IETF Seamoby Working Group Internet Draft Marco Liebsch Category: Experimental Ajoy Singh (Editors) Hemant Chaskar Daichi Funato Eunsoo Shim draft-ietf-seamoby-card-protocol-06.txt Expires: June 2004 December 2003 Candidate Access Router Discovery Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 10 of RFC 2026. 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 To view the list of Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Abstract To enable seamless IP-layer handover of a mobile node (MN) from one access router (AR) to another, the MN is required to discover the identities of candidate ARs (CARs) for handover, along with their capabilities, prior to the initiation of the IP-layer handover. The act of discovery of CARs has two aspects to it: Identifying the IP addresses of the CARs and finding the capabilities of those CARs. This process is called "candidate access router discovery" (CARD). At the time of IP-layer handover, that CAR, whose capabilities is a good match to the preferences of the MN, may be chosen as the target AR for handover. The protocol described in this document allows a mobile node to perform CARD. [Page 1] Internet-Draft Candidate Access Router Discovery December 2003 TABLE OF CONTENTS 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 4 2. TERMINOLOGY. . . . . . . . . . . . . . . . . . . . . . . . . 5 3. CARD PROTOCOL FUNCTIONS. . . . . . . . . . . . . . . . . . . 6 3.1 Reverse Address Translation. . . . . . . . . . . . . . . . 6 3.2 Discovery of CAR Capabilities. . . . . . . . . . . . . . . 6 4. CARD PROTOCOL OPERATION. . . . . . . . . . . . . . . . . . . 7 4.1 Conceptual Data Structures . . . . . . . . . . . . . . . . 10 4.2 Mobile Node - Access Router Operation. . . . . . . . . . . 10 4.2.1 Mobile Node Operation. . . . . . . . . . . . . . . . . 10 4.2.2 Current Access Router Operation. . . . . . . . . . . . 12 4.3 Current Access Router - Candidate Access Router Operation. 13 4.3.1 Current Access Router Operation. . . . . . . . . . . . 13 4.3.2 Candidate Access Router Operation. . . . . . . . . . . 15 4.4 CARD Signaling Failure Recovery. . . . . . . . . . . . . . 16 4.4.1 MN-AR Signaling Failure. . . . . . . . . . . . . . . . 16 4.4.2 AR-AR Signaling Failure. . . . . . . . . . . . . . . . 16 4.5 CARD Protocol Message Piggybacking on the MN-AR Interface. 16 4.6 CARD Protocol Security . . . . . . . . . . . . . . . . . . 18 5. PROTOCOL MESSAGES. . . . . . . . . . . . . . . . . . . . . . 19 5.1 CARD Messages for the Mobile Node-Access Router interface. 19 5.1.1 CARD Main Header Format. . . . . . . . . . . . . . . . 19 5.1.2 CARD Options Format. . . . . . . . . . . . . . . . . . 21 5.1.2.1 CARD Request Option. . . . . . . . . . . . . . . . 22 5.1.2.2 CARD Reply Option. . . . . . . . . . . . . . . . . 23 5.1.3 Sub-Options Format . . . . . . . . . . . . . . . . . . 24 5.1.3.1 L2 ID Sub-Option . . . . . . . . . . . . . . . . . 25 5.1.3.2 Preferences Sub-Option . . . . . . . . . . . . . . 26 5.1.3.3 Requirements Sub-Option. . . . . . . . . . . . . . 27 5.1.3.4 Capability Container Sub-Option. . . . . . . . . . 27 5.1.3.5 Address Sub-Option . . . . . . . . . . . . . . . . 28 5.1.4 Capability AVP Encoding Rule . . . . . . . . . . . . . 29 5.2 CARD Messages for the inter-Access Router Protocol Operation . . . . . . . . . . . . . . . . . . . . . . 30 5.2.1 Protocol Transport . . . . . . . . . . . . . . . . . . 30 5.2.2 Protocol Main Header . . . . . . . . . . . . . . . . . 30 5.2.3 Protocol Payload Types . . . . . . . . . . . . . . . . 31 5.3 Overview on sub-options'/payload types' usage. . . . . . . 31 6. SECURITY CONSIDERATIONS. . . . . . . . . . . . . . . . . . . 32 6.1 Assumptions . . . . . . . . . . . . . . . . . . . . . . . 32 6.2 Security Association between AR and AR . . . . . . . . . . 32 [Page 2] Internet-Draft Candidate Access Router Discovery December 2003 6.3 Security Association between AR and MN . . . . . . . . . . 33 6.4 DoS Attack . . . . . . . . . . . . . . . . . . . . . . . . 33 7. PROTOCOL CONSTANTS . . . . . . . . . . . . . . . . . . . . . 34 8. IANA CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . 35 9. NORMATIVE REFERENCES . . . . . . . . . . . . . . . . . . . . 36 10. INFORMATIVE REFERENCES . . . . . . . . . . . . . . . . . . . 36 11. AUTHORS' ADDRESSES . . . . . . . . . . . . . . . . . . . . . 37 12. IPR STATEMENTS . . . . . . . . . . . . . . . . . . . . . . . 37 13. COPYRIGHT NOTICE . . . . . . . . . . . . . . . . . . . . . . 38 14. CONTRIBUTORS . . . . . . . . . . . . . . . . . . . . . . . . 38 15. ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . 38 Appendix A MAINTENANCE OF ADDRESS MAPPING TABLES IN ACCESS ROUTERS. . . . . . . . . . . . . . . . . . . 39 Appendix A.1 Centralized Approach using a Server Functional Entity. . . . . . . . . . . . . . . . . . . . . . . 39 Appendix A.2 Decentralized Approach using Mobile Terminals' Handover. . . . . . . . . . . . . . . . . . . . . . 40 Appendix B APPLICATION SCENARIOS . . . . . . . . . . . . . . . 43 Appendix B.1 CARD Operation in a Mobile IPv6 Enabled Wireless LAN Network . . . . . . . . . . . . . . . . . . . . 43 Appendix B.2 CARD Operation in a Fast Mobile IPv6 enabled network . . . . . . . . . . . . . . . . . . . . . . 46 [Page 3] Internet-Draft Candidate Access Router Discovery December 2003 Conventions used in this document 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 [Brad97]. 1. INTRODUCTION IP mobility protocols, such as Mobile IP, enable mobile nodes to execute IP-level handover among access routers. Additionally, work is underway [Kood03][Malk03] to extend the mobility protocols to allow seamless IP handover. The pre-requisite for the seamless IP mobility protocols is the knowledge of candidate access routers (CARs) to which a mobile node can be handed over to. The CAR discovery protocol enables to acquire information about the access routers that are candidates for the mobile node's next handover. The CAR discovery involves identifying a CAR's IP address as well as its capabilities that the mobile node might use for its handover decision. There are cases when a mobile node has a choice of candidates to perform handover to different CARs. The mobile node would choose one based on a match between the mobile node's requirements on a handover candidate and the CAR's capabilities. However, the decision algorithm itself is out of scope of this document. The problem statement of the CAR discovery is discussed in [TKCK02]. In this document, a protocol is described to perform CAR discovery. Section 3 describes two main functions of the CAR discovery protocol. Then, Section 4 describes the core part of the CARD protocol operation. Finally, the protocol messages' format is described in Section 5. In Appendix A, two optional approaches are described to build a local table (CAR table), holding CARs' IP addresses and associated access points' layer-2 addresses, dynamically in access routers. This mapping is required in access routers to identify an individual CAR's IP address and to perform reverse address translation. However, the core protocol, as described in this document up to Section 5, assumes this local CAR table (Section 4.1) in access routers to be available and filled with the IP addresses of the CARs (and their associated APs' L2 addresses) throughout the core part of the draft. [Page 4] Internet-Draft Candidate Access Router Discovery December 2003 2. TERMINOLOGY This document uses terminology defined in TERMS [MaKo03]. In addition, the following terms are used: Access Router (AR) An IP router residing in an access network and connected to one or more APs. An AR offers IP connectivity to MNs. Candidate AR (CAR) An AR to which a MN has a choice of performing IP-level handover. Capability of an AR A characteristic of the service offered by an AR that may be of interest to a MN when the AR is being considered as a handover candidate. L2 ID Identifier of an AP that uniquely identifies that AP. For example, in 802.11 PCF, this could be a MAC address of an AP. CARD Initiating Trigger L2 trigger used to initiate CARD process. For example, a MN can initiate CARD as soon as it detects L2 identifier of a new AP during link layer scan. [Page 5] Internet-Draft Candidate Access Router Discovery December 2003 3. CARD PROTOCOL FUNCTIONS A CARD protocol accomplishes the following functions. 3.1 Reverse Address Translation If a MN can listen to L2 IDs of new APs prior to making a decision about IP-level handover to CARs, a mechanism is needed for reverse address translation. This function of the CARD protocol enables the MN to map the received L2 ID of an AP to the IP address of the associated CAR that connects to the AP. To get the CAR's IP address, the MN sends the L2 ID of the AP to the current AR and the current AR provides the associated CAR's IP address to the MN. 3.2 Discovery of CAR Capabilities Information about capabilities of CARs can assist the MN in making optimized handover decisions. This capability information serves as input to the target AR selection algorithm. Some of the capability parameters of CARs can be static, while others can change with time. Definition of capabilities is out of scope of this document. Encoding rules for capabilities and the format of a capability container for capability transport are specified in Section 5. There are two approaches for MNs to acquire address and capability information of CARs. One is that the MN sends an explicit request to its current AR and the current AR provides address and capability information to the MN. The other is that the current AR periodically advertises address and capability information of CARs to the MNs over downlink channels without being previously solicited by a MN. [Page 6] Internet-Draft Candidate Access Router Discovery December 2003 4. CARD PROTOCOL OPERATION The CARD protocol is used to allow MNs resolving the L2 ID of one or more APs, which are candidates the MN may initiate a handover to, to the IP address of the associated CARs, as well as to discover these CARs' capabilities. Furthermore, the protocol allows ARs to populate and maintain their local CAR table (Section 4.1) with the capabilities of CARs. For this, the CARD protocol makes use of a CARD Request and CARD Reply protocol message between a MN and its current AR (Section 5.1.2), and between a MN's current AR and individual CARs respectively (Section 5.2.2). To allow a MN to retrieve its CARs' address and capability information, the CARD Request and CARD Reply messages used between a MN and its current AR may contain one or more access points' L2 IDs and the IP addresses of associated CARs respectively. Optionally, the CARD Reply messages can also contain CARs' capability information. A CAR's capabilities are specified as a list of attribute-value pairs, which are conveyed in a Capability Container message parameter. Information about the CAR(s) and associated capabilities MAY be used by the MN to perform target access router selection during its IP handover. The current AR initiates capability exchange with a CAR either when it receives a CARD Request message from a MN, containing possibly parameters carrying identifier(s) (L2 ID) of newly discovered AP(s), or when it detects that some of its CAR table's capability entries are about to expire. Upon completion of the MN- solicited capability exchange between a MN's current AR and CARs, the current AR MUST notify the desired capabilities to the MN by sending a CARD Reply message having the appropriate message parameters appended. The current AR MAY also send periodically unsolicited CARD Reply messages to all connected MNs. This behavior of the AR SHALL depend upon the local policies of the network service providers and needs to be configured administratively. The unsolicited CARD Reply SHALL be multicast from ARs, using the multicast address CARD_UNSOL_MC_ADDR given in section 7 as destination address. For unsolicited CARD Reply messages sent to connected MNs, the AR MUST set the U-flag of the CARD Reply to indicate to MNs that this particular CARD Reply message has been sent without being solicited. The CARD protocol also enables a MN to optionally indicate its preferences on capabilities of interest to its current AR by including the Preferences message parameter in the CARD Request message. The MN's current AR MAY use this information to perform optional capability pre-filtering for optimization purposes and returns only these capabilities of interest to the requesting MN. [Page 7] Internet-Draft Candidate Access Router Discovery December 2003 The format of this optional Preferences message parameter is described in Section 5.1.3.2. Optionally, the MN can provide its current AR with a list of capability attribute-value pairs, indicating not only the capability parameters (attributes) as required for capability pre-filtering, but also a specific value for a particular capability. This allows the MN's current AR performing CAR pre-filtering and to send only address and capability information of CARs, whose capability values meet the requirements of the MN, back to the requesting MN. The format of this optional Requirements message parameter is described in Section 5.1.3.3. As an example, using the optional Preferences message parameter, a MN may indicate to its current AR that it is interested only in IEEE802.11a interface specific capability parameters, since this is the only interface the MN has implemented. Hence, the MN's current AR sends back only CARs' IEEE802.11a specific capabilities. Similarly, using the optional Requirements message parameter, a MN may indicate to its current AR that it is only interested in CARs that can satisfy a given QoS constraint. Here, a MN sends the respective QoS attribute with the QoS constraint value to its current AR using the optional Requirements message parameter. The QoS constraint is denoted as an attribute-value pair and encapsulated with the Requirements message parameter, which is appended to the MN-originated CARD Request message. The Requirements message parameter may be used to indicate the cut off values of the capabilities for the desired CAR(s). Based on the received optional list of attributes in the Preferences parameter or a list of attribute-value pairs in the Requirements message parameter, the MN's current AR MAY use these parameters for deciding the content of the solicited CARD Reply message, which is to be sent back to the MN. Alternatively, in case no optimization with regard to capability or CAR pre-filtering is performed by the MN's current AR, the current AR MAY choose to silently ignore the optional Requirements and Preferences message parameter as received in the CARD Request message. The CARD protocol operation, as described in this section, distinguishes signaling messages exchanged between a MN and its current AR and signaling messages exchanged between ARs. Hence, description of signaling messages described in the following sections has a preceding identifier, referring to the associated interface. Messages that are exchanged between a MN and AR are precluded with "MN-AR", messages between ARs with "AR-AR" respectively. [Page 8] Internet-Draft Candidate Access Router Discovery December 2003 +--------------+ (3)AR-AR CARD Request +----------+ | Current |------------------------->| CAR | | AR |<-------------------------| | +--------------+ (4)AR-AR CARD Reply +----------+ ^ | | | MN-AR MN-AR | | CARD Reply(5) CARD Request(2) V +--------------+ | Mobile | | Node |<-- CARD Init Trigger +--------------+ (1) Figure 1: MN initiated CARD Protocol Overview Figure 1 describes the operation of the MN initiated CARD Request/Reply protocol. On reception of the access points' L2 IDs or the appearance of a CARD initiation trigger (1), the MN may pass on one or more AP L2 ID(s) to its current AR using the MN-AR CARD Request message (2). In case the MN wants its AR to perform capability discovery in addition to reverse address translation, this must be indicated in the MN-AR CARD Request message by setting the C-flag. If the C-flag is not set, the AR receiving the CARD Request message will perform only reverse address translation. The MN's current AR resolves the L2 ID to the IP address of the associated CAR or, in case the MN has not attached any L2 ID message parameters, it just reads out all CARs' IP address information using the reverse address translation information (L2 ID to IP address mapping) from its local CAR table. In case one or more capability entries have expired in the current AR's CAR table, the current AR directly contacts the CAR and performs capability discovery with it via an AR-AR CARD Request (3) and AR-AR CARD Reply (4) protocol message handshake. The current AR then updates the capability entries in its local CAR table and passes on the IP address of the CAR(s) and, in case capability information has been requested, associated capabilities to the MN using the MN-AR CARD Reply message (5). Since the MN-AR CARD Request is sent when a MN discovers new AP(s) during link layer scanning or receipt of an unsolicited beacon, sometimes a MN might send frequent MN-AR CARD Requests, thereby overwhelming its current AR with CARD Request signaling messages. To counteract this problem, the MN MUST NOT send more than CARD_REQUEST_RATE requests per second. If the MN sends requests more frequently, the AR SHOULD rate limit the MN to CARD_REQUEST_RATE. 4.1 Conceptual Data Structures [Page 9] Internet-Draft Candidate Access Router Discovery December 2003 AR(s) SHALL maintain a L2-L3 address mapping table (CAR table) that will be used to resolve L2 IDs of candidate APs to the IP address of associated CARs. This address-mapping table can be configured statically for the CARD protocol operation. Optionally, the CAR table MAY be populated dynamically, using either a server-based or a handover-based approach, as referred to in appendices A.1 and A.2 respectively. ARs SHOULD also keep and maintain individual CARs' capabilities in the local CAR table, taking the associated capability lifetime into account. If the lifetime of an individual capability entry has expired, the respective capability is to be discovered and to be updated when requested from a connected MN or upon receipt of un- solicited CARD Reply message from the neighboring CAR(s). AR may also initiate capability exchange prior to expiration of the capabilities associated with a CAR in the CAR table thereby populating its CAR table.The ARs' CAR table may be implemented differently, hence additional details are not provided here. MNs SHOULD maintain discovered address and capability information of CARs in a local cache to avoid requesting the same information repeatedly and to select an appropriate target AR from the list of CARs as quickly as possible when a handover is imminent. MNs and ARs SHOULD maintain sequence numbers of latest received unsolicited CARD Reply messages in their local cache to allow identification of recent information and replay attacks. In case a MN receives both solicited and unsolicited CARD Reply messages, the MN should always consider the latest information received as valid. 4.2 Mobile Node - Access Router Operation 4.2.1 Mobile Node Operation To initiate CARD, a MN sends a CARD Request to its current AR, requesting it to resolve the L2 ID of nearby access points to the IP address of associated CARs, and also to obtain capability parameters associated with these CARs. In case the requesting MN wants its current AR to resolve specific L2 IDs, the MN-AR CARD Request MUST contain the CARD protocol specific L2 ID message parameters. If the MN wants its AR to perform only reverse address translation without appending the CARs' capabilities, the MN refrains from setting the C-flag in the CARD Request message. If the MN wants to perform capability discovery, the CARD Request MUST set the C-flag. The CARD Request MAY also contain the Preferences or Requirements message parameter, indicating the MN's preferences on capability attributes of interest or its requirements on CARs' capability attribute-value pairs to its current AR. [Page 10] Internet-Draft Candidate Access Router Discovery December 2003 In case the MN appends multiple L2 ID sub-options to a CARD Request, the AR MUST assume each L2 ID is associated with an AP, which connects to a different CAR. Since L2 IDs, address information and capability information are transmitted with separate sub-options, each sub-option carries a Context-ID, to allow matching parameters that belong together. Hence, the MN MUST assign different Context-ID values to the L2 ID sub-options it appends to the CARD Request message. The Status-Code field in the CARD Request message MUST always be set to NONE (0x00) by a MN. When sending the CARD Request protocol message, the MN MUST set the message's sequence number to allow correlation of replies with requests. Successive new CARD Request protocol messages must have the sequence number incremented respectively. Upon power on or reboot the MN SHALL set the sequence number of the first outgoing CARD Request Message to 0. To support error recovery in case a MN-AR CARD Request or a MN-AR CARD Reply is lost, the sending MN performs signaling failure recovery according to the timeout-based mechanism as described in section 4.4.1. This allows detection of lost signaling messages and retransmission. Upon receipt of the corresponding MN-AR CARD Reply message, the MN co-relates the CARD Reply with appropriate CARD Request message and then processes all MN-AR CARD Reply message parameters to retrieve its CARs' address and capability information. If MN is unable to co- relate the CARD Reply with any previously sent CARD Request messages, the MN SHOULD then silently discard the reply. This may happen when MN reboots after sending CARD Request Message to the connected AR. Processing the Context-ID of Address sub-options allows the MN to assign the resolved IP address of a specific CAR to a L2 ID. In some cases a L2 ID parameter is present in a CARD Reply message. The Status-Code field in the L2 ID parameter indicates one of the following reasons for being sent towards the MN. RESOLVER ERROR Status-Code indication: In case the MN's current AR could not resolve a particular L2 ID, this status code is returned to the MN. MATCH Status-Code indication: If an L2 ID is encountered that shares a CAR with a previously resolved L2 ID, the AR returns MATCH to the MN. This status code is an indicator that the Context-ID of this particular L2 ID sub-option has been adapted to the Context-ID of the associated CAR's Address [Page 11] Internet-Draft Candidate Access Router Discovery December 2003 and Capability Container sub-option, which is sent with this CARD Reply message. This approach avoids sending the same CAR's address and capability information multiple times with the same CARD Reply message in case two or more L2 IDs resolve to the same CAR. MN uses the adapted Context-ID received in the L2 ID sub-option as the key to find the serving CAR of the given AP from the content of the received CARD Reply message. . CANDIDATE Status-Code indication: In case the MN does not append any L2 ID to the CARD Request or in case of an un-solicited CARD Reply, an AR sends back L2 ID and address information of all CARs. Since the received parameters' Context-IDs cannot be correlated with a L2 ID's Context-ID of a previously sent request, the AR chooses values for the Context-ID and marks these candidate L2 IDs with CANDIDATE in the status code of the distributed L2 IDs. However, individual values of L2 IDs' Context-ID allow the MN to assign a particular L2 ID to the associated Address and the possibly received Capability Container sub-option. 4.2.2 Current Access Router Operation Upon receipt of a MN's MN-AR CARD-Request, the connected AR SHALL resolve the requested APs' L2 ID to the IP address of the associated CAR(s). In case no L2 ID parameter has been sent with the MN-AR CARD Request message, the MN's current AR retrieves all CARs' IP address and capability information from its local CAR table, assuming the MN requested CARs' capabilities by setting C-flag of the CARD Request message. In the first case, where the AR resolves only requested L2 IDs, the AR does not send back the L2 ID to the requesting MN. If, however, two or more L2 IDs match the same CAR information, the L2 ID sub- option is sent back to the MN, indicating MATCH in the Status-Code field of the L2 ID. Furthermore, the AR sets the Context-ID of the returned L2 ID to the value of the resolved CAR's L2 ID, Address and Capability Container sub-option. In case an AR cannot resolve a particular L2 ID, this L2 ID sub-option is to be sent back to the MN, indicating RESOLVER ERROR in the L2 ID sub-option's Status-Code field. In the second case, where the AR did not receive any L2 ID with a CARD Request, all candidate APs' L2 IDs are sent to a requesting MN with the CARD Reply message. Here, the AR marks the Status-Code of individual L2 IDs as CANDIDATE, indicating to the MN, that the associated Context-ID cannot be matched with the ID of a previously sent request. [Page 12] Internet-Draft Candidate Access Router Discovery December 2003 In any case, the AR MUST set the Context-ID of the Address and the Capability Container sub-option to the same value of the associated L2 ID sub-option. Optionally, when allowed by local policies and supported by respective ARs for capability discovery, the AR MAY retrieve a subset of capabilities or CARs, satisfying the optionally appended Preferences and Requirement message parameter, from its local CAR table. CARs' address information along with associated capabilities are then delivered to the MN using the MN-AR CARD Reply message. The CARs' IP address as well as the capabilities SHALL be encoded according to the format for CARD protocol message parameters as defined in Section 5.1.3 of this document. The capabilities are encoded as attribute-value pairs, which are encapsulated in a Capability Container message parameter according to the format defined in Section 5.1.3.4. The responding current AR SHALL copy the sequence number received in the MN-AR CARD Request to the MN-AR CARD Reply. In case the MN-AR CARD Reply message is lost, the MN requests the same information again after a timeout ARs detect a request for retransmission when receiving a MN-AR CARD Request because the sequence number is same as in the previously received request. In this case, ARs assume that the previously sent MN-AR CARD Reply message was lost and retransmit the CARD Reply message. The AR SHOULD rate limit retransmitted MN-AR CARD Request messages to avoid DoS attack. To enforce rate limiting, AR should silently discard CARD Request Message if the received rate of retransmitted CARD Request from a Mobile Node exceeds 1 per second. The CARD protocol optionally allows service providers to configure an AR to send periodic unsolicited CARD Reply messages to all connected mobile nodes. The unsolicited CARD Reply is delivered via multicast to MN(s). The current AR sets the U-flag of the unsolicited CARD Reply to indicate that the message is being sent unsolicited. L2 ID sub-options, which append to an unsolicited CARD Reply message, MUST indicate CANDIDATE in the L2 ID sub-option's Status-Code. An unsolicited CARD Reply message MAY be advertised immediately after a major change in CARs' capabilities Subsequent unsolicited CARD Reply messages must be released within the interval MIN_CARD_ADVERT_INTERVAL and MAX_CARD_ADVERT_INTERVAL for a configurable amount of advertisements. The actual interval for an individual unsolicited CARD Reply is a randomly chosen value between these two boundary values. Consecutive unsolicited CARD Reply messages MUST have the sequence number incremented for each message respectively to counteract replay attacks. [Page 13] Internet-Draft Candidate Access Router Discovery December 2003 4.3 Current Access Router - Candidate Access Router Operation 4.3.1 Current Access Router Operation The MN's current AR MAY initiate capability exchange with CARs either when it receives a MN-AR CARD Request or when it detects that one or multiple of its local CAR table's capability entries' lifetime is about to expire. Upon receipt of a MN-AR CARD Request, the MN's current AR retrieves the IP address of the associated CAR(s) from its local CAR table. Then the AR SHOULD issue an AR-AR CARD Request to the respective CAR(s) if complete capability information of a CAR is not available in the current AR's CAR table. The AR MAY also issue the AR-AR CARD Request when it detects that one or multiple of its local CAR table's entries are about to expire. The AR-AR CARD Request message format is defined in Section 5.2.2. The AR MUST set the sequence number of the CARD Request to one more than the previously used sequence number value. The AR MAY append its own capabilities, which are encoded as attribute-value pairs and encapsulated with the Capability Container message parameter, to the released AR-AR CARD Request. In case the AR-AR CARD Request conveys the current AR's capabilities to the CAR, the associated Capability Container can have any value set for the Context-ID, since there is no need for the receiving CAR to process this field due to the absence of a L2 ID and an Address sub-option. Furthermore, the current AR MAY set the P-flag in the Capability Container sub-option to inform the CAR about its own capability to perform CARD protocol message piggybacking. Optionally, a current AR MAY append the Preferences sub-option to the AR-AR CARD Request to obtain only capability parameters of interest from a CAR. To support error recovery in case an AR-AR CARD Request or an AR-AR CARD Reply gets lost, the sending AR performs signaling failure recovery according to the timeout-based mechanism as described in section 4.4.2. This allows detection of lost inter-AR signaling messages and performing retransmissions. Upon receipt of the AR-AR CARD Reply, which has been sent by the CAR in response to the previously sent request, the MN's current AR SHALL extract the capability information from the payload of the received message and store the received capabilities in its local CAR table. The lifetime of individual capabilities is to be set according to the lifetime indicated for each capability received. The value of the table entries' timeout shall depend upon the nature of individual capabilities. In case the inter-AR CARD signaling has [Page 14] Internet-Draft Candidate Access Router Discovery December 2003 been initiated due to a previously received MN-AR CARD Request, the AR now sends the MN-AR CARD Reply to the Mobile Node. Optionally, CARs can send unsolicited CARD Reply messages to globally adjacent ARs. In case the current AR receives an unsolicited CARD Reply message from one CAR it has an entry in its local CAR table, the current AR has to check that the sequence number of the received CARD Reply has increased compared to the previously received unsolicited CARD Reply message, which has been sent from the same CAR. Then, the current AR can update its local CAR table according to the received capabilities. 4.3.2 Candidate Access Router Operation Upon receipt of an AR-AR CARD Request, a CAR shall extract the capabilities of the MN's current AR from the payload of the received message, assuming the sending AR appended its own capabilities to the AR-AR CARD Request. The CAR SHALL store the received capabilities in its CAR table and set the timer for individual capabilities appropriately. The value of the table entries' timeout depends upon the nature of capabilities of AR-AR CARD Reply message. The CAR must include the same sequence number to the AR-AR CARD Reply Message as received in AR-AR CARD Request Message. The AR-AR CARD Reply shall include the CAR's capabilities as list of attribute-value pairs in the Capability Container message parameter. In case the sending AR has appended an optional Preferences sub- option, the CAR MAY perform capability filtering and send back only these capabilities, which are of interest to the requesting AR, identified according to the Preferences sub-option. Since the AR-AR CARD Reply is based on a previously received AR-AR CARD Request, the CAR MUST set the U-flag of the AR-AR CARD Reply to 0. In case the AR-AR CARD Reply message is lost on its way towards the requesting AR, the AR will request the same information again from the CAR after a timeout CARs can detect a request for retransmission when receiving an AR-AR CARD Request with the same sequence number as the previously received request. In this case, CARs must assume that the previously sent AR-AR CARD Reply message was lost and must retransmit the AR-AR CARD Reply message. Optionally, the CAR MAY send an unsolicited CARD Reply message to globally adjacent ARs in case one or more of its capability parameters change. The unsolicited CARD Reply messages should have as destination address the adjacent ARs' unicast address and must have the U-flag set. Consecutive unsolicited CARD Reply messages MUST have the sequence number incremented respectively. To avoid that unsolicited CARD Reply messages are sent too frequently, CARs SHOULD wait at least for MIN_CARD_UPDATE_INTERVAL before sending an [Page 15] Internet-Draft Candidate Access Router Discovery December 2003 updating message to a globally adjacent AR. The CAR MUST set the U- flag in unsolicited AR-AR CARD Reply messages. 4.4 CARD Signaling Failure Recovery For a variety of reasons, the packets carrying CARD protocol signaling may be dropped. In this section we consider mechanisms for recovery from the CARD signaling failures. Broadly the CARD signaling failures can be categorized in MN-AR signaling failures and AR-AR signaling failures. 4.4.1 MN-AR Signaling Failure Recovery It is likely that either a MN-AR CARD Request or MN-AR CARD Reply may be dropped due to poor radio link conditions. A MN SHALL retransmit the CARD Request using the same message sequence number, if it does not receive a CARD Reply within MR_AR_CARD_TIMEOUT seconds. The MN SHALL retry sending the MN-AR CARD Request for a pre-configured number of times (MN_AR_CARD_RETRIES) before declaring the protocol message exchange aborted. The MN SHALL silently discard any duplicate MN-AR CARD Reply messages received from its current AR and take the latest information received as valid. 4.4.2 AR-AR Signaling Failure Recovery It is likely that an AR-AR CARD Request or AR-AR CARD Reply may be dropped due to congestion at the intermediate routers or poor link conditions. The MN's current AR MAY retransmit the AR-AR CARD Request using the same message sequence number, if it does not receive a CARD Reply within AR_AR_CARD_TIMEOUT seconds. The current AR MAY retry the AR-AR CARD Request message for a pre-configured number of times (AR_AR_CARD_RETRIES) before declaring the protocol message exchange as aborted. The current AR SHALL silently discard any duplicate AR-AR CARD Reply messages received from the CAR and take the latest information received as valid. To avoid superfluous requests for retransmission on the MN-AR interface caused by a failure in signaling between ARs, the specified MN_AR_CARD_TIMEOUT value is larger than the value of.the AR-AR CARD signaling time including possible retransmissions between ARs. This ensures that a MN requests its current AR for retransmission only in case the MN-AR CARD Request or the MN-AR CARD Reply is lost, as well as when the AR-AR CARD procedure has aborted. [Page 16] Internet-Draft Candidate Access Router Discovery December 2003 4.5 CARD Protocol Message Piggybacking on the MN-AR Interface CARD supports another mode of CAR information distribution, in which the capabilities are distributed piggybacked on a fast handover protocol. To allow MNs and ARs appending the ICMP-option type CARD Request and CARD Reply (Section 5.1.2) to the ICMP-type Fast Mobile IPv6 [Kood03] signaling messages, the MN and AR should know about the signaling peer's capability for CARD protocol message piggybacking. This requires dynamic discovery of piggybacking capability using the P-flag in the MN-AR CARD Request and the MN-AR CARD Reply message, as well as in the Capability Container message parameter. The format of these messages and parameters is described in Section 5.1. If the MN has not received an unsolicited CARD Reply message, the MN sends the very first CARD Request to its current AR using the ICMP- type CARD main header for transport, as described in Section 5.1.1. In case the MN supports CARD protocol message piggybacking, the P- flag in this very first CARD Request message is set. On reception of the CARD Request message, current AR learns about the MN's piggybacking capability. To indicate its piggybacking capability, the AR sets the P-flag in the CARD Reply message. In case the AR does not support piggybacking, all subsequent CARD protocol messages between the MN and the AR are sent stand-alone, using the CARD main header. In case both nodes, the MN and its current AR, support CARD protocol message piggybacking, subsequent CARD protocol messages can be conveyed as an option via the Fast Mobile IPv6 Router Solicitation for Proxy (RtSolPr) and Proxy Router Advertisement (PrRtAdv) messages. During the CARD process, a MN learns about CARÆs piggybacking capability during the discovery phase, since the Capability Container, as described in Section 5.1.3.4, also carries a P-flag. This allows the MN to immediately perform CARD protocol message piggybacking after a handover to a selected CAR, assumed this CAR supports CARD protocol piggybacking. If a MN prefers the reverse address translation function of the Fast Mobile IPv6 protocol, it can use CARD protocol message piggybacking to retrieve only the CARs' capability information. To indicate that reverse address translation is not required, the piggybacked CARD Request message MUST have the A-flag set. These causes the current AR to append only Capability Container sub-options To associate a Capability Container, sent as a parameter of the CARD Reply message, to the IP address for the appropriate CAR, the Context-ID of an individual Capability Container MUST be used as an index, pointing to the associated IP address in the PrRtAdv message options. The Context-ID of individual Capability Containers is set appropriately by the MN's current AR. Details about how individual Context-ID values can be associated with a particular IP address option of the PrRtAdv message is out of the scope of this document. [Page 17] Internet-Draft Candidate Access Router Discovery December 2003 An application scenario for the CARD-function piggybacking is described in Appendix B.2. 4.6 CARD Protocol Security The MN-AR and AR-AR messages' authenticity MUST be ensured using IPsec ESP [AtKe98] in transport mode. The CARD protocol assumes that there will be an appropriate IPsec Security Association (SA) between a MN and its connected AR, which MAY be used to secure MN-AR CARD messages. It is also assumed that neighboring ARs SHALL establish an appropriate SA to secure the AR-AR CARD messages. IPSec ESP MUST be used with a non-null integrity protection and origin authentication algorithm and SHOULD be used with a non-null encryption algorithm for protecting the confidentiality of the CARD information. [Page 18] Internet-Draft Candidate Access Router Discovery December 2003 5. PROTOCOL MESSAGES 5.1 CARD Messages for the Mobile Node-Access Router Interface 5.1.1 CARD Main Header Format Hosts and Access Routers use the CARD ICMP-type main header when CARD protocol messages, cannot be conveyed via another outgoing ICMP-type message. 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 | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+- - - - IP Fields: Source Address: An IP address assigned to the sending interface. Destination Address: An IP address assigned to the receiving interface. Hop Limit: 255 Encapsulating Security Payload (ESP) Header: IPSec ESP MUST be used with a non-null integrity protection and origin authentication algorithm and SHOULD be used with a non-null encryption algorithm for protecting the confidentiality of the CARD information. ICMP Fields: Type T.B.A (To be assigned) Code 0 Checksum The ICMP checksum. [Page 19] Internet-Draft Candidate Access Router Discovery December 2003 Reserved This field is currently unused. It MUST be initialized with zero by the sender and MUST be ignored by the receiver. Valid Options: CARD Request: The CARD Request allows entities to request CARD specific information from ARs. To support processing the CARD Request message on the receiver side, further sub-options may be carried, serving as input to the reverse address translation function and/or capability discovery function. CARD Reply: The CARD Reply carries parameters, previously requested with a CARD Request, back to the sender of the CARD Request. In case of unsolicited address information and capabilities are to be sent to a node, the sender uses the CARD Reply without receiving an explicit CARD Request. Further sub-options will be associated with the CARD Reply message. Valid Sub-Options: Layer-2 ID (mandatory): The Layer-2 ID sub-option [5.1.3.1] carries information about the type of an access point as well as the Layer-2 address of the access point associated with the CAR, whose IP address and capability information is to be resolved. Capability container (mandatory): The Capability container sub-option carries information about a single CAR's capabilities. The format of this sub-option is described in Section 5.1.3.4. Address (mandatory): The Address sub-option carries information on an individual CAR's resolved IP address. The format of the Address sub-option is described in Section 5.1.3.5. Preferences sub-option (optional): The Preferences sub-option carries information about attributes of interest to the requesting entity. Attributes are encoded according to the AVP encoding rule as described in Section 5.1.4. For proper settings of AVP Code and Data [Page 20] Internet-Draft Candidate Access Router Discovery December 2003 field, please see Section 5.1.3.2. This sub- option is used only in case of performing optional capability pre-filtering on ARs and provides only capabilities of interest to a requesting MN. Requirements (optional): The Requirements sub-option carries information about attribute-value pairs required for pre- filtering of CARs on a MN's current AR. This parameter conveys MN specific attribute-value pairs to allow a MN's current AR to send only information about CARs of interest back to the requesting MN. CARs are filtered on ARs according to CARs' capability parameters and given policy or threshold, as encoded in the Requirements sub-option. Attribute-value pairs are encoded according to the AVP encoding rule as described in Section 5.1.4. Rules for proper setting of the AVP Code and Data field for the Requirements sub-option are described in Section 5.1.3.3. 5.1.2 CARD Options Format All options are of the form: 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 | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ... ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fields: Type: 8-bit identifier of the type of option. The options defined in this document are: Option Name Type -------------------------------------------------- MN-AR CARD Request T.B.A MN-AR CARD Reply T.B.A [Page 21] Internet-Draft Candidate Access Router Discovery December 2003 Length: 8-bit unsigned integer. The length of option including the type and length fields in units of 8 octets. The value 0 is invalid. 5.1.2.1 CARD Request 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 |P|C|A| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Options +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - - Fields: Type: T.B.A Length: The length of the option in units of 8 octets, including the type and length fields as well as sub-options. Flags: P-flag: Indicates CARD protocol message piggybacking capability of the CARD Request message sender. A description for proper use of this flag can be found in Section 4.5 of this document. C-flag: Indicates that the requesting entity is interested also in associated CARs' capabilities. If the MN wants the AR to append CARs' capability parameters to the CARD Reply in addition to address information, the MN must set this flag. A-flag: Indicates that the requesting entity does NOT want the receiver of this message to perform reverse address translation. This flag could be set in case CARD protocol messages are piggybacked with a protocol that performs reverse address translation. For details refer to Section 4.5 The flag combination A=1 and C=0 is invalid. The AR should discard the invalid condition log appropriate error messages. Reserved bits MUST be initialized with 0. [Page 22] Internet-Draft Candidate Access Router Discovery December 2003 Sequence Number: Allows correlating requests with replies. Valid Sub-Options: - L2 ID sub-option - Preferences sub-option - Requirements sub-option To ensure meeting requirements on boundary alignment, individual sub-options MUST meet the 32-bit boundary alignment requirements respectively. To meet the 8n boundary alignment requirement of the entire CARD Request option, the CARD option reply MUST be padded if necessary to meet the 8n alignment constraint. 5.1.2.2 CARD Reply 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 |P|U| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Options +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - - Fields: Type: T.B.A Length: The length of the option in units of 8 octets, including the type and length fields as well as sub-options. Flags: P-flag: Indicates CARD protocol message piggybacking capability of the CARD Reply message sender. A description for proper use of this flag can be found in Section 4.5 of this document. U-flag: Indicates an unsolicited CARD Reply. A description for proper use of this flag can be found in Section 4 of this document. Reserved bits MUST be initialized with 0. Sequence Number: [Page 23] Internet-Draft Candidate Access Router Discovery December 2003 Allows correlating requests with replies. Valid Sub-Options: - L2 ID sub-option - Capability Container sub-option - Address sub-option To ensure meeting requirements on boundary alignment, individual sub-options MUST meet 32-bit boundary alignment requirements respectively. To meet the 8n boundary alignment requirement of the entire CARD Reply option, the CARD option reply MUST be padded if necessary to meet the 8n alignment constraint. 5.1.3 Sub-Options Format All sub-options are of the form: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Option Type|Sub-Option Len | Sub-Option Data . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Sub-Option Type: 8-bit identifier of the type of option. The sub-options defined in this document are: Sub-Option Name Type -------------------------------------------- L2 ID 0x01 Address 0x02 Capability Container 0x03 Preferences 0x04 Requirements 0x05 Option-Length: 8-bit unsigned integer. Indicates the length of the option. For details on how this value needs to be set be referred to the description of individual sub- options in the following Sections. Since some sub-options have variable lengths in value, individual sub-options MUST be aligned on 32-bit boundary. [Page 24] Internet-Draft Candidate Access Router Discovery December 2003 5.1.3.1 L2 ID Sub-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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Option Type|Sub-Option Len | Context-ID | Status Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | L2-Type | L2 ID . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - - Sub-Option Type: 0x01 Sub-Option Length: Length of the sub-option (including type and length fields) in units of octets. Context-ID: Associated L2 ID, IP address and capability parameters that belong to the same node (AR) but are encoded in separate sub-options. Status Code: This field allows ARs to inform a requesting entity about processing results for a particular L2 ID. The L2 ID sub-option MUST be sent back to the requesting entity with a CARD Reply message. The following status codes are specified: 0x00: NONE - This value MUST be set in case the L2 ID is appended to a CARD Request. 0x01: CANDIDATE - This value MUST to be set by an AR when sending a L2 ID sub-option in a CARD Reply for information about candidate APs' L2 IDs. Candidate L2 IDs can be sent either with an unsolicited CARD Reply or in case a MN does not request for resolution of specific L2 IDs with a CARD Request. In this case, the AR MUST set the Context-ID field of individual parameters to a value that allows matching associated L2 ID, address and capability information on the receiver side. 0x02: MATCH - This value is set by an AR to identify that this L2 ID matches previously resolved CAR information for a different L2 ID. The AR sets this value for the Status Code, matches the associated Context-ID with one of the previously resolved L2 ID and [Page 25] Internet-Draft Candidate Access Router Discovery December 2003 sends the L2 ID back to the requesting entity with the CARD Reply message. 0x03: RESOLVER ERROR - This value MUST be set by an AR in case the L2 ID cannot be resolved. To notify the requesting entity, the AR sets this value for the Status Code and sends the L2 ID sub-option back to the requesting entity with the CARD Reply message. L2 type: Indicates the interface type. The L2 type identifier also serves as an indication of the subsequent L2 ID field's length without padding. The following types are initially defined: Technology | L2 type --------------+--------- IEEE802.11a | T.B.A. IEEE802.11b | T.B.A. IEEE802.11g | T.B.A. L2 ID: The variable length Layer-2 identifier of an individual CAR's access point. 5.1.3.2 Preferences Sub-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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Option Type|Sub-Option Len | Preferences +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Sub-Option Type: 0x04 Sub-Option Length: Length of the sub-option (including type and length fields) in units of octets. Preferences: List of capability attribute values (section 5.1.4). Only ATTRIBUTE (AVP Code, see section 5.1.4) fields MUST be present and set for individual capabilities, which are of interest to the requesting entity. The LIFETIME and VALUE (Data) indicator will not be processed and can be omitted. The AVP LENGTH indicator is also not present, since the preferences are indicated only with a list of [Page 26] Internet-Draft Candidate Access Router Discovery December 2003 16-bit encoded ATTRIBUTE fields. In case 32-bit boundary alignment requirements cannot be met with the list of ATTRIBUTE values, padding the missing 16-bit MUST be done with an ATTRIBUTE value of 0x0000. The use of the Preferences sub-option is optional and for optimization purpose. 5.1.3.3 Requirements Sub-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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Option Type|Sub-Option Len | Requirements +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Sub-Option Type: 0x05 Sub-Option Length: Length of the sub-option (including type and length fields) in units of octets. Requirements: AVP encoded requirements (see Section 5.1.4) AVPs MUST be encoded according to the rule described in Section 5.1.4. Both, the ATTRIBUTE (AVP Code) and VALUE (Data) field MUST be present and set appropriately. The use of the Requirements sub-option is optional and for optimization purpose. 5.1.3.4 Capability Container Sub-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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Option Type|Sub-Option Len | Context-ID |P| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVPs +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - - Sub-Option Type: 0x03 [Page 27] Internet-Draft Candidate Access Router Discovery December 2003 Sub-Option Length: Length of the sub-option in units of 8 octets. The sub-option Length does not include the length of the Capability Container sub-option header, which comprises the sub-option Type field, the sub-option Length field, the Context-ID, the P-flag and the Reserved field. Context-ID: L2 ID, IP address and capability parameters that belong to the same node (AR) but are encoded in separate sub-options. Flags: P-flag: Indicates piggybacking capability of the CAR whose capabilities are conveyed in this Capability Container. This flag allows a MN already after a CARD process to know about a selected new AR's piggybacking capability. Reserved bits MUST be initialized with 0. AVPs: AVPs are a method of encapsulating capability information relevant for the CARD protocol. See Section 5.1.4 for the AVP encoding rule. 5.1.3.5 Address Sub-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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Option Type|Sub-Option Len | Context-ID | Address Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - Sub-Option Type: 0x02 Sub-Option Length: Length of the sub-option (including type and length fields) in units of octets. Context-ID: L2 ID, IP address and capability parameters that belong to the same node (AR) but are encoded in separate sub-options. Address Type: Indicates the type of the address. [Page 28] Internet-Draft Candidate Access Router Discovery December 2003 0x01 IPv4 0x02 IPv6 Address: The Candidate Access Router's IP address. 5.1.4 Capability AVP encoding rule 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Code | AVP Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attribute Lifetime | Data . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - - AVP Code: Identifies the attribute uniquely. The AVP Code 0x0000 is reserved and MUST NOT be assigned to a capability. AVP Length: The two octet AVP length field indicates the number of octets in this AVP, including the AVP Code, AVP Length, Reserved, Lifetime and Data field. Reserved: This field is reserved for future use and MUST be set to 0. Lifetime: Specifies the lifetime of the encoded capability in seconds. In case of a static capability, the Lifetime field MUST be set to the maximum value (0xffff), which indicates that the lifetime of this capability parameter never expires. A lifetime value of 0x0000 deletes a capability entry. Data: This variable length field has the Value of the capability attribute encoded. Note: This document provides no detailed information on how to encode the capability attribute's value, which is to be encoded in the Data field of the generic message format described above. Also details on the interpretation of individual capability parameters are out of scope of this document. 5.2 CARD Messages for the Inter-Access Router Protocol Operation 5.2.1 Protocol Transport [Page 29] Internet-Draft Candidate Access Router Discovery December 2003 For the CARD protocol operation between a MN's current AR and CARs, UDP [Post80] is used for transport of CARD protocol messages. The associated UDP port for the CARD protocol operation is T.B.A. To protect CARD protocol messages between ARs, the IPsec ESP [AtKe98] MUST be used with a non-null integrity protection and origin authentication algorithm and SHOULD be used with a non-null encryption algorithm for protecting the confidentiality of the CARD information. 5.2.2 Protocol Main Header The protocol main header comprises the first 8 octets: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version|U| Res.| Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ - - - Version: Indicates the version of the protocol. The version described in this document is version 1. U-flag: Indicates an unsolicited AR-AR CARD Reply message if set to 1. This flag MUST be set to 0 in case the CARD Reply has been previously solicited or in case the message is a CARD Request. Reserved: This field is currently reserved and MUST be set to 0. Type: Message type. The following message types are specified for this interface: Message Type -------------------------------------- AR-AR CARD Request 0x01 AR-AR CARD Reply 0x02 Sequence number: Allows correlating requests with responses. [Page 30] Internet-Draft Candidate Access Router Discovery December 2003 5.2.3 Protocol Payload Types On this protocol interface, the Capability Container parameter is used to convey capabilities between ARs. Optionally, the Preferences parameter can be used for capability pre-filtering during the inter- AR capability discovery procedure. Payload types and encoding rules are the same as described for the respective sub-option types in Section 5.1 for the MN-AR interface. The same TLV-encoded format is used to attach the options as payload to the protocol main header. 5.3 Overview on sub-options'/payload types' usage The following table indicates, which sub-options or payload types are relevant for the various interfaces in CARD protocol functions. Description Type Interface | | / \ | | MN-AR AR-AR --------------------------------------------------------------- L2 ID 0x01 x Address 0x02 x Capability Container 0x03 x x Preferences 0x04 x x Requirements 0x05 x [Page 31] Internet-Draft Candidate Access Router Discovery December 2003 6. SECURITY CONSIDERATIONS 6.1 Assumptions It is important to note that it is assumed in the protocol that each AR has the correct information in the CAR table about the identities of the geographically neighboring APs and their associated ARs and the association relationship between the APs and the ARs. It is assumed that the ARs registered in the CAR table at each AR are authorized to participate in the CARD protocol. Any security concern regarding the procedure to discover the CAR identities is not considered here. Verifying the authorization status of particular ARs with respect to participating in the CARD protocol is a part of the discovery procedures and thus is not considered here either. The appendices of this draft describe procedures for discovering the identities of the geographically adjacent ARs and APs and relevant security considerations. It is assumed also that each AR has the correct information about APs associated with the AR or capability to get it. It could be done as static configuration at the AR or a protocol could be used between the AR and the APs for dynamic discovery and exchange of information such as MAC addresses and operating channels of the APs. It is out of scope of this document. 6.2 Security Association between AR and AR Each AR receives capability information from its neighboring ARs. If the message is not protected from modification, a malicious attacker can modify the information, which can cause undesirable impacts on the applications using the information. Also if the information is delivered in plain text, a third party can read it. To prevent the information from being compromised, the CARD messages between ARs MUST be authenticated. The messages also MAY be encrypted for privacy of the information. How to establish a security association is out of scope of this document. But it is assumed that the two CARs can establish a security association. IPsec ESP is the default mechanism for message authentication between ARs. Also, IPsec ESP is the default method for message encryption. Which capability information is collected in the CAR table and allowed to be disclosed depends on the administration policy. In particular, if the CARD protocol runs between ARs in different domains as well as within the same domain, different policies could [Page 32] Internet-Draft Candidate Access Router Discovery December 2003 be established regarding capability information disclosure. The policy can be implemented locally at each AR and thus it is not dealt with here. 6.3 Security Association between AR and MN A malicious node can send bogus CARD Reply messages to MNs by masquerading the AR. The MN MUST authenticate the CARD Reply messages from the AR. IPsec ESP is the default mechanism for CARD signaling message authentication between an AR and a MN. Also, IPsec ESP is the default method for message encryption. Authentication of unsolicited CARD Reply messages, which are multicast from an AR towards MNs, is an open issue and the specification of an appropriate protection mechanism is out of scope of this document. 6.4 DoS Attack An AR can be overwhelmed with CARD Request messages or even CARD Reply messages. A MN can also be overwhelmed with CARD Reply messages. The AR or MN SHOULD implement a rate limiting policy so that it does not send or process more than a certain number of messages per period. The AR should also implement a rate limiting policy in accepting CARD Request messages from any particular AR or MN. A rate limiting policy is described in Section 4. An attacker can send a huge list of capability information by masquerading ARs. It can cause overflow in the buffer for the CAR table at ARs or MNs. So the AR or the MN should put a limit on the size of the capability information for an AR. Making authentication of CARD protocol messages mandatory supports protection of ARs against CARD Request flooding with spoofed addresses, since authenticating the requests makes DoS less likely as the attacker's identity is revealed and its account can be disabled. [Page 33] Internet-Draft Candidate Access Router Discovery December 2003 7. PROTOCOL CONSTANTS Mobile Node protocol constants: MN_AR_CARD_TIMEOUT: 1 second This timer value specifies the timeout of an expected CARD Reply message on a MN after a previously released CARD Request message has been sent to the MN's current AR. MN_AR_CARD_RETRIES: 5 This value specifies the number of retries when sending a MN-AR CARD Request from a MN before declaring the message exchange aborted. CARD_REQUEST_RATE: 2 requests/second This value specifies the maximum rate a MN is allowed to send new CARD Requests to an AR. Access Router protocol constants: AR_AR_CARD_TIMEOUT: 300 milliseconds This timer value specifies the timeout of an expected CARD Reply message on an AR after a previously released CARD Request message has been sent to a CAR. AR_AR_CARD_RETRIES: 2 This value specifies the number of retries when sending an AR-AR CARD Request from a MN's current AR to a CAR before declaring the message exchange aborted. MIN_CARD_ADVERT_INTERVAL (MN-AR): 1 second MAX_CARD_ADVERT_INTERVAL (MN-AR): 60 seconds MIN_CARD_UPDATE_INTERVAL (AR-AR): 60 seconds CARD_UNSOL_MC_V6_ADDR: T.B.A (To be assigned by IANA) CARD_UNSOL_MC_V4_ADDR: T.B.A (To be assigned by IANA) [Page 34] Internet-Draft Candidate Access Router Discovery December 2003 8. IANA CONSIDERATIONS This section is to provide the Internet Assigned Numbers Authority (IANA) with guidelines to allow assignment and registration of values related to the Candidate Access Router Discovery protocol, in accordance with [NaAl98]. The protocol described in this document requires a new ICMP type to be assigned by the IANA for the CARD protocol main header (Section 5.1.1). Furthermore, two new ICMP option types (Section 5.1.2) are to be assigned for the protocol operation between a Mobile Node and its current Access Router for the Mobile IP Fast Handover Protocol [Kood03] and for the standalone use of CARD between the MN and AR. The protocol also requires a UDP port number to be assigned for the inter-Access Router CARD protocol operation (Section 5.2.1). To uniquely identify specific access technologies in the L2-Type field of a CARD L2 ID sub-option, the IANA should also set up a registry to assign fixed numbers for well-known access technologies (Section 5.1.3.1). Initially, values for IEEE802.11a, IEEE802.11b and IEEE802.11g should be assigned. To allow MNs receiving unsolicited CARD Reply messages only in case they are of interest to them, a well-known multicast IP address for IPv4 and IPv6 (link-local) needs to be assigned by IANA for that purpose (section 7). For future assignment of capability APV codes (Section 5.1.4), it is recommended that assignment will be done on the basis of Designated Experts. 9. NORMATIVE REFERENCES [Brad97] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [Kemp02] Kempf, J., "Problem Description: Reasons For Performing Context Transfers Between Nodes in an IP Access Network", RFC 3374, September 2002. [NaNS98] Narten, T., et al., "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [Post80] Postel, J., "User Datagram Protocol", RFC 768, August 1980. [AtKe98] Atkinson, R., Kent, S.,"IP Encapsulating Security Payload (ESP)", RFC 2406, November 1998. [NaAl98] Narten, T., Alvestrand, H., "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998. [Page 35] Internet-Draft Candidate Access Router Discovery December 2003 10. INFORMATIVE REFERENCES [TKCK02] Trossen, D., Krishanmurthi, G. Chaskar, H., Kempf, J., "Issues in candidate access router discovery for seamless IP-level handoffs", Work in Progress, October 2002. [Kris02] Krishanmurti, G., "Requirements for CAR Discovery Protocolsö, Work in Progress, October 2002. [Kenw02] Kenward, B., "General Requirements for Context Transfer", Work in Progress, October 2002. [MaKo03] Manner, J., Kojo, M. (Ed), "Mobility Related Terminology", Work in Progress, April 2003. [Kood03] Koodli, R, et al., "Fast handoffs for Mobile IPv6", Work in Progress, October 2003. [Funa02] Funato, D. et al., "Geographically Adjacent Access Router Discovery Protocolö, Work in Progress, June 2002. [Tros03] Trossen, D. et al., "A Dynamic Protocol for Candidate Access-Router Discovery", Work in Progress, March 2003. [ShGi00] Shim, E., Gitlin, R., "Fast Handoff Using Neighbor Information", Work in Progress, November 2000. [Malk03] El Malki, K. et al., "Low Latency Handoffs in Mobile IPv4", Work in Progress, October 2003. 11. AUTHORS' ADDRESSES Hemant Chaskar Nokia Research Center 5 Wayside Road Burlington, MA 01803, USA Phone: +1 781-993-3785 Email: Hemant.Chaskar@nokia.com Daichi Funato NTT DoCoMo USA Labs 181 Metro Drive, Suite 300 San Jose, CA 95110, USA Phone: +1 408-451-4736 Email: funato@docomolabs-usa.com Marco Liebsch NEC Network Laboratories [Page 36] Internet-Draft Candidate Access Router Discovery December 2003 Kurfuersten-Anlage 36 , 69115 Heidelberg Germany Phone: +49 6221-90511-46 Email: marco.liebsch@ccrle.nec.de Eunsoo Shim NEC Laboratories America, Inc. 4 Independence Way Princeton, NJ 08540, USA Phone: +1 609-951-2909 Email: eunsoo@nec-labs.com Ajoy Singh Motorola Inc 1501 West Shure Dr, USA Phone: +1 847-632-6941 Email: asingh1@email.mot.com 12. IPR STATEMENTS The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights. Please refer to http://www.ietf.org/ietf/IPR for more information. 13. COPYRIGHT NOTICE "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. [Page 37] Internet-Draft Candidate Access Router Discovery December 2003 This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." 14. CONTRIBUTORS The authors would like to thank Vijay Devarapalli (Nokia) and Henrik Petander (Helsinki University of Technology) for formally reviewing the protocol specification draft and providing valuable comments and input for technical discussions. The authors would also like to thank James Kempf for reviewing and providing lots of valuable comments on the previous version (version 5) of the draft. 15. ACKNOWLEDGEMENTS The authors would like to thank (in alphabetical order) Dirk Trossen, Govind Krishnamurthi, James Kempf, Madjid Nakhjiri, Pete McCann, Rajeev Koodli, Robert C. Chalmers and other members of the Seamoby WG for their valuable comments on the previous versions of the document as well as for the general CARD related discussion and feedback. In addition, the authors would like to thank Erik Nordmark for providing valuable insight about the piggybacking of CARD options upon Fast Mobile IPv6 messages. [Page 38] Internet-Draft Candidate Access Router Discovery December 2003 APPENDIX A: MAINTENANCE OF ADDRESS MAPPING TABLES IN ACCESS ROUTERS This appendix provides information on two optional CAR table maintenance schemes for reverse address mapping in access routers. Details on these mechanisms are out of the scope of this document and intention of this appendix is to provide only a basic idea on flexibly extensions to the CARD protocol as described in this document. Appendix A.1 Centralized Approach using a Server Functional Entity The centralized approach performs CARD over the MN-AR interface as described in Chapter 4 of this document. Additionally, the centralized approach introduces a new entity, the CARD server, to assist the current AR in performing reverse address translation. The centralized approach requires neighboring AR(s) to register with the CARD server to populate the reverse address translation table. The registration of AR(s) addresses with the CARD server is performed prior to initiation of any reverse address translation request. Figure A.1 illustrates a typical scenario of the centralized CARD operation. In this example, ARs have registered their address information with a CARD server in advance. When a MN discovers the L2 ID of APs during L2 scanning, the MN passes one or more L2 ID(s) to its current AR and the AR resolves it to the IP address of the AR. For this, the AR first checks whether the mapping information is locally available in its CAR table. If not, the MN's current AR queries a CARD server with the L2 ID. In response, the CARD server returns the IP address of the CAR to the current AR. Then, the current AR directly contacts the respective CAR and performs capability discovery with it. The current AR then passes the IP address of the CAR and associated capabilities to the MN. The current AR then stores the resolved IP address within its local CAR table. The centralized CARD protocol operation introduces additional signaling messages, which are exchanged between the MN's current AR and the CARD server. The signaling messages between an AR and the CARD server function are shown with the preceding identifier "AR- Server", referring to the associated interface. An initial idea of performing reverse address translation using a centralized server has been described in [Funa02]. [Page 39] Internet-Draft Candidate Access Router Discovery December 2003 +----------+ +------------>| CARD |<-------------+ |+------------| Server |-------------+| || +----------+ || || || || ~~~~~~~~~~~ || (3)AR-Server||(4)AR-Server{ } ||(0) CARD CARD || CARD { } ||Reg Req/ Request || Reply { IP Cloud } | Reply || { } || || { } || |V ~~~~~~~~~~~ V| +---------+ (5)AR-AR CARD Request +-----+-----+ | Current |------------------------->| CAR | CAR | | AR |<-------------------------| 1 | 2 | +---------+ (6)AR-AR CARD Reply +-----+-----+ ^ | | | (2)MN-AR | |(7)MN-AR | | CARD | | CARD | | Request| V REPLY +---+ +---+ +--------------+ (1) AP1 L2 ID +--|AP1| |AP2| | Mobile |<---------------------+ +---+ +---+ | Node |<--------------------------------+ +--------------+ (1) AP2 L2 ID Figure A.1: Centralized Approach for L2-L3 mapping Appendix A.2 Decentralized Approach using Mobile Terminals' Handover This approach performs CARD over the MN-AR interface as described in Chapter 4. However, it employs one additional message, called the Router Identity message, over the MN-AR interface to enable ARs to learn about the reverse address translation tables of their neighboring ARs, without being dependent on any centralized server. In this approach, CAR identities in the CAR table of an AR are maintained as soft state. The entries for CARs are removed from the CAR table if not refreshed before the timeout period expires and are created or refreshed according to the following mechanism. The key idea behind the decentralized approach is to bootstrap and maintain the association between two ARs as neighbors of each other using the actual handover of MNs occurring between them as input. The first handover between any two neighboring ARs serves as the bootstrap handover to invoke the discovery procedure and the [Page 40] Internet-Draft Candidate Access Router Discovery December 2003 subsequent handover serve to refresh the association between the neighboring ARs. After the bootstrap handover, the MNs can perform CARD and thus seamless handover using the CAR information. This idea was presented in [ShGi00] and [Tros03]. Maintenance of the CAR table could be done using an additional option for the CARD protocol operation performed between a MN and its current AR. This message serves as Router Identity message. Upon the completion of an inter-AR handover, the MN SHOULD send a Router Identity message to its current AR. This message contains the identity (IP address) of the previous AR (pAR), and can be sent as a specific sub-option in the MN-AR CARD Request message. It SHOULD be acknowledged with the MN-AR CARD Reply. The Router Identity message enables the MN's current AR to learn that the pAR (still) has an AP whose coverage overlaps with one of the APs of the current AR and vice versa. With this information, the MN's current AR can create or refresh an entry for the pAR as its neighbor. If handover cease between two particular ARs, the associated entries will eventually timeout and removed from each AR's CAR table. Prior to trusting the MN's report, however, the current AR may perform a number of checks to ensure the validity of the received information. One simple method is to verify the accuracy of the Router Identity message by sending an AR-AR CARD Request message to the pAR. The AR-AR CARD Request includes the identity of the MN. Upon receiving this message, the pAR has to verify that the MN was indeed attached to it during a reasonable past interval and respond to the current AR. In this way, each handover of a MN results in a bi-directional discovery process between the two participating ARs. Upon receiving a positive verification response, the current AR creates or refreshes as applicable the entry for the pAR in its local CAR table. In the former case, the current AR and the pAR exchange capabilities using the AR-AR CARD Request and AR-AR CARD Reply protocol messages. When a new entry is created, the ARs MUST exchange their reverse address translation tables. They may exchange other capabilities at this time or may defer it to a later time when some MN undergoing handover between them performs CARD as described in section 4. In the later (refresh) case, ARs may exchange capabilities or defer it until a later time when another MN undergoes handover. Finally, note that in a handover-based protocol, a first handover between a pAR and a MN's current AR cannot use CARD, as this handover bootstraps the CAR table. However, in long term, such a handover will only amount to a small fraction of total successful handover between the two AR(s). Also, if the MN engaging in such a first handover is running a non-delay sensitive application at the time of handover, the user may not even realize its impact. [Page 41] Internet-Draft Candidate Access Router Discovery December 2003 APPENDIX B: APPLICATION SCENARIOS This section provides two examples of an application scenario for CARD protocol operation. One scenario describes a CARD protocol operation in a Mobile IPv6 (MIPv6) network, providing access to the infrastructure via wireless LAN Access Points and associated Access Routers. A second scenario describes CARD protocol operation in a Mobile IPv6 enabled network, which has enhanced support for fast handover integrated (Fast Mobile IPv6), also providing wireless LAN access to the infrastructure. Appendix B.1 CARD Operation in a Mobile IPv6 Enabled Wireless LAN Network This application scenario assumes a moving MN having access to the infrastructure through wireless LAN (IEEE802.11) APs. Mobility management is performed using the Mobile IPv6 protocol. The following figure illustrates the assumed access network design. ----------------------------- / \ +----+ | NETWORK |---| HA | \ / +----+ ----------------------------- | | +-----+ +-----+ | AR1 |---------+ | AR2 | +-----+ | +-----+ | subnet 1 | |subnet 2 +-----+ +-----+ +-----+ | AP1 | | AP2 | | AP3 | +-----+ +-----+ +-----+ ^ ^ ^ \ \ \ v +-----+ | MN | - - ->>>- - - ->>> +-----+ Figure B.1: Assumed network topology A Mobile IPv6 Home Agent (HA), maintains location information for the MN in its binding cache. From Figure B.1, the MN holds a care-of address for the subnet 1, supported by AR1. As the MN moves, the MN's current environment offers two further wireless LAN APs with increasing link-quality as candidate APs for a handover. To [Page 42] Internet-Draft Candidate Access Router Discovery December 2003 facilitate decision making, parameters associated with ARs are taken into account during the decision process. The AR-related parameters can be, for example, available QoS resources or the type of access technologies supported from an AR. To learn about these candidate ARs' capabilities and associated IP address information, the MN performs CARD. This requires retrieving information about candidate APs' L2 IDs Furthermore, associated link-quality parameters are retrieved to ascertain, whether or not approaching APs are eligible candidates for a handover. Assume AP2 and AP3 are suitable candidate APs. The MN encapsulates both L2 IDs (AP2 and AP3) into a CARD Request message, using the L2 ID sub-option, and sends it to its current AR (AR1). AR1 resolves each L2 ID, listed in L2 ID options to the associated IP address of the respective CAR, making use of its local CAR table. According to the environment illustrated in Figure B.1, the associated AR IP address of the candidate AP2 will be the same as the MN is currently attached to, which is AR1. Respective IP address of the candidate AR, to which AP3 is connected to, is the address of AR2. Since IP addresses of the MN's CARs are now known to AR1, AR1 retrieves the CARs' capabilities from the CAR table, assumed it has valid entries for respective capability parameters To refresh dynamic capabilities, whose associated lifetime in AR1's CAR table has expired, AR1 performs Inter-AR CARD for capability discovery. Since capability information for AR1 is known to AR1, a respective Inter-AR CARD Request is sent only to AR2. AR2 in response sends a CARD Reply message back to AR1, encapsulating the requested capability parameters with the signaling message, in a Capability Container sub-option. Now, AR1 sends its own capabilities and the dynamically discovered ones of AR2 back to the MN via a CARD Reply message. Furthermore, AR1 stores the capability parameters of AR2 with the associated lifetimes in its local CAR table. On reception of the CARD Reply message, the MN performs target AR selection, taking AR1's and AR2's capability parameters as well as associated APs' link-quality parameters into account. In case the selected AP is AP2, no IP handover needs to be performed. In case AP3 and the associated AR2 are selected, the MN needs to perform an IP handover according to the Mobile IPv6 protocol operation. Figure B.2 illustrates the signaling flow of the previously described application scenario of CARD within a Mobile IPv6 enabled network. MN AP1 AR1 AP2 AP3 AR2 | | | | | | | connected | | | | | 0-------------0-------0 | | | [Page 43] Internet-Draft Candidate Access Router Discovery December 2003 | | | | | | | | | | | | | | | | | <~~~~~~~~~L2-SCAN (AP2)~~~~~| | | | <~~~~~~~~~L2-SCAN (AP3)~~~~~~~~~~~~~~~~~| | | | | | | (MN-AR) CARD Req | | | | |-------------------->| (AR-AR) CARD Req | | | |---------------------------------------->| | | | (AR-AR) CARD Repl | | (MN-AR) CARD Repl |<----------------------------------------| |<--------------------| | | | | | | | | | [target AR | | | | | selection] | | | | | | | | | | | // // // // // // [either...] | | | | | | | | | | | |-------- L2 attach --------->| | | | | | | | | | connected | | | | 0---------------------0-------0 | | | | | | | | // // // // // // [... or] | | | | | | | | | | | |--------------- L2 attach -------------->| | | | | | | | | connected | | | | 0-----------------------------------------0---------------------0 | | | | | | | | | | MIPv6 Binding Update to the HA | | |------------------------------------------------ - - - > | | | | | | | Figure B.2: CARD protocol operation within a Mobile IPv6 enabled wireless LAN network. Appendix B.2 CARD Operation in a Fast Mobile IPv6 Network This application scenario assumes ARs can perform the fast handover protocol sequence for Mobile IPv6 [Kood03]. The MN scans for new APs [Page 44] Internet-Draft Candidate Access Router Discovery December 2003 for handover similar to Figure B.1 To discover the ARs (CARs), the MN attaches a MN-AR CARD Request option to the ICMP-type Fast Mobile IPv6 RtSolPr message, which is sent to the MN's current AR (pAR, previous AR). Candidate APs' L2 IDs are encapsulated using the CARD protocol's L2 ID sub-options, which allow the MN to send multiple L2 IDs of candidate APs to its current AR (potentially replaces the "New Attachment Point Link-Layer Address" option of the Fast Mobile IPv6 protocol). The pAR resolves the received list of candidate APs' L2 IDs to the IP address of associated CARs. The pAR checks its local CAR table to retrieve information about the CARs' capabilities. If any table entries have expired, the pAR acquires this CAR's capabilities by sending an AR-AR CARD Request to the respective CAR. The CAR replies with an AR-AR CARD Reply message, encapsulating all capabilities in a Capability Container sub-option and attaching them to the CARD Reply option. On reception of the CARs' capability information, the pAR updates its local CAR table and forwards the address and capability information to the MN of attaching a MN-AR CARD Reply option, to the Fast Mobile IPv6 PrRtAdv message. When the MN's handover is imminent, the MN selects its new AR and the associated new AP from the discovered list of CARs. According to the Fast Mobile IPv6 protocol, the MN notifies the pAR of the selected new AR with the Fast Binding Update (F-BU) message, allowing the pAR to perform a fast handover according to the Fast Mobile IPv6 protocol. Optionally, the pAR could perform selection of an appropriate new AR on behalf of the MN after the pAR has the MN's CARs' addresses and associated capabilities available. The MN must send its requirements for the selection process to its pAR together with the MN-AR CARD Request message After the pAR has selected the MN's new AR, the address and associated capabilities of the chosen new AR are sent to the MN with the CARD Reply option, in the Fast Mobile IPv6 PrRtAdv message. Figure B.3 illustrates how CARD protocol messages and functions work together with the Fast Mobile IPv6 protocol. MN pAR NAR CAR2 | | as CAR1 | | | | | |-------RtSolPr------>| | | | [MN-AR CARD Req] |-- AR-AR CARD Req*->| | | |-- AR-AR CARD Req*------------>| | |<--AR-AR CARD Repl*------------| | |<--AR-AR CARD Repl*-| | [Page 45] Internet-Draft Candidate Access Router Discovery December 2003 |<------PrRtAdv-------| | | | [MN-AR CARD Repl] | | | | | | | NAR selection | | | |------F-BU---------->|--------HI--------->| | | |<------HACK---------| | | <--F-BACK--|--F-BACK--> | | | | | | Disconnect | | | | forward | | | packets===============>| | | | | | | | | | Connect | | | | | | | RS (with FNA option)======================>| | |<-----------RA (with NAACK option)--------| | |<=================================== deliver packets | | | | Figure B.3: Fast Handover protocol sequence with CARD protocol options *) In Figure B.3, the CARD protocol interaction between the pAR and CARs is only required in case the lifetime of any capability entries in the pAR's CAR table have expired. Otherwise, the pAR can respond to the requesting MN immediately after retrieving the CARs' address and capability information from its CAR table. [Page 46]