Mobile IP Working Group Jahanzeb Faizan Internet-Draft Hesham El-Rewini Expires: May, 2004 Southern Methodist University Mohammad Khalil Nortel Networks November, 2003 Problem Statement: Home Agent Reliability draft-jfaizan-mipv6-ha-reliability-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract In Mobile-IPv6, Mobile Node is dependent on a single Home Agent for the seamless roaming over the Internet. Mobile-IPv6 also allows deployment of multiple Home Agents on the subnet for providing continuous service to Mobile Node in case of serving Home Agent failure. But switching of service from the failed Home Agent to another functional Home Agent on the Home Subnet is problematic and the base Mobile-IPv6 specifications does not currently have well-described solutions. This document aims to describe and illustrate these problems, and propose some guidelines for possible solutions. Faizan. Expires May, 2004 [Page 1] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Overview of the Problem . . . . . . . . . . . . . . . . . 3 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. Mobile-IPv6 Deployment Scenario . . . . . . . . . . . . . . . .5 3. Problem statement . . . . . . . . . . . . . . . . . . . . . . .5 3.1 Failure Detection . . . . . . . . . . . . . . . . . . . . 5 3.2 IPsec Security Association with new Home Agent . . . . . .6 4. Solution Guidelines . . . . . . . . . . . . . . . . . . . . . .7 4.1 Security Implications . . . . . . . . . . . . . . . . . . 7 4.2 IPsec Security with new Home Agent . . . . . . . . . . . .7 4.3 Seamless failure . . . . . . . . . . . . . . . . . . . . .7 4.4 Mobile Node functionality . . . . . . . . . . . . . . . . 7 4.5 Messages over air interface . . . . . . . . . . . . . . . 7 4.6 Home Agent addition and failure . . . . . . . . . . . . . 7 4.7 Scalability . . . . . . . . . . . . . . . . . . . . . . . 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . .10 Faizan. Expires May, 2004 [Page 2] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 1. Introduction Mobile-IPv6[1] is designed to allow a Mobile Node to change its point of IP subnet attachment in the Internet at the network or IP layer. The Mobile Node is always identified by it Home Address regardless of its current network location. Its mobility is not limited by conventional IP network boundaries. The Mobile-IPv6 system consists of Mobile Node and Home Agent. Home Agent remains at conventional IPv6 subnet called the Home Subnet and when the Mobile Node is at the Home Subnet then the packets sent to it are routed through conventional IPv6[5] routing mechanism. When the Mobile Node is not at Home Subnet it registers its remote point of attachment address called Care of Address with the Home Agent. This allows Home Agent to forward packets, addressed to the Mobile Node at its Home Network, to its current location. In Mobile-IPv6 system, as currently specified, a single Home Agent services Mobile Node(s). Mobile-IPv6 also allows deployment of multiple Home Agents on the same subnet so that if the serving Home Agent fails then any other Home Agent on the subnet can provide service to the Mobile Node. The goal of this draft is to: o Articulate the problems resulting from the failure of a serving Home Agent and switching of service to another Home Agent. o Specify a set of framework guidelines to evaluate proposed solutions. 1.1 Overview of the Problem In Mobile-IPv6[1], Mobile Node registers and establish a connection with only one Home Agent which provides continuous service to it. The Mobile Node is reliant on this Home Agent for its connectivity. Thus the Home Agent represents the possibility of a single point of failure for Mobile-IPv6. A Home Agent may be responsible for multiple Mobile Nodes on the Home Subnet. The failure of a single Home Agent may then result in the loss of connectivity for numerous Mobile Nodes located throughout the Internet. Thus the Home Agent and Mobile Node taken together have a shared fate. A Mobile Node cannot afford the loss of its Home Agent. To overcome this problem Mobile-IPv6 allows deployment of multiple Home Agents on the Home Subnet so that upon the failure of serving Home Agent, another Home Agent can take over the functions of failed Home Agent and thus provide continuous service to the Mobile Node(s) registered with failed Home Agent. This transfer of service from the failed Home Agent to a new working Home Agent is problematic and the current specification of Mobile-IPv6 [1] Faizan. Expires May, 2004 [Page 3] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 does not provide solution to these problems. 1.2 Terminology Mobile-IPv6 Mobile IP for IPv6 [1] Mobile Node A node that can change its point of attachment from one link to another, while still being reachable via its home address. IP Internet Protocol Version 6 (IPv6).[5] Home Address A unicast routable address assigned to a Mobile Node, used as the permanent address of the Mobile Node. This address is within the Mobile Node's Home Subnet. Conventional IPv6 routing mechanisms will deliver packets destined for a Mobile Node's Home Address to its Home Subnet. Home Network A network, possibly virtual, having a network prefix matching that of a Mobile Node's Home Address. Home Agent A router on a Mobile Node's Home Network which tunnels datagrams for delivery to the Mobile Node when it is away from home, and maintains current location information for the Mobile Node. Care of Address A unicast routable address associated with a Mobile Node while visiting a foreign network. IPsec Security Association An IPSec security association is a cooperative relationship formed by the sharing of cryptographic keying material and associated context. Security associations are simplex. That is, two security associations are needed to protect bidirectional traffic between two nodes, one for each direction. Registration The process during which a Mobile Node sends a Binding Update to its Home Agent causing a binding for the Mobile Node to be registered. Faizan. Expires May, 2004 [Page 4] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 The keywords "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 [6]. 2. Mobile-IPv6 Deployment Scenario This section describes a basic deployment scenario where multiple Home Agents, referred as HAs 1..n, have to coexist on the same Home Subnet to provide continuous service to Mobile Node (MN) in case of failure of the serving Home Agent. Mobile Node runs both Mobile-IPv6 Mobile Node functionality along with IPsec client software. Also all the HAs 1..n run Mobile-IPv6 Home Agent functionality along with IPsec server software. Initially MN is registered and have IPv6 tunnel with HA_1. ..Foreign Network.. ......Home Network............ . . . . . +----+ . . +-------+ . . |MN | .<=========> . | HA_1 | . . | | . . +-------+ +-------+ . . +----+ . . ..... | HA_n | . . . . +-------+ +-------+ . . . . | HA_2 | . . . . +-------+ . ................... .............................. Figure 1 3. Problem statement This section uses the scenario discussed in section 2 to describe the problems associated with the failure of serving Home Agent and as the result of this switching of service to another Home Agent on the subnet. Consider the failure of HA_1. and switching of service to a new HA_x (where x = 2..n) on the same subnet. This whole process of failure and switching is problematic. The problems are discussed in the following sub-sections. 3.1 Failure Detection Transfer of service from the failed HA_1 to new HA_x will occur after the detection of failure by MN. MN could detect the failure of HA_1 under certain conditions. These are listed below. Faizan. Expires May, 2004 [Page 5] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 o When MN sends Binding Update(BU) message to the failed HA_1 and does not receive matching Binding Acknowledgment(BA) message, it will retransmit BUs until timeout occurs. Upon this MN will come to know about the failure of HA_1. o Similarly when MN sends Mobile Prefix Solicitation(PS) message to the failed HA_1 and does not receive Mobile Prefix Advertisement, it will retransmit PSs until timeout occurs and that's how it will come to know that HA_1 has failed. According to Mobile-IPv6[1] MN after sending first BU or PS message to failed HA_1 will wait for a initial timeout period which is set to INITIAL_BINDACK_TIMEOUT (1 second) in case of BU and INITIAL_SOLICIT_TIMER (3 seconds) in case of PS. This timeout period will be doubled for each subsequent BU or PS message until value of MAX_BINACK_TIMEOUT (32 seconds) is reached. MN MAY send infinite BUs or PSs to failed HA_1 before the final timeout occurs. So the detection of failed HA_1 will be delayed by a considerable amount of time. Also there will be many useless messages transmitted over the air interface during this period. Moreover BU and PS are not periodic rather on demand. MN will send BU only to register new Care of Address or to extend the lifetime of existing registration with its serving Home Agent. Similarly MN will send PS only when its serving Home Agent's address is about to become invalid. As a result MN will suffer packet loss and disconnectivity problems. This could have noticeable performance implications on real-time applications. 3.2 IPsec Security Association with new Home Agent Once the failure is detected, MN will try to register its Care of Address with any other Home Agent on the subnet. For this MN must know which other Home Agents are available on the subnet. MN MAY start Dynamic Home Agent Discovery(DHAD)[1] protocol and as the result will get list of available Home Agents on the subnet. MN could then select HA_x (in our scenario) on the list as its potential serving Home Agent. MN will send BU message to HA_x setting Home Registration(H) bit. According to the base specification of Mobile-IPv6[1] MN and HA_x MUST use IPsec Security Associations to protect the integrity and authenticity of the BUs and BAs. If there is no existing Security Association to protect the BU, MN will initiate IKE[2] (referred as Dynamic Keying) according to the guidelines defined in [3]. The latency casued by IKE transcations might cause performance degradation. Faizan. Expires May, 2004 [Page 6] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 The problem of Dynamic Keying can be avoided by Manual Keying. It involves out-of-band entry of Security Associations in MN and Home Agent. MN can be statically configured for a set of Home Agents among HAs 1..n and corresponding Security Associations before launching MN in the Mobile-IPv6 network. This will allow MN to register with any other Home Agent and use appropriate Security Associations upon the failure of it's serving Home Agent. But this policy is not flexible enough to accommodate the dynamic nature of subnets. 4. Solution Guidelines This section describes guidelines for a solution to the above mentioned problems. The subsections discuss the guidelines in a decreasing order of importance. 4.1 Security Implications The solution MUST NOT introduce any new security vulnerabilities to the Mobile-IPv6[1]. 4.2 IPsec Security with new Home Agent The solution SHOULD provide a mechanism to quickly establish IPsec Security Association between the Mobile Node and the new Home Agent such that the service interruption is minimimal. 4.3 Seamless failure It is strongly recommendated that the failure of Home Agent should be transparent from the Mobile Node. This will contribute in minimizing the period of service interruption. 4.4 Mobile Node functionality The solution SHOULD cause minimal modification to the Mobile Node as it is defined by Mobile-IPv6[1]. 4.5 Messages over air interface The solution SHOULD avoid introducing new messages more than what has been defined by Mobile-IPv6[1]. 4.6 Home Agent addition and failure The solution SHOULD provide recovery mechanism for the failed Home Agent. Also any new Home Agent added on the subnet SHOULD be ready to serve in minimum amount of time possible. Faizan. Expires May, 2004 [Page 7] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 4.7 Scalability The solution complexity MUST increase at most linearly with the number of Mobile Nodes registered and Home Agents configured on the subnet. References [1] Perkins, C., Johnson, D. and J. Arkko, "Mobility Support in IPv6", draft-ietf-mobileip-ipv6-24 (work in progress), August 2003. [2] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [3] Arkko, J., Devarapalli, V. and F. Dupont, "Using IPsec to Protect Mobile IPv6 Signaling between Mobile Nodes and Home Agents", draft-ietf-mobileip-mipv6-ha-ipsec-06 (work in progress), June 2003. [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [5] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [6] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Authors' Addresses Jahanzeb Faizan Southern Methodist University Computer Science and Engineering Department. 6425 N Ownby Dr., SIC #300D Dallas, TX, 75205, USA Phone +1 214-768-3712, Fax +1 214-768-3085 EMail: jfaizan@smu.edu Hesham El-Rewini Southern Methodist University Computer Science and Engineering Department. 6425 N Ownby Dr., SIC #306C Dallas, TX, 75205, USA Faizan. Expires May, 2004 [Page 8] Internet-Draft Home Agent Reliability, Problem Statement November, 2003 Phone +1 214-768-3278, Fax +1 214-768-3085 EMail: rewini@engr.smu.edu Mohammad Khalil Nortel Networks Richardson, TX, USA Phone: +1 972-685-0564 EMail: mkhalil@nortelnetworks Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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