mobility management scheme, because the MN cannot know the network topology that gives rise to the inefficiencies. If the cost of maintaining a prefix is not made available to the mobile node, it may attempt to infer the cost through heuristic mechanisms. For example, it can measure increased end-to-end latency after a mobility event, and attribute the increased latency to a longer end-to-end path. However, this method does not inform the MN about the network bandwidth being expended or network state being maintained on its behalf. Alternatively, a MN may attempt to count mobility events or run a timer in an attempt to guess at which older prefixes are more costly and in need of being released. However, these methods fail because the number of mobility events is not an indication of how far the MN has moved in a topological sense from its original attachment point which is what gives rise to the costs outlined above. Re-allocating an address upon expiration of a timer may introduce uneccessary and burdensome signaling load on the network and air interface. McCann & Kaippallimalil Expires September 8, 2015 [Page 3] Internet-Draft Prefix Cost March 2015 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 [1]. 1.2. Abbreviations MN Mobile Node MPTCP Multi-Path Transmission Control Protocol ND Neighbor Discovery PIO Prefix Information Discovery SeND Secure Neighbor Discovery 2. Prefix Cost Sub-option This document defines a prefix cost option to be carried in router advertisements. It is a sub-option that carries meta-data as defined by Korhonen et al. [7] 0 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TBD1 | 1 |C| Reserved1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Cost | Reserved2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Prefix Cost suboption The prefix cost is carried as a 16-bit, unsigned number in network byte order. An higher number indicates an increased cost. 3. Host Considerations Prefix Cost in a Router Advertisement PIO serves as a hint for the MN to use along with application type, MN policy configuration on network cost and available alternative routes to determine the IP addresses and routes used. For example, if the application is downloading a large file, it may want to maintain an IP address and route until the download is complete. On the other hand, some applications may use multiple connections (e.g., with MPTCP) and may not want to maintain an IP address above a configured cost. It could also be the case that the MN maintains the IP address even at high cost if there is no alternative route/address. These decisions are made based on configured policy, and interaction with applications, all of which are internal to the MN and outside the scope of this memo. McCann & Kaippallimalil Expires September 8, 2015 [Page 4] Internet-Draft Prefix Cost March 2015 When the MN is ready to release an IP address, it may send a DHCPv6 [5] Release message. The network may also monitor the status of a high cost connection with Neighbor Unreachability Detection (NUD) [2], [6], and determine that an address is not used after the NUD timeout. The network should not continue to advertise this high cost route following the explicit release of the address or NUD timeout. It can initiate the release of network resources dedicated to providing the IP address to the MN. 4. Security Considerations Security of the prefix cost option in the PIO needs to be considered. Neighbor Discovery (ND) and Prefix Information Option (PIO) security are described in [2] and [3]. A malicious node on a shared link can advertise a low cost route in the prefix cost option and cause the MN to switch. Alternatively, an incorrect higher cost route in the prefix cost option can result in the suboptimal use of network resources. In order to avoid such on-link attacks, SeND [4] can be used to reject Router Advertisements from nodes whose identities are not validated. 5. IANA Considerations This memo defines a new Prefix Information Option (PIO) sub-option in Section 2. 6. References 6.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [3] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, November 2005. [4] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [5] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. McCann & Kaippallimalil Expires September 8, 2015 [Page 5] Internet-Draft Prefix Cost March 2015 [6] Nordmark, E. and I. Gashinsky, "Neighbor Unreachability Detection Is Too Impatient", RFC 7048, January 2014. 6.2. Informative References [7] Korhonen, J., Patil, B., Gundavelli, S., Seite, P., and D. Liu, "IPv6 Prefix Properties", draft-korhonen-6man-prefix- properties-02 (work in progress), July 2013. Authors' Addresses Peter J. McCann (editor) Huawei 400 Crossing Blvd, 2nd Floor Bridgewater, NJ 08807 USA Phone: +1 908 541 3563 Email: peter.mccann@huawei.com John Kaippallimalil Huawei 5340 Legacy Dr., Suite 175 Plano, TX 75024 USA Email: john.kaippallimalil@huawei.com McCann & Kaippallimalil Expires September 8, 2015 [Page 6]