An IPv6 Distributed Client Mobility Management approach using existing mechanisms
Author(s): Fabio Giust, Carlos Bernardos, Antonio de la Oliva
The use of centralized mobility management approaches -- such as Mobile IPv6 -- poses some difficulties to operators of current and future networks, due to the expected large number of mobile users and their exigent demands. All this...
DMM Working Group CJ. Bernardos Internet-Draft A. de la Oliva Intended status: Informational UC3M Expires: January 14, 2014 F. Giust IMDEA Networks and UC3M July 13, 2013 An IPv6 Distributed Client Mobility Management approach using existing mechanisms draft-bernardos-dmm-cmip-00 Abstract The use of centralized mobility management approaches -- such as Mobile IPv6 -- poses some difficulties to operators of current and future networks, due to the expected large number of mobile users and their exigent demands. All this has triggered the need for distributed mobility management alternatives, that alleviate operators' concerns allowing for cheaper and more efficient network deployments. This draft describes a possible way of achieving a distributed mobility behavior with Client Mobile IP, based on Mobile IPv6 and the use of Cryptographic Generated Addresses. 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 January 14, 2014. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. Bernardos, et al. Expires January 14, 2014 [Page 1] Internet-Draft A DMM solution for CMIP July 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Description of the solution . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. Normative References . . . . . . . . . . . . . . . . . . . 10 6.2. Informative References . . . . . . . . . . . . . . . . . . 10 Appendix A. Comparison with Requirement document . . . . . . . . 11 A.1. Distributed Processing . . . . . . . . . . . . . . . . . . 11 A.2. Transparency to Upper Layers when needed . . . . . . . . . 12 A.3. IPv6 deployment . . . . . . . . . . . . . . . . . . . . . 12 A.4. Existing mobility protocols . . . . . . . . . . . . . . . 12 A.5. Co-existence with deployed networks and hosts . . . . . . 12 A.6. Security considerations . . . . . . . . . . . . . . . . . 13 A.7. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Bernardos, et al. Expires January 14, 2014 [Page 2] Internet-Draft A DMM solution for CMIP July 2013 1. Introduction Most of the currently standardized IP mobility solutions, like Mobile IPv6 [RFC6275], or Proxy Mobile IPv6 [RFC5213] rely to a certain extent on a centralized mobility anchor entity. This centralized network node is in charge of both the control of the network entities involved in the mobility management (i.e., it is a central point for the control signalling), and the user data forwarding (i.e., it is also a central point for the user plane). This makes centralized mobility solutions prone to several problems and limitations, as identified in [I-D.ietf-dmm-requirements]: longer (sub-optimal) routing paths, scalability problems, signaling overhead (and most likely a longer associated handover latency), more complex network deployment, higher vulnerability due to the existence of a potential single point of failure, and lack of granularity on the mobility management service (i.e., mobility is offered on a per-node basis, not being possible to define finer granularity policies, as for example per-application). There are basically two main approaches that are being researched now: one aimed at making Mobile IPv6 work in a distributed way, and another one doing the same exercise for Proxy Mobile IPv6 (see the document [I-D.ietf-dmm-best-practices-gap-analysis]). In this draft we describe a solution to achieve a DMM behavior with a CMIP (MIPv6) solution. This document is based on a research paper of the same authors, called "Flat Access and Mobility Architecture: an IPv6 Distributed Client Mobility Management solution" [GOB+11]. 2. Terminology The following terms used in this document are defined in the Mobile IPv6 specification [RFC6275]: Home Agent (HA) Home Link Home Address (HoA) Care-of Address (CoA) Binding Update (BU) Binding Acknowledgement (BA) The following terms are defined and used in this document: Bernardos, et al. Expires January 14, 2014 [Page 3] Internet-Draft A DMM solution for CMIP July 2013 DAR (Distributed Anchor Router). First hop routers where the mobile nodes attach to. They also play the role of mobility managers for the IPv6 addresses they anchor. HDAR (Home Distributed Anchor Router). DAR which plays the role of Home Agent for a particular IPv6 address (i.e., DAR where that IPv6 address is anchored). 3. Description of the solution Distributed Mobility Management approaches try to overcome the limitations of the traditional centralized mobility management, i.e., Mobile IP, by bringing the mobility anchor closer to the MN. Following this idea, in our approach -- that we call Flat Access and Mobility Architecture (FAMA) -- the MIPv6 centralized home agent is moved to the edge of the network, being deployed in the default gateway of the mobile node. That is, the first elements that provide IP connectivity to a set of MNs are also the mobility managers for those MNs. In the following we will call these access routers Distributed Anchor Routers (DARs). The diagram in Figure 1 depicts the operations of the proposed solution. When a mobile node attaches to a distributed anchor router, it gets an IPv6 address which is topologically anchored at the DAR (Pref1::addr1 - HoA1). In the scheme we assume the address configuration takes place through a Router Solicitation/Router Advertisement handshake. While attached to this DAR, the mobile can send and receive traffic using HoA1 without traversing any tunneling nor special packet handling. If the the mobile node moves to a different DAR, it gets a new IPv6 address from the new access router (Pref2::addr2 - HoA2). In case the MN wants to keep the reachability of the IPv6 address(es) it obtained from the previous DAR (note that this decision is dynamic and it is out of scope of this document, it can be done on an application basis for example), the host has to involve its MIPv6 stack, by sending a Binding Update to the DAR where the IPv6 address is anchored, using the address obtained from the current DAR as care-of address (in our example the MN binds HoA2 as CoA to DAR1). Bernardos, et al. Expires January 14, 2014 [Page 4] Internet-Draft A DMM solution for CMIP July 2013 +-----+ +-----+ +-----+ +-----+ +-----+ | MN | |DAR1 | |DAR2 | | CN1 | | CN2 | +-----+ +-----+ +-----+ +-----+ +-----+ | | | | | |-Rtr. Sol.->| | | | |<-Rtr. Adv.-| | | | | | | | | Pref1::addr1 | | | | conf. (HoA1) | | | | | | | | | |<-----------+--IP flow 1------------->| | | | | | | - o - o - o - o - o Handover to DAR2 o - o - o - o - o - o - | | | | | |--------Rtr. Sol.------->| | | |<-------Rtr. Adv.--------| | | Pref2::addr2 | | | | conf. (HoA2) | | | | |----BU----->| | | | | (CoA=HoA2) | | | | |<---BA------| | | | |(-tnl est.-)| | | | | | | | | |(<---------)+--IP flow 1------------->| | | | | | | |<--------------IP flow 2-+------------------------>| | | | | | Figure 1: Signalling after the first handover In this way, the IPv6 address that the node wants to maintain in use (Pref1::addr1) plays the role of home address (HoA1), and the DAR from where that address was configured plays the role of Home Agent (for that particular address). In this scenario, old flows are anchored to the previous DAR (DAR1), which is in charge to encaspulate the packets and deliver them to the MN's CoA. The IP tunnel is bi-directional, so the MN does the same when sending packets with the old address (HoA1). Conversely, new IP flows are started using the address configured at the new DAR (HoA2). These flows are handled by the new DAR as a plain IPv6 router. Note that the FAMA approach basically enables a mobile node to simultaneously handle several IPv6 addresses -- each of them anchored at a different DAR -- ensuring their continuous reachability by using Mobile IPv6 in a distributed fashion (i.e., each access router is a potential home agent for the address it delegates, if required). Figure 2 illustrates the above case in which the MN is connected to Bernardos, et al. Expires January 14, 2014 [Page 5] Internet-Draft A DMM solution for CMIP July 2013 DAR2, but flow1 is anchored at DAR1, because it was started by the MN using the IPv6 address Pref1::addr1, configured when the MN was connected to DAR1. In the same example, the MN starts flow2 using Pref2::addr2, assigned by DAR2. +---+ +---+ |CN1| |CN2| +*--+ +*--+ * * * * ***** * flow1 * * flow2 * * * * * * +---*-+ +----*+ +-----+ | * | ___ | *| | | |DAR1**(__*\-+DAR2*+-----+DAR3 | | | \*\| *| | | +-----+ \*\----*+ +-----+ \*\ * \*\ * flow1 using \*--*+ flow2 using Pref1::addr1 |* *| Pref2::addr2 |*MN*| +----+ Operations sequence Packets flow Figure 2: MN's flows forwarding in FAMA The same operations take place if the MN moves to another DAR. The MN obtains a new address (Pref3::addr3 - HoA3), which is indicated as CoA in the BU messages sent by the MN to the previous DARs. This distributed address anchoring is enabled on demand and on a per- address granularity, which means that depending on the user needs, it might be the case that all, some or none of the IPv6 addresses that a mobile node configures while moving within a FAMA domain, are kept reachable and used by the mobile. The scheme in Figure 3 depicts the example where the MN updates all the previous DARs, mapping the corresponding HoA with the new CoA Bernardos, et al. Expires January 14, 2014 [Page 6] Internet-Draft A DMM solution for CMIP July 2013 +-----+ +-----+ +-----+ +-----+ +-----+ | MN | |DAR1 | |DAR2 | |DAR3 | | CNs | +-----+ +-----+ +-----+ +-----+ +-----+ | | | | | (<-----------)--IP flow 1-------------------------->| | | | | | |<--------------IP flow 2-+------------------------>| | | | | | - o - o - o - o - o Handover to DAR2 o - o - o - o - o - o - | | | | | |--------------Rtr. Sol.-------------->| | |<-------------Rtr. Adv.---------------| | Pref3::addr3 | | | | conf. (HoA3) | | | | |----BU----->| | | | | (CoA=HoA.) | | | | |<---BA------| | | | |(-tnl est.-)| | | | |------------BU---------->| | | | (CoA=HoA3) | | | |<-----------BA-----------| | | |(---------tnl est.------)| | | | | | | | |(<---------)+-IP flow 1--------------------------->| | | | | | |(<------------IP flow 2-)+------------------------>| | | | | | |<-------------IP flow 3---------------+----------->| | | | | | Figure 3: Signalling after a second handover In traditional Mobile IPv6, the communication between the MN and the HA is secured through IPsec [RFC4877]. Following a similar approach in FAMA is difficult due to the large number of security associations that would be required, since any gateway of the access network can play the role of home agent for any mobile node. In order to overcome this problem and provide authentication between the DAR and the MNs, we propose the use of Cryptographically Generated Addresses [RFC3972] (CGAs), as introduced in [I-D.laganier-mext-cga]. CGAs are a powerful mechanism allowing authentication of the packets and requires no public-key infrastructure, hence it is well-suited for this application. Following the ideas presented above, every time an MN attaches to a DAR, it configures a CGA from a prefix anchored at the DAR (e.g., by using stateless address auto-configuration mechanisms). This address Bernardos, et al. Expires January 14, 2014 [Page 7] Internet-Draft A DMM solution for CMIP July 2013 can then be used by the MN to establish a communication with a remote Correspondent Node (CN) while attached to that particular DAR. If the mobile then moves to a new DAR (nDAR), the following two cases are possible: i) there is no need for the address that was configured at the previous DAR (pDAR) to survive the movement: in this case there is no further action required; ii) the mobile wants to keep the reachability of the address configured at pDAR: in this case Mobile IPv6 is triggered, and the MN sends a Binding Update (BU) message to the pDAR, using the address configured at the previous DAR as home address, and the address configured at the new DAR as care-of address. This BU includes the CGA parameters and signature [I-D.laganier-mext-cga], which are used by the receiving DAR to identify the MN as the legitimate owner of the address. Although the use of CGAs does not impose a heavy burden in terms of performance, depending on the number of MNs handled at the DAR, the processing of the CGAs can be problematic. To reduce the complexity of the proposed protocol, we suggest an alternative mechanism to authenticate any subsequent signaling packets exchanged between the MN and the DAR (in case the mobile performs a new attachment to a different DAR). This alternative method relies on the use of a Permanent Home Keygen Token (PHKT), which will be used to generate the Authorization option that the MN has to include in all next Binding Update messages. This token is forwarded to the MN in the Binding Acknowledgment message, sent on reply to the BU. The procedure is depicted in Figure 4. Once the signaling procedure is completed, a bi-directional tunnel is established between the mobile node and the DAR where the IPv6 address is anchored (the "home" DAR -- HDAR -- for that particular address), so the mobile can continue using the IPv6 address. Bernardos, et al. Expires January 14, 2014 [Page 8] Internet-Draft A DMM solution for CMIP July 2013 ------ ------- | MN | | DAR | ------ ------- | | CGA | | config |-- BU + CGA param + signature ------>| | | MN PHKT |<----------------------- BA + PHKT --| auth caching | | | | (first handoff) PHKT | | refresh,| | next |-- BU(PHKT auth) ------------------->| handoffs,| | MN de-reg |<------------------------------ BA --| auth | | | | (subsequent signaling) Figure 4: Signaling between the MN and the DAR In case the MN performs any subsequent movements and it requires to maintain the reachability of an address for which it has already sent a BU, the following BU messages can be secured using the PHKT exchanged before, reducing the computational load at the receiving DAR. Note that on every attachment of a node to a DAR, the terminal also obtains a new IPv6 address which is topologically anchored at that DAR, and that this address can be used for new communications (avoiding in this way the tunneling required when using an address anchored at a different DAR). A mobile can keep multiple IPv6 addresses active and reachable at a given time, and that requires to send -- every time the MN moves -- a BU message to all the previous DARs that are anchoring the IP flows that the MN wish to maintain. 4. IANA Considerations TBD. 5. Security Considerations Although the approach documented in this document is attractive for the reduced signaling overhead caused by the mobility support, it can Bernardos, et al. Expires January 14, 2014 [Page 9] Internet-Draft A DMM solution for CMIP July 2013 be misused in some particular scenarios by malicious nodes that wish to export an incorrect CoA in the BU message, since it does provide proof of the MN's reachability at the visited network. Indeed, the CGA approach assures that the BU message has been sent by the legitimate HoA's owner but it does not make sure that same MN to be reachable at the CoA indicated. This requires further analysis. A possible approach to provide a more secure solution is the following: a Return Routability procedure similar to the one defined in MIPv6 Route Optimization can be used to mitigate the aforementioned security issue. The Return Routability procedure starts after the handoff. Instead of sending the BU message, the MN sends a Care-of Test Init message (CoTI). This message is replied by the DAR with a Care-Of Test message containing a CoA Keygen Token. The MN can now send a BU using both Home and CoA Keygen tokens to proof its reachability at both the HoA and the CoA. The message and the knowledge of both tokens is a proof that the MN is the legitimate node who has sent the BU and also is reachable at the CoA indicated. As all security improvements, the one proposed incurs in a performance penalty, in this case an increase in the handover delay. Specifically this enhanced security approach requires four messages to be exchanged between the MN and the DAR instead of the two messages of the original solution. In terms of handover delay, it increases it by a factor of two, as the new solution requires to two Round Trip Times (RTTs) to conclude, instead of one. 6. References 6.1. Normative References [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC3972, March 2005. [RFC4877] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with IKEv2 and the Revised IPsec Architecture", RFC4877, April 2007. [RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", RFC5213, August 2008. [RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support in IPv6", RFC6275, July 2011. 6.2. Informative References [GOB+11] Giust, F., de la Oliva, A., and CJ. Bernardos, "Flat Access and Mobility Architecture: an IPv6 Distributed Bernardos, et al. Expires January 14, 2014 [Page 10] Internet-Draft A DMM solution for CMIP July 2013 Client Mobility Management solution", 3rd IEEE International Workshop on Mobility Management in the Networks of the Future World (MobiWorld 2011), colocated with IEEE INFOCOM 2011 , 2011. [I-D.ietf-dmm-best-practices-gap-analysis] Liu, D., Zuniga, J., Seite, P., Chan, A., and C. Bernardos, "Distributed Mobility Management: Current practices and gap analysis", draft-ietf-dmm-best-practices-gap-analysis-01 (work in progress), June 2013. [I-D.ietf-dmm-requirements] Chan, A., Liu, D., Seite, P., Yokota, H., and J. Korhonen, "Requirements for Distributed Mobility Management", draft-ietf-dmm-requirements-05 (work in progress), June 2013. [I-D.laganier-mext-cga] Laganier, J., "Authorizing Mobile IPv6 Binding Update with Cryptographically Generated Addresses", draft-laganier-mext-cga-01 (work in progress), October 2010. Appendix A. Comparison with Requirement document In this section we descrbe how our solution addresses the DMM requirements listed in [I-D.ietf-dmm-requirements]. A.1. Distributed Processing "IP mobility, network access and routing solutions provided by DMM MUST enable distributed processing for mobility management of some flows so that traffic does not need to traverse centrally deployed mobility anchors and thereby avoid non-optimal routes." In our solution, a DAR is responsible to handle the mobility for those IP flows started when the MN is attached to it. As long as the MN remains connected to the DAR's access links, the IP packets of such flows can benefit from the optimal path. When the MN moves to another DAR, the path becomes non-optimal for ongoing flows, as they are anchored to the previous DAR, but newly started IP sessions are forwarded by the new DAR through the optimal path. Bernardos, et al. Expires January 14, 2014 [Page 11] Internet-Draft A DMM solution for CMIP July 2013 A.2. Transparency to Upper Layers when needed "DMM solutions MUST provide transparent mobility support above the IP layer when needed. Such transparency is needed, for example, when, upon change of point of attachment to the network, an application flow cannot cope with a change in the IP address. However, it is not always necessary to maintain a stable home IP address or prefix for every application or at all times for a mobile node." Our DMM solution operates at the IP layer, hence upper layers are totally transparent to the mobility operations. In particular, ongoing IP sessions are not disrupted after a change of access network. The routability of the old address is ensured by the IP tunnel with the old DAR. New IP sessions are started with the new address. From the application's perspective, those processes which sockets are bound to a unique IP address do not suffer any impact. For the other applications, the sockets bound to the old address are preserved, whereas next sockets use the new address. A.3. IPv6 deployment "DMM solutions SHOULD target IPv6 as the primary deployment environment and SHOULD NOT be tailored specifically to support IPv4, in particular in situations where private IPv4 addresses and/or NATs are used." The DMM solution we propose targets IPv6 only. A.4. Existing mobility protocols "A DMM solution SHOULD first consider reusing and extending IETF- standardized protocols before specifying new protocols." This DMM solution is derived from the operations and messages specified in [RFC6275], [RFC3972], and [I-D.laganier-mext-cga]. A.5. Co-existence with deployed networks and hosts "The DMM solution MUST be able to co-exist with existing network deployments and end hosts. For example, depending on the environment in which DMM is deployed, DMM solutions may need to be compatible with other deployed mobility protocols or may need to co-exist with a network or mobile hosts/routers that do not support DMM protocols. The mobile node may also move between different access networks, where some of them may support neither DMM nor another mobility protocol. Furthermore, a DMM solution SHOULD work across different networks, possibly operated as separate administrative domains, when allowed by the trust relationship between them." Bernardos, et al. Expires January 14, 2014 [Page 12] Internet-Draft A DMM solution for CMIP July 2013 The proposed solution can provide a fallback mechanism employing legacy Mobile IPv6, for instance forcing the MN to use only one DAR. Moreover, this solution applies when the MN is connected to an administrative domain not supporting trust relationships. Indeed, all the IP sessions can remain anchored to the DARs of the "home" domain. Our solution can be deployed across different domains with trust agreements. A.6. Security considerations "DMM protocol solutions MUST consider security risks introduced by DMM into the network. Such considerations may include authentication and authorization mechanisms that allow a mobile host/router to use the mobility support provided by the DMM solution; measures against redirecting traffic to the wrong host when providing DMM support; signaling message protection for authentication, integrity and confidentiality." The proposed solution uses a CGA-based security system to enable authentication and authorization of mobile hosts. A.7. Multicast "DMM SHOULD enable multicast solutions in flexible distribution scenario. This flexibility pertains to the preservation of IP multicast nature from the perspective of a mobility entity and transmission of multicast packets to/from various multicast- enabled entities. Therefore, this flexibility enables different IP multicast flows with respect to a mobile host to be managed (e.g., subscribed, received and/or transmitted) using multiple multicast-enabled endpoints." This solution does not include multicast traffic in its scope. Nevertheless, it allows combining multicast support solutions, such as local subscription at each DAR, which would result in a flexible distribution scenario. Bernardos, et al. Expires January 14, 2014 [Page 13] Internet-Draft A DMM solution for CMIP July 2013 Authors' Addresses Carlos J. Bernardos Universidad Carlos III de Madrid Av. Universidad, 30 Leganes, Madrid 28911 Spain Phone: +34 91624 6236 Email: firstname.lastname@example.org URI: http://www.it.uc3m.es/cjbc/ Antonio de la Oliva Universidad Carlos III de Madrid Av. Universidad, 30 Leganes, Madrid 28911 Spain Phone: +34 91624 8803 Email: email@example.com URI: http://www.it.uc3m.es/aoliva/ Fabio Giust Institute IMDEA Networks and Universidad Carlos III de Madrid Av. del Mar Mediterraneo, 22 Leganes, Madrid 28918 Spain Email: firstname.lastname@example.org Bernardos, et al. Expires January 14, 2014 [Page 14]