Network Working Group Zhengming. Ma Internet-Draft Lin. Wang Intended status: Informational SUN YAT-SEN UNIVERSITY Expires: May 17, 2012 November 14, 2011 Improved Hierarchical Mobile IPv6 (IHMIPv6) Mobility Management draft-ma-mext-ihmipv6-00.txt Abstract In HMIPv6 (RFC5213), a mobile node has three IPv6 addresses: HoA, RCoA and LCoA. Outside the domain of a MAP, RCoA is used for routing, while HoA is used for authentication. Hence HA and CN should maintain the binding of RCoA and HoA. Inside the domain of a MAP, RCoA is used for authentication, while LCoA is used for routing. Hence MAP should maintain the binding of RCoA and LCoA. Since RCoA is used for authentication, it should be unique to a mobile node. Therefore, how many mobile nodes there are inside domain of a MAP, how many different RCoAs the MAP has to allocate to the mobile nodes. In this Internet Draft, an improved or alternative solution to HMIPv6 is presented, where RCoA is no longer used for authentication inside the domains of a MAP. RCoA is used only for routing outside the domain of a MAP, as LCoA does inside the domain of a MAP. Inside the domain of a MAP, HoA is used for authentication, as it does outside the domain of a MAP. Since RCoA is no longer used for authentication, only one RCoA will be enough for all mobile nodes inside the domain of a MAP. Remark: This Internet Draft is based on HMIPv6 (RFC5380). Only those parts in HMIPv6 related to RCoA have been rewritten, while the other parts in HMIPv6 remain almost unchanged. 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." Ma & Wang Expires May 17, 2012 [Page 1] Internet-Draft IHMIP November 2011 This Internet-Draft will expire on May 17, 2012. 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Ma & Wang Expires May 17, 2012 [Page 2] Internet-Draft IHMIP November 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview of IHMIPv6 . . . . . . . . . . . . . . . . . . . . . 6 3.1. IHMIPv6 Operations . . . . . . . . . . . . . . . . . . . . 7 4. Mobile IPv6 Extension - Local Binding Update . . . . . . . . . 9 5. Neighbor Discovery Extension: The MAP Option . . . . . . . . . 10 6. Overview of IHMIPv6 . . . . . . . . . . . . . . . . . . . . . 11 6.1. Mobile Node Operation . . . . . . . . . . . . . . . . . . 11 6.1.1. Sending Packets to Correspondent Nodes . . . . . . . . 13 6.2. MAP Operations . . . . . . . . . . . . . . . . . . . . . . 13 6.3. Home Agent Operations . . . . . . . . . . . . . . . . . . 14 6.4. Correspondent Node Operations . . . . . . . . . . . . . . 14 6.5. Local Mobility Management Optimization within a MAP Domain . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7. MAP Discovery . . . . . . . . . . . . . . . . . . . . . . . . 15 7.1. Mobile Node Operation . . . . . . . . . . . . . . . . . . 15 8. Updating Previous MAPs . . . . . . . . . . . . . . . . . . . . 15 9. Note on MAP Selection by the Mobile Node . . . . . . . . . . . 16 9.1. MAP Selection in Distributed MAP Environment . . . . . . . 16 9.2. MAP Selection in a Flat Mobility Architecture . . . . . . 18 10. Detection and Recovery from MAP Failures . . . . . . . . . . . 18 11. Tunelling Impacts on MTU . . . . . . . . . . . . . . . . . . . 19 12. Security Considerations . . . . . . . . . . . . . . . . . . . 19 12.1. Mobile Node - MAP Security . . . . . . . . . . . . . . . . 20 12.2. Mobile Node - Correspondent Node Security . . . . . . . . 21 12.3. Mobile Node - Home Agent Security . . . . . . . . . . . . 22 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22 Ma & Wang Expires May 17, 2012 [Page 3] Internet-Draft IHMIP November 2011 1. Introduction This specification introduces the concept of an improved hierarchical Mobile IPv6 network, utilizing a node called the Mobility Anchor Point (MAP). Mobile IPv6 [RFC3775] allows nodes to move within the Internet topology while maintaining reachability and ongoing connections between mobile and correspondent nodes. To do this, a mobile node sends binding updates (BUs) to its home agent (HA) every time it moves. The mobile node may send data packets via its home agent immediately after sending the binding update, but the home agent will not be able to route traffic back to the mobile node before it receives the binding update. This incurs at least half a round-trip delay before The mobile node may send data packets via its home agent immediately after sending the binding update, but the home agent will not be able to route traffic back to the mobile node before it receives the binding update. This incurs at least half a round-trip delay before packets are again forwarded to the right place. There is an additional delay for sending data packets if the mobile node chooses to wait for a binding acknowledgement (BA). The round-trip times can be relatively long if the mobile node and its home agent are in different parts of the world. For the reasons given above, Hierarchical Mobile IPv6[RFC5380] comes up with two important entities- the mobility anchor point(MAP) and the access router(AR). One MAP administers several ARs. The mobile node (MN) gets two addresses while accessing the Internet through AR. One of the two addresses is the Regional CoA (RCoA), the other is the local CoA (LCoA). MAP maintains the binding of RCoA and LCoA, and that the binding of HoA and RCoA is maintains by HA and CN. The source address of all the messages and packets sent by MN is RCoA, as well as the destination address of all the messages and packets replied by the correspondent node is RCoA. Such messages and packets will be routed to MAP, which will check the binding of RCoA and LCoA in its binding cache and sends the messages and packets to MN through the tunnel between MAP and AR. In the process of MN's moving, MAP updates its binding of RCoA and LCoA by means of receiving the local binding update message (LBU) from MN and replying the Local binding acknowledgement message (LBA) to MN if MN doesn't move out of the range covered by a MAP which means only LCoA has changed and RCoA has no change. If MN moves out of a MAP domain's boundaries which means both LCoA and RCoA have changed, MN should update the binding of RCoA and LCoA in MAP's binding cache, and also Ma & Wang Expires May 17, 2012 [Page 4] Internet-Draft IHMIP November 2011 update the binding of HoA and RCoA in the binding cache of HA and CN. In fact, MN usually moves within a small domain, that is to say, it roams within a local MAP domain. Here only LCoA has changed and RCoA has no change, thus HMIPv6 just needs to update the binding of RCoA and LCoA in MAP by the interaction of LBU and LBA without updating the binding caches in HA and CN. In this way, it can reduce a lot of signaling interactions. However, HMIPv6 should distribute a different RCoA for each MN in a MAP domain, though the data packets which use RCoA as their destination addresses are routed to the same MAP. In spite of infinite address space of IPv6, the address resource is limited as to a specified network. Therefore, according to the HMIPv6, this document prompts a improved hierarchical mobile IPv6 communication method in which all MNs accessed to the same MAP domain use a public IPv6 address so that it can save the IP address resource effectively. 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 [RFC2119]. In addition, the following terms are introduced: Access Router (AR) The AR is the mobile node's default router. The AR aggregates the outbound traffic of mobile nodes. Home address (HoA) A unicast routable address assigned to a mobile node. This address is within the mobile node's home link. A mobile node with an IPv6 home agent is assigned an IPv6 home address. Mobility Anchor Point (MAP) A Mobility Anchor Point is a router located in a network visited by the mobile node. The MAP doesn't give any treatment to the messages and packets from AR, but the MAP should get the HoA by analysising the messages or packets from the external. Regional Care-of Address (RCoA) An RCoA is an address allocated by the MAP to the mobile node. Ma & Wang Expires May 17, 2012 [Page 5] Internet-Draft IHMIP November 2011 HMIPv6-Aware Mobile Node An HMIPv6-aware mobile node is a mobile node that can receive and process the MAP option received from its default router. An HMIPv6- aware mobile node must also be able to send local binding updates (binding update with the M flag set). On-Link Care-of Address The LCoA is the on-link CoA configured on a mobile node's interface based on the prefix advertised by its default router. In [RFC3775], this is simply referred to as the care-of address. Local Binding Update The MN sends a local binding update to the MAP in order to establish a binding between the RCoA and LCoA. 3. Overview of IHMIPv6 This Improved Hierarchical Mobile IPv6 scheme continues to use the function, the MAP, and minor extensions to the mobile node operation. The correspondent node and home agent operations will not be affected. This solution is independent of the underlying access technology, allowing mobility within or between different types of access networks. A mobile node entering a MAP domain will receive Router Advertisements containing information about one or more local MAPs. The MN can bind its current location (on-link CoA) with the MAP's address (MAPA). Acting as a local HA, the MAP will receive all packets on behalf of the mobile node it is serving and will encapsulate and forward them directly to the mobile node's current address. If the mobile node changes its current address within a local MAP domain (LCoA), it only needs to register the new address with the MAP. Hence, only MAPA needs to be registered with correspondent nodes and the HA. The MAPA which equivalent to RCoA[RFC5380] does not change as long as the MN moves within a MAP domain (see below for definition). This makes the mobile node's mobility transparent to correspondent nodes it communicates with. A MAP domain's boundaries are defined by the Access Routers (ARs) advertising the MAP information to the attached mobile nodes. The detailed extensions to Mobile IPv6 and operations of the different nodes will be explained later in this document. Ma & Wang Expires May 17, 2012 [Page 6] Internet-Draft IHMIP November 2011 It should be noted that the IHMIPv6 concept is also simply an extension to the Mobile IPv6 protocol. An IHMIPv6-aware mobile node with an implementation of Mobile IPv6 SHOULD choose to use the MAP when discovering such capability in a visited network. However, in some cases the mobile node may prefer to simply use the standard Mobile IPv6 implementation. For instance, the mobile node may be located in a visited network within its home site. In this case, the HA is located near the visited network and could be used instead of a MAP. In this scenario, the mobile node would only update the HA whenever it moves. The method to determine whether the HA is in the vicinity of the MN (e.g., same site) is outside the scope of this document. 3.1. IHMIPv6 Operations The network architecture shown in Figure 1 illustrates an example of the use of the MAP in a visited network. In Figure 1, the MAP can help in providing seamless mobility for the mobile node as it moves from Access Router 1 (AR1) to Access Router 2(AR2), while communicating with the correspondent node. A multi- level hierarchy is not required for a higher handover performance. Hence, it is sufficient to locate one or more MAPs (possibly covering the same domain) at any position in the operator's network. Ma & Wang Expires May 17, 2012 [Page 7] Internet-Draft IHMIP November 2011 +-------+ | HA | +-------+ +----+ | | CN | | +----+ | | +-------+-----+ | |RCoA +-------+ | MAP | +-------+ | | | +--------+ | | | | +-----+ +-----+ | AR1 | | AR2 | +-----+ +-----+ LCoA1 LCoA2 +----+ | MN | +----+ ------------> Movement Figure 1:Improved Hierarchical Mobile IPv6 domain Upon arrival in a visited network, the mobile node will discover the global address of the MAP. This address is stored in the Access Routers and communicated to the mobile node via Router Advertisements (RAs). An option for RAs is defined later in this specification. This is needed to inform mobile nodes about the presence of the MAP (MAP Discovery). The discovery phase will also inform the mobile node of the distance of the MAP from the mobile node. For example, the MAP function could be implemented as shown in Figure 1, and, at the same time, also be implemented in AR1 and AR2. In this case, the mobile node can choose the first hop MAP or one further up in the hierarchy of routers. The details on how to choose a MAP are provided in Section 10. The process of MAP Discovery continues as the mobile node moves from one subnet to the next. Every time the mobile node detects movement, it will also detect whether it is still in the same MAP domain. The Router Advertisement used to detect movement will also inform the mobile node, through Neighbor Discovery [RFC4861] and the MAP option, whether it is still in the same MAP domain. As the mobile node roams Ma & Wang Expires May 17, 2012 [Page 8] Internet-Draft IHMIP November 2011 within a MAP domain, it will continue to receive the same MAP option included in Router Advertisements from its AR. If a change in the advertised MAP's address is received, the mobile node MUST act on the change by sending binding updates to its HA and correspondent nodes. If the mobile node is not HMIPv6-aware, then no MAP Discovery will be performed, resulting in the mobile node using the Mobile IPv6 [RFC3775] protocol for its mobility management. On the other hand, if the mobile node is HMIPv6-aware it SHOULD choose to use its HMIPv6 implementation. If so, the mobile node will first need to register with a MAP by sending it a BU containing its home address and on-link address (LCoA). The home address used in the BU is the HoA. The MAP MUST store this information in its binding cache to be able to forward packets to their final destination when received from the different correspondent nodes or HAs. The mobile node will always need to know the original sender of any received packets to determine if route optimization is required. This information will be available to the mobile node because the MAP does not modify the contents of the original packet. Normal processing of the received packets (as described in [RFC3775]) will give the mobile node the necessary information. To use the network bandwidth in a more efficient manner, a mobile node may decide to register with more than one MAP simultaneously and to use each MAP address for a specific group of correspondent nodes. For example, in Figure 1, if the correspondent node happens to exist on the same link as the mobile node, it would be more efficient to use the first hop MAP (in this case assume it is AR1) for communication between them. This will avoid sending all packets via the "highest" MAP in the hierarchy and thus will result in more efficient usage of network bandwidth. The mobile node can also use its current on-link address (LCoA) as a CoA, as specified in [RFC3775]. The LCoA included in the binding update MUST be the mobile node's address, derived from the prefix advertised on its link. 4. Mobile IPv6 Extension - Local Binding Update This section outlines the extensions proposed to the binding update specified in [RFC3775]. A new flag is added: the M flag, which indicates MAP registration. When a mobile node registers with the MAP, the M flag MUST be set to distinguish this registration from a BU being sent to the HA or a correspondent node. Ma & Wang Expires May 17, 2012 [Page 9] Internet-Draft IHMIP November 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence # | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |H|L|K|M| Reserved | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2:Local Binding Update M If set to 1, it indicates a MAP registration. 5. Neighbor Discovery Extension: The MAP Option 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Dist | Pref |R| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Global IP Address for MAP + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3:The MAP option Type IPv6 Neighbour Discovery option. Its value is 23. Ma & Wang Expires May 17, 2012 [Page 10] Internet-Draft IHMIP November 2011 Length 8-bit unsigned integer. The length of the option and MUST be set to 3. Dist A 4-bit unsigned integer identifying the distance between MAP and the receiver of the advertisement, measure in the number of hops and starting from 1 if the MAP is on the same link as the mobile node. A distance value of zero MUST NOT be used. Pref The preference field, used as an indicator of operator preference. A 4-bit unsigned integer. A decimal value of 15 indicates the highest preference. When comparing two potential MAPs, the mobile node SHOULD inspect this field as a tie-breaker for MAPs that have equal Dist values. Valid Lifetime The minimum value (in seconds) of both the valid lifetime of the prefix used to form the MAP's address. This value indicates the validity of the MAP's address. Global Address One of the MAP's global addresses. 6. Overview of IHMIPv6 This section describes the IHMIPv6 protocol. In HMIPv6, the mobile node has two addresses, an RCoA on the MAP's link and an on-link CoA (LCoA). In IHMIPv6, the node has one address, an on-link CoA (LCoA), without using an RCoA on the MAP's link. HMIPv6 protocol requires updating the mobile nodes' implementation only. The HA and correspondent node are unchanged. The MAP performs the function of a "local" HA that binds the mobile node's LCoA to an MAPA. 6.1. Mobile Node Operation When a mobile node moves into a new MAP domain (i.e., its MAP changes), it needs to configure two addresses: an MAPA and an on-link CoA (LCoA). After discovering the global address of the MAP to acquire an MAPA, the mobile node sends a local BU to the MAP with the M flags set. The local BU is a BU defined in [RFC3775] and includes Ma & Wang Expires May 17, 2012 [Page 11] Internet-Draft IHMIP November 2011 the mobile node's HoA in the Home Address option. The LCoA is used as the source address of the BU. This BU will bind the mobile node's HoA to its LCoA. The MAP (acting as an HA) will then return a binding acknowledgement to the MN. This acknowledgement either identifies the binding as successful or contains the appropriate fault code. No new error codes need to be supported by the mobile node for this operation. The mobile node MUST silently ignore binding acknowledgements that do not contain a routing header type 2, which includes the mobile node's HoA. Following a successful registration with the MAP, a bi-directional tunnel between the mobile node and the MAP is established. All packets sent by the mobile node are tunneled to the MAP. The outer header contains the mobile node's LCoA in the source address field, and the MAP's address in the destination address field. The inner header contains the mobile node's HoA in the source address field, and the peer's address in the destination address field. Similarly, all packets addressed to the MAPA are intercepted by the MAP and tunnelled to the mobile node's LCoA according to the HoA in the payload of packets. This specification allows a mobile node to use more than one MAPA if it received more than one MAP option. In this case, the mobile node MAY perform the binding update procedure for each MAPA. After registering with the MAP, the mobile node MUST register its new MAPA with its HA by sending a BU that specifies the binding (MAPA, home address), as in Mobile IPv6. The mobile node's home address is used in the Home Address option and the MAPA is used as the care-of address in the source address field. The mobile node may also send a similar BU (i.e., that specifies the binding between the home address and the MAPA) to its current correspondent nodes. The mobile node SHOULD wait for the binding acknowledgement from the MAP before registering the MAPA with other nodes (e.g., CN or HA, if available). It should be noted that when binding the MAPA with the HA and correspondent nodes, the binding lifetime MUST NOT be larger than the mobile node's binding lifetime with the MAP, which is received in the binding acknowledgement. In order to speed up the handover between MAPs and reduce packet loss, a mobile node SHOULD send a local BU to its previous MAP, specifying its new LCoA. Packets in transit that reach the previous MAP are then forwarded to the new LCoA. The MAP will receive packets addressed to MAPA. Packets will be tunnelled from the MAP to the mobile node's LCoA. The mobile node will de-capsulate the packets and process them in the normal manner. Ma & Wang Expires May 17, 2012 [Page 12] Internet-Draft IHMIP November 2011 When the mobile node moves within the same MAP domain, it should only register its new LCoA with its MAP. In this case, the MAPA remains unchanged. Note that a mobile node may send a BU containing its LCoA (instead of MAPA) to correspondent nodes. If these nodes are connected to the same link, packets will then be routed directly, without going through the MAP. 6.1.1. Sending Packets to Correspondent Nodes The mobile node can communicate with a correspondent node through the HA, or in a route-optimized manner, as described in [RFC3775]. When communicating through the HA, the message formats in [RFC3775] are used. If the mobile node communicates directly with the correspondent node(i.e., the CN has a binding cache entry for the mobile node), the mobile node MUST use the same address used to create a binding cache entry in the correspondent node (MAPA) as a source address. According to [RFC3775], the mobile node MUST also include a Home Address option in outgoing packets. The Home Address option MUST contain the mobile node's home address. 6.2. MAP Operations In [RFC5380], it is stated that the MAP acts like an HA and it intercepts all packets addressed to registered mobile nodes and tunnels them to the corresponding LCoA, which is stored in its binding cache. Outside the MAP domain, the messages or packets can be sent to MN by HA or CN, as described in [RFC5380]. According to [RFC3775], all the messages should include the home address option which should contains the mobile node's home address. The packets sent to MN by CN use HoA as the destination address or its routing header type 2 contains HoA in a route-optimized manner. In IHMIPv6, there is a extension to the MAP which can analysis the HoA from the packets. MAP maintains the binding of HoA and LCoA, HA maintains the binding of HoA and MAPA. CN should maintain the binding of HoA and MAPA in a route-optimized manner. MAP does nothing with the messages and packets from the tunnel between AR and MAP, with the mobile node being the tunnel entry point and the MAP being the tunnel exit point ,as described in [RFC5380]. As to the packets and messages from CN or HA, firstly MAP analsises the HoA from the packets and messages, and then checks the binding of Ma & Wang Expires May 17, 2012 [Page 13] Internet-Draft IHMIP November 2011 HoA and LCoA for HoA in its binding cache, and sends the packets and messages to MN by the tunnel between MAP and AR. 6.3. Home Agent Operations The support of IHMIPv6 is completely transparent to the HA's operation. Packets addressed to a mobile node's home address will be forwarded by the HA to its MAP, as described in [RFC3775]. 6.4. Correspondent Node Operations IHMIPv6 is completely transparent to correspondent nodes. 6.5. Local Mobility Management Optimization within a MAP Domain In the same MAP domain, all the mobile nodes use the same address, MAPA, other than use different RCoAs in [RFC5380]. The messages or packets using MAPA as the destination address will be routed to the MAP. The routing function of RCoA will be instead by that of MAPA, as well as, the identity recognition function of RCoA will be instead by that of HoA. RCoA is replaced by MAPA in the LBU and LBA messages defined in [RFC5380], while HoA is contained in the LBU and LBA messages. IHMIPv6-aware mobile nodes can use their MAPA as the source address and use a Home Address option. In other words, the MAPA can be used as a source address for upper layers. Using this feature, the mobile node will be seen by the correspondent node as a fixed node while moving within a MAP domain. This usage of the MAPA does not have the cost of Mobile IPv6 (i.e., no bindings or Home Address options are sent over the Internet), but still provides local mobility management to the mobile nodes with near-optimal routing. Although such use of MAPA does not provide global mobility (i.e., communication is broken when a mobile node changes its MAPA), it would be useful for several applications (e.g., web browsing). The validity of the MAPA as a source address used by applications will depend on the size of a MAP domain and the speed of the mobile node. Furthermore, because the support for BU processing in correspondent nodes is not mandated in [RFC3775], this mechanism can provide a way of obtaining route optimization without sending BUs to the correspondent nodes. Enabling this mechanism can be done by presenting the MAPA as a temporary home address for the mobile node. This may require an implementation to augment its source address selection algorithm with the knowledge of the MAPA in order to use it for the appropriate applications. Ma & Wang Expires May 17, 2012 [Page 14] Internet-Draft IHMIP November 2011 7. MAP Discovery This section describes how a mobile node obtains the MAP address and subnet prefix, and how ARs in a domain discover MAPs. This specification requires network administrators to manually configure the MAP option information in ARs; future mechanisms may be defined to allow MAPs to be discovered dynamically. 7.1. Mobile Node Operation When an HMIPv6-aware mobile node receives a Router Advertisement, it should search for the MAP option. One or more options may be found for different MAP IP addresses. A mobile node SHOULD register with the MAP having the highest preference value. A MAP with a preference value of zero SHOULD NOT be used for new local BUs (i.e., the mobile node can refresh existing bindings but cannot create new ones). However, a mobile node MAY choose to register with one MAP over another, depending on the value received in the distance field, provided that the preference value is above zero. A MAP option containing a valid lifetime value of zero means that this MAP MUST NOT be selected by the MN. A valid lifetime of zero indicates a MAP failure. When this option is received, a mobile node MUST choose another MAP and create new bindings. Any existing bindings with this MAP can be assumed to be lost. If no other MAP is available, the mobile node MUST NOT attempt to use IHMIPv6. If a multi-homed mobile node has access to several ARs simultaneously (on different interfaces), it SHOULD use an LCoA on the link defined by the AR that advertises its current MAP. A mobile node MUST store the received option(s) in order to choose at least one MAP to register with. Storing the options is essential, as they will be compared to other options received later for the purpose of the movement detection algorithm. A mobile node MAY choose to register with more than one MAP simultaneously, or use both the MAPA and its LCoA as care-of addresses simultaneously with different correspondent nodes. 8. Updating Previous MAPs When a mobile node moves into a new MAP domain, the mobile node may send a BU to the previous MAP requesting it to forward packets addressed to the mobile node's new MAPA. An administrator MAY restrict the MAP from forwarding packets to LCoAs outside the MAP's Ma & Wang Expires May 17, 2012 [Page 15] Internet-Draft IHMIP November 2011 domain. However, it is RECOMMENDED that MAPs be allowed to forward packets to LCoAs associated with some of the ARs in neighbouring MAP domains, provided that they are located within the same administrative domain. For instance, a MAP could be configured to forward packets to LCoAs associated with ARs that are geographically adjacent to ARs on the boundary of its domain. This will allow for a smooth inter-MAP handover as it allows the mobile node to continue to receive packets while updating the new MAP, its HA and, potentially, correspondent nodes. 9. Note on MAP Selection by the Mobile Node IHMIPv6 provides a flexible mechanism for local mobility management within a visited network. As explained earlier, a MAP can exist anywhere in the operator's network (including the AR). Several MAPs can be located within the same domain independently of each other. In addition, overlapping MAP domains are also allowed and recommended. Both static and dynamic hierarchies are supported. When the mobile node receives a Router Advertisement including a MAP option, it should perform actions according to the following movement detection mechanisms. In a hierarchical Mobile IP network, such as the one described in this document, the mobile node should be: o "Eager" to perform new bindings. o "Lazy" in releasing existing bindings. The above means that the mobile node should register with any "new" MAP advertised by the AR (Eager). The method by which the mobile node determines whether the MAP is a "new" MAP is described in Section 9.1. The mobile node should not release existing bindings until it no longer receives the MAP option (or receives it with a lifetime of zero) or the lifetime of its existing binding expires (Lazy). This Eager-Lazy approach, described above, will assist in providing a fallback mechanism in case of the failure of one of the MAP routers, as it will reduce the time it takes for a mobile node to inform its correspondent nodes and HA about its new care-of address. 9.1. MAP Selection in Distributed MAP Environment The mobile node needs to consider several factors to optimally select one or more MAPs, where several MAPs are available in the same domain. Ma & Wang Expires May 17, 2012 [Page 16] Internet-Draft IHMIP November 2011 There are no benefits foreseen in selecting more than one MAP and forcing packets to be sent from the higher MAP down through a hierarchy of MAPs. This approach may add forwarding delays and eliminate the robustness of IP routing between the highest MAP and the mobile node; therefore, it is prohibited by this specification. Allowing more than one MAP ("above" the AR) within a network should not imply that the mobile node forces packets to be routed down the hierarchy of MAPs. However, placing more than one MAP "above" the AR can be used for redundancy and as an optimization for the different mobility scenarios experienced by mobile nodes. The MAPs are used independently of each other by the MN (e.g., each MAP is used for communication to a certain set of CNs). In terms of the distance-based selection in a network with several MAPs, a mobile node may choose to register with the furthest MAP to avoid frequent re-registrations. This is particularly important for fast mobile nodes that will perform frequent handoffs. In this scenario, the choice of a more distant MAP would reduce the probability of having to change a MAP and informing all correspondent nodes and the HA. In a scenario where several MAPs are discovered by the mobile node in one domain, the mobile node may need sophisticated algorithms to be able to select the appropriate MAP. These algorithms would have the mobile node speed as an input (for distance-based selection) combined with the preference field in the MAP option. However, this specification proposes that the mobile node use the following algorithm as a default, where other optimized algorithms are not available. The following algorithm is simply based on selecting the MAP that is most distant, provided that its preference value did not reach a value of zero. The mobile node operation is shown below: 1. Receive and parse all MAP options. 2. Arrange MAPs in a descending order, starting with the furthest MAP (i.e., MAP option having largest Dist field). 3. Select first MAP in list. 4. If either the preference value or the valid lifetime fields are set to zero, select the following MAP in the list. 5. Repeat step (4) while new MAP options still exist, until a MAP is found with a non-zero preference value and a non-zero valid lifetime. Implementing the steps above would result in mobile nodes selecting, by default, the most distant or furthest available MAP. This will continue until the preference value reduces to zero. Following this, Ma & Wang Expires May 17, 2012 [Page 17] Internet-Draft IHMIP November 2011 mobile nodes will start selecting another MAP. 9.2. MAP Selection in a Flat Mobility Architecture Network operators may choose a flat architecture in some cases where a Mobile IPv6 handover may be considered a rare event. In these scenarios, operators may choose to include the MAP function in ARs only. The inclusion of the MAP function in ARs can still be useful to reduce the time required to update all correspondent nodes and the HA. In this scenario, a mobile node may choose a MAP (in the AR) as an anchor point when performing a handoff. This kind of dynamic hierarchy (or anchoring) is only recommended for cases where inter-AR movement is not frequent. 10. Detection and Recovery from MAP Failures This specification introduces a MAP that can be seen as a local home agent in a visited network. A MAP, like a home agent, is a single point of failure. If a MAP fails, its binding cache content will be lost, resulting in loss of communication between mobile and correspondent nodes. This situation may be avoided by using more than one MAP on the same link and by utilising a form of context transfer protocol between them. However, MAP redundancy is outside the scope of this document. In cases where such protocols are not supported, the mobile node would need to detect MAP failures. The mobile node can detect this situation when it receives a Router Advertisement containing a MAP option with a lifetime of zero. The mobile node should then start the MAP Discovery process and attempt to register with another MAP. After it has selected and registered with another MAP, it will also need to inform correspondent nodes and the home agent if its MAPA has changed. Access Routers can be triggered to advertise a MAP option with a lifetime of zero (indicating MAP failure) in different ways: o By manual intervention. o In a dynamic manner. One way of performing dynamic detection of MAP failure can be done by probing the MAP regularly (e.g., every 10 seconds). If no response is received, an AR MAY try to aggressively probe the MAP for a short period of time (e.g., once every 5 seconds for 15 seconds); if no reply is received, a MAP option may be sent with a valid lifetime value of zero. The exact mechanisms for probing MAPs is outside the Ma & Wang Expires May 17, 2012 [Page 18] Internet-Draft IHMIP November 2011 scope of this document. The above text simply shows one example of detecting failures. This specification does not mandate a particular recovery mechanism. However, any mechanism between the MAP and an AR SHOULD be secure to allow for message authentication, integrity protection, and protection against replay attacks. Note that the above suggestion for detecting MAP failure may not detect MAP failures that might take place between probes, i.e.,if a MAP reboots between probes. 11. Tunelling Impacts on MTU This specification requires the mobile node to tunnel outgoing traffic to the MAP. Similarly, the MAP tunnels inbound packets to the mobile node. If the mobile node has a home agent elsewhere on the Internet, this will result in double encapsulations of inbound and outbound packets. This may have impacts on the mobile node's path MTU. Hence, mobile nodes MUST consider the encapsulation of traffic between the node and the MAP when calculating the available MTU for upper layers. 12. Security Considerations This specification introduces a new concept to Mobile IPv6, namely, a Mobility Anchor Point that acts as a local home agent. It is crucial that the security relationship between the mobile node and the MAP is strong; it MUST involve mutual authentication, integrity protection, and protection against replay attacks. Confidentiality may be needed for payload traffic, such as when the mobile node is unwilling to reveal any traffic to the access network beyond what is needed for the mobile node to attach to the network and communicate with a MAP. Confidentiality is not required for binding updates to the MAP. The absence of any of these protections may lead to malicious mobile nodes impersonating other legitimate ones or impersonating a MAP. Any of these attacks will undoubtedly cause undesirable impacts to the mobile node's communication with all correspondent nodes having knowledge of the mobile node's MAPA. Three different relationships (related to securing binding updates) need to be considered: 1. The mobile node - MAP 2. The mobile node - correspondent node Ma & Wang Expires May 17, 2012 [Page 19] Internet-Draft IHMIP November 2011 3. The mobile node - home agent 12.1. Mobile Node - MAP Security In order to allow a mobile node to use the MAP's forwarding service, initial authorisation (specifically for the service, not for the MAPA) MAY be needed. Authorising a mobile node to use the MAP service can be done based on the identity of the mobile node exchanged during the security association (SA) negotiation process. The authorisation may be granted based on the mobile node's identity or based on the identity of a Certificate Authority (CA) that the MAP trusts. For instance, if the mobile node presents a certificate signed by a trusted entity (e.g., a CA that belongs to the same administrative domain, or another trusted roaming partner), it would be sufficient for the MAP to authorise the use of its service. Note that this level of authorisation is independent of authorising the use of a particular MAPA. Similarly, the mobile node trusts the MAP if it presents a certificate signed by the same CA or by another CA that the mobile node is configured to trust (e.g., a roaming partner). It is likely that some deployments would be satisfied with the use of self-signed certificates for either the mobile node or the MAP or both. This guarantees that the mobile node and the MAP are authenticated for address allocation and future binding updates without the need for identity authentication. Hence, the use of trusted third-party certificates is not required by this specification. It is important to note that in this specification, authentication and authorisation are effectively the same thing. All the MAP needs in order to allocate the mobile node an MAPA is to authenticate the mobile node and verify that it belongs to a trusted group (based on its certificate). IKEv2 MUST be supported by the mobile node and the MAP. IKEv2 allows the use of Extensible Authentication Protocol (EAP) as a mechanism to bootstrap the security association between the communicating peers. Hence, EAP can be used with IKEv2 to leverage the Authentication, Authorization, and Accounting (AAA) infrastructure to bootstrap the SA between the mobile node and the MAP. Such a mechanism is useful in scenarios where an administrator wishes to avoid the configuration and management of certificates on mobile nodes. A MAP MAY support the use of EAP over IKEv2. If EAP is used with IKEv2, the EAP method runs between the mobile node and a AAA server. Following a successful authentication, the resulting keying material can be used to bootstrap IKEv2 between the MAP and the mobile node. The specification of which EAP methods Ma & Wang Expires May 17, 2012 [Page 20] Internet-Draft IHMIP November 2011 should be used or how keys are transported between the MAP and the AAA server is outside the scope of this document. HMIPv6 uses an additional registration between the mobile node and its current MAP. As explained in this document, when a mobile node moves into a new domain (i.e., served by a new MAP), it obtains an MAPA and an LCoA and registers the binding between these two addresses with the new MAP. The MAP then verifies the BU and creates a binding cache entry with the MAPA and LCoA. Whenever the mobile node gets a new LCoA, it needs to send a new BU that specifies the binding between its MAPA and its new LCoA. This BU needs to be authenticated; otherwise, any host could send a BU for the mobile node's MAPA and hijack the mobile node's packets. The MAP does not need to have prior knowledge of the identity of the mobile node or its home address. As a result, the SA between the mobile node and the MAP can be established using any key establishment protocols such as IKEv2. A return routability test is not necessary. The MAP needs to set the SA for the MAPA (not the LCoA). This can be performed with IKEv2 [RFC4306]. The mobile node uses its LCoA as the source address, but specifies that the MAPA should be used in the SA. This is achieved by using the MAPA as the identity in the IKE CHILD_SA negotiation. This step is identical to the use of the home address in IKE CHILD_SA when negotiating with the home agent. The IPsec Peer Authorization Database (PAD) entries and configuration payloads described in [RFC4877] for allocating dynamic home addresses SHOULD be used by the MAP to allocate the RCoA for mobile nodes. Binding updates between the MAP and the mobile node MUST be protected with either Authentication Header (AH) or Encapsulating Security Payload (ESP) in transport mode. When ESP is used, a non-null authentication algorithm MUST be used. The Security Policy Database (SPD) entries in both the home agent and the mobile node are identical to those set up for the home agent and mobile node, respectively, as outlined in [RFC4877]. 12.2. Mobile Node - Correspondent Node Security Mobile IPv6 [RFC3775] defines a return routability procedure that allows mobile and correspondent nodes to authenticate binding updates and acknowledgements. This specification does not impact the return routability test defined in [RFC3775]. However, it is important to note that mobile node implementers need to be careful when selecting Ma & Wang Expires May 17, 2012 [Page 21] Internet-Draft IHMIP November 2011 the source address of the HoTI and CoTI messages, defined in [RFC3775]. The source address used in HoTI messages SHOULD be the mobile node's home address unless the mobile node wishes to use the RCoA for route optimisation. The packet containing the HoTI message is encapsulated twice. The inner encapsulating header contains the RCoA in the source address field and the home agent's address in the destination address field. The outer encapsulating header contains the mobile node's LCoA in the source address field and the MAP's address in the destination field. 12.3. Mobile Node - Home Agent Security The security relationship between the mobile node and its home agent, as discussed in [RFC3775], is not impacted by this specification. The relationship between the MAP and the mobile node is not impacted by the presence of a home agent. 13. IANA Considerations Both the MAP option and M flag were allocated for RFC 4140 and will continue to be used by this specification. Authors' Addresses Zhengming Ma SUN YAT-SEN UNIVERSITY GuangZhou, Higher Mega Center 510006 China Email: issmzm@mail.sysu.edu.cn Lin Wang SUN YAT-SEN UNIVERSITY GuangZhou, Higher Mega Center 510006 China Email: darling135603@163.com Ma & Wang Expires May 17, 2012 [Page 22]