AAA Working Group Pat R. Calhoun Internet Draft Airespace draft-ietf-aaa-diameter-mobileip-15.txt Tony Johansson Category: Standards Track Bytemobile Inc Charles E. Perkins Nokia Research Center Tom Hiller (editor) Lucent Technologies November 2003 Diameter Mobile IP Application Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. 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. 1. Abstract This document specifies a Diameter application that allows a Diameter server to authenticate, authorize and collect accounting information for Mobile IP services rendered to a mobile node. Combined with the Inter-Realm capability of the base protocol, this application allows mobile nodes to receive service from foreign service providers. Diameter Accounting messages will be used by the foreign and home agents to transfer usage information to the Diameter servers. 2. Conventions used in this document <Add any conventions that you use in your document here. Common conventions are listed below.> In examples, "C:" and "S:" indicate lines sent by the client and server respectively. Calhoun et al Standards Track - March 2004 1 Diameter MIP November 2003 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [2]. 3. Introduction Mobile IP, as defined in [MOBILEIP], defines a method that allows a mobile node to change its point of attachment to the Internet with minimal service disruption. Mobile IP does not provide any specific support for mobility across disparate administrative domains, and therefore does not specify how usage can be accounted for, which has limited the applicability of Mobile IP in a IPv4 commercial deployment. The Mobile IP specification as defined in [MOBILEIP] recommends mobile nodes to have a static home address and a home agent. However this may not be always possible in certain deployment scenarios. Recent developments in areas that impact IP mobility in the IETF allow Mobile IP [MOBILEIP] to work just as well when mobile nodes do not have a static home agent and home address. In addition, another specification [MIPNAI] allows a mobile node to use its NAI instead of its home address, which better accommodates current administrative practice. This document specifies Application-ID 4 to the Diameter base protocol [DIAMBASE] that allows a Diameter server to authenticate, authorize and collect accounting information for Mobile IP services rendered to a mobile node. This application MUST NOT be used in conjunction with the Mobile IPv6 protocol. Combined with the Inter-Realm capability of the Diameter base protocol, this application allows mobile nodes to receive service from foreign service providers. The Diameter Accounting messages will be used by the foreign and home agents to transfer usage information to the Diameter servers. The Mobile IP protocol [MOBILEIP] specifies a security model that requires that mobile nodes and home agents share a pre-existing security association, which leads to scaling and configuration issues. This specification defines Diameter functions that allow the AAA server to act as a Key Distribution Center (KDC), whereby dynamic session keys are created and distributed to the mobility entities for the purposes of securing Mobile IP Registration messages. Strong authentication and confidentiality of session keys is required, and is to be provided via mutually authenticated TLS or IPsec. As with the Diameter base protocol, AAA servers implementing the Mobile IP application can process users' identities supplied in a Network Access Identifier (NAI) format [NAI], which is used for Diameter message routing purposes. Mobile nodes include their NAI in Registration messages, as defined in [MIPNAI]. The use of the NAI is consistent with the roaming model defined by the ROAMOPS Working Group [EVALROAM]. Calhoun Standards Track - March 2003 2 Diameter MIP November 2003 A home AAA server (AAAH) and foreign AAA server (AAAF), which support the Mobile-IP authentication application MAY maintain session-state or MAY be session-stateless. AAA redirect agents and AAA relay agents MUST not maintain session-state. The AAAH, AAAF, proxies and relays agents MUST maintain transaction state. Given the nature of Mobile IP, a re-authentication can only be initiated by a mobile node, which does not participate in the Diameter message exchanges. Therefore Diameter server initiated re- auth does not apply to this application. Furthermore, the nature of Mobile IP also means that the mobile node will do handoffs between different foreign agents. To guarantee that a registered user always ends up in the same initial AAAH, the mobile node SHOULD always include the AAAH NAI [AAANAI]. Finally, to assist the AAAH in routing the messages to a mobile node's home agent the mobile node SHOULD always include the HA NAI [AAANAI]. If the mobile node does not support the Mobile IP AAA NAI extension [AAANAI], this MAY limit the functionality that can be offered to such a mobile node. The Diameter Mobile-IP Application meets the requirements specified in [MIPREQ, CDMA2000]. Later subsections in this introductory section provide some examples and message flows of the Mobile IP and Diameter messages that occur when a mobile node requests service in a foreign network. In this document, the role of the "attendant" [MIPREQ] is performed by either the home agents (for co-located mobile nodes) or foreign agents for the Mobile-IP Application, and these terms will be used interchangeably. 3.2 Inter-Realm Mobile IP When a mobile node requests service by issuing a Registration Request to the foreign agent, the foreign agent creates the AA-Mobile-Node- Request (AMR) message, which includes the AVPs defined in section 2.1. The Home Address, Home Agent, Mobile Node NAI and other important fields are extracted from the registration messages for possible inclusion as Diameter AVPs. The AMR message is then forwarded to the local Diameter server, known as the AAA-Foreign, or AAAF. Visited Realm Home Realm +--------+ +--------+ Calhoun Standards Track - March 2003 3 Diameter MIP November 2003 |abc.com | AMR/AMA |xyz.com | | AAAF |<------------------->| AAAH | +->| server | server-server | server | | +--------+ communication +--------+ | ^ ^ | AMR/AMA | client-server | HAR/HAA | | communication | v v v +---------+ +---------+ +---------+ | Foreign | | Foreign | | Home | | Agent | | Agent | | Agent | +---------+ +---------+ +---------+ ^ | Mobile IP | v +--------+ | Mobile | | Node | mn@xyz.com +--------+ Figure 1: Inter-Realm Mobility Upon receiving the AMR, the AAAF follows the procedures outlined in [DIAMBASE] to determine whether the AMR should be processed locally, or if it should be forwarded to another Diameter server, known as the AAA-Home, or AAAH. Figure 1 shows an example in which a mobile node (mn@xyz.com) requests service from a foreign provider (abc.com). The request received by the AAAF is forwarded to xyz.com's AAAH server. Figure 2 shows the message flows involved when the foreign agent invokes the AAA infrastructure to request that a mobile node be authenticated and authorized. Note that it is not required that the foreign agent invoke AAA services every time a Registration Request is received from the mobile, but rather only when the prior authorization from the AAAH expires. The expiration time of the authorization is communicated through the Authorization-Lifetime AVP in the AA-Mobile-Node-Answer (AMA, see section 2.2) from the AAAH. Mobile Node Foreign Agent AAAF AAAH Home Agent Calhoun Standards Track - March 2003 4 Diameter MIP November 2003 ----------- ------------- ------------ ---------- ------- Advertisement & <--------- Challenge Reg-Req&MN-AAA ----> AMR------------> Session-Id = foo AMR------------> Session-Id = foo HAR-----------> Session-Id = bar <----------HAA Session-Id = bar <-----------AMA Session-Id = foo <------------AMA Session-Id = foo <-------Reg-Reply Figure 2: Mobile IP/Diameter Message Exchange The foreign agent (as shown in Figure 2) MAY provide a challenge, which gives it direct control over the replay protection in the Mobile IP registration process, as described in [MIPCHAL]. The mobile node includes the Challenge and MN-AAA authentication extension to enable authorization by AAAH. If the authentication data supplied in the MN-AAA extension is invalid, AAAH returns the response (AMA) with the Result-Code AVP set to DIAMETER_AUTHENTICATION_REJECTED. The above scenario causes the MN-FA and MN-HA keys to be exposed to Diameter agents all along the Diameter route. A more proper approach is to eliminate the AAAF and other Diameter agents as follows: Calhoun Standards Track - March 2003 5 Diameter MIP November 2003 Local redirect Home FA AAAF Agent Server AMR ----------------> AMA (Redirect) ----------------> AMA (Redirect) <---------------- AMA (Redirect) <---------------- Setup Security Association <--------------------------------------------------> AMR --------------------------------------------------> AMA (MN-FA key) <--------------------------------------------------- Figure 3: Use of a Redirect Server with AMR/AMA Figure 4 shows the HA and the AAAH are in the same network so it is likely that the HAAA knows the IP address of the HA, and the redirect server would therefore not be needed, but are shown for completeness. The FA still provides the challenge and the mobile sends the RRQ, etc., as in the previous figure, however these were eliminated from Figure 3 and 4 to reduce figure clutter. The redirect server eliminates the AAAF and any other Diameter agents from seeing the keys as they are transported to the FA and HA. Local Redirect Home HA Agent Server HAR <-------------------- HAA (Redirect) --------------------> Setup Security Association <----------------------------------------> HAR (MN-HA key) <----------------------------------------- HAA -----------------------------------------> Figure 4: Use of a Redirect Server with HAR/HAA Accounting messages are sent via Diameter agents, not the direct connection, unless network policies dictate otherwise. Calhoun Standards Track - March 2003 6 Diameter MIP November 2003 A mobile node with AAA NAI extension support [AAANAI], which has been previously authenticated and authorized, MUST always include the assigned home agent in the HA Identity subtype of the AAA NAI extension, and the authorizing Home AAA server in the AAAH Identity subtype of the AAA NAI extension, when re-authenticating. So, in the event that the AMR generated by the FA is for a session that was previously authorized, it MUST include the Destination-Host AVP, with the identity of the AAAH found in the AAAH-NAI, and the MIP-Home- Agent-Host AVP with the identity and realm of the assigned HA found in the HA-NAI. If on the other hand the mobile node does not support the AAA NAI extension, the FA may not have the identity of the AAAH and the identity and realm of the assigned HA. This means that without support of the AAA NAI extension, the FA may not be able to guarantee, that the AMR will be destined to the same AAAH, which previously authenticated and authorized the mobile node, since the FA may not know the identity of the AAAH. If the mobile node was successfully authenticated, the AAAH checks if the home agent was located in the foreign realm, by checking Home- Agent-In-Foreign-Network flag of the MIP-Feature-Vector AVP. Other AVP's like the MIP-Home-Agent-Host AVP and the MIP-Originating- Foreign-AAA AVP may also be used to verify the location of the home agent. If the home agent is located in the home realm, then the AAAH sends an HAR message to the home agent, which contains a MIP-Reg- Request AVP. However, as in the case of the AMA and the MN-FA key, using Diameter agents exposes the MN-HA key to Diameter agents along the way. Figure 4 shows the use of a redirect server to avoid this problem. If the home agent was not located in the foreign realm, the AAAH checks for the MIP-Home-Agent-Address AVP and if present the MIP- Home-Agent-Host AVP. If one was specified, the AAAH checks that the address is that of a known home agent and that the mobile node is allowed to request this particular home agent, and that the home agent's identity is included in the MIP-Home-Agent-Host AVP. If no home agent was specified, and if the MIP-Feature-Vector has the Home- Agent-Requested flag set, and if allowed by policy in the home realm, the AAAH SHOULD allocate a home agent on behalf of the mobile node. This can be done in a variety of ways, including using a load- balancing algorithm in order to keep the load on all home agents equal. The actual algorithm used and the method of discovering the home agents is outside the scope of this specification. The AAAH then sends an Home-Agent-MIP-Request (HAR), which contains the Mobile IP Registration Request message data encapsulated in the MIP-Reg-Request AVP, to the assigned or requested Home Agent. Refer to Figure 4 if the HA does not have a direct path to the HA. The AAAH MAY allocate a home address for the mobile node, while the Home Agent MUST support home address allocation. In the event the AAAH handles address allocation, it includes it in a MIP-Mobile-Node- Address AVP within the HAR. The absence of this AVP informs the Home Agent to perform the allocation. Calhoun Standards Track - March 2003 7 Diameter MIP November 2003 During the creation of the HAR, the AAAH MUST use a different session identifier than the one used in the AMR/AMA (see Figure 2). If the AAAH is session-stateful, it MUST send the same session identifier for all HARs initiated on behalf of a given mobile node's session. Otherwise, if the AAAH is session-stateless, it will manufacture a unique session-id for every HAR. A mobile node's session is identified via its identity in the User- Name AVP, the MIP-Mobile-Node-Address and the MIP-Home-Agent-Address AVPs. This is necessary in order to allow the session state machine, defined in the base protocol [DIAMBASE], to be used unmodified with this application. Therefore, an STR from a foreign agent would free the session from the foreign agent, but not the one towards the home agent (see figure 5). STR, Session-Id = foo STR, Session-Id = bar ---------------------> <-------------------- +----+ +------+ +------+ +----+ | FA | | AAAF | | AAAH | | HA | +----+ +------+ +------+ +----+ <--------------------- ---------------------> STA, Session-Id = foo STA, Session-Id = bar Figure 5: Session Termination and Session Identifiers Upon receipt of the HAR, the home agent first processes the Diameter message. The home agent processes the MIP-Reg-Request AVP and creates the Registration Reply, encapsulating it within the MIP-Reg-Reply AVP. In the creation of the Registration Reply the Home Agent must include the HA NAI and the AAAH NAI, which will be created from the Origin-Host AVP and Origin-Realm AVP of the HAR. If a home address is needed, the home agent MUST also assign one and include the address in both the Registration Reply and within the MIP-Mobile-Node-Address AVP. The HA MUST include an Acct-Multi-Session-Id AVP in the HAA returned to the AAAH. Upon receipt of the HAA, the AAAH creates the AA- Mobile-Node-Answer (AMA) message, includes the Acct-Multi-Session-Id that was present in the HAA, and the MIP-Home-Agent-Address, MIP- Mobile-Node-Address AVPs in the AMA message. See Figure 3 and 4 for the use of the redirect agent for the secure transport of the HAA and AMA messages. 3.3 Support for Mobile IP Handoffs Given the nature of Mobile IP, a mobile node MAY receive service from many foreign agents during a period of time. However, the home realm should not view these handoffs as different sessions, since this could affect billing systems. Furthermore, many foreign agents do not communicate, which makes it quite difficult for AAA information to be exchanged between these entities. Therefore, it MUST be assumed that Calhoun Standards Track - March 2003 8 Diameter MIP November 2003 a foreign agent is not aware that a registration request from a mobile node has been previously authorized. A handoff registration request from a mobile node will cause an AMR to be sent to its AAAF. The AMR will include a new session identifier, and MAY be sent to an AAAF in the visited network other than the AAAF, which received the previous AMR. However, with the usage of the AAA NAI, this AMR is guaranteed to be received by the AAAH to which the user is currently registered. As discussed above, it may be undesirable for keys, such as the MN-FA keys, to be exposed to any Diameter Agents. In this case the FA should establish a security association with the AAAH directly, using redirects as described above. This completely eliminates the AAAF from the transaction. Since the AAAH may be session-stateless, it is necessary for the resulting HAR received by the HA to be identified as a continuation of an existing session. If the HA receives an HAR for a mobile node, with a new session identifier, and the HA can guarantee that this request is to extend service for an existing service, then the HA MUST be able to modify its internal session state information to reflect the new session identifier. It is necessary for accounting records to have some commonality across handoffs in order for correlation to occur. Therefore, the home agent MUST send the same Acct-Multi-Session-Id AVP value in all HAAs for the mobile's session. That is, the HA generates a unique Acct-Multi-Session-Id when receiving an HAR for a new session, and returns this same value in every HAA for the session. This Acct- Multi-Session-Id AVP will be returned to the foreign agent by the AAAH in the AMA. Both the foreign and home agents MUST include the Acct-Multi-Session-Id in the accounting messages. ACR, Session-Id = foo ACR, Session-Id = bar Acct-Multi-Session-Id = a Acct-Multi-Session-Id = a ---------------------> <-------------------- +----+ +------+ +------+ +----+ | FA | | AAAF | | AAAH | | HA | +----+ +------+ +------+ +----+ <--------------------- ---------------------> ACA, Session-Id = foo ACA, Session-Id = bar Figure 6: Accounting messages w/ Mobile IP Application 3.4 Allocation of Home Agent in Foreign Network The Diameter Mobile IP application allows a home agent to be allocated in a foreign network, as required in [MIPREQ, CDMA2000]. When a foreign agent detects that the mobile node has a home agent address equal to 0.0.0.0 or 255.255.255.255 in the Registration Request message, it MUST add a MIP-Feature-Vector AVP with the Home- Calhoun Standards Track - March 2003 9 Diameter MIP November 2003 Agent-Requested flag set to one. If the home agent address is equal to 255.255.255.255, then the foreign agent also MUST set the Home- Address-Allocatable-Only-in-Home-Realm flag equal to one. If the home agent address is set to 0.0.0.0, the foreign agent MUST set the Home- Address-Allocatable-Only-in-Home-Realm flag equal to zero. When the AAAF receives an AMR message with the Home-Agent-Requested flag set to one, and the Home-Address-Allocatable-Only-in-Home-Realm flag equal to zero, the AAAF MAY set the Foreign-Home-Agent-Available flag in the MIP-Feature-Vector AVP to inform the AAAH that it is willing and able to assign a Home Agent for the mobile node. When doing so, the AAAF MUST include the MIP-Candidate-Home-Agent-Host AVP and the MIP-Originating-Foreign-AAA-AVP. The MIP-Candidate-Home- Agent-Host AVP contains the identity of the home agent that would be assigned to the mobile node and the MIP-Originating-Foreign-AAA AVP contains the identity of the AAAF. In the event that the mobile node with AAA NAI extension support [AAANAI] has been previously authorized by the AAAH and now needs to be re-authenticated, and requests to keep the assigned home agent in the foreign network, the mobile node MUST include the HA NAI and the AAAH NAI in the registration request to the FA. Upon receipt, the FA will create the AMR including the MIP-Home-Agent-Address AVP, the Destination-Host AVP based on the AAAH NAI and include the MIP-Home- Agent-Host AVP based on the home agent NAI. If the AAAF authorizes the use of the requested home agent, the AAAF MUST set the Home- Agent-In-Foreign-Network bit in the MIP-Feature-Vector AVP. In the event that the mobile node that does not support the AAA NAI extension has been previously authorized by the AAAH and now needs to be re-authenticated, and requests to keep the assigned home agent in the foreign network, the mobile node sends a registration request without the AAA NAI and the HA NAI. Upon receipt, the FA will create the AMR including the MIP-Home-Agent-Address AVP. If the AAAF authorizes the use of the requested home agent, and if it has knowledge that the requested home agent is in its own domain, the AAAF MUST set the Home-Agent-In-Foreign-Network bit in the MIP- Feature-Vector AVP. As above, the use of Diameter servers in this exchange will expose keys. If this is deemed undesirable, a redirect server approach should be utilized to communicate the AMR to the AAAH. This causes the FA to communicate the AMR directly to the AAAH via a security association. When the AAAH receives an AMR message, it first checks the authentication data supplied by the mobile node, according to the MIP-Reg-Request AVP and MIP-MN-AAA-Auth AVP, and determines whether to authorize the mobile node. If the AMR indicates that the AAAF has offered to allocate a Home Agent for the mobile node, i.e. the Foreign-Home-Agent-Available is set in the MIP-Feature-Vector AVP, or the AMR indicates that the AAAF has offered a previously allocated Home Agent for the mobile node, i.e. the Home-Agent-In-Foreign- Calhoun Standards Track - March 2003 10 Diameter MIP November 2003 Network is set in the MIP-Feature-Vector AVP, then the AAAH must decide whether its local policy would allow the user to have a Home Agent in the foreign network or to keep the Home Agent in the foreign network. If so, and after checking authorization from the data in the AMR message, the AAAH sends the HAR message to Home Agent by including the Destination-Host AVP set to the value found in the AMR's MIP-Candidate-Home-Agent-Host AVP or MIP-Home-Agent-Host AVP if the HA has been previously allocated and authorized by the AAAH. If the HA has not been previously allocated by the foreign domain, the HAR sent by the AAAH does not contain the MIP-Home-Agent-Address. If the AAAH does not have the IP address of the HA and if there isn't a security association, then a redirect server approach of Figure Y should be utilized to communicate the HAR to the HA. This requires a security association between the AAAH and HA be established. If the redirect server cannot resolve the HA, or no security association can be established, the AAAH MUST return an AMA with the Result-Code AVP set to DIAMETER_ERROR_END_TO_END_MIP_KEY_ENCRYPTION. If Diameter agents are being used (i.e., there is no redirect server, etc.) the AAAH sends the HAR to the originating AAAF. In this HAR the Destination-Host AVP is set to the value found in the AMR's MIP- Originating-Foreign-AAA AVP, and the MIP-Home-Agent-Host AVP or the MIP-Candidate-Home-Agent-Host AVP found in the AMR are copied into the HAR. Therefore, the AAAH MUST always copy the MIP-Originating-Foreign-AAA AVP from the AMR message to the HAR message. In cases when another AAAF receives the HAR, this new AAAF will send the HAR to the HA. Visited Home Realm Realm +--------+ ------- AMR -------> +--------+ | AAAF | <------ HAR -------- | AAAH | | | | | +--->| server | ------- HAA -------> | server | | +--------+ <------ AMA -------- +--------+ | ^ | | | | HAR/HAA | AMR | | AMA v | v +---------+ +---------+ | Home | | Foreign | | Agent | | Agent | +---------+ +---------+ ^ +--------+ | | Mobile |<----------+ | Node | Mobile IP +--------+ Figure 7: Home Agent allocated in Visited Realm Calhoun Standards Track - March 2003 11 Diameter MIP November 2003 Upon receipt of a HAA from the Home Agent in the visited realm, the AAAF forwards the HAA to the AAAH in the home realm. The AMA is then constructed, and issued to the AAAF, and finally to the FA. If the Result-Code indicates success, the HAA and AMA MUST include the MIP- Home-Agent-Address and the MIP-Mobile-Node-Address AVPs. Mobile Node Foreign Agent Home Agent AAAF AAAH ----------- ------------- ------------- ---------- ---------- <----Challenge---- Reg-Req (Response)-> ------------AMR-------------> -----AMR----> <----HAR----- <-----HAR------ ------HAA------> -----HAA----> <----AMA----- <-------------AMA------------ <---Reg-Reply---- Figure 8: Mobile IP/Diameter Message Exchange when HA is allocated in Visited Realm Figures 9 and 10 shows the secure approach involving redirect agents. Local Redirect Home FA FAAA Agent Server AMR ---------------> AMR (Redirect, f-HA) --------------------> AMA (Redirect, f-HA)) <-------------------- AMA (Redirect, f-HA) <--------------- AMR (f-HA) ------------------------------------------------------> AMA (MN-FA key) <------------------------------------------------------ Figure 9: Use of Redirect Server for AMR/AMA Calhoun Standards Track - March 2003 12 Diameter MIP November 2003 Local Redirect Home HA Agent Server HAR <---------------------- HAA (Redirect) ----------------------> HAR (MN-HA key) <------------------------------------------ HAA ------------------------------------------> Figure 10: Use of Redirect Server for HAR/HAA If the mobile node moves to another foreign Network, it MAY either request to keep the same Home Agent within the old foreign network, or request to get a new one in the new foreign network. If the AAAH is willing to provide the requested service, the AAAH will have to provide services for both visited networks, e.g., key refresh, per Figures 9 and 10. 3.5 Co-located Mobile Node In the event that a mobile node registers with the Home Agent as a co-located mobile node, there is no foreign agent involved. Therefore, when the Home Agent receives the Registration Request, an AMR message is sent to the local AAAH server, with the Co-Located- Mobile-Node bit set in the MIP-Feature-Vector AVP. The Home Agent also includes the Acct-Multi-Session-Id AVP in the AMR sent to the AAAH, as the AAAH may find this a useful piece of session-state or log entry information. Home Realm +--------+ | AAAH | | | | server | +--------+ ^ | | | AMR | | AMA | v +--------+ +---------+ | Mobile | Registration | Home | | Node |-------------->| Agent | +--------+ Request +---------+ Calhoun Standards Track - March 2003 13 Diameter MIP November 2003 Figure 11: Co-located Mobile Node If the MN-HA-Key-Requested bit was set in the AMR message from the Home Agent, the home agent and mobile node's session keys would be present in the AMA message. Figure 12 shows the secure solution using redirect servers. In Figure 12, the Proxy AAA represents any AAA server or servers that the HA may use. This applies to the visited or home network. Local redirect Home HA Proxy AAA Agent Server AMR ---------------> AMR (Redirect) --------------------> AMA (Redirect) <--------------------- AMA (Redirect) <---------------- Setup Security Association <------------------------------------------------------> AMR -------------------------------------------------------> AMA (MN-HA key) <------------------------------------------------------- Figure 12: Use of Redirect Server for Co-located CoA and AMR/AMA 3.6 Key Distribution Center (KDC) In order to allow the scaling of wireless data access across administrative domains, it is necessary to minimize the specific security associations required. This means that each Foreign Agent should not be required have a pre-configured shared security association with each Home Agent on the Internet, nor should the mobile node be required to have a pre-configured shared security association with any specific home agent or any specific foreign agent, as defined in [MOBILEIP]. Diameter Mobile IP application solves this by including a key distribution center (KDC), which means that after a Mobile Node is authenticated, the authorization phase includes the generation of sessions keys. Specifically, three keys are generated and are required by [MOBILEIP]: - K1 - the MN-HA Key, which will work as security association between the Mobile Node and the Home Agent. - K2 - the MN-FA Key, which will work as the security association Calhoun Standards Track - March 2003 14 Diameter MIP November 2003 between the Mobile Node and the Foreign Agent - K3 - the FA-HA Key, which will work as the security association between the Foreign Agent and the Home Agent Figure 13 depicts the new security associations used for Mobile-IP message integrity using the keys derived by the DIAMETER server. +--------+ +--------+ |Foreign | K3 | Home | |Agent |<-------------------->| Agent | | | | | +--------+ +--------+ ^ ^ | K2 K1 | | +--------+ | | | Mobile | | +------>| Node |<------+ | | +--------+ Figure 13 - Security Association after Key Distribution If the home agent is assigned in the home network, each key is generated and encrypted by the home Diameter server. If instead the home agent is assigned in the foreign network the K3 key is generated and encrypted by the foreign network's local Diameter server, while the K1 and K2 is still generated and encrypted by the home Diameter server. The keys destined for the foreign and home agent are propagated to the mobility nodes via the Diameter protocol, and the keys must be protected either by IPSec or TLS security associations that exist directly between the HA and AAAH or the FA and AAAF, as explained above. The keys destined for the mobile node must also be propagated via the Mobile IP protocol and must therefore instead follow the mechanisms described in [aaa-keys]. In [MIPKEYS], the keys distributed to the mobile node are instead sent as a nonce, and the mobile node and the home Diameter will use the nonce and the long-term shared secret to create the keys (see section 5.2). Once the session keys have been established and propagated, the mobility devices can exchange registration information directly as defined in [MOBILEIP] without the need of the Diameter infrastructure. However the session keys have a lifetime, after which the Diameter infrastructure must be invoked again to acquire new session keys. 3.7 Diameter Session Termination A foreign and home agent following this specification MAY expect their respective Diameter servers to maintain session state information for each mobile node in their networks. In order for the Calhoun Standards Track - March 2003 15 Diameter MIP November 2003 Diameter Server to release any resources allocated to a specific mobile node, the mobility agents MUST send a Session-Termination- Request (STR) to the Diameter server that authorized the service. The Session-Termination-Request (STR) MUST be issued by the mobility agents if the Authorization Lifetime has expired and no subsequent MIP registration request have been received. The home Diameter server SHOULD only deallocate all resources after the STR is received from the home agent. This ensures that a mobile node that moves from one foreign agent to another (hand-off) does not cause the Home Diameter Server to free all resources for the mobile node. When deallocating all of the mobile node's resources the home Diameter server (and the foreign Diameter server in case of HA allocated in foreign network) MUST destroy all session keys that may still be valid. In the event that the AAAF wishes to terminate a session, its Abort- Session-Request (ASR) [DIAMBASE] message SHOULD be sent to the FA. Similarly, the AAAH SHOULD send its message to the Home Agent. 3.8 Advertising application support Diameter nodes conforming to this specification MAY advertise support by including the value of four (4) in the Auth-Application-Id or the Acct-Application-Id AVP of the Capabilities-Exchange-Request and Capabilities-Exchange-Answer command [DIAMBASE]. 4.0 Command-Code Values This section defines Command-Code [DIAMBASE] values that MUST be supported by all Diameter implementations conforming to this specification. The following Command Codes are defined in this specification: Command-Name Abbreviation Code Section ----------------------------------------------------------- AA-Mobile-Node-Answer AMA 260 2.2 AA-Mobile-Node-Request AMR 260 2.1 Home-Agent-MIP-Answer HAA 262 2.4 Home-Agent-MIP-Request HAR 262 2.3 4.1 AA-Mobile-Node-Request The AA-Mobile-Node-Request (AMR), indicated by the Command-Code field set to 260 and the 'R' bit set in the Command Flags field, is sent by an attendant, acting as a Diameter client, to a server in order to request the authentication and authorization of a mobile node. The foreign agent (or home agent in the case of a co-located Mobile Node) uses information found in the Registration Request to construct the following AVPs that are to be included as part of the AMR: Calhoun Standards Track - March 2003 16 Diameter MIP November 2003 Home Address (MIP-Mobile-Node-Address AVP) Home Agent address (MIP-Home-Agent-Address AVP) Mobile Node NAI (User-Name AVP [DIAMBASE]) MN-HA Key Request (MIP-Feature-Vector AVP) MN-FA Key Request (MIP-Feature-Vector AVP) MN-AAA Authentication Extension (MIP-MN-AAA-Auth AVP) Foreign Agent Challenge Extension (MIP-FA-Challenge AVP) Home Agent NAI (MIP-Home-Agent-Host AVP) Home AAA server NAI (Destination-Host AVP [DIAMBASE]) If the mobile node's home address is zero, the foreign or home agent MUST NOT include a MIP-Mobile-Node-Address AVP in the AMR. If the home agent address is zero or all ones, the MIP-Home-Agent-Address AVP MUST NOT be present in the AMR. If a home agent is used in a visited network, the AAAF MAY set the Foreign-Home-Agent-Available flag in the MIP-Feature-Vector AVP in the AMR message to indicate that it is willing to assign a Home Agent in the visited realm. If the mobile node's home address is all ones, the foreign or home agent MUST include a MIP-Mobile-Node-Address AVP, set to all ones. If the mobile node includes the home agent NAI and the home AAA server NAI [AAANAI], the foreign agent MUST include the MIP-Home- Agent-Host AVP and the Destination-Host AVP in the AMR. Message Format <AA-Mobile-Node-Request> ::= < Diameter Header: 260, REQ, PXY > < Session-ID > { Auth-Application-Id } { User-Name } { Destination-Realm } { Origin-Host } { Origin-Realm } { MIP-Reg-Request } { MIP-MN-AAA-Auth } [ Acct-Multi-Session-Id ] [ Destination-Host ] [ Origin-State-Id ] [ MIP-Mobile-Node-Address ] [ MIP-Home-Agent-Address ] [ MIP-Feature-Vector ] [ MIP-Originating-Foreign-AAA ] [ Authorization-Lifetime ] [ Auth-Session-State ] [ MIP-FA-Challenge ] [ MIP-Candidate-Home-Agent-Host ] [ MIP-Home-Agent-Host ] [ MIP-HA-to-FA-SPI ] * [ Proxy-Info ] Calhoun Standards Track - March 2003 17 Diameter MIP November 2003 * [ Route-Record ] * [ AVP ] 4.2 AA-Mobile-Node-Answer The AA-Mobile-Node-Answer (AMA), indicated by the Command-Code field set to 260 and the 'R' bit cleared in the Command Flags field, is sent by the AAAH in response to the AA-Mobile-Node-Request message. The User-Name MAY be included in the AMA if present in the AMR. The Result-Code AVP MAY contain one of the values defined in section 3.0, in addition to the values defined in [DIAMBASE]. An AMA message with the Result-Code AVP set to DIAMETER_SUCCESS MUST include the MIP-Home-Agent-Address AVP, MUST include the MIP-Mobile- Node-Address AVP, and includes the MIP-Reg-Reply AVP if and only if the Co-Located-Mobile-Node bit was not set in the MIP-Feature-Vector AVP. The MIP-Home-Agent-Address AVP contains the Home Agent assigned to the mobile node, while the MIP-Mobile-Node-Address AVP contains the home address that was assigned. The AMA message MUST contain the MIP-FA-to-HA-Key, MIP-FA-to-MN-Key if they were requested in the AMR, and they were present in the HAR. The MIP-MN-to-HA-Key and MIP-HA-to- MN-Key AVPs MUST be present if the session keys were requested in the AMR, and the Co-Located-Mobile-Node bit was set in the MIP-Feature- Vector AVP. An AMA message with the Result-Code AVP set to DIAMETER_LIMITED_SUCCESS MAY include the MIP-Home-Agent-Address AVP if a dynamically assigned home agent was requested by the mobile node. Upon receipt of this result code, the foreign agent MUST issue the Registration Request to the Home Agent in the manner described in [MOBILEIP]. An AMA message with the Result-Code set to DIAMETER_MULTI_ROUND_AUTH MAY include mobile node session key AVPs (see Section 6.1) such as the MIP-MN-to-FA-Key AVP and the MIP-MN-to-HA-Key AVP. If such an AVP is present in the AMA message, the foreign agent MUST include the corresponding Mobile IP key distribution extension in the Registration Reply it sends to the mobile node. This is to support multi-roundtrip authentication mechanisms. Message Format <AA-Mobile-Node-Answer> ::= < Diameter Header: 260, PXY > < Session-Id > { Auth-Application-Id } { Result-Code } { Origin-Host } { Origin-Realm } [ Acct-Multi-Session-Id ] [ User-Name ] [ Authorization-Lifetime ] Calhoun Standards Track - March 2003 18 Diameter MIP November 2003 [ Auth-Session-State ] [ Error-Message ] [ Error-Reporting-Host ] [ Re-Auth-Request-Type ] [ MIP-Feature-Vector ] [ MIP-Reg-Reply ] [ MIP-MN-to-FA-Key ] [ MIP-MN-to-HA-Key ] [ MIP-FA-to-MN-Key ] [ MIP-FA-to-HA-Key ] [ MIP-HA-to-MN-Key ] [ MIP-Key-Lifetime ] [ MIP-Type-Algorithm ] [ MIP-Home-Agent-Address ] [ MIP-Mobile-Node-Address ] * [ MIP-Filter-Rule ] [ Origin-State-Id ] * [ Proxy-Info ] * [ AVP ] 4.3 Home-Agent-MIP-Request The Home-Agent-MIP-Request (HAR), indicated by the Command-Code field set to 262 and the 'R' bit set in the Command Flags field, is sent by the AAA to the Home Agent. If the Home Agent is to be assigned in a foreign network, the HAR is issued by the AAAH and forwarded by the AAAF. If the HAR message does not include a MIP-Mobile-Node-Address AVP, and the Registration Request has 0.0.0.0 for the home address, and the HAR is successfully processed, the Home Agent MUST allocate the mobile nodes address. If on the other hand the home agent's local AAA server allocates the mobile node's home address, the local AAA server MUST include the assigned address in an MIP-Mobile-Node- Address AVP. When session keys are requested for use by the mobile node (see section 5.0), the AAAH MUST create them and include them in the HAR message. When a Foreign-Home session key is requested, it will be created and distributed by the AAA server in the same realm as the home agent. Message Format <Home-Agent-MIP-Request> ::= < Diameter Header: 262, REQ, PXY > < Session-Id > { Auth-Application-Id } { Authorization-Lifetime } { Auth-Session-State } { MIP-Reg-Request } { Origin-Host } { Origin-Realm } { User-Name } { Destination-Realm } Calhoun Standards Track - March 2003 19 Diameter MIP November 2003 { MIP-Feature-Vector } [ Destination-Host ] [ MIP-MN-to-HA-Key ] [ MIP-MN-to-FA-Key ] [ MIP-HA-to-MN-Key ] [ MIP-HA-to-FA-Key ] [ MIP-HA-to-FA-SPI ] [ MIP-Key-Lifetime ] [ MIP-Originating-Foreign-AAA ] [ MIP-Mobile-Node-Address ] [ MIP-Home-Agent-Address ] [ MIP-Type-Algorithm ] * [ MIP-Filter-Rule ] [ Origin-State-Id ] * [ Proxy-Info ] * [ Route-Record ] * [ AVP ] 4.4 Home-Agent-MIP-Answer The Home-Agent-MIP-Answer (HAA), indicated by the Command-Code field set to 262 and the 'R' bit cleared in the Command Flags field, is sent by the Home Agent to its local AAA server in response to a Home- Agent-MIP-Request. The User-Name MAY be included in the HAA if present in the HAR. If the home agent allocated a home address for the mobile node, the address MUST be included in the MIP-Mobile-Node- Address AVP. The Result-Code AVP MAY contain one of the values defined in section 3.0 instead of the values defined in [DIAMBASE]. Message Format <Home-Agent-MIP-Answer> ::= < Diameter Header: 262, PXY > < Session-Id > { Auth-Application-Id } { Result-Code } { Origin-Host } { Origin-Realm } [ Acct-Multi-Session-Id ] [ User-Name ] [ Error-Reporting-Host ] [ Error-Message ] [ MIP-Reg-Reply ] [ MIP-Home-Agent-Address ] [ MIP-Mobile-Node-Address ] [ MIP-FA-to-HA-SPI ] [ MIP-FA-to-MN-SPI ] [ Origin-State-Id ] * [ Proxy-Info ] * [ AVP ] 5.0 Result-Code AVP Values Calhoun Standards Track - March 2003 20 Diameter MIP November 2003 This section defines new Result-Code [DIAMBASE] values that MUST be supported by all Diameter implementations that conform to this specification. 5.1 Transient Failures Errors that fall within the transient failures category are used to inform a peer that the request could not be satisfied at the time it was received, but MAY be able to satisfy the request in the future. DIAMETER_ERROR_MIP_REPLY_FAILURE 4005 This error code is used by the home agent when processing of the Registration Request has failed. DIAMETER_ERROR_HA_NOT_AVAILABLE 4006 This error code is used to inform the foreign agent that the requested Home Agent cannot be assigned to the mobile node at this time. The foreign agent MUST return a Mobile IP Registration Reply to the mobile node with an appropriate Error code. DIAMETER_ERROR_BAD_KEY 4007 This error code is used by the home agent to indicate to the local Diameter server that the key generated is invalid. DIAMETER_ERROR_MIP_FILTER_NOT_SUPPORTED 4008 This error code is used by a mobility agent to indicate to The home Diameter server that the requested packet filter Rules cannot be supported. 5.2 Permanent Failures Errors that fall within the permanent failures category are used to inform the peer that the request failed, and should not be attempted again. DIAMETER_ERROR_NO_FOREIGN_HA_SERVICE 5024 This error is used by the AAAF to inform the AAAH that allocation of a home agent in the foreign domain is not permitted at this time. DIAMETER_ERROR_END_TO_END_MIP_KEY_ENCRYPTION 5025 This error is used by the AAAF / AAAH to inform that the requested Mobile IP session keys could not be encrypted with the CMS strong security application and therefore failed. 5.0 Mandatory AVPs The following table describes the Diameter AVPs defined in the Mobile IP application, their AVP Code values, types, possible flag values and whether the AVP MAY be encrypted. Calhoun Standards Track - March 2003 21 Diameter MIP November 2003 Due to space constraints, the short form IPFiltrRule is used to represent IPFilterRule and DiamIdent is used to represent DiameterIdentity. +--------------------------+ | AVP Flag rules | |----+-----+----+-----|----+ AVP Section | | |SHLD| MUST|MAY | Attribute Name Code Defined Value Type |MUST| MAY | NOT| NOT|Encr| -----------------------------------------|----+-----+----+-----|----| MIP-Filter-Rule 342 5.8 IPFiltrRule| M | P | | V | Y | MIP-Auth-Input- 338 5.6.2 Unsigned32 | M | P | | V | Y | Data-Length | | | | | | MIP- 339 5.6.3 Unsigned32 | M | P | | V | Y | Authenticator-Length | | | | | | MIP- 340 5.6.4 Unsigned32 | M | P | | V | Y | Authenticator-Offset | | | | | | MIP-Candidate- 336 5.9 DiamIdent | M | P | | V | N | Home-Agent-Host | | | | | | MIP-Home-Agent- 348 5.11 DiamIdent | M | P | | V | N | Host | | | | | | MIP-FA-Challenge 344 5.7 OctetString| M | P | | V | Y | MIP-Feature- 337 5.5 Unsigned32 | M | P | | V | Y | Vector | | | | | | MIP-Home-Agent- 334 5.4 Address | M | P | | V | Y | Address | | | | | | MIP-MN-AAA-Auth 322 5.6 Grouped | M | P | | V | Y | MIP-MN-AAA-SPI 341 5.6.1 Unsigned32 | M | P | | V | Y | MIP-Mobile-Node- 333 5.3 Address | M | P | | V | Y | Address | | | | | | MIP-Reg-Request 320 5.1 OctetString| M | P | | V | Y | MIP-Reg-Reply 321 5.2 OctetString| M | P | | V | Y | MIP-Originating- 347 5.10 Grouped | M | P | | V | Y | Foreign-AAA | | | | | | 5.1 MIP-Reg-Request AVP The MIP-Reg-Request AVP (AVP Code 320) is of type OctetString and contains the Mobile IP Registration Request [MOBILEIP] sent by the mobile node to the foreign agent. 5.2 MIP-Reg-Reply AVP The MIP-Reg-Reply AVP (AVP Code 321) is of type OctetString and contains the Mobile IP Registration Reply [MOBILEIP] sent by the home agent to the foreign agent. 5.3 MIP-Mobile-Node-Address AVP Calhoun Standards Track - March 2003 22 Diameter MIP November 2003 The MIP-Mobile-Node-Address AVP (AVP Code 333) is of type Address and contains the mobile node's home IP address. 5.4 MIP-Home-Agent-Address AVP The MIP-Home-Agent-Address AVP (AVP Code 334) is of type Address and contains the mobile node's home agent IP address. 5.5 MIP-Feature-Vector AVP The MIP-Feature-Vector AVP (AVP Code 337) is of type Unsigned32 and is added with flag values set by the foreign agent or by the AAAF owned by the same administrative domain as the foreign agent. The foreign agent SHOULD include MIP-Feature-Vector AVP within the AMR message it sends to the AAAF. Flag values currently defined include: 1 Mobile-Node-Home-Address-Requested 2 Home-Address-Allocatable-Only-in-Home-Realm 4 Home-Agent-Requested 8 Foreign-Home-Agent-Available 16 MN-HA-Key-Request 32 MN-FA-Key-Request 64 FA-HA-Key-Request 128 Home-Agent-In-Foreign-Network 256 Co-Located-Mobile-Node The flags are set according to the following rules. If the mobile node includes a valid home address (i.e., not equal to 0.0.0.0 or 255.255.255.255) in its Registration Request, the foreign agent zeroes the Mobile-Node-Home-Address-Requested flag in the MIP- Feature-Vector AVP. If the mobile node sets the home address field equal to 0.0.0.0 in its Registration Request, the foreign agent sets the Mobile-Node- Home-Address-Requested flag to one. If the mobile node sets the home agent field equal to 255.255.255.255 in its Registration Request, the foreign agent sets both the Home- Agent-Requested flag and the Home-Address-Allocatable-Only-in-Home- Realm flag to one in the MIP-Feature-Vector AVP. If the mobile node sets the home agent field equal to 0.0.0.0 in its Registration Request, the foreign agent sets the Home-Agent-Requested flag to one, and zeroes the Home-Address-Allocatable-Only-in-Home- Realm flag in the MIP-Feature-Vector AVP. Whenever the foreign agent sets either the Mobile-Node-Home-Address- Requested flag or the Home-Agent-Requested flag to one, it MUST set the MN-HA-Key-Request flag to one. The MN-HA-Key-Request flag is also Calhoun Standards Track - March 2003 23 Diameter MIP November 2003 set to one if the mobile node includes a Generalized MN-HA Key Request [MIPKEYS] extension, with the subtype set to AAA. If the mobile node includes a Generalized MN-FA Key Request [MIPKEYS] extension with the AAA subtype in its Registration Request, the foreign agent sets the MN-FA-Key-Request flag to one in the MIP- Feature-Vector AVP. If the mobile node requests a home agent in the foreign network either by setting the home address field to all ones, or by specifying a home agent in the foreign network, and the AAAF authorizes the request, the AAAF MUST set the Home-Agent-In-Foreign- Network bit to one. If the Home Agent receives a Registration Request from the mobile node indicating that the MN is acting as a co-located mobile node, the home agent sets the Co-Located-Mobile-Node bit to one. If the foreign agent's local policy allows it to receive AAA session keys, and it does not have any existing FA-HA key with the home agent, the foreign agent MAY set the FA-HA-Key-Request flag The foreign agent MUST NOT set the Foreign-Home-Agent-Available, and Home-Agent-In-Foreign-Network flag to one. When the AAAF receives the AMR message, it MUST first verify that the sender was an authorized foreign agent. The AAAF then takes any actions indicated by the settings of the MIP-Feature-Vector AVP flags. The AAAF then MAY set additional flags. Only the AAAF may set the Foreign-Home-Agent-Available and Home-Agent-In-Foreign-Network flags to one. This is done according to local administrative policy. When the AAAF has finished setting additional flags according to its local policy, then the AAAF transmits the AMR with the possibly modified MIP-Feature-Vector AVP to the AAAH. 5.6 MIP-MN-AAA-Auth AVP The MN-AAA-Auth AVP (AVP Code 322) is of type Grouped and contains some ancillary data to simplify processing of the authentication data in the Mobile IP Registration Request [MOBILEIP, MIPCHAL] by the target AAA server. Its value has the following ABNF grammar: MIP-MN-AAA-Auth ::= < AVP Header: 322 > { MIP-MN-AAA-SPI } { MIP-Auth-Input-Data-Length } { MIP-Authenticator-Length } { MIP-Authenticator-Offset } * [ AVP ] 5.6.1 MIP-MN-AAA-SPI AVP The MIP-MN-AAA-SPI AVP (AVP Code 341) is of type Unsigned32 and indicates the algorithm by which the targeted AAA server (AAAH) Calhoun Standards Track - March 2003 24 Diameter MIP November 2003 should attempt to validate the Authenticator computed by the mobile node over the Registration Request data. 5.6.2 MIP-Auth-Input-Data-Length AVP The MIP-Auth-Input-Data-Length AVP (AVP Code 338) is of type Unsigned32 and contains the length, in bytes, of the Registration Request data (data portion of MIP-Reg-Request AVP) that should be used as input to the algorithm (indicated by the MN-AAA-SPI AVP) used to determine whether the Authenticator Data supplied by the mobile node is valid. 5.6.3 MIP-Authenticator-Length AVP The MIP-Authenticator-Length AVP (AVP Code 339) is of type Unsigned32 and contains the length of the authenticator to be validated by the targeted AAA server (i.e., AAAH). 5.6.4 MIP-Authenticator-Offset AVP The MIP-Authenticator-Offset AVP (AVP Code 340) is of type Unsigned32 and contains the offset into the Registration Request Data, of the authenticator to be validated by the targeted AAA server (i.e., AAAH). 5.7 MIP-FA-Challenge AVP The MIP-FA-Challenge AVP (AVP Code 344) is of type OctetString and contains the challenge advertised by the foreign agent to the mobile node. This AVP MUST be present in the AMR if the mobile node used the RADIUS-style MN-AAA computation algorithm. 5.8 MIP-Filter-Rule AVP The MIP-Filter-Rule AVP (AVP Code 342) is of type IPFilterRule, and provides filter rules that need to be configured on the foreign or home agent for the user. The packet filtering rules are set by the AAAH by adding one or more MIP-Filter-Rule AVPs in the HAR if destined for the home agent and/or in the AMA if destined for the foreign agent. 5.9 MIP-Candidate-Home-Agent-Host The MIP-Candidate-Home-Agent-Host AVP (AVP Code 336) is of type DiameterIdentity and contains the identity of a home agent in the foreign network that the AAAF proposes be dynamically assigned to the mobile node. 5.10 MIP-Originating-Foreign-AAA AVP The MIP-Originating-Foreign-AAA AVP (AVP Code 347) if of type Grouped, and contains the identity of the AAAF, which issues the AMR to the AAAH. The MIP- Originating-Foreign-AAA AVP MUST only be used Calhoun Standards Track - March 2003 25 Diameter MIP November 2003 in cases when the home agent is or may be allocated in a foreign domain. If present in the AMR, the AAAH MUST copy the MIP- Originating-Foreign-AAA AVP into the HAR. MIP-Originating-Foreign-AAA ::= < AVP Header: 347 > { Origin-Realm } { Origin-Host } * [ AVP ] 5.11 MIP-Home-Agent-Host AVP The MIP-Home-Agent-Host AVP (AVP Code 348) if of type Grouped, and contains the identity of the assigned Home Agent. If present in the AMR, the AAAH MUST copy the MIP-Home-Agent-Host AVP into the HAR. MIP-Home-Agent-Host ::= < AVP Header: 348 > { Destination-Realm } { Destination-Host } * [ AVP ] 6.0 Key Distribution Center The mobile node and mobility agents use session keys to compute authentication extensions applied to registration messages, as defined in [MOBILEIP]: Mobile-Foreign, Foreign-Home and Mobile-Home. If session keys are requested the AAA server(s) MUST return the key material after the mobile node is successfully authenticated and authorized. The SPI values are used as key identifiers, meaning that each session key has its own SPI value; nodes that share a key also share an SPI. The mobile node proposes SPIs for use in computing the Mobile-Foreign and Mobile-Home authentication extensions, via the Mobile IP AAA Key Request extensions [MIPKEYS], while the home agent allocates the Mobile-Foreign, Mobile-Home and Foreign-Home SPIs. Once the session keys have been distributed, subsequent Mobile IP registrations need not invoke the AAA infrastructure until the keys expire. These registrations MUST include the Mobile-Home authentication extension. In addition, subsequent registrations MUST also include Mobile-Foreign authentication extension if the Mobile- Foreign key was generated and distributed by AAA; similarly for subsequent use of the Foreign-Home authentication extensions. 6.1 Authorization Lifetime vs. MIP Key Lifetime The Diameter Mobile IP application makes use of two timers - the Authorization-Lifetime AVP [DIAMBASE] and the MIP-Key-Lifetime AVP. The Authorization-Lifetime contains the number of seconds before the mobile node must issue a subsequent MIP registration request. The Calhoun Standards Track - March 2003 26 Diameter MIP November 2003 content of the Authorization-Lifetime AVP corresponds to the Lifetime field in the MIP header [MOBILEIP]. The MIP-Key-Lifetime AVP contains the number of seconds before session keys destined for the mobility agents and the mobile node expire. A value of zero indicates infinity (no timeout). If not zero, the value of the MIP-Key-Lifetime AVP MUST be at least equal to the value in the Authorization Lifetime AVP. 6.2 Key Material vs. Session Key As described in section 1.6, session keys and nonces are generated by the AAAH and are transmitted to the home agent, foreign agent and mobile node. Security associations destined for the home and foreign agents are established via transmission of session keys and SPIs, protected by transmission-level security as defined in [DIAMBASE]. Where it is necessary to protect the nonces, session keys, and SPIs from untrusted Diameter agents, end-to-end security mechanisms are required to eliminate the all Diameter Agents between the FA or HA and the AAAH, as outlined above. In [MIPKEYS] the mobile node security associations are established via nonces transmitted to the mobile node via Mobile IP. To provide the nonces, the AAAH must generate a random [RANDOM] value of at least 128 bits [MIPKEYS]. The mobile node then uses the nonce to derive the MN-HA and MN-FA session keys. More details of the MN-HA and the MN-FA session key creation procedure are found in [MIPKEYS]. It is important that the hashing algorithm used by the mobile node to construct the session key is the same as the one used by the AAAH in the session key generation procedure. The AAAH therefore indicates the algorithm used along with the key material. The Foreign-Home session key is shared between two mobility agents: the FA and HA. Since this key is not destined for the mobile node, there is no need to follow the session key generation procedures detailed above. Instead, the AAAH generates a random [RANDOM] value of at least 128 bits for use as the Foreign-Home session key. See sections 7.0 for details about the format of the AVPs used to transport the session keys. 6.3 Distributing the Mobile-Home Session Key If the mobile node does not have a Mobile-Home session key, then the AAAH is likely to be the only entity trusted that is available to the mobile node. Thus, the AAAH has to generate the Mobile-Home session key, and encode it for eventual consumption by the mobile node and home agent. Calhoun Standards Track - March 2003 27 Diameter MIP November 2003 The distribution of the MN-HA key to the HA has been specified above. The HA and AAAH establish a security association (IPSec or TLS) and transport the key over that security association. If no security association exists between the AAAH and the home agent, and a security association cannot be established the AAAH MUST return a Result-Code AVP with DIAMETER_ERROR_END_TO_END_MIP_KEY_ENCRYPTION. The AAAH also has to arrange for the key to be delivered to the mobile node. Unfortunately, the AAA server only knows about Diameter messages and AVPs, and the mobile node only knows about Mobile IP messages and extensions [MOBILEIP]. For this purpose, AAAH includes the Mobile-Home session Key Material AVP into a MIP-MN-to-HA-Key AVP, which is added to the HAR message, and delivered either to a local home agent or a home agent in the visited network. The AAAH has to rely on the home agent (that also understands Diameter) to transfer the keying material (nonce) into a Mobile IP Generalized MN-HA Key Reply extension [MIPKEYS] in the Registration Reply message, using the SPI proposed by the Mobile Node in the MN-HA Key Request From AAA Subtype extension. The home agent can format the Reply message and extensions correctly for eventual delivery to the mobile node. The resulting Registration Reply is added to the HAA's MIP-Reg-Reply AVP. The AAAH parses the HAA message, transforms it into an AMA containing an MIP-Reg-Reply AVP, and sends the AMA message to the foreign agent. The foreign agent then uses that AVP to recreate a Registration Reply message containing the Generalized MN-HA Key Reply extension for delivery to the mobile node. In summary, the AAAH generates the Mobile-Home key material, which is added to the MIP-MN-to-HA-Key AVP, and a session key, which is added to the MIP-HA-to-MN-Key AVP. These AVPs are delivered to the home agent in an HAR message. The home agent retains the session key for its own use, and copies the key material (nonce) from the MIP-MN-to- HA-Key AVP into a Generalized MN-HA Key Reply extension, which is appended to the Mobile IP Registration Reply message. This Registration Reply message MUST also include the Mobile-Home authentication extension, created using the newly allocated Mobile- Home session key. The home agent then includes the Registration Reply message and extensions into a MIP-Reg-Reply AVP as part of the HAA message to be sent back to the AAA server. 6.4 Distributing the Mobile-Foreign Session Key The Mobile-Foreign session key material (nonce) is also generated by AAAH (upon request) and is added to the MIP-MN-to-FA-Key Material AVP, which is added to the HAR, and copied by the home agent into a Generalized MN-FA Key Reply Extension [MIPKEYS] to the Mobile IP Registration Reply message, using the SPI proposed by the mobile node in the MN-FA Key Material From AAA Request Subtype extension. The AAAH includes the session key in the MIP-FA-to-MN-Key AVP in the AMA, Calhoun Standards Track - March 2003 28 Diameter MIP November 2003 to be used by the foreign agent in the computation of the Mobile- Foreign authentication extension. 6.5 Distributing the Foreign-Home Session Key If the foreign agent requests a foreign home key, it also includes a MIP-HA-to-FA-SPI AVP in the AMR to convey the SPI to be used by the home agent for this purpose. The AAAH generates the Foreign-Home session key and distributes it to both the HA and the FA over respective security associations to each using the MIP-HA-to-FA and MIP-FA-to-HA-Key AVPs. The HA conveys the SPI the FA should use in the HAA; the AAAH later includes that in the MIP-FA-HA-Key AVP, along with the session key. Refer to Figures 3, 4, 9, and 10 for the messages involved. 7.0 Key Distribution Center (KDC) AVPs The Mobile-IP protocol defines a set of security associations shared between the mobile node, foreign agent and home agent. These three security associations (Mobile-Home, Mobile-Foreign, and Foreign-Home) can be dynamically created by the AAAH, and has previously been described in section 1.6 and 5.2. AAA servers supporting the Diameter Mobile IP Application MUST implement the KDC AVPs defined in this document. The names of the KDC AVPs indicate the two entities sharing the security association defined by the key or the key material; the intended receiver of the AVP is the first named entity. So, for instance, the MIP-MN-to-HA-Key AVP contains the Mobile-Home key material (nonce), which the mobile node will use to derive the Mobile-Home Key, and the MIP-HA-to-MN-Key AVP contains the Mobile- Home key for the home agent. The following table describes the Diameter AVPs defined in the Mobile IP application, their AVP Code values, types, possible flag values and whether the AVP MAY be encrypted. [Editor note: The following table has errors.] +--------------------------+ | AVP Flag Rules | |----+-----+----+-----|----+ AVP Section | | |SHLD| MUST|MAY | Attribute Name Code Defined Value Type |MUST| MAY | NOT| NOT|Encr| -----------------------------------------|----+-----+----+-----|----| MIP-Algorithm- 345 7.8 Enumerated | M | P | | V | Y | Type | | | | | | MIP-FA-to-HA-Key 328 7.2 Grouped | M | P | | V | Y | MIP-FA-to-HA-SPI 318 7.11 Unsigned32 | M | P | | V | Y | MIP-HA-to-FA-SPI 3** 7.14 Unsigned32 | M | P | | V | Y | MIP-FA-to-MN-Key 326 7.1 Grouped | M | P | | V | Y | Calhoun Standards Track - March 2003 29 Diameter MIP November 2003 MIP-FA-to-MN-SPI 319 7.10 Unsigned32 | M | P | | V | Y | MIP-HA-to-FA-Key 329 7.3 Grouped | M | P | | V | Y | MIP-HA-to-MN-Key 332 7.4 Grouped | M | P | | V | Y | MIP-Key-Lifetime 367 7.13 Unsigned32 | M | P | | V | Y | MIP-Key-Material 335 7.12 OctetString| M | P | | V | Y | MIP-MN-to-FA-Key 325 7.5 Grouped | M | P | | V | Y | MIP-MN-to-HA-Key 331 7.6 Grouped | M | P | | V | Y | MIP-Replay-Mode 346 7.9 Enumerated | M | P | | V | Y | MIP-Session-Key 343 7.7 OctetString| M | P | | V | Y | 7.1 MIP-FA-to-MN-Key AVP The MIP-FA-to-MN-Key AVP (AVP Code 326) is of type Grouped, and contains the foreign agent's session key, which it shares with the mobile node. Its Data field has the following ABNF grammar: MIP-FA-to-MN-Key ::= < AVP Header: 326 > { MIP-FA-to-MN-SPI } { MIP-Algorithm-Type } { MIP-Session-Key } * [ AVP ] 7.2 MIP-FA-to-HA-Key AVP The MIP-FA-to-HA-Key AVP (AVP Code 328) is of type Grouped, and contains the foreign agent's session key, which it shares with the home agent. Its Data field has the following ABNF grammar: MIP-FA-to-HA-Key ::= < AVP Header: 328 > { MIP-FA-to-HA-SPI } { MIP-Algorithm-Type } { MIP-Session-Key } * [ AVP ] 7.3 MIP-HA-to-FA-Key AVP The MIP-HA-to-FA-Key AVP (AVP Code 329) is of type Grouped, and contains the Home Agent's session key, which it shares with the foreign agent. Its Data field has the following ABNF grammar: MIP-HA-to-FA-Key ::= < AVP Header: 329 > { MIP-Algorithm-Type } { MIP-Session-Key } * [ AVP ] 7.4 MIP-HA-to-MN-Key AVP The MIP-HA-to-MN-Key AVP (AVP Code 332) is of type Grouped, and contains the Home Agent's session key, which it shares with the mobile node. Its Data field has the following ABNF grammar: Calhoun Standards Track - March 2003 30 Diameter MIP November 2003 MIP-HA-to-MN-Key ::= < AVP Header: 332 > { MIP-Algorithm-Type } { MIP-Replay-Mode } { MIP-Session-Key } * [ AVP ] 7.5 MIP-MN-to-FA-Key AVP The MIP-MN-to-FA-Key AVP (AVP Code 325) is of type Grouped, and contains the mobile node's key material (a nonce), which it uses to derive the session key it shares with the foreign agent. The home agent uses this AVP in the construction of the Mobile IP "Unsolicted MN-FA Key from AAA Subtype" extension [MIPKEYS]. The SPI in the extension's FA SPI field is allocated by the home agent, but it SHOULD take into consideration the SPI requested by the mobile node in the "MN-FA Key Request From AAA Subtype" extension. MIP-MN-to-FA-Key ::= < AVP Header: 325 > { MIP-Algorithm-Type } { MIP-Key-Material } { MIP-MN-AAA-SPI } * [ AVP ] 7.6 MIP-MN-to-HA-Key AVP The MIP-MN-to-HA-Key AVP (AVP Code 331) is of type Grouped, and contains the mobile node's key material, which it uses to derive the session key it shares with the Home Agent. The Home Agent uses this AVP in the construction of the Mobile IP "Unsolicted MN-HA Key from AAA Subtype" extension [MIPKEYS]. The SPI in the extension's HA SPI field is allocated by the Home Agent, but it SHOULD take into consideration the SPI requested by the mobile node in the "MN-HA Key Request From AAA Subtype" extension. MIP-MN-to-HA-Key ::= < AVP Header: 331 > { MIP-Algorithm-Type } { MIP-Replay-Mode } { MIP-Key-Material } { MIP-MN-AAA-SPI } * [ AVP ] 7.7 MIP-Session-Key AVP The MIP-Session-Key AVP (AVP Code 343) is of type OctetString and contains the Session Key to be used between two Mobile IP entities. 7.8 MIP-Algorithm-Type AVP The MIP-Algorithm-Type AVP (AVP Code 345) is of type Enumerated, and contains the Algorithm identifier used to generate the associated Mobile IP authentication extension. The following values are currently defined: Calhoun Standards Track - March 2003 31 Diameter MIP November 2003 1 HMAC-MD5 [HMAC] 2 HMAC-SHA-1 [HMAC] 7.9 MIP-Replay-Mode AVP The MIP-Replay-Mode AVP (AVP Code 346) is of type Enumerated and contains the replay mode the Home Agent should use when authenticating the mobile node. The following values are supported (see [MOBILEIP] for more information): 1 None 2 Timestamps 3 Nonces 7.10 MIP-FA-to-MN-SPI AVP The MIP-FA-to-MN-SPI AVP (AVP Code 319) is of type Unsigned32, and contains the Security Parameter Index the foreign agent is to use to refer to the session key it shares with the mobile node. The SPI created MUST NOT be a value between zero (0) and 255, which is the reserved namespace defined in [MOBILEIP]. This AVP MAY be added in the HAA message by the home agent for the AAAH's use in MIP-FA-to-MN- SPI AVP of the MIP-FA-to-MN-Key AVP. 7.11 MIP-FA-to-HA-SPI AVP The MIP-FA-to-HA-SPI AVP (AVP Code 318) is of type Unsigned32, and contains the Security Parameter Index the foreign agent is to use to refer to the session key it shares with the home agent. The SPI created MUST NOT be a value between zero (0) and 255, which is the reserved namespace defined in [MOBILEIP]. If FA-HA keys are being generated, this AVP MUST be added in the HAA message by the Home Agent for the AAAH's (or AAAF's) use in providing the value of the MIP-FA-to-HA-SPI member of the grouped MIP-FA-to-HA-Key AVP. 7.12 MIP-Key-Material AVP The MIP-Key-Material AVP (AVP Code 335) is of type OctetString and contains the key material sent to the mobile node. The mobile node follows the procedures in [MIPKEYS] to generate the session key used to authenticate Mobile IP registration messages. 7.13 MIP-Key-Lifetime AVP The MIP-Key-Lifetime AVP (AVP Code 367) is of type Unsigned32 and represents the period of time (in seconds) for which the session key is valid. The session key MUST NOT be used if the lifetime has expired; if the key lifetime expires while the session to which it Calhoun Standards Track - March 2003 32 Diameter MIP November 2003 applies is still active, either the session key MUST be changed or the or the session MUST be terminated. 7.14 MIP-HA-to-FA-SPI AVP The MIP-HA-to-FA-SPI AVP (AVP Code 3**) is of type Unsigned32, and contains the Security Parameter Index the home agent is to use to refer to the session key it shares with the foreign agent. The SPI created MUST NOT be a value between zero (0) and 255, which is the reserved namespace defined in [MOBILEIP]. If FA-HA keys are being generated, this AVP MUST be added in the HAA message by the Home Agent for the AAAH's (or AAAF's) use in providing the value of the MIP-HA-to-FA-SPI member of the grouped MIP-HA-to-FA-Key AVP. The FA should provide this to the AAAH in the AMR, as it should control the assignment of this SPI. 8.0 Accounting AVPs [Editor note: Will anyone use the AVPs of this section? Deployments using MIP, e.g., 3GPP2 have VSAs for this purpose.] 8.1 Accounting-Input-Octets AVP The Accounting-Input-Octets AVP (AVP Code 363) is of type Unsigned64, and contains the number of octets in IP packets received from the user. This AVP MUST be included in all Accounting-Request messages and MAY be present in the corresponding Accounting-Answer messages as well. 8.2 Accounting-Output-Octets AVP The Accounting-Output-Octets AVP (AVP Code 364) is of type Unsigned64, and contains the number of octets in IP packets sent to the user. This AVP MUST be included in all Accounting-Request messages and MAY be present in the corresponding Accounting-Answer messages as well. 8.3 Acct-Session-Time AVP The Acct-Time AVP (AVP Code 46) is of type Unsigned32, and indicates the length of the current session in seconds. This AVP MUST be included in all Accounting-Request messages and MAY be present in the corresponding Accounting-Answer messages as well. 8.4 Accounting-Input-Packets AVP The Accounting-Input-Packets (AVP Code 365) is of type Unsigned64, and contains the number of IP packets received from the user. This AVP MUST be included in all Accounting-Request messages and MAY be present in the corresponding Accounting-Answer messages as well. Calhoun Standards Track - March 2003 33 Diameter MIP November 2003 8.5 Accounting-Output-Packets AVP The Accounting-Output-Packets (AVP Code 366) is of type Unsigned64, and contains the number of IP packets sent to the user. This AVP MUST be included in all Accounting-Request messages and MAY be present in the corresponding Accounting-Answer messages as well. 8.6 Event-Timestamp AVP The Event-Timestamp (AVP Code 55) is of type Time, and MAY be included in an Accounting-Request message to record the time that this event occurred on the mobility agent, in seconds since January 1, 1970 00:00 UTC. 9.0 AVP Occurrence Tables The following tables presents the AVPs defined in this document, and specifies in which Diameter messages they MAY, or MAY NOT be present. Note that AVPs that can only be present within a Grouped AVP are not represented in this table. The table uses the following symbols: 0 The AVP MUST NOT be present in the message. 0+ Zero or more instances of the AVP MAY be present in the message. 0-1 Zero or one instance of the AVP MAY be present in the message. 1 One instance of the AVP MUST be present in the message. 9.1 Mobile IP Command AVP Table The table in this section is limited to the Command Codes defined in this specification. +-----------------------+ | Command-Code | |-----+-----+-----+-----+ Attribute Name | AMR | AMA | HAR | HAA | ------------------------------|-----+-----+-----+-----+ Authorization-Lifetime | 0-1 | 0-1 | 1 | 0 | Auth-Application-Id | 1 | 1 | 1 | 1 | Auth-Session-State | 0-1 | 0-1 | 1 | 0 | Acct-Multi-Session-Id | 0-1 | 0-1 | 0 | 0-1 | Destination-Host | 0-1 | 0 | 0-1 | 0 | Destination-Realm | 1 | 0 | 1 | 0 | Error-Message | 0 | 0-1 | 0 | 0-1 | Error-Reporting-Host | 0 | 0-1 | 0 | 0-1 | MIP-Candidate-Home-Agent-Host | 0-1 | 0 | 0-1 | 0 | MIP-Home-Agent-Host | 0-1 | 0 | 0-1 | 0 | MIP-Originating-Foreign-AAA | 0-1 | 0 | 0-1 | 0 | MIP-FA-Challenge | 0-1 | 0 | 0 | 0 | Calhoun Standards Track - March 2003 34 Diameter MIP November 2003 MIP-FA-to-HA-Key | 0 | 0-1 | 0-1 | 0 | MIP-FA-to-HA-SPI | 0 | 0 | 0 | 0-1 | MIP-HA-to-FA-SPI | 0 | 0 | 0 | 0-1 | MIP-MN-to-FA-Key | 0 | 0-1 | 0 | 0 | MIP-FA-to-MN-SPI | 0 | 0 | 0 | 0-1 | MIP-MN-to-FA-SPI | 0 | 0 | 0 | 0-1 | MIP-MN-to-HA-Key | 0 | 0-1 | 0 | 0 | MIP-HA-to-MN-SPI | 0 | 0 | 0 | 0-1 | MIP-MN-to-HA-SPI | 0 | 0 | 0 | 0-1 | MIP-Feature-Vector | 0-1 | 0-1 | 1 | 0 | MIP-Filter-Rule | 0 | 0+ | 0+ | 0 | MIP-Home-Agent-Address | 0-1 | 0-1 | 0-1 | 0-1 | MIP-Key-Lifetime | 0 | 0-1 | 0-1 | 0 | MIP-MN-AAA-Auth | 1 | 0 | 0 | 0 | MIP-Mobile-Node-Address | 0-1 | 0-1 | 0-1 | 0-1 | MIP-Reg-Reply | 0 | 0-1 | 0 | 0-1 | MIP-Reg-Request | 1 | 0 | 1 | 0 | Origin-Host | 1 | 1 | 1 | 1 | Origin-Realm | 1 | 1 | 1 | 1 | Origin-State-Id | 0-1 | 0-1 | 0-1 | 0-1 | Proxy-Info | 0+ | 0+ | 0+ | 0+ | Redirect-Host | 0 | 0+ | 0 | 0+ | Redirect-Host-Usage | 0 | 0-1 | 0 | 0-1 | Redirect-Max-Cache-Time | 0 | 0-1 | 0 | 0-1 | Result-Code | 0 | 1 | 0 | 1 | Re-Auth-Request-Type | 0 | 0-1 | 0 | 0 | Route-Record | 0+ | 0 | 0+ | 0 | Session-Id | 1 | 1 | 1 | 1 | User-Name | 1 | 0-1 | 1 | 0-1 | ------------------------------|-----+-----+-----+-----| 9.2 Accounting AVP Table The table in this section is used to represent which AVPs defined in this document are to be present in the Accounting messages, defined in [DIAMBASE]. +-------------+ | Command-Code| |------+------+ Attribute Name | ACR | ACA | -------------------------------------|------+------+ Accounting-Input-Octets | 1 | 0-1 | Accounting-Input-Packets | 1 | 0-1 | Accounting-Output-Octets | 1 | 0-1 | Accounting-Output-Packets | 1 | 0-1 | Acct-Multi-Session-Id | 1 | 0-1 | Acct-Session-Time | 1 | 0-1 | MIP-Feature-Vector | 1 | 0-1 | MIP-Home-Agent-Address | 1 | 0-1 | MIP-Mobile-Node-Address | 1 | 0-1 | Event-Timestamp | 0-1 | 0 | -------------------------------------|------+------+ Calhoun Standards Track - March 2003 35 Diameter MIP November 2003 10.0 IANA Considerations This section contains the namespaces that have either been created in this specification, or the values assigned to existing namespaces managed by IANA. 10.1 Command Codes This specification assigns the values 260 and 262 from the Command Code namespace defined in [DIAMBASE]. See section 2.0 for the assignment of the namespace in this specification. 10.2 AVP Codes This specification assigns the values 318-348 and 363-367 from the AVP Code namespace defined in [DIAMBASE]. See sections 4.0 and 6.0 for the assignment of the namespace in this specification. 10.3 Result-Code AVP Values This specification assigns the values 4005-4008, and 5024-5025 from the Result-Code AVP (AVP Code 268) value namespace defined in [DIAMBASE]. See section 3.0 for the assignment of the namespace in this specification. 10.4 MIP-Feature-Vector AVP Values There are 32 bits in the MIP-Feature-Vector AVP (AVP Code 337) that are available for assignment. This document assigns bits 1-9, aslisted in section 4.5. The remaining bits should only be assigned via Standards Action [IANA]. 10.5 MIP-Algorithm-Type AVP Values As defined in Section 6.8, the MIP-Algorithm-Type AVP (AVP Code 345) defines the values 1-3. All remaining values are available for assignment via Designated Expert [IANA]. 10.6 MIP-Replay-Mode AVP Values As defined in Section 6.9, the MIP-Replay-Mode AVP (AVP Code 346) defines the values 1-3. All remaining values, except zero, are available for assignment via Designated Expert [IANA]. 10.7 Application Identifier Calhoun Standards Track - March 2003 36 Diameter MIP November 2003 This specification assigns the value four (4) to the Application Identifier namespace defined in [DIAMBASE]. See section 1.8 for more information. 11.0 Security Considerations This specification describes a Mobile IP Diameter Application for authenticating and authorizing a Mobile IP mobile node. The authentication algorithm used is dependent upon the transforms used within the Mobile IP protocol, and [MIPCHAL]. This specification, conjunction with [MIPKEYS] also defines a method by which the home Diameter server can create and distribute session keys and nonces for use in authenticating and integrity-protecting Mobile IP registration messages [MOBILEIP]. The key distribution is asymmetric since communication with the mobile node occurs via the Mobile IP protocol [AAAKEY, MOBILEIP], while communication to the Home Agent and Foreign Agent occurs via the Diameter protocol. Where untrusted Diameter agents are present, end-to-end security MUST be used Between the AAAH and the HA/FA. Nonces are sent to the mobile node, which are used to generate the session keys via the HMAC-MD5 one-way function. If the nonces are compromised, then the pre-shared key between the mobile node and the home Diameter server would be vulnerable to an offline dictionary attack. To prevent this, the pre-shared key between the mobile node and the home Diameter server SHOULD be a randomly chosen quantity of at least 96 bits. Since the session key is determined by the long-term secret and the nonce, the nonce SHOULD be temporally and globally unique; if the nonce were to repeat, then so would the session key. To prevent this, a nonce is strongly recommended to be random [RANDOM] value of at least 128 bits. The long-term secret between the MN and HA MUST be periodically refreshed, to guard against recovery of the long-term secret due to nonce reuse or other factors. This is accomplished using out-of-band mechanisms, which are not specified in this document. It should also be noted that it is not recommended to set the MIP- Session-Key AVP value equal to zero, since keeping session keys for a long time (no refresh) increases the level of vulnerability. 12.0 References 12.1 Normative [DIAMBASE] P. Calhoun, H. Akhtar, J. Arkko, E. Guttman, A. Rubens, "Diameter Base Protocol", draft-ietf-aaa-diameter- 17.txt (editor queue status), December 2002. [IANA] Narten, Alvestrand, "Guidelines for Writing an IANA C Calhoun Standards Track - March 2003 37 Diameter MIP November 2003 Considerations Section in RFCs", BCP 26, RFC 2434, October 1998 [MOBILEIP] C. Perkins, Editor. IP Mobility Support. RFC 3344, August 2002. [MIPCHAL] C. Perkins, P. Calhoun, "Mobile IP Challenge/Response Extensions", draft-ietf-mip4-rfc3012bis-00.txt. November 2003. [NAI] B. Aboba, M. Beadles "The Network Access Identifier." RFC 2486. January 1999. [HMAC] H. Krawczyk, M. Bellare, and R. Cannetti. HMAC: Keyed Hashing for Message Authentication. RFC 2104, February 1997. [MIPKEYS] C. Perkins, P. Calhoun, "AAA Registration Keys for Mobile IP", draft-ietf-mipv4-aaa-key-00.txt, IETF work in progress, November 2003. [AAANAI] F. Johansson, T.Johansson, "AAA NAI for Mobile IP Extension", draft-mobileip-aaa-nai-05.txt, IETF work In progress, March 2003. 12.2 Informative [MIPREQ] S. Glass, S. Jacobs, C. Perkins, "Mobile IP Authentication, Authorization, and Accounting Requirements". RFC 2977. October 2000. [CDMA2000] T. Hiller and al, "CDMA2000 Wireless Data Requirements for AAA", RFC 3141, June 2001. [KEYWORDS] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [EVALROAM] B. Aboba, G. Zorn, "Criteria for Evaluating Roaming Protocols", RFC 2477, January 1999. [MIPNAI] P. Calhoun, C. Perkins, "Mobile IP Network Address Identifier Extension", RFC 2794, March 2000. [RANDOM] D. Eastlake, 3rd, S. Crocker, and J. Schiller. Radomness Recommendations for Security. RFC 1750, Internet Engineering Task Force, December 1994. 13.0 Acknowledgements The authors would like to thank Nenad Trifunovic, Haseeb Akhtar and Pankaj Patel for their participation in the pre-IETF Document Reading Calhoun Standards Track - March 2003 38 Diameter MIP November 2003 Party, to Erik Guttman for his very useful proposed text, and to Fredrik Johansson, Martin Julien and Bob Kopacz for their very useful contributed text. The authors would also like to thank the participants of 3GPP2's TSG- X working group for their valuable feedback and also the following people for their contribution in the development of the protocol: Kevin Purser, Thomas Panagiotis, Mark Eklund, Paul Funk, Michael Chen, Henry Haverinen, Johan Johansson. In addition, general text for use with the redirect server were borrowed from Diameter-EAP text by Pasi Eronen. Pat Calhoun would like to thank Sun Microsystems since most of the effort put into this document was done while he was in their employ. 14.0 Authors' Addresses Questions about this memo can be directed to: Pat Calhoun Airespace 110 Nortech Parkway San Jose, CA 95154 USA Phone: +1 408-635-2023 Email: pcalhoun@airespace.com Tony Johansson Bytemobile, Inc 2029 Stierlin Court Mountain View, California 94043 USA Phone: +1 650-641-7817 Fax: +1 650-641-7701 E-Mail: tony.johansson@bytemobile.com Charles E. Perkins Nokia Research Center 313 Fairchild Drive Mountain View, California 94043 USA Phone: +1 650-625-2986 Fax: +1 650-625-2502 E-Mail: charliep@iprg.nokia.com Tom Hiller Lucent Technologies 1960 Lucent Lane Calhoun Standards Track - March 2003 39 Diameter MIP November 2003 Naperville, IL 60566 USA Phone: +1 630-979-7673 E-mail: tomhiller@lucent.com Calhoun Standards Track - March 2003 40 Diameter MIP November 2003 Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation 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 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 Calhoun Standards Track - March 2003 41
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