Internet Engineering Task Force S. Glass Mobile IP Working Group Sun Microsystems Internet Draft M. Chandra Cisco Systems July 2002 Registration Revocation in Mobile IP draft-ietf-mobileip-reg-revok-03.txt Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. This document is a submission to the Mobile IP Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the MOBILE-IP@STANDARDS.NORTELNETWORKS.COM mailing list. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at: http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at: http://www.ietf.org/shadow.html. Distribution of this memo is unlimited. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page i Internet Draft Registration Revocation in Mobile IP Glass, Chandra Abstract During the original design of Mobile IP, the need for an administrative domain to be able to actively revoke a current Mobile IP registration was recognized. Due to the lack of a specific scenario requiring such a mechanism, it was decided that instead of an active revocation mechanism explicitly for the purpose of registration revocation, a passive mechanism, namely short registration lifetimes, and the denial of subsequent registrations from a mobile node, would likely be sufficient for this purpose. Investigations into requirements for a AAA protocol within the AAA working group have forced reconsideration of a more pro-active Mobile IP registration revocation feature whereby both domains providing Mobile IP services can be made aware that the service is being suspended. In the ideal model, revocations must be possible from either home or foreign domains, so any registration revocation mechanism being defined must provide a signaling mechanism between the two that identify registration(s) being released, implying that since Mobile IP services are no longer being provided on one side of the registration, they need not be provided on the other. In some cases the current registration may be terminated to simply force the mobile node to renegotiate its registration, but in other cases renegotiation may not be allowed. Either one of these reasons is sufficient to justify this mechanism. Moreover, there should also be a mechanism in place whereby the mobile node whose registration has been terminated can also be informed that such a revocation has occurred, if only so it may understand it is not longer being provided Mobile IP services, though the reasons for such a revocation need not necessarily be immediately relayed. This mechanism would ideally be independent of the signaling mechanism between the agents identified above so as to leave actual notification of the mobile node up to a separate policy of the domains in question. This document defines such a general use registration revocation mechanism meeting these requirements. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page ii Internet Draft Registration Revocation in Mobile IP Glass, Chandra Table of Contents: 1. Introduction................................................... 1 2. Motivation..................................................... 2 3. Revocation Messages Formats..................................... 3 3.1 Revocation Support Extension................................ 4 3.2 Revocation Message.......................................... 6 3.2.1 Revocation Mask......................................... 9 3.2.2 Replay Protection....................................... 12 3.3 Revocation Acknowledgment Message........................... 13 4. Registration Revocation Overview............................... 15 4.1 Mobile Node Notification.................................... 15 4.2 Registration Revocation Mechanism - Notification............ 17 4.2.1 Home Domain Revoking a Registration..................... 19 4.2.1.1 Home Agent Responsibilities......................... 19 4.2.1.2 Foreign Agent Responsibilities...................... 20 4.2.1.3 Co-located Mobile Node Responsibilities............. 20 4.2.2 Foreign Domain Revoking a Registration.................. 21 4.2.2.1 Foreign Agent Responsibilities...................... 21 4.2.2.2 Home Agent Responsibilities......................... 22 4.2.3 Mobile Node De-registering a Registration............... 23 4.3 The Use of Bits............................................. 23 4.3.1 The 'R' Bit in Use...................................... 24 4.3.2 The 'D' Bit in Use...................................... 25 5. An Example of the New Messages in Use.......................... 26 5.1 The Registration Phase...................................... 26 5.2 The Revocation Phase........................................ 27 6. No New Error Codes............................................. 28 7. Multiple Binding Support....................................... 28 7.1 Other Random Protocol Details............................... 29 8. Security Considerations........................................ 29 Appendix A: Registration Revocation in 'R' and 'D' Bit Worlds...... 31 Appendix B: Disparate Address, and Receiver Considerations......... 32 Appendix C: Using Registration Revocation to Help Release Resources 33 Acknowledgments.................................................... 35 Where to Direct Comments........................................... 35 References......................................................... 36 Full Copyright Statement........................................... 37 Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page iii Internet Draft Registration Revocation in Mobile IP Glass, Chandra 1. Introduction During the original design of Mobile IP, the need for an administrative domain to be able to actively revoke a current Mobile IP registration was recognized. Due to the lack of specific need for such a mechanism, however, it was decided that a passive mechanism, namely the denial of a subsequent registration from a mobile node, in conjunction with the recommendation for short registration lifetimes, was sufficient for this purpose. Investigations into the requirements for a AAA protocol specific to Mobile IP have forced reconsideration of a more pro-active Mobile IP registration revocation feature whereby if either domain wishes to revoke a current registration, this can be communicated to the other domain providing mobile ip services for the mobile node whose binding is being revoked, and potentially also have the mobile node informed that it is no longer receiving mobile ip services. A mobility agent which receives a revocation notification no longer has to provide services to the mobile node whose registration has been revoked. This means resources being consumed to provide mobile-ip services for a mobile node that has stopped receiving mobile-ip services by one agent can be reclaimed by the other agent in a more timely fashion than if it had to wait for the binding to expire. This has a favorable impact on resolving accounting issues with respect to this binding in both domains as the actual lifetime of the registration is more accurately relayed. Moreover, should foreign domain policy allow for it, informing the mobile node that it is no longer being provided mobile ip services enables that mobile node to react faster than if it had to discover this for itself (e.g. by waiting to have its attempt to re-register denied). This is crucial as revocation messages are also useful when it is desireable to prompt a mobile node to reregister. For example, if reverse tunnels are now required by home domain policy, revoking registrations that don't use reverse tunnelings prompt reregistration, which can be denied with error 138: "reverse tunnel is mandatory, and 'T' bit not set" [2]. A general registration revocation mechanism is defined to handle these situations. The protocol is broken into two disjoint pieces. First, a mechanism to inform the mobile node of the revocation of it's current binding is described using a mechanism which already exists in the base Mobile IP protocol [1]. This means any mobile node which is designed to comply with [1] will understand it's registration has been revoked. Next, a signaling mechanism between home and foreign agents is described which allows either the home or foreign domain to inform the other it has torn down the current tunnel, allowing both to free up the resources associated with the identified Mobile IP binding, and to acknowledge this understanding. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 1 Internet Draft Registration Revocation in Mobile IP Glass, Chandra The mechanism described in this documennt is intended for mobility agents playing the active role in ending a mobile node's service, and is relayed between them. The revocation/release messages defined here are a logical addition to the messages defined in [1] for the generic Mobile IP registration process, and apply to situations where mobility agents need to play an active role in administering Mobile IP registrations. This document therefore describes methods to be used only when mobility agents are initiating, and/or coordinating the release of mobile ip services. The mechanism described in this document do not replace the methods described in [1] for de-registration messages as those apply to situations where the mobile node is playing the active role in informing the home agent of its location when it has roamed e.g. back to its home subnet. This is to say the revocation message defined by this document is NOT for use by colocated mobile nodes that are terminating their registration as deregistration requests are already sufficient for this purpose. A co-located mobile node, however, may wish to process the messages defined in this document as it is a useful mechanism to trigger the renegotiation of required services from the home domain. This reader is assumed to be familiar with the concepts and terminology used in [1], and [3]. Knowledge of the concepts of [4] and [5] are also be beneficial. The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [6]. 2. Motivation Mobile IP [1] defines registration of a mobile node's location to provide connectivity between the mobile node and its home domain, facilitating communication between mobile nodes and any correspondent node. At any time, either home or foreign agent may wish to stop servicing a mobile node, or for administrative reasons may no longer be required to service a mobile node. However, no mechanism has been described to inform the mobility agent providing Mobile IP services at the other end of the tunnel that such services have been terminated. If the home agent stops providing mobile ip services (for a mobile node), the foreign agent will simply stop seeing tunnel packets for the mobile node, just as if a route stopped functioning, or if there is simply no traffic for the mobile node. If, before prematurely shutting down a binding, the home agent is capable of sending a revocation message to the foreign agent, both the foreign agent and the mobile node get earlier indication, and the mobile node may need to renegotiate another binding. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 2 Internet Draft Registration Revocation in Mobile IP Glass, Chandra If the foreign agent shuts down the tunnel, the home agent will continue sending tunnel packets, which will likely be silently discarded. An aware mobile node may notice the lack of response to packets it is generating, eventually guessing its binding may have vanished, and provoking an attempt to re-register. Only at that time will the mobile node get a registration denied error with some hint as to why its service was stopped, and by which agent. A more common scenario occurs when a mobile node roams away from a foreign agent, which now no longer needs to provide Mobile IP services to it. Notification of this state-change by a home agent could be useful to it (see Appendix C). A revocation protocol is also useful in scenarios where a timely release of resources is desirable, regardless of whether the mobile node's binding was administratively revoked or terminated for another reason. Clearly, a more active mechanism needs to be provided allowing more timely communication between the three Mobile IP entities in the various administrative domains. 3. Revocation Message Formats This section details the format of the signaling protocol between home and foreign agents, or from a home agent to a co-located mobile node. The following message-types are introduced by this document for relaying revocation information: - Revocation Support Extension: An extension appended to a registration request or registration reply by a mobility agent indicating its support of registration revocation. This message is also used to indicate whether an agent will acknowledge receipt of a revocation message, and/or convey its wishes as to the notification of a mobile node regarding termination of its registration. This extension may also be appended to a registration request by a colocated mobile node to indicate its understanding of revocation messages. - Revocation Message: A message sent by a mobility agent to inform another mobility agent, or colocated mobile node, that it is revoking the binding of a[t least one] mobile node. These messages are not sent by mobile nodes, but may be received by colocated mobile nodes. - Revocation Acknowledgment Message: A message to indicate the successful receipt of a revocation message. These messages are sent by mobility agent, or colocated mobile nodes. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 3 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 3.1 Revocation Support Extension The Mobile IP revocation support extension MUST be attached to a registration message by any entity that wants to receive revocation messages. Normally, this is either a foreign agent, or a home agent, however a colocated mobile node MAY also include a revocation support extension in its registration request. In all cases, the extension MUST be protected by the appropriate authenticator [1]. The foreign agent MAY also attach a revocation extension to an agent advertisement to indicate to the link upon which it is advertising that it supports revocations, in the event knowledge of this support is critical to the mobile node's choice of foreign agents. It is NOT necessary that all foreign agents on a link support registration revocation (unlike support of the 'R' bit as described by [1]). The user is referred to Section 8, and [5] for a discussion surrounding security issues of agent advertisements. The format of the revocation support extension is based on the Type-Length-Value Extension Format given in [1] and is defined as follows: 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 |A|I| reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type TBA - Skippable (e.g. 135). See below. Length Length (in bytes). Does NOT include Type and Length (in accordance with [1]). 'A' Bit When this bit is set to '1', the mobility agent is specifying that it will send a revocation acknowledgment in receipt of a registration revocation message for this registration if the other side agrees to do the same (see Sections 3.2 and 4.2). Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 4 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 'I' Bit This bit is set to '1' by a mobility agent to indicate it supports the use of the 'I' bit in revocation messages (see Sections 3.2 and 4.2). Note that in all revocation scenarios the use of the 'I' bit requires acknowledgment, so if the 'I' bit is set to 1 in a revocation extension, the 'A' bit MUST also be set to '1'. When sent by a foreign agent: If set to 1, indicates to the home agent that the foreign agent is willing to have the 'I' bit in the revocation process (as set by the home agent) determine whether the mobile node is informed of the revocation, or not. If set to 0, indicates to the home agent that the foreign agent will follow its own policy with regards to informing the mobile node in the event of a revocation. When sent by a home agent, in response to a revocation extension in which the 'I' bit was set to 1: If set to 1, the home agent agrees to use the 'I' bit in either the revocation message, or the revocation acknowledgment to indicate to the foreign agent whether the mobile node should be informed. If set to 0, the home agent will not use the 'I' bit in either the revocation message, or the revocation acknowledgment, yeilding to the foreign agent's default behaviour. Reserved Reserved for future use. MUST be set to 0 on sending, MUST be ignored on receiving. When appearing in a registration request, or registration reply, the Mobile IP registration support extension MUST be protected ether by a Foreign-Home Authentication Extension, or Mobile-Home authentication extension, or any other equivalent mechanism [1], e.g. AAA [A], [B]. If the extension appearing in either of the above registration messages is NOT protected, the appropriate action as described by [1] MUST be taken. It is important to note that this extension is of the skippable variety, that is if the receiving mobility agent doesn't understand this extension, it MUST skip it, and continue processing the remainder Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 5 Internet Draft Registration Revocation in Mobile IP Glass, Chandra of the registration request. This is so a home agent can continue to process the registration request a foreign agent has forwarded to it, and send a registration reply even though the home agent doesn't support registration revocation, or isn't willing to participate in registration revocation for this particular binding. In this way, if local policy in the foreign domain requires registrations to be made only with home agents which support this feature, the foreign agent may actively deny the registration with this home agent, and indicate this to the mobile node (e.g. via 65 "administratively prohibited"). In this way, use of registration revocation can be negotiated for each registration, and each domain has a clear understanding of what is expected. In contrast, if this extension were not skippable, a home agent which doesn't understand the revocation extension would silently discard the registration, and there would be no feedback to either the foreign agent, or the mobile node. 3.2 Revocation Message The format of revocation message is analogous to registration request and registration reply messages [1]. IP fields: Source Address In the case of the home agent issuing the registration revocation, the address registered with the care-of address as that of the home agent. In the case of the foreign agent issuing the registration revocation: If the registration being revoked is NOT for a co-located mobile node, the address registered with the home agent as the care-of address. In the case of the revocation of a co-located mobile node, any of the addresses of the foreign agent associated with the foreign agent NAI which MUST have been included in the most recent registration request to the home agent. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 6 Internet Draft Registration Revocation in Mobile IP Glass, Chandra Destination Address In the case of the home agent issuing the registration revocation: In the case where the revocation is not for a co-located mobile node, the address identified as the care-of address of the mobile node, In the case where the home agent is notifying the foreign agent servicing a co-located mobile node, any of the addresses associated with the NAI of the foreign agent included in the most recent approved registration request. In the case of the foreign agent issuing the registration revocation, the address registered as that of the home agent by the mobile node whose registration is being revoked. UDP fields: Source Port variable Destination Port 434 The UDP header is followed by the Mobile IP fields shown below 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 | Mask |A|I| reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Foreign Domain Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Domain Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Domain Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Foreign Domain Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type TBA e.g. 7 (Registration Revocation) Mask A set of flags indicating the applicability of the registration revocation. See Section 3.2.1 for definitions. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 7 Internet Draft Registration Revocation in Mobile IP Glass, Chandra A Acknowledge bit. This bit MUST only be used if acknowledgment support was negotiated in the last successful registration of at least one of the mobile nodes whose registration is being revoked. If not, the results can be unpredictable. Set to '0' when the revoking agent does NOT want an acknowledgment for this revocation message. Set to '1' when the revoking agent is expecting an acknowledgment of this revocation message. I Inform bit. This bit MUST only be used if 'I' bit support was negotiated in the revocation extension messages passed in the registration process. If not, the results can be unpredictable. If sent by the home agent: Set to '0' when the mobile node should NOT be informed of the revocation. Set to '1' to request that the mobile node be informed of the revocation. If sent by the foreign agent: Set to '1' to ask the home agent if the mobile node should be informed of the revocation. Note that in this case the foreign agent MUST also set the 'A' bit to indicate to the home agent that it needs to acknowledge this revocation message. reserved MUST be sent as 0, ignored when received. Home Address The IP address of the mobile node whose registration is being revoked, or the subnet address indicating that all mobile nodes belonging to this subnet are having their registration revoked, or the zero address if all mobile nodes who are registered using this home agent and this care-of address are being revoked. See Section 3.2.1. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 8 Internet Draft Registration Revocation in Mobile IP Glass, Chandra Foreign Domain Address The IP address identified as being in the foreign domain. This is either the foreign agent's IP address, or the co-located care-of address, or the subnet address of either of these indicating that all mobile nodes using a care-of address on the identified subnet are having their bindings revoked, or the zero address if all mobile node bindings using the identified Home Domain Address are being revoked. See Section 3.2.1. Home Domain Address The IP address identified as being in the home domain. This is either the home agent's IP address, or the subnet address indicating that all mobile nodes using a home agent on the identified subnet are having their bindings revoked. See Section 3.2.1. Home Domain and Foreign Domain Identifier Fields Each of these is a 32-bit number used for protecting against replay attacks analogous to the use of timestamps in [1]. See Section 3.2.2. An example of the use of revocation messages is given in Section 5. 3.2.1 Revocation Mask The use of the revocation mask is OPTIONAL. If it is not used, it MUST be set to all zeros. The registration revocation message MAY use this to indicate the "extent" of the revocation, and is used in combination with the address fields defined above. The following bit- values are defined. Note the low-order bits apply to addresses, and the high-order bits apply to NAIs. Value Meaning ----- ----------------------------------------------------------- 0x01 Applies to all bindings where the mobile node home address belongs to the same subnet as the address appearing in the home address field. The address appearing in the home address field MUST either be that of a registered mobile node, or a subnet address. The issuing agent MUST include a prefix-length extension defined by [1] appearing after the revocation message to indicate the bits of address being effected (e.g. 10.1.1.128, prefixLen=25). Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 9 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 0x02 Applies to all bindings where the care-of address belongs to the same subnet as the address appearing in the foreign domain address field. The address appearing in the foreign domain address field MUST either be the co-located address belonging to a mobile node, or a subnet address. The issuing agent MUST include a prefix-length extension as defined by [1] appearing after the revocation message to indicate the bits of address being effected (e.g. 10.1.1.192, prefixLen=26). 0x04 Applies to all bindings where the registration is using the same foreign address appearing in the foreign domain address field. The address appearing in the foreign domain address filed MUST either the address registered as the foreign agent address, or a subnet address in which case the issuing agent MUST include a prefix-length extension as defined by [1] appearing after the revocation message to indicate the bits of address being effected (e.g. 10.1.1.224, prefixLen=27). 0x08 Applies to all bindings where the registration is using the same home agent address appearing in the Home Domain Address field. The address appearing in the Home Domain Address field MUST either be the address registered as the home agent address, or a subnet address. The issuing agent MUST include a prefix-length extension as defined by [1] appearing after the revocation message to indicate the bits of address being effected (e.g. 10.1.1.240, prefixLen=28). Note that this address MUST NOT be the zero address, see Appendix B. 0x10 Applies to all bindings with the same administrative domain as the mobile node. The issuing agent MUST include the NAI of [one of] the mobile nodes whose registration is being revoked in an NAI extension, appearing after the revocation message. 0x20 Applies to all bindings with the same administrative domain as the care-of address. The issuing agent MUST include the care-of domain's NAI in an NAI extension, appearing after the revocation message. 0x40 Applies to all bindings with the same administrative domain as the foreign agent. The issuing agent MUST include the foreign agent NAI in an NAI extension appearing after the revocation message. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 10 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 0x80 Applies to all bindings with the same administrative domain as the home agent. The issuing agent MUST include the home agent NAI in an NAI extension appearing after the revocation message. When multiple flags are set, the corresponding prefix-length and NAI extensions MUST appear in the same order, "left-to-right" as the flags. e.g. if the 0x02 and 0x01 bits are set, the first prefix length extension is for the subnet of the care-of address, and the second prefix length extension is for the subnet of the home address. For example, if the home agent is revoking bindings for all mobile nodes belonging to a particular home domain (and registered with the same foreign agent), the home agent sets the mask to 0x01, and includes the prefix length extension for that subnet. When the foreign agent receives an authenticated message in which the mask is set to 0x01, it understands that all mobile nodes whose home addresses fall in the subnet range indicated by the home address field and the prefix length extension (using the home agent whose address appears in the home agent address field) have been revoked. For authentication where domain bindings are being revoked, the appropriate NAI MUST be included in the revocation message. For example, a foreign agent revoking all binding from the same NAI domain as mn@home.domain would set the mask to 0x10, and include an NAI extension after the revocation message including the NAI mn@home.domain. When the foreign agent receives an authenticated message in which the mask is set to 0x10, it understands that all mobile nodes that used an NAI containing @home.domain have been revoked. As always, revocation messages MUST be authenticated, and the scope of the revocation MUST only apply to the subset of bindings between the revoking agent, and the agent receiving the revocation message. For example, if foreign agent x.y.z.t sends a revocation message to home agent a.b.c.d for mobile node a.b.c.x, and sets the revocation mask to 0x01, the home agent MUST NOT revoke all of its bindings for mobile nodes on the same home link as the revoked mobile node, but only those mobile nodes that are also visiting this foreign agent. Note: the distinction between bindings in the same subnet as the CoA (0x02), and bindings in the same subnet as the foreign agent (0x04) is to be able to discern bindings which may be on different links and being served by the same foreign agent, i.e., a foreign agent may be servicing different classless subnets [7], or it may be multihomed though using the same CoA for all these subnets. See the Appendix B on disparate address support in [2] for a related discussion. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 11 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 3.2.2 Replay Protection As registration revocation messages are designed to terminate service for a mobile node, replay protection is crucial to prevent denial of service attacks by "malicious repeaters" - those who store datagrams with the intent of replaying them at a later time (a form of "man-in-the-middle" attack). Such a packet, presuming it passed authentication the first time, would pass subsequent times, and not be discrigarded without a replay protection mechanism to identify the datagram as a repeat. Moreover, since datagrams are not guaranteed to arrive unduplicated, a replay may occur by "design". The same caveat applies to reflected packets (which may be indistinguishable from "malicious repeaters"). Replay protection is handled in direct analogy with the mechanism defined by [1], through two 32-bit identifier fields in the registration revocation message. - The agent revoking a registration sets its Identifier field to a valid timestamp, and sets the other Identifier field to 0. The revoking agent MUST append an authenticator. Upon receipt of an authenticated revocation message, the agent checks the other agent's Identifier field to make sure it is not a replay of an old revocation message received from the same agent. If the agent Identifier field implies this packet is a replay, that revocation message MUST be silently discarded. - When building a revocation acknowledgment message (in response to a revocation message in which the 'A' bit is set), the acknowledging agent copies the Identifier field of the other agent from the revocation message into the revocation acknowledgment packet, and sets its identifier field to a valid timestamp. The revocation acknowledgment message MUST be protected with a valid authenticator. - Upon receiving a valid revocation acknowledgment, the revoking agent checks its Identifier field to make sure it matches its identifier from the revocation message it sent, and also checks the other agent's Identifier field, which MUST be non-zero. Note: as it is possible for a mobile node to register at different times with different home agents, and at different times with different foreign agents, it is crucial that it not be required that this ID field be unique in messages from different agents as there is no method for this information to be communicated between agents. For example, if a mobile node has simultaneous bindings with multiple foreign agents, and these are being revoked, it is possible the revocation message from one of the foreign agents may contain an ID field that happens to match that of the other registered foreign agent. This MUST NOT result in one of these revocation message being Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 12 Internet Draft Registration Revocation in Mobile IP Glass, Chandra ignored. As agents are useing timestamps for replay protection, they will natually be incremented with each revocation. With the use of timestamps only one revocation attempt per second may be made for any registration, or set of registrations with each agent peer. The reader should note that the ID field used in the replay protection of registration requests in [1] suffers from the same limitations. 3.3 Revocation Acknowledgment Message The format of revocation acknowledgment message is analogous to the revocation message. IP fields: Source Address Copied from the destination address of the received registration revocation message for which this registration revocation acknowledgment message is being generated. Destination Address Copied from the source address of the received registration revocation message for which this registration revocation acknowledgment message is being generated. UDP fields: Source Port 434 (copied from the destination port of the revocation message) Destination Port Copied from the source port of the revocation message. The UDP header is followed by the Mobile IP fields shown below: 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 |I| reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Agent Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 13 Internet Draft Registration Revocation in Mobile IP Glass, Chandra Type TBA, e.g. 9 (Registration Revocation) Length 10. The length of the revocation acknowledgemnt message, not including Type and Length fields. I Inform bit. The 'I' bit MUST only be used in revocation acknowledgment messages if it was set to '1' in the revocation message. If used by a foreign agent: Set to '1' to indicate to the home agent that the mobile node was/will be informed of the revocation. Set to '0' to indicate to the home agent that the mobile node was/will not be informed of the revocation Set to the OPPOSITE of what the home agent set the 'I' bit to in the revocation message to indicate the foreign agent is NOT revealing whether the mobile node was informed or not. See Section 4.1.1.2 for an example. If used by the home agent: Set to '1' by the home agent to request the foreign agent inform the mobile node of the revocation. Set to '0' by the home agent to request the foreign agent not inform the mobile node of the revocation. reserved MUST be sent as 0, ignored when received. Identification Fields A 32-bit number used for protecting against replay attacks. See Section 3.2.2. An example of the use of the revocation messages is given in Section 5. A registration revocation acknowledgment message MUST only be sent in response to a registration revocation messages in which the 'A' bit was set to 1. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 14 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 4. Registration Revocation Overview Registration Revocation consists of two disjoint pieces, a signaling mechanism between the tunnel endpoints, and a signaling mechanism between a foreign agent and a mobile node. A co-located mobile node, i.e., a mobile node which is decapsulating its own tunnel traffic, MAY implement the tunnel endpoint-signaling portion of this protocol in order to understand revocation messages from its home agent. However, a co-located mobile node does not have to implement the sending of revocation messages as deregistration messages defined in [1] are sufficient for this purpose. 4.1 Mobile Node Notification A mechanism which provides a foreign agent a way to actively notify a mobile node that its binding has been reset already exists in [1], though it has been overlooked for this purpose. The following paragraph contains a brief overview of the mechanics of the sequence number in agent advertisement from [1] so the mechanism by which the foreign agent 'implies' to the mobile node that its binding is no longer active is clearly understood. When a foreign agent begins sending agent advertisements, it starts with a sequence number of 0, and [monotonically] increments the sequence number with each subsequent agent advertisement. In order for a mobile node to be able to distinguish between a foreign agent that has simply exhausted the sequence number space from one which has been reset, and thereby lost the mobile node's binding information, a foreign agent sets the sequence number to 256 instead of rolling to 0. In this way, a mobile node would have to miss, at that time, 256 advertisements in a row to mistake a reset as a roll-over. Moreover, the lifetimes contained within an agent advertisement should be set in such a way that when a mobile node believes it has missed 3 beacons, the entry for this foreign agent should time out, and if the mobile node is registered there, it should send an agent solicitation [1]. If, however, an agent is somehow reset, it will begin advertising with a sequence number of 0, and the mobile node can presume this foreign agent has lost its binding, and the mobile node SHOULD re-register to make sure it is still obtaining Mobile IP services through this foreign agent. Leveraging this mechanism, a foreign agent may consciously notify all mobile nodes currently bound to it that it has "reset" all their bindings, even if the agent itself has not been reset, by simply [re]setting the sequence number of the next agent advertisement to 0. Moreover, a foreign agent may inform all mobile nodes currently bound to it they should re-register with a different foreign agent by simultaneously setting the sequence number to 0, and also setting the Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 15 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 'B' bit [1] in the advertisement to 1, indicating this foreign agent is busy and is not accepting new registrations. In these situations, any mobile node in compliance with [1] will presume this foreign agent has lost its binding, and must re-register if they wish to re-establish Mobile IP functionality with their home subnet. To indicate to any registered mobile node that its binding no longer exists, the foreign agent with which the mobile node is registered may unicast an agent advertisement with the sequence number set to 0 to the mobile node [1], [3]. Moreover, if such a foreign agent wishes to indicate to the mobile node that its binding has been revoked, and that the mobile node should not attempt to renew it's registration with it, the foreign agent MAY also set the 'B' bit to 1 [1] in these agent advertisements, indicating it is busy, and is not accepting new registrations. All mobile nodes compliant with [1] will understand this means the agent is busy, and MAY either immediately attempt to re-register with another agent in their foreign-agent cache, or MAY solicit for additional agents. In the latter case, a foreign agent can optionally remember the mobile node's binding was revoked, and respond to the solicit in the same way, namely with the 'B' bet set to 1. It should be noted, though, that since the foreign agent is likely to not be setting the 'B' bit to 1 in its broadcasted agent advertisements (sent to the entire link), the revoked mobile node, upon hearing this agent's multicast agent advertisement without the 'B' bit set may attempt to [re]register with it. If this happens, depending of foreign domain policy, the foreign agent can simply deny the mobile node with an appropriate error code (e.g., "administratively prohibited"). At this time, a mobile node MAY use foreign agent fallback to attempt to register with a different foreign agent as described in [1]. Mobile nodes which understand this revocation mechanism may understand that a unicast agent advertisement with the sequence number reset to 0 could indicate a revocation, and may attempt to register, or co-locate (e.g. if the mobile node is in multiple coverage areas with a single, or multiple interfaces). In any case, a mobile node must be able to continue to operate as described by [1], even if their registration has been revoked since many mobile nodes may not understand the concept of revocation. Agent Advertisements unicast to a mobile node MUST be sent as described in [1], in addition to any methods currently in use on the link to make them secure or authenticatable by the mobile node, which are highly desirable to protect from denial-of-service attacks [5]. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 16 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 4.2 Registration Revocation Mechanism - Notification Any active mechanism designed to be useful to both home and foreign domains must contain a way to securely revoke a current binding. This means the registration process must supply both home and foreign domains with enough information to be able to inform the other side of any revocation. Moreover, a revocation message MUST NOT be sent for a registration that has expired, and MUST only be sent prior to the expiration of a mobile node's registration. As in [1], any information the foreign agent appends to the registration request MUST be protected by a Foreign-Home authenticator, as MUST any information outside the Mobile-Home authenticator in the corresponding registration reply. Due to the nature of a domain wishing to participate in registration revocation, it is likely the authenticators would be required by policy between the home and foreign domain anyway. In the case of a co-located mobile node, all such signaling MUST (continue to be) protected by the Mobile-Home authenticator. However, a mobile node that is terminating any of its own bindings MUST NOT send a revocation message to its home agent, as the method described in [1], namely deregistering a care-of address, is sufficient, and the mechanism detailed in this document is not meant to replace it. During the registration process, if the foreign agent wishes to participate in revocation messages with the home domain, it MUST share a security association with the home agent indicated in the registration request sent by the mobile node (or the home domain if there exists an applicable authentication mechanism, and that mechanism is in-use), and MUST append a revocation support extension (defined in Section 3.1) to the registration request. If the corresponding registration reply from this home agent does not contain a revocation support extension, the foreign agent MAY assume the home agent/domain does not understand registration revocation, or is unwilling to participate. Note that in this case, as specified in [1], both registration request and registration reply MUST still contain a home-foreign authenticator. If a home agent wishes to participate in revocation messages with the foreign domain, it MUST share a security relationship with the foreign agent which sent the registration request (or with the foreign domain if there exists an applicable authentication mechanism, and that mechanism is in-use), and MUST append a revocation support extension to the registration reply. If the registration request from a foreign agent does not contain a revocation support extension, the home agent MAY assume the foreign agent/domain does not understand registration revocation, or is unwilling to participate specifically for this mobile node. The home agent MAY include a revocation support extension in the registration reply anyway. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 17 Internet Draft Registration Revocation in Mobile IP Glass, Chandra If a co-located mobile node wishes to be informed of a released binding by the home agent, it MUST insert a revocation support extension into the registration request which MUST be protected by the mobile-home authenticator. If the revocatation extension is not included in any registration message, either by a foreign agent or co-located mobile node in a registration request, or by a home agent in a registration reply, the receiver of such a registration message SHOULD assume the sender does not understand revocation messages. Revocation support is considered to be negotiated when both sides have included a revocation support extension during a successful registration exchange. The 'A' bit in the revocation extension is used to indicate the desire to use acknowledgment messages in response to revocation messages for the binding to which they are attached. The use of acknowledgment messages for this registration is negotiated, this is offered by the foreign agent, and agreed to by the home agent. More precisely, by sending a revocation extension in which the 'A' bit is set, the foreign agent is indicating it would like the home agent to resend any revocation message for this registration for which it does not receive a revocation acknowledgment message, and is offering to do the same for the home agent with regards to this registration. The home agent then can disagree, in which case it simply does not set the 'A' bit, or agree by setting the 'A' bit to 1 in the revocation extension appearing in the registration reply. The 'I' bit in the revocation extension is used to indicate that the decision to inform the mobile node that its binding has gone away will be left to the home agent. As with the 'A' bit, this functionality is offered by the foreign agent, and accepted by the home agent. More precisely, by sending a revocation extension attached to a registration request in which the 'I' bit is set to 1, the foreign agent is indicating to the home agent that it MAY leave the decision to inform this mobile node that its registration has gone away to the home agent. The term "MAY" is used here because it is recognized that domain policy may change during the lifetime of any registration. The home agent can acknowledge that it wishes to do this by setting the 'I' bit to 1, or it can indicate it will not do so by setting the 'I' bit to 0 in the revocation extension appearing in the registration reply. All revocation messages and revocation acknowledgement messages MUST contain valid authenticators, namely home-foreign authenticators if the communication is between home and foreign agents, or mobile-home authenticators if the communication is between home agents and co-located mobile nodes. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 18 Internet Draft Registration Revocation in Mobile IP Glass, Chandra If any agent, or co-located mobile node receives a registration revocation message that does not contain a valid authenticator, namely a home-foreign authenticator if the revocation message is between home and foreign agents, or a mobile-home authenticator if the message is from home agent to co-located mobile node, the revocation message MUST be ignored, and silently discarded. 4.2.1 Home Domain Revoking/Releasing a Registration The following section details the responsibilities of each party depending on the functionality negotiated in the revocation support extension when the home domain is revoking a registration. 4.2.1.1 Home Agent Responsibilities In the case where a home agent is revoking/releasing a mobile node's binding, and revocation support has been negotiated, the home agent MUST notify the foreign domain address it is terminating the tunnel entry point by sending a revocation message. Note that the foreign domain address can either be the foreign agent's care-of address, or a co-located care-of address. Note that if a colocated mobile node included a revocation support extension in its registration request, and passed it to a foreign agent (because the 'R' bit was set) which also included a revocation support extension, there may be a need to send a revocation message to both. If the 'A' bit was negotiated because it was set to '1' in both revocation extensions passed in the registration process, the home agent MUST set the 'A' bit in the revocation message and expect a revocation acknowledgment in return. If the home agent does not receive a revocation acknowledgment message with in a reasonable amount of time, it MUST retransmit the message. How long the home agent waits to retransmit, and how many times the message is retransmitted is only limited by the specification that the home agent MUST NOT send more than one revocation per second for a particular binding, SHOULD fall-back in analogy with the registration guidelines in [1], and MUST NOT retransmit revocation acknowledgement messages beyond the normal life of the revoked binding. If the mobile node whose registration is being revoked is NOT co-located, and the use of the 'I' bit was negotiated in the registration process, the home agent MUST set the 'I' bit to 1 if the home agent would like the mobile node informed of the revocation. Conversely, if the home agent does not want the mobile node notified, it MUST set the 'I' bit to 0. A Home-Foreign authenticator MUST be included in the registration revocation message. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 19 Internet Draft Registration Revocation in Mobile IP Glass, Chandra If the mobile node whose registration is being revoked is co-located (the 'D' bit was set in the most recently approved registration request), and indicated in the registration process that it wishes to receive revocation messages from the home agent, the revocation message MUST be protected by a Home-Mobile authenticator. 4.2.1.2 Foreign Agent Responsibilities Upon receiving a registration revocation message, the foreign agent MUST check the Home-Foreign authenticator in analogy to [1], and if the packet passes authentication, the foreign agent MUST identify the binding(s) described by the home agent as being released using the information in the revocation message, namely the addresses identified by the mobile node address, the foreign domain address, and the home domain address. Upon locating such bindings, if the 'A' bit was negotiated in the registration phase, and the 'A' bit is now set in the revocation message, the foreign agent MUST respond with a revocation acknowledgement sent to the source address of the revocation message. If the 'I' bit was also negotiated, the foreign agent MUST check the value of the 'I' bit in the revocation message, and if it is set to 1, MUST notify the mobile node that it's binding has been revoked by the methods described in Section 4.1, and MUST set the 'I' bit to 1 in the revocation extension to be sent to the home agent. If however, since the negotiation of the 'I' bit in the most recent registration, the policy on the foreign domain has changed so that use of the 'I' bit is no longer allowed, the foreign agent MUST abide by the new policies with regards to notification of the mobile node, and MUST set the 'I' bit in the revocation acknowledgement to the OPPOSITE of what was sent by the home agent. This indicates to the home agent that its wishes were not necessarily followed, and the setting of the 'I' bit does not indicate whether the moblile node was notified or not. The foreign agent may also free up any resources that were being used by the former binding(s), and discontinue all Mobile IP services for the identified mobile nodes. 4.2.1.3 Co-located Mobile Node Responsibilities Upon receiving a revocation message, the co-located mobile node MUST check the Mobile-Home authenticator, and if the packet passes authentication, the mobile node MUST verify that the information contained in the revocation messages identifies the home agent with which it has a current binding, that this binding identifies correctly this mobile node and any foreign domain address it is currently using. If the mobile node is able to identify such a binding, the mobile node SHOULD immediately terminate any reverse tunnel encapsulation it is using to this home agent. The mobile node may also free up any other resources associated with the former binding. In addition, if the 'A' bit was negotiated in the registration process, and the 'A' bit was set in the revocation message, the mobile node MUST immediately Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 20 Internet Draft Registration Revocation in Mobile IP Glass, Chandra generate a revocation acknowledgment message in response. The revocation acknowledgment message MUST be sent to the IP source address of the revocation message, and it MUST be protected by a Mobile-Home authenticator for authentication by the home agent. 4.2.2 Foreign Domain Revoking/Releasing a Registration The following section details the responsibilities of each party depending on the functionality negotiated in the revocation support extension when the foreign domain is revoking a registration. 4.2.2.1 Foreign Agent Responsibilities In the case where the foreign domain is revoking/releasing a mobile node's binding, if revocation support has been negotiated, the foreign agent MUST inform the home agent it is shutting down the tunnel exit point (and reverse tunnel entry point). This will allow the home agent to stop generating tunnel packets from datagrams destined for the mobile node, and also allow it to free resources it is currently reserving to provide mobile-ip services to the mobile node. If the most recent registration request indicated the mobile node is using a co-located care-of address (the 'D' bit was set), and hence the registration request doesn't contain any information about the foreign agent, the foreign agent MUST include an NAI extension for identification by the home agent in the revocation message. A Foreign-Home authenticator MUST be appended in the registration revocation message. (Note: it is presumed the foreign agent had the 'R' bit set when such a colocated mobile node last registered, but even if not, obviously the foreign agent is aware of this binding. In this case, the foreign agent is implying to the home agent this it and/or the foreign domain in general have some way of controlling communications between the mobile node and home agent, and therefore a revocation message in this case implies to the home agent that such lines of communication are going away. See Section 4.3.1 "Use of the 'R' bit"). If the 'A' bit was negotiated in the revocation extension, the foreign agent SHOULD set the 'A' bit to 1 in the revocation message. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 21 Internet Draft Registration Revocation in Mobile IP Glass, Chandra If the use of the 'I' bit was negotiated, the foreign agent MUST NOT inform any mobile node of its revocation at this time. Instead, the foreign agent MUST set the 'I' bit to 1 in the revocation message, thereby asking the home agent to use the 'I' bit in the revocation acknowledgment to indicate if it should notify the effected mobile nodes. As an exception to this, the only time the FA may choose to not set the 'I' bit is in the case where policy on the foreign domain has changed since the most recent sucessful registration, and the foreign agent is no longer able to use the 'I' bit. In this case the foreign agent MUST set the 'I' bit to 0, and follow the policies of the foreign domain with regard to notifying the mobile node.. Note, when setting the 'I' bit to 1, the 'A' bit necessarily needs to also be set to 1. If the use of the 'I' bit was not negotiated, the foreign agent MAY inform the mobile node of its revocation as described in Section 4.1, before sending the revocation message to the home agent, just after sending the revocation message to the home agent, or after it receives a revocation acknowledgment message from the home agent. If the 'A' bit was set in the revocation message, the foreign agent SHOULD wait for a revocation acknowledgment message from the home agent. How long the foreign agent waits to retransmit, and how many times the message is retransmitted is only limited by the specification that the foreign agent MUST NOT send more than one revocation per second for a particular binding, SHOULD fall-back in analogy with the registration guidelines in [1], and MUST NOT retransmit revocation acknowledgement messages beyond the normal life of the revoked binding. 4.2.2.2 Home Agent Responsibilities Upon receiving a registration revocation message, the home agent MUST check the Foreign-Home authenticator. If the packet passes authentication, the home agent MUST locate the binding(s) identified by the home agent as being released using the information in the revocation message, namely the addresses identified by the mobile node address, the foreign domain address, and the home domain address. Since these bindings are no longer active, the home agent can free up any resources associated with the former bindings and discontinue all Mobile IP services for them. If the 'A' bit was set in the revocation message, the home agent MUST send a revocation acknowledgment to the IP source address of the registration revocation message. If a home agent receives a registration revocation message that does not contain a Foreign-Home authenticator, or a bad Foreign-Home authenticator, the registration revocation message MUST be ignored, and silently discarded. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 22 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 4.2.3 Mobile Node Deregistering a Registration The cases where a mobile node is registered with its home agent, whether it is registered directly with its home agent (as in the case of co-location), or registered via a foreign agent (if it is co-located or not), and wishes to terminate it's own binding, the mobile node SHOULD simply deregister the appropriate care-of Address with its home agent as described by [1]. Note that when a co-located mobile node includes a revocation extension in its registration request, it will expect to see a revocation extension in the registration reply from the home agent acknowledging that the home agent is willing to send revocation messages to such a mobile node. However, the home agent should understand that it will not receive revocation messages from such a mobile node, so the decision to include a revocation extension in the registration reply MUST NOT be made based on the home agent's desire to see such messages. A co-located mobile node, and home agent MAY negotiate the use of the 'A' bit, and use it in the revocation process. 4.3 The Use of Bits Several of the bits used in the registration process play an important role in the topology of the binding, and therefore the revocation. The 'R' bit in the agent advertisement is an effective way to assure that the foreign domain is provided with the binding information necessary to revoke it. This is especially important in the case of a co-located mobile node whose registration request may otherwise by-pass the foreign agent. How the foreign domain enforces this policy is beyond the scope of this document, but a few examples are through either restricted access to topologically correct addresses with which to co-locate, or some form of access control lists on the routers, etc. The 'D' bit in the registration request is a sign to a home domain that a foreign agent address does NOT appear in the registration request, and so the home agent may be missing the necessary information to be able to notify the foreign domain in the event of a registration revocation. A home agent that receives a registration request in which the 'D' bit is set SHOULD look for a foreign agent NAI extension appearing after the Mobile-Home authenticator indicating the foreign agent to which any revocation messages are to be sent. Note that if the registration request came from a foreign agent (e.g. the 'R' bit was set), then the source address of the registration request could be that of the foreign agent. The home agent SHOULD check to see if that address is not the care-of address Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 23 Internet Draft Registration Revocation in Mobile IP Glass, Chandra identified in the care-of address field of the registration request. Alternatively, as any such NAI extension MUST be secured via a foreign-home authenticator [1], the security association identified by the foreign agent's NAI MAY be used to identify an IP address to which any revocation message is to be sent. More information, and an example, is provided in "Appendix A: registration revocation in 'R' and 'D' Bit Worlds." 4.3.1 The 'R' Bit in Use If the foreign agent wishes to be able to revoke a mobile node's registration, it MUST set the 'R' bit in its agent advertisements. A foreign agent advertising the 'R' bit requests every mobile node, even one that is co-located, to register [the co-located address as its care-of address] with the foreign agent, making the foreign agent then capable of revoking the mobile node's registration as it is now privy to the information in the registration request, namely the mobile node's link address, home IP address, and the address of the mobile node's home agent. The foreign agent will then be capable of unicasting an agent advertisement to the mobile node, and sending a registration revocation message to the home agent, as described in Sections 4.1 and 4.2.2. This makes advertising the 'R' bit attractive in domains that wish to have control over registered mobile nodes, and moreover, sending revocation notification to the home domain may be a contractual necessity. Enforcement of the 'R' bit is beyond the scope of this document, and when the foreign domain wishes to be able to enforce the revocation, and/or to notify the home domain of revoked registrations, such an enforcement mechanism is crucial. A co-located mobile node sets the 'D' bit in its registration request, and since by definition the co-located address is topologically significant for the link the mobile node is visiting, the registration request may be sent directly to the home agent even in the presence of agent advertisements in which the 'R' bit is set (though this is considered "bad form", and the 'R' bit is a "hint" to the mobile node that such direct contact is policed in some way. Even so, nothing may be preventing the mobile node from trying to register directly with its home agent. In the event a foreign domain wishes to enforce the revocation of a co-located mobile node's registration, the foreign domain MUST be able to control the flow of datagrams to, and/or from, the mobile node. The easiest way to do this is to not accept registration requests from co-located mobile nodes, though there are other mechanisms available which allow co-location. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 24 Internet Draft Registration Revocation in Mobile IP Glass, Chandra 4.3.2 The 'D' bit in Use If the mobile node has set the 'D' bit in the registration request, and forwards the registration via a foreign agent (see Section 4.3.1), and the foreign agent determines it will accept the registration from the mobile node, then the foreign agent MUST append a revocation extension if it wants to be notified of registration revocations for this mobile node (in addition to any already included by the mobile node and protected by the mobile-home authenticator). The foreign agent MAY also append the prefix length extension [1] that appears in the agent advertisements on the link from which the mobile node is registering. The inclusion of the prefix length extension is so the home agent understands the topology of the link the mobile node is visiting in the event it wants to issue a single registration revocation for multiple mobile nodes visiting the same link. In order to authenticate these extensions, the foreign agent MUST append its NAI extension, which MUST be followed by a Foreign-Home authenticator. Note that registration requests where the 'D' bit is set, and which are relayed through a foreign agent due to the advertising of the 'R' bit can contain the foreign agent address as the source address of the registration request as received by the home agent. A home agent MUST verify that the source address of this registration request is not the same as the care-of address contained in the registration request; note that according to [1] the home agent is required to send the registration reply to the source IP address of the registration request. If the home agent wishes to support registration revocation for this binding, which can be conveyed to either the co-located mobile node, or the foreign agent whose NAI appears in the registration request, it MUST include a revocation support extension in the mobile-home portion of the registration reply if it agrees to notify the mobile node of a release of this registration, and/or MUST include a revocation support extension in the foreign-home portion of the registration reply if it agrees to notify the foreign agent of a release of this registration. Note that, as determined by the security association with the foreign agent, it may be necessary for the home agent to include its NAI extension for use by the foreign agent in authenticating the registration reply. Upon release of this registration, if revocation support was negotiated with BOTH the co-located mobile node, and the foreign agent, revocation messages for this binding MUST be first sent to the mobile node's co-located care-of address to ensure that they reach it. A revocation message MUST then be sent to the foreign agent. If the revocation message was sent to the foreign agent first, there may be no way for a revocation message to then reach the mobile node. Also, in order for the home agent to be able to send a revocation message to the foreign agent, it is presumed that the source IP address of the Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 25 Internet Draft Registration Revocation in Mobile IP Glass, Chandra registration request is that of the foreign agent, or that the security association between the home and foreign agents contains (among other things) the NAI and IP addresses of the foreign agent. 5 An Example of the New Messages in Use For clarity, the following examples are meant to illustrate the use of these messages in the registration phase, and the revocation phase. In cases where there may be some question to the order of processing, any order indicated by [1] MUST be followed. 5.1 The Registration Phase A foreign agent that supports registration revocation, and has a security association with a home agent to which it is forwarding a registration request SHOULD include the revocation support extension after the Mobile-Home authenticator. If the foreign agent wishes to receive a revocation acknowledgment from the home agent in the event that the registration for this mobile node is revoked, and/or if it is willing to send a revocation acknowledgment message in response to a revocation message from the home agent for this mobile node, it MUST set the 'A' bit to '1'. Furthermore, if the foreign agent supports the use of the 'I' bit, and is willing to let the home agent decide if the mobile node should be informed of the revocation of its registration, it SHOULD set the 'I' bit to '1'. Additionally, the foreign agent MUST append a Foreign-Home authenticator to the registration request, and include any other extension needed by the foreign agent to verify the authenticator [1]. Upon receiving a registration request containing a revocation extension, a home agent that supports registration revocation SHOULD include a revocation support extension in the registration reply. If the 'A' bit is set in the revocation extension sent by the foreign agent, a home agent that wishes that foreign agent to retransmit lost (unacknowledged) revocation message, and agrees to do the same, MUST set the 'A' bit in its revocation extension to '1'. Furthermore, if the foreign agent set the 'A' bit to 1, and also set 'I' bit to 1 in its revocation extension, and the home agent supports the use of the 'I' bit, and wishes to determine whether this mobile node is to be informed in the event that its registration has been revoked, the home agent SHOULD set the 'A' bit, and the 'I' bit in its registration extension to '1'. Additionally, the home agent MUST append a Home-Foreign authenticator to the registration request, and include any other extension needed by the foreign agent to verify the authenticator [1]. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 26 Internet Draft Registration Revocation in Mobile IP Glass, Chandra Upon receiving the authenticated registration reply, the foreign agent should check the revocation support extension. If none is present, the foreign agent MAY presume the home agent doesn't understand revocation messages, or is unwilling to participate. If a revocation support extension is present, and since the foreign agent included the revocation extension in the registration request with the 'A' and 'I' bit set, the foreign agent MUST check the 'A' bit to see if the home agent will provide revocation acknowledgment services (if they were requested), and should also check the 'I' bit to see if the home agent wants to decide if the mobile node should be notified in the event this registration is revoked. 5.2 The Revocation Phase If a foreign agent wishes to revoke a mobile node's registration, it generates a revocation message. If the 'A' bit was negotiated in the revocation extension for this registration, the foreign agent SHOULD set the 'A' bit in the revocation message to 1. If the 'A' bit and 'I' bits were negotiated in the revocation extensions, and the foreign agent is willing to let the home agent indicate whether this mobile node should be informed that its registration has been revoked, it SHOULD set both the 'A' bit and the 'I' bit to 1; it MUST NOT set the 'I' bit to 1 without setting the 'A' bit to 1. The foreign agent MUST also place the address of the mobile node whose registration it wishes to revoke in the home address field, the address that mobile node registered as the care-of address in the foreign domain field, and the address the mobile node registered in the home domain address field. The foreign agent MUST also insert the Foreign Domain Identifier, and set the home domain Identifier to 0. The foreign agent MUST append a foreign-home authenticator, and any additional information it needs to include for the home agent to validate it (e.g. if the care-of address is not its own, it can use its NAI extension). Upon receiving the above revocation message, the home agent assures the revocation is protected with a valid Foreign-Home authenticator. The home agent uses either the foreign agent NAI if present, or the address identified as the foreign domain address to identify the security association, and authenticate the revocation message. If the authenticator is bad, the home agent MUST ignore, and silently discard the revocation message. If the authenticator is good, the home agent uses the mobile node home address, foreign domain address, and home domain address to locate the mobile node(s) whose registration(s) is/are being revoked. If the 'A' bit was negotiated in the registration phase for the binding(s) identified, and set to 1 in the revocation message, the home agent MUST generate a revocation acknowledgement message. If the 'I' bit was negotiated in the registration phase for the binding(s) identified, the home agent MUST check to see if the 'A' bit and 'I' bit are both set to '1' in the Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 27 Internet Draft Registration Revocation in Mobile IP Glass, Chandra revocation message. If so, and the home agent wishes for the identified mobile node(s) to be informed of the revocation, it MUST set the 'I' bit in the revocation acknowledgement to 1, or if the home agent does not wish the identified mobile node(s) to be informed of the revocation, it MUST set the 'I' bit in the revocation acknowledgement to 0. The home agent then copies the addresses, and the foreign agent identifier field into the reply, and inserts its own timestamp into the home agent identifier field. The home agent MUST protect the revocation acknowledgment with a Home-Foreign authenticator (and any other extension necessary for the foreign agent to authenticate the Home-Foreign authenticator, e.g. its NAI extension). Upon receiving a valid revocation acknowledgment, if the foreign agent set the 'I' bit in the revocation message to 1, it MUST check the 'I' bit in the revocation acknowledgement, and if set to 1, MUST notify the mobile node of the revocation, or if the 'I' bit is set to 0 in the revocatoin acknowledgement, the foreign agent MUST NOT notify the mobile node of the revocation. 6. No New Error Codes As the intent of a registration revocation message is not a request to discontinue services, but is a notification that Mobile IP services are discontinued, there are no new error codes. If any registration revocation fails authentication, or replay protection (as described in Section 4), it MUST be silently discarded, and Mobile IP services MUST NOT be suspended. Registration revocation messages which are authenticated MUST be checked to make sure the information they contain accurately identifies a current session. If so, the registration revocation message indicates the mobility agent that sent the message has already terminated, or is about to terminate, its Mobile IP services for the identified registrations. Hence, the receiving agent can free any resources currently being used for the registrations being revoked. 7. Multiple Binding Support RFC 3220 [1] allows a mobile node to register multiple care-of addresses with its home agent. Each one of these bindings is it's own discrete registration, and hence can be treated as a separate case for registration revocation. Consider the situation where a mobile node has multiple care-of addresses registered with a single foreign agent (either because the mobile node has multiple co-located care-of addresses and the foreign agent has the 'R' bit set, or because the foreign agent is multi-homed). Either agent can indicate the Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 28 Internet Draft Registration Revocation in Mobile IP Glass, Chandra revocation of all these bindings by setting the care-of address field to the zero address (and their addresses in the correct places), indicating all care-of addresses being used by the indicated mobile node that are bound to the agent identifying itself by this revocation message. If a foreign agent revokes a particular mobile node's binding(s) with it, the home agent MAY or MAY NOT then revoke any of the mobile node's other bindings (with other foreign agents). If a home agent is revoking one of a mobile node's bindings, it MAY revoke none, or all of the mobile node's other bindings as it sees fit. If a home agent decides to revoke a single binding for a mobile node, the foreign agent MAY decide to revoke other bindings for the same mobile node as it sees fit. The revocation mask is designed to make revoking multiple bindings easier to specify, and in situations where network topologies make revoking multiple mobile node bindings difficult to specify numerically through use of NAIs. 7.1 Other Random Protocol Details If a home agent receives a registration revocation from a foreign agent indicating the registration for a co-located mobile node has been revoked, the home agent MUST verify this message is coming from the same foreign agent that relayed the registration request for this binding. If this can not be verified, or it can be determined that the foreign agent issuing this registration revocation is not the foreign agent which relayed the registration request for the current binding, the home agent MUST silently ignore this revocation message. This means if a mobile node has one or more bindings with different co-located care-of addresses, and in addition has one or more bindings using foreign agent provided care-of addresses (as in the case of multi-homed foreign agent), each set of bindings must be revoked separately. 8. Security Considerations RFC 3220 [1] defines a security mechanism that MUST be used by home agents and mobile nodes, and optionally foreign agents. All messages defined in this document MUST use the security mechanisms defined in [1], and are therefore as secure as those in [1]. As registration revocation, when performed, terminates Mobile IP services being provided to the mobile node, it is crucial that all security and replay protection mechanisms be verified before a mobility agent recognizes that the other agent has revoked a mobile node's binding, and frees up the resources it has reserved for this service. Messages Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 29 Internet Draft Registration Revocation in Mobile IP Glass, Chandra which are sent link-local (e.g. between mobile node and foreign agent) MAY also be secured by methods outlined in [1], but have no relation to the enhancements described by this document. RFC 2794 [4] describes the use of the Network Access Identifier in Mobile IP. Its relevant use here is for agents to be able to identify each other in a revocation message. In cases where foreign and home domains are going to approve registrations from co-located mobile nodes (registering with the 'D' bit [1]), and in topologies where the foreign agent is setting the 'R' bit in its agent advertisements [1], if the agents are going to use their NAIs to identify themselves, the security association they share MUST include the IP address the registration revocation messages are to be sent to, and will be sent from. For a more involved discussion, see Appendix A. It has been recognized that agent advertisements as defined in [1] provide a denial-of-service potential [5]. This is because the agent advertisements as defined in [1] may be spoofed by other machines residing on the link. This may make it possible for such nodes to trick the mobile node into believing its registration has been revoked either by unicasting such an advertisement to the link-local address of the mobile node, or by broadcasting it to the subnet, thereby tricking all mobile nodes registered with a particular foreign agent into believing all their registrations have been lost. There has been some work in this working group and others (e.g. IPSec) to secure such router advertisements, though at the time of this publication, no solutions have become common practice. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 30 Internet Draft Registration Revocation in Mobile IP Glass, Chandra Appendix A: Registration Revocation in 'R' and 'D' Bit Worlds. Two issues influence the registration of a mobile node on a foreign subnet. First is the mobile node's desire to co-locate (use of the 'D' bit). Second is whether the foreign domain is requiring registration through foreign agents (the infamous 'R' bit). This leads to several different registration topologies in Mobile IP (note: cases where the mobile node is using a private address are considered in Appendix B): - The most generic is the mobile node that doesn't co-locate, and registers using a foreign agent's care-of address (regardless of the state of the 'R' bit in the foreign agent advertisements) to its home agent. In this case, all the necessary information to revoke a mobile node's registration is contained in the registration. The security association between the agents can be based on IP address, or NAI. - Second is a mobile node that co-locates, then registers directly to its home agent without registering through a foreign agent (foreign agents ignored, 'R' bit irrelevant). In this case, the home agent MAY notify the mobile node that its registration is being revoked, but it isn't possible through Mobile IP for the foreign domain to revoke a mobile node's registration in this way, nor is it possible for a foreign domain to suspend Mobile IP services being provided to a co-located mobile node as the mobile node is doing its own tunnel decapsulations. - Lastly is a mobile node that co-locates setting the 'D' bit, then due to the presence of the 'R' bit in the agent advertisement(s), registers through a foreign agent with its home agent. In the last case, the mobile node has set MNaddr in the registration request to it's home address, HAaddr to that of its home agent, and COaddr to its co-located address. Note that nowhere in this registration request appears the IP address of any foreign agent. Upon sending the registration request to a foreign agent, that foreign agent processes the registration, remembering the information it contains. If the foreign agent shares a security association with the identified home agent, it MUST append its NAI, and a Foreign-Home authenticator. The foreign agent then sends the registration request to the identified home agent using its IP address as the source address of the datagram. Upon receiving such a registration request, the home agent MUST check the Foreign-Home authenticator. It does so by using the NAI if present, or perhaps the source address of the request. The registration reply the home agent sends MAY contain the home agent's NAI, but it MUST contain an Home-Foreign authenticator if Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 31 Internet Draft Registration Revocation in Mobile IP Glass, Chandra a Foreign-Home authenticator was present in the registration request, and the home agent MUST send the registration reply to the source address of the registration request [1], in this case the IP address of the foreign agent. Note that in cases where a Foreign Agent is able to revoke the registration of a co-located mobile node, it is expected that such a foreign agent has the power to control the data-flow of a co-located mobile node even though tunnel datagrams are being addressed directly to the mobile node. This is akin to how such a foreign agent would enforce the 'R' bit, preventing the mobile node from sending the registration request directly to the home agent. Appendix B: Disparate Address, and Receiver Considerations Since the registration revocation message comes from a source address that is topologically routable from the interface receiving the datagram, the agents, by definition, are topologically connected (if this were not the case, the initial registration mechanism would have failed). If either are connecting this topologically connected region to one or more disparate address spaces no problems are foreseen. In order for the mobile node to have successfully registered with its home agent, it MUST have provided to the network to which it is currently attached a routable address of its home agent. Conversely, the care-of address being used by the mobile node must also be topologically significant to the home agent in order for the registration reply to have been received, and the tunnel initiated. By definition, then, the home agent address and the care-of address must each be significant, and either address must for a unique pair in the context of this mobile node to both agents. Another way of understanding this is that the tunnel endpoint are in some way connected, and hence are unique as far as the other end is concerned. The address at the other end of the tunnel, in combination with the address of the mobile node, must form a unique pair that can be identified by the agent receiving the registration revocation message. As an example, consider a mobile node who's home address lies in disparate address space A behind it's home agent. MN[a]-----[c]FA[b]-----((()))-----[b]HA[a]-----[a]CN Address Some topologically Address Space C connected network Space A Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 32 Internet Draft Registration Revocation in Mobile IP Glass, Chandra If we assume there must be a tunnel in existence at the time of the registration revocation, namely between FA[b] and HA[b], then the pair {FA[b],MN[a]} is guaranteed to be unique in the home agent bindings, and the pair {HA[b],MN[a]} is guaranteed to be unique in the foreign agent's visitor list. As a result of this, a home agent receiving a registration revocation message and foreign-home authenticator for MN[a] from FA[b] is able to determine the unique mobile node address being deregistered (if one is provided). Conversely a foreign agent receiving a registration revocation message and Home-Foreign authenticator for MN[a] from HA[b] is able to determine the unique mobile node address being deregistered. If a foreign agent receives a registration revocation message with the home agent field set to the zero address it MUST be silently ignored. This is to prevent confusion in the case of overlapping private addresses; when multiple mobile nodes are registered via the same care-of address using the same (disparate/private) home address, the home agent address is the only way a foreign agent can discern these mobile nodes. Appendix C: Using Registration Revocation to Help Release Resources When a mobile node moves out/around a foreign domain from where it had registered, relevant resources at a previous foreign agent may be consumed until its visitor entry for the mobile node expires. For example, consider a cdma2000 network deployment using Mobile IP. The Wireless IP Network Standard [8] defines foreign agent/Packet Data Servicing Node (PDSN) procedures for managing the PPP session for a mobile node, i.e., when the Radio Network opens an R-P session for an mobile node, the foreign agent/PDSN initiates establishment of a PPP session. As an mobile node moves from one foreign domain serviced by a foreign agent/PDSN (source PDSN) to another PDSN (target PDSN) during an inter-PDSN handoff, a Mobile IP registration is sent to the home agent and a new PPP session is established at the target PDSN. The PPP session at the source PDSN remains exhausted until the PPP inactivity timer expires. Maintaining these PPP sessions may consume valuable resources at the source PDSN that could otherwise be used to support additional mobile nodes. Registration revocation messages can be used to help identify resources that could be released (without actually having an administrative revocation). To accomplish this, the revocation support extension would need to be appended to a registration request as it is forwarded by a foreign agent that supports registration revocation. Note that the revocation Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 33 Internet Draft Registration Revocation in Mobile IP Glass, Chandra support extension is protected by the FA-HA authenticator. When a home agent that supports registration revocation receives such a registration request, as required by this specification it MUST record the capability of this foreign agent. The home agent may then use a registration revocation message to notify this foreign agent if the mobile node's care-of address changes, e.g., when the mobile node moves from one foreign agent to another, or when the mobile node deregisters with the home agent. As a result, upon receipt of an authenticated revocation message, the foreign agent can delete the visitor entry for this mobile node, thereby releasing the resources being used to support it. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 34 Internet Draft Registration Revocation in Mobile IP Glass, Chandra Acknowledgments The authors would like to thank Rajesh Bhalla, Kent Leung, and Alpesh Patel for their work on draft-subbarao-mobileip-resource-00.txt "Releasing Resources in Mobile IP" of which the revocation support extension, and the acknowledgment mechanism are contained in this document. Where to Direct Comments Questions and comments about this draft should be directed at the Mobile IP working group: mobile-ip@sunroof.eng.sun.com Questions and comments about this draft may also be directed to the authors: Steven M. Glass Madhavi W. Chandra Solaris Network Technologies IOS Technologies Division Sun Microsystems Cisco Systems 1 Network Drive 7025 Kit Creek Road Burlington, MA. 01801 Research Triangle Park, NC 27709 Phone: 1.781.442.0504 Phone: 1.919.392.8387 Fax: 1.781.442.1706 E-mail: Steven.Glass@Sun.COM E-mail: mchandra@cisco.com The working group may also be contacted via the current chairs: Basavaraj Patil Phil Roberts Nokia Corporation Megisto Systems, Inc. 6000 Connection Drive 20251 Century Blvd M/S M8-540 Suite 120 Irving, Texas 75039 Germantown, MD 20874 USA USA Phone: +1 972-894-6709 Phone: +1 301-444-1700 Fax : +1 972-894-5349 Fax: +1 301-515-3675 E-Mail: Basavaraj.Patil@nokia.com E-Mail: proberts@megisto.com Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 35 Internet Draft Registration Revocation in Mobile IP Glass, Chandra References [A] Mobile IP Authentication, Authorization, and Accounting Requirements RFC 2977, October 2000 S. Glass, T. Hiller, S. Jacobs, C. Perkins. [B] Criteria for Evaluating AAA Protocols for Network Access RFC 2989, November 2000 B. Aboba, P. Calhoun, S. Glass, T. Hiller, P. McCann, H. Shiino, P. Walsh, G. Zorn, G. Dommety, C. Perkins, B. Patil, D. Mitton, S. Manning, M. Beadles, X. Chen, S. Sivalingham, A. Hameed, M. Munson, S. Jacobs, B. Lim, B. Hirschman, R. Hsu, H. Koo, M. Lipford, E. Campbell, Y. Xu, S. Baba, E. Jaques [1] IP Mobility Support for IPv4 RFC 3220, January 2002 C. Perkins, Editor. [2] Reverse Tunneling for Mobile IP, revisited RFC 3024, January 2001 G. Montenegro, Editor. [3] ICMP Router Discovery Messages RFC 1256, September 1991 S. Deering, Editor. [4] Mobile IP Network Access Identifier Extension for IPv4 RFC 2794, March 2000 P. Calhoun, C. Perkins. [5] Security Issues in Mobile IP draft-glass-mobileip-securities-issues-02.txt S. Glass. [6] Key Words for us in RFCs to INdicate Requirement Levels RFC 2119, March 1997 S. Bradner [7] CIDR and Classful Routing RFC 1817, August 1995 Y. Rekhter CIDR: an Address Assignment and Aggregation Strategy RFC 1519, September 1993 V. Fuller, T. Li, J. Yu, K. Varadhan An Architecture for IP Address Allocation with CIDR RFC 1518, September 1993 Y. Rekhter, T. Li [8] TIA/EIA/IS-835, Wireless IP Network Standard, June 2000. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 36 Internet Draft Registration Revocation in Mobile IP Glass, Chandra Full Copyright Statement "Copyright (C) The Internet Society (2001 - 2002). 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. 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. Expires December 2002 draft-ietf-mobileip-reg-revok-03.txt Page 37