Mobile IP Working Group Milind Kulkarni INTERNET-DRAFT Alpesh Patel Category: Standards Track Kent Leung Date : 8 January 2004 Cisco Systems Inc. Mobile IPv4 Dynamic Home Agent Assignment draft-ietf-mip4-dynamic-assignment-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Abstract Mobile IP (RFC 3344) uses the Home Agent (HA) to anchor sessions of a roaming Mobile Node (MN). This draft proposes a messaging mechanism for dynamic home agent assignment and HA redirection. The goal is to provide a mechanism to assign an optimal HA for a Mobile IP session while allowing any suitable method for HA selection. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 1] Internet Draft Dynamic HA Assignment 8 January 2004 Table of Contents 1. Introduction......................................................2 2. Terminology.......................................................3 3. Problem Statement.................................................4 3.1 Scope............................................................5 3.2 Dynamic Home Agent Discovery in RFC 3344.........................5 3.3 NAI usage and dynamic HA assignment..............................5 3.4 Redirected HA address extension..................................5 4. Messaging mechanism for dynamic HA assignment/redirection.........6 4.1 Messaging for dynamic HA assignment..............................6 4.1.1 Example with Message Flow Diagram..............................6 4.2 Messaging for HA redirection.....................................8 4.2.1 Example with Message Flow Diagram..............................9 4.2.2 HA Rejects Registration Request and suggests redirection.......9 5. Mobility Agent Considerations for dynamic HA assignment..........10 5.1 Mobile Node Considerations......................................10 5.1.1 MN using FA CoA...............................................11 5.1.2 MN using Collocated CoA.......................................11 5.1.3 Refreshing Assigned HA Address on Mobile Node.................12 5.2 Foreign Agent Considerations....................................12 5.3 Home Agent Considerations.......................................12 5.3.1 Assigned Home Agent Considerations............................13 6. Requested Home Agent Selection...................................15 7. Error Values.....................................................16 8. IANA Considerations..............................................16 9. Security Considerations..........................................17 9.1 Message Authentication Codes....................................17 9.2 Areas of Security Concern in this Protocol......................17 10. Backward Compatibility Considerations...........................18 11. Change Log......................................................18 12. Intellectual Property Rights....................................18 13. Acknowledgements................................................19 14. References......................................................19 Authors' Addresses..................................................20 Full Copyright Statement............................................20 1. Introduction This document adds to the Mobile IP protocol [1], by proposing a messaging mechanism for dynamic home agent assignment and home agent redirection during initial registration. The goal is to assign an optimal HA for a Mobile IP session. The mobile node MUST use Network Access Identifier (NAI) extension for home address assignment. MN requests the network to dynamically assign an HA by setting HA field to ALL-ZERO-ONE-ADDR (defined in next section) in initial Registration Request. If the request is accepted, the HA field in successful Registration Reply contains the HA Kulkarni, Patel, Leung Expires July 8, 2004 [Page 2] Internet Draft Dynamic HA Assignment 8 January 2004 address. The requested HA can suggest an alternate HA and if so, the Registration Reply is rejected with a new error code (REDIRECT-HA-REQ) and the alternate HA address is specified in a new extension (REDIRECTED-HA-ADDRESS). Alternately, MN can set the HA field to a unicast address. The HA receiving the Registration Request can suggest an alternate HA and if so, the Registration Reply is rejected with a new error code (REDIRECT-HA-REQ) and the alternate HA address is specified in a new extension (REDIRECTED-HA-ADDRESS). The HA can reject the request if the HA in request does not match any of its own addresses. The messaging mechanism proposed here is generic and can be used as a common foundation to facilitate dynamic HA assignment using any suitable method. No specific method is either mandated or suggested. The HA receiving Registration Request may suggest an alternate HA (HA redirection) for a number of reasons; including but not limited to HA load-balancing, geographical proximity, administrative policy etc. 2. Terminology ALL-ZERO-ONE-ADDR: IP address 0.0.0.0 or 255.255.255.255. An address of 255.255.255.255 would indicate assigning HA in home domain. An address of 0.0.0.0 would mean MN just needs a dynamic HA, it does not care whether in home or visited domain. Requested HA: Destination IP address of Home Agent that the first Registration Request is sent to. Must be a unicast IP address. This address can be obtained as described in section 5.4. Assigned HA: If registration is successful, this Home Agent address field is obtained from successful Registration Reply. Redirected HA: If the registration is rejected with error code (REDIRECT-HA-REQ), the HA being referred to is specified in a new extension (REDIRECTED-HA-ADDRESS). AAA server: Authentication, Authorization and Accounting Server. DNS: Domain Name Service. DHCP: Dynamic Host Configuration Protocol. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 3] Internet Draft Dynamic HA Assignment 8 January 2004 MN: Mobile Node as defined in RFC 3344. HA: Home Agent as defined in RFC 3344. FA: Foreign Agent as defined in RFC 3344. CoA: Care of Address. CCoA: Collocated Care of Address. MN HoA: Mobile Node's Home Address. NAI: Network Access Identifier [2]. Src IP: Source IP address of the packet. Dest IP: Destination IP address of the packet. 3. Problem Statement Mobile IPv4 NAI Extension for IPv4 [2] introduced the concept of identifying a MN by the NAI and enabling dynamic home address assignment. When the home address is dynamically assigned, it is desirable to discover the Home Agent dynamically or inform the MN about an optimal HA to use for a multitude of reasons, such as: If the distance between the visited network and the home network of the mobile node is large, the signaling delay for these registrations may be long. In such a case the MN will be anchored to its distant home agent, resulting in tunneled traffic traveling a long distance between home agent and the mobile node. When a Mobile IP session initiates, if the mobile node can be assigned an home agent which is close to the mobile node it can drastically reduce the latency between the home agent and mobile node. Also, in a large scale Mobile IP deployment, it is cumbersome to provision MNs with multiple HA addresses. It is desirable to achieve some form of load balancing between multiple HAs in the network. Dynamic HA assignment and/or HA redirection lets the network select the optimal HA from among a set of HAs and thus achieve load balancing among a group of HAs. Local administrative policies is yet another reason for dynamic HA assignment/HA redirection during the start of a Mobile IP session. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 4] Internet Draft Dynamic HA Assignment 8 January 2004 The problem of discovering a Mobile nodeÆs HA address is acknowledged in the MIPv6 working group as part of [8]. 3.1 Scope This specification assumes that the Mobile Node and Assigned Home Agent are in the same administrative domain. The scenario where the Mobile Node and its anchoring Assigned Home Agent are in different administrative domain is beyond the scope of this specification. The draft introduces the terms Requested/Assigned/Redirected HA (section 5.4). These terms are merely HA addresses and used for depending upon the direction of the registration request or reply. The discovery of Requested/Assigned/Redirected HA can be done by various means, which are network and/or deployment specific and hence this discovery/assignment of Requested/Assigned/Redirected HA is kept outside the scope of this specification. 3.2 Dynamic Home Agent Discovery in RFC 3344 Mobile IP RFC 3344 specifies the mechanism for discovering the mobile node's home agent using subnet-directed broadcast IP address in the home agent field of the Registration Request. This mechanism was designed for mobile nodes with a static home address and subnet prefix, anchored on fixed home network. But using subnet-directed broadcast as the destination IP address of the Registration Request, it is unlikely that the Registration Request will reach the home subnet because routers will drop these packets by default. See CERT Advisory CA-1998- 01 Smurf IP Denial-of-Service Attacks [3]. 3.3 NAI usage and dynamic HA assignment Mobile IPv4 NAI Extension for IPv4 [2] introduced the concept of identifying a MN by the NAI and enabling dynamic home address assignment. This document mandates that while using dynamic HA assignment, MN MUST use NAI and obtain a home address. MN can still suggest a static home address in Registration Request, but must take the address in Registration Reply as the home address for the session. This reference to obtaining home address using NAI is as per [2]. 3.4 Redirected HA address extension The Redirected HA address extension, shown in figure 1, contains the address of the HA where the MN should attempt the next registration. It is a skippable extension and MUST be Kulkarni, Patel, Leung Expires July 8, 2004 [Page 5] Internet Draft Dynamic HA Assignment 8 January 2004 included in Registration Reply when the reply code is REDIRECT- HA-REQ. 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 | Redirected-HA-Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: The Redirected HA address Extension Type REDIRECTED-HA-ADDRESS (skippable) [1] Length 4 HA-Address The address of redirected HA 4. Messaging mechanism for dynamic HA assignment/redirection 4.1 Messaging for dynamic HA assignment 1. MN sets the Home Agent address field in the Registration Request to ALL-ZERO-ONE-ADDR. 2. The MN (if using collocated CoA) or FA (if using FA CoA) sends the Registration Request to the "Requested HA". 3. "Requested HA" is the home agent, which processes the Registration Request in accordance with RFC 3344 and as per the specification in this document. It creates mobility binding for successful Registration Request. It also sends Registration Reply to the MN. 4. The MN obtains an "Assigned HA" address from the HA field in the successful Registration Reply and uses it for the remainder of the session. 5. Subsequent Registration Request messages for renewal are sent to the Assigned HA. Section 5.3.1 describes the Assigned HA in detail. Some ideas on how to select the Requested HA are briefly covered in section 6. 4.1.1 Example with Message Flow Diagram Detailed explanation of this specification is best described with the help of a railroad diagram and description. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 6] Internet Draft Dynamic HA Assignment 8 January 2004 Figure 2 shows one specific example of a Mobile Node using FA Care of Address. Other scenarios such as mobile node using collocated care of address are not described below, but the behavior is similar. MN FA Requested/Assigned HA | 1 | | |------------>| 2 | | |--------------->| | | | | | | | | 3 | | 4 |<---------------| |<------------| | | | | | | 5 | |----------------------------->| | | | Figure 2: Example of Message flows for the specification 1. MN sets the Home Agent address field in the Registration Request to ALL-ZERO-ONE-ADDR. Since MN is using FA CoA in this example, it sends the Registration Request to the FA. The Registration Request looks as follows: +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | MN | FA | | ALL-ZERO-ONE-ADDR |FA CoA | +-----------------------------------------------------------+ 2. The FA sends the Registration Request to the Requested HA. The Registration Request looks: +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA | +-----------------------------------------------------------+ 3. HA processes the Registration Request in accordance with RFC 3344 and the messaging defined in this document and creates mobility binding for successful request. HA then sends Registration Reply to the FA, which looks as follows. The Assigned HA address corresponds to the HA receiving and processing the request (and is same as Requested HA, only the name is changed for registration reply). Kulkarni, Patel, Leung Expires July 8, 2004 [Page 7] Internet Draft Dynamic HA Assignment 8 January 2004 +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | |Assigned|CoA or NATed| | Assigned HA |FA CoA/| | HA | Src IP | | | | +-----------------------------------------------------------+ 4. The FA relays the Registration Reply to the MN, as follows. +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | FA | MN | | Assigned HA |FA CoA/| +-----------------------------------------------------------+ 5. The MN obtains Assigned HA address from the HA field in the successful Registration Reply and uses it for the remainder of the session. MN sends subsequent Re-Registration or De- Registration Requests for the remaining session directly to the Assigned HA. 4.2 Messaging for HA redirection 1. MN sets the Home Agent address field in the Registration Request to ALL-ZERO-ONE-ADDR or unicast address. 2. The MN (if using collocated CoA) or FA (if using FA CoA) sends the Registration Request to the "Requested HA". 3. When HA receives the Registration Request, if the unicast HA address in Request does not match any of its addresses, HA can reject the request with Reply code REDIRECT-HA-REQ and suggest an alternate HA. If the HA field is set to ALL-ZERO-ONE-ADDR, HA may reject the request with Reply code REDIRECT-HA-REQ and suggest an alternate HA. HA may reject the Request for a number of reasons, which are outside the scope of this specification. If the HA rejects the Request, the HA field in the Reply is set to this HAs address. The HA that is being referred to is specified in REDIRECTED-HA-ADDRESS extension. The presence of this extension is mandatory when the reply code is set to REDIRECT-HA-REQ. HA sends the Reply to the FA/MN 4. FA sends the Reply to the MN. 5. If the error code is set to REDIRECT-HA-REQ, MN obtains the HA address from REDIRECTED-HA-ADDRESS and sends a Registration Request to this HA. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 8] Internet Draft Dynamic HA Assignment 8 January 2004 4.2.1 Example with Message Flow Diagram Figure 3 shows one specific example of a Mobile Node using FA Care of Address. MN FA Requested HA Redirected HA | 1 | | | |------------>| 2 | | | |--------------->| | | | | | | | | | | | 3 | | | 4 |<---------------| | |<------------| | | | | | | | | 5 | | |-------------------------------------------------> | | | | | Figure 3: Example of Message flows for the specification 4.2.2 HA Rejects Registration Request and suggests redirection 1. MN sets the Home Agent address field in the Registration Request to ALL-ZERO-ONE-ADDR or unicast HA address. Since MN is using FA CoA in this example, it sends the Registration Request to the FA. The Registration Request looks as follows: +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | MN | FA | | ALL-ZERO-ONE-ADDR |FA CoA | | | | | or unicast addr | | +-----------------------------------------------------------+ 2. The FA sends the Registration Request to the Requested HA. Note that the Requested HA could be different from the unicast HA address in the Request. The Registration Request looks: +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA | | | | | or unicast addr | | +-----------------------------------------------------------+ 3. HA processes the Registration Request in accordance with RFC 3344 and the messaging defined in this document. If the Kulkarni, Patel, Leung Expires July 8, 2004 [Page 9] Internet Draft Dynamic HA Assignment 8 January 2004 registration is successful, but local configuration/ administrative policy etc. directs HA to refer the MN to another HA, HA rejects the Request with error code REDIRECT-HA- REQ. HA fills in the address of the directed HA in the REDIRECTED-HA-ADDRESS extension. HA then sends Registration Reply reject to the FA, which looks as follows: +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | |CoA or NATed| | HA |FA CoA | | HA | Src IP | | | | +-----------------------------------------------------------+ | REDIRECTED-HA-ADDRESS extension | +-----------------------------------------------------------+ 4. The FA relays the Registration Reply to the MN, as follows. +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | FA | MN | | HA |FA CoA/| +-----------------------------------------------------------+ | REDIRECTED-HA-ADDRESS extension | +-----------------------------------------------------------+ 5. If MN can authenticate the Reply, MN extracts the HA address from REDIRECTED-HA-ADDRESS extension and sends Registration Request to this HA. 5. Mobility Agent Considerations for dynamic HA assignment Following sections describe the behavior of each mobility agent in detail. 5.1 Mobile Node Considerations The mobile node MUST use NAI extension for home address assignment when using the messaging mechanism in this document. A mobile node MUST set the Home Agent field in the Registration Request to a unicast address or an ALL-ZERO-ONE-ADDR, which is either 255.255.255.255 or 0.0.0.0. The Registration Request MUST be protected by a valid authenticator as specified in [1] or [5]. Configuring security associations is deployment specific and hence outside the scope of this specification. The security associations between a MN and an individual HA may also be dynamically derived during the dynamic HA assignment, based on a shared secret between MN and AAA infrastructure. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 10] Internet Draft Dynamic HA Assignment 8 January 2004 The mobile node must maintain the remaining Mobile IP session with the Assigned HA. Following sections describe MN behavior in FA CoA mode and collocated CoA mode. 5.1.1 MN using FA CoA When a mobile node initiates Mobile IP session, it MUST set the home agent address field in the Registration Request to unicast address or ALL-ZERO-ONE-ADDR. The destination IP address of Registration Request is the FA. The FA will determine the Requested HA and forward the Registration Request to the Requested HA. Registration Request processing takes place on the Requested HA as per the specification in this draft. The Registration Request MUST be appropriately authenticated for the HA to validate the Request. If successful Registration Reply is received, MN obtains Assigned HA from the HA field of Reply. If Registration Reply is received with code REDIRECT-HA-REQ, MN MUST authenticate the Reply based on HA address in HA field of Reply and attempt Registration with the HA address specified in the REDIRECTED-HA-ADDRESS extension. 5.1.2 MN using Collocated CoA Mobile Node in collocated CoA mode MUST set the home agent address field in the Registration Request to unicast address or ALL-ZERO-ONE-ADDR. The destination IP address of the Registration Request is the Requested HA. Some ideas to select a Requested HA are briefly covered in section 6. If successful Reply is received, the MN obtains Assigned HA address from successful Registration Reply. The MN MUST cache the Assigned HA address for the length of the Mobile IP session. The mobile node then MUST use this previously cached Assigned HA address as the home agent address in subsequent re- registration and de-registration request(s). This will make sure that the mobile node will always be anchored to the assigned home agent with which it was initially registered. If Registration Reply is received with code REDIRECT-HA-REQ, MN MUST authenticate the Reply based on HA address in HA field of Reply and attempt Registration with the HA address specified in the REDIRECTED-HA-ADDRESS extension. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 11] Internet Draft Dynamic HA Assignment 8 January 2004 5.1.3 Refreshing Assigned HA Address on Mobile Node When the Mobile IP session terminates, the mobile node MAY clear the Assigned HA address cached as the home agent address. It MAY request a new HA address for the new Mobile IP session. The advantage of this approach is that the mobile node will be always anchored to an optimal home agent from where it initiated Mobile IP session. 5.2 Foreign Agent Considerations When the mobile node is using foreign agent CoA, it sends the Registration Request to the foreign agent. When the FA receives a Registration Request with HA address field set to ALL-ZERO- ONE-ADDR, it obtains the Requested HA address to forward the Registration Request. Some ideas to select a Requested HA are briefly covered in section 6. If the FA cannot obtain the Requested HA to forward a Registration Request from MN, it MUST reject request with error code NONZERO-HA-REQD. Backward compatibility issues related to the mobility agents are addressed in section 9. 5.3 Home Agent Considerations Home Agent can process an incoming Registration Request in one of the following three ways: MN or FA sends the Registration Request to the Requested HA. The term Requested HA has meaning in context of the Registration Request message. When the Requested HA successfully processes Registration Request and creates a binding and sends a Reply with its address, it becomes the Assigned HA. The term Assigned HA is meaningful in context of a Registration Reply message. Home Agent receiving the request with HA field set to ALL-ZERO- ONE-ADDR MAY reject the request even if successfully authenticated for a multitude of reasons and suggest an alternate HA address in Reply. In such a case, the HA puts own address in HA field of Reply and sets the Reply code to REDIRECT-HA-REQ and adds the REDIRECTED-HA-ADDRESS extension. Home Agent receiving the request with HA field set to a unicast address not matching any of its addresses MUST reject the request even if successfully authenticated. This rejected message has the code 136 as defined in RFC3344 (3.8.3.2). HA Kulkarni, Patel, Leung Expires July 8, 2004 [Page 12] Internet Draft Dynamic HA Assignment 8 January 2004 may reject the message with code REDIRECT-HA-REQ and suggest an alternate HA to use in the REDIRECTED-HA-ADDRESS extension. 5.3.1 Assigned Home Agent Considerations The HA that processes the incoming Registration Request fully in accordance with RFC 3344 and this specification becomes the Assigned HA. The Registration Request terminates at the Assigned HA. The Assigned HA creates mobility bindings and sends Registration Reply to the MN by copying its address in the home agent field and as the source IP address of the Reply. There are two IP addresses to consider, destination IP address and Home Agent address field in the Registration Request. When destination IP address is unicast, only one HA receives the Registration Request. This HA should unambiguously accept or deny the registration, regardless of the value in the Home Agent field. When the Home Agent field is non-unicast, the HA should set the value to its own IP address in the Registration Reply. The following table summarizes the behavior of Assigned HA. No. Dest IP Addr HA field Processing at Assigned HA -- ------------ ------------ ------------------------- 1 Unicast Unicast û RFC 3344: Normal HA processing Same as Dest per RFC 3344. IP addr Unicast û RFC 3344: HA denies the Different registration with error code than Dest IP 136 and sets HA field to its Addr own IP address in the reply as per section 3.8.3.2. OR New Behavior: Dest IP corresponds to the HA receiving RRQ, if authentication is successful, reject RRQ with a new error code (REDIRECT-HA- REQ). HA puts its address in HA address field of Reject. HA suggests an alternate HA to use in the new REDIRECTED-HA- ADDRESS extension. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 13] Internet Draft Dynamic HA Assignment 8 January 2004 2 Unicast non-unicast RFC 3344: HA denies the registration with error code 136 and sets HA field to its own IP address in the reply as per section 3.8.3.2. ALL-ZERO- New Behavior: Accept the RRQ as ONE-ADDR per this specification. Authenticate the RRQ and create mobility binding if the HA is acting as Assigned HA. Set HA field to its own IP address in the Registration Reply. OR New Behavior: Dest IP corresponds to the HA receiving RRQ, if authentication is successful, reject RRQ with a new error code (REDIRECT-HA- REQ). HA puts its address in HA address field of Reject. HA suggests an alternate HA to use in the new REDIRECTED-HA- ADDRESS extension 3 Non-unicast Unicast RFC 3344: HA rejects with error code 136 and sets HA field to its own IP address in the reply per section 3.8.2.1. 4 Non-unicast Non-unicast RFC 3344: HA rejects with error code 136 and sets HA field to its own IP address in the reply per section 3.8.2.1. Table 1: Registration Request handling at Assigned HA This specification proposes an enhancement to case #1 from RFC 3344. As per this specification, when a HA receives a Registration Request and the HA address (unicast) does not match its own address(es), HA can reject the request with the error code REDIRECT-HA-REQ and suggest an alternate HA. This redirection can be used for load-balancing, geographical proximity based on care-of-address or a multitude of reasons. HA puts its own address in HA field on Registration Reply Kulkarni, Patel, Leung Expires July 8, 2004 [Page 14] Internet Draft Dynamic HA Assignment 8 January 2004 message and put the address of the redirected HA in the REDIRECTED-HA-ADDRESS extension. This specification also proposes a subtle difference in behavior for case #2 above from RFC 3344. As per the messaging proposed here, the mobile node (or the foreign agent) sends the Registration Request to the Requested HA address, which is a unicast address. Because HA does not receive Registration Request that is sent to the subnet-directed broadcast address, RFC 3344 section 3.8.2.1 doesn't apply. Although the Home Agent field in the Registration Request is not a unicast address, the destination IP address is a unicast address. This avoids the problem associated with subnet-directed broadcast destination IP address that may result in multiple HAs responding. Thus, there is no need to deny the registration as stated in RFC 3344 section 3.8.3.2. When the destination IP address is a unicast address and Home Agent field is ALL-ZERO-ONE-ADDR, the HA accepts/denies registration and sets HA field to its own IP address in the reply (i.e. registration is not rejected with error code 136). HA can reject the request with the error code REDIRECT-HA-REQ and suggest an alternate HA. This redirection can be used for load-balancing, geographical proximity based on care-of-address or a multitude of reasons. HA puts its own address in HA field on Registration Reply message and put the address of the redirected HA in the REDIRECTED-HA-ADDRESS extension. If HA accepts the Request, HA field in Reply is set to this HA address. The Assigned HA performs standard validity checks on the Registration Request. If there is any error, the Registration Request is rejected with error codes specified in RFC 3344. 6. Requested Home Agent Selection The destination IP address of the first Registration Request in the Mobile IP session is the Requested HA. This address MUST be a unicast IP address. Some ideas on how to select the Requested HA are briefly covered in this section, however this draft neither suggests nor mandates any specific mechanism. There can be more methods for selecting the HA to the MN. Here is a high level overview of some possibilities: DHCP: MN performs DHCP to obtain an IP address on the visited network. The Requested HA is learned from the DHCP Mobile IP Kulkarni, Patel, Leung Expires July 8, 2004 [Page 15] Internet Draft Dynamic HA Assignment 8 January 2004 Home Agent Option 68 [4]. MN sends Registration Request directly to this HA and receives the Assigned HA to be used for the remainder of the Mobile IP session. AAA: MN performs challenge/response [5] with the FA. The FA retrieves the Requested HA from the AAA server and forwards the Registration Request directly to this HA. The Assigned HA sends Registration Reply to the FA, which relays it to the MN. MN uses the Assigned HA for the remainder of the Mobile IP session. DNS: In this case hostname of HA is configured on MN or obtained by some other means û e.g. using a service location protocol. MN performs DNS lookup on the HA hostname. The DNS infrastructure provides resource record with information to identify the nearest HA to the MN. The MN sends Registration Request directly to the HA and receives the Assigned HA to be used for remainder of the Mobile IP session. Static configuration: HA address is statically configured on MN. The MN uses the configured address to send the Registration Request. 7. Error Values Each entry in the following table contains the name and value for the error code to be returned in a Registration Reply. It also includes the section in which the error code is first mentioned in this document. Error Name Value Section Description ---------- ----- ------- ----------------------------- NONZERO-HA-REQD XX 5.2 Non-zero HA address required in Registration Request. REDIRECT-HA-REQ YY 5.3.1 Reregister with suggested HA. 8. IANA Considerations The code value NONZERO-HA-REQD defined in Section 7 correspond to error values conventionally associated with the rejection by the foreign agent (i.e. value in the range 64-127). The code value REDIRECT-HA-REQ defined in Section 7 correspond to error Kulkarni, Patel, Leung Expires July 8, 2004 [Page 16] Internet Draft Dynamic HA Assignment 8 January 2004 values conventionally associated with the rejection by the home agent (i.e. value in the range 128-192). The extension REDIRECTED-HA-ADDRESS defined in section 3.3 corresponds to a skippable extension. IANA should record the values as defined in Section 7 and 3.3. 9. Security Considerations This specification assumes that the Mobile Node and Assigned Home Agent are in the same administrative domain. This specification does not change or degrade the security model established in RFC-3344. Most of the time Mobile Nodes will be connected to the network via wireless link. Such links are vulnerable to passive eavesdropping, replay attacks or many other types of attacks. They are considered below. 9.1 Message Authentication Codes The Registration Request and Reply messages are protected by a valid authenticator as specified in RFC 3344. Configuring security associations is a deployment specific issue and is covered by other specifications in Mobile IP WG. There can be many ways of configuring security associations, but this specification does not mandate any specific way. An example is where the security association between a MN and an individual HA (Dynamic or Assigned) is dynamically derived during the dynamic HA assignment, based on a shared secret between MN and AAA infrastructure, as defined in [7]. The Registration Request is protected with MN-AAA authentication extension and Registration Reply is protected with MHAE. Since the security association is shared between MN and AAA, any dynamically assigned HA in the local domain can proxy authenticate the MN using AAA as per [7]. The Assigned Home Agent authenticates Registration Request from the mobile node as specified in RFC-3344 and RFC-3012. The MN also authenticates the Registration Reply from the Assigned HA, thus the existing trust model in RFC 3344 is maintained. 9.2 Areas of Security Concern in this Protocol As per the messaging in this draft, the Assigned Home Agent will process the incoming Registration Request as per RFC-3344. Hence the Assigned Home Agent will have same security concerns as that of the Home Agent in RFC-3344. They are addressed in Section 5 ôSecurity Considerationsö of RFC-3344. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 17] Internet Draft Dynamic HA Assignment 8 January 2004 10. Backward Compatibility Considerations Legacy Home Agent: Legacy home agents may reject the Registration Request with error code 136 because the Home Agent field is not a unicast address. However, some legacy HA implementations may coincidentally process the Registration Request in accordance with this draft, when the HA field in RRQ is set to ALL-ZERO- ONE-ADDR. Legacy Foreign Agent: Legacy foreign agents may forward Registration Request with home agent field set to ALL-ZERO-ONE-ADDR by setting the destination IP address to ALL-ZERO-ONE-ADDR. This will result packet being dropped or incidentally handled by a next hop HA, adjacent to the FA. Legacy Mobile Node: MN that does not set HA field to ALL-ZERO-ONE-ADDR will continue to achieve its registrations through statically configured HA. In collocated mode, the endpoint of the MN's tunnel is the Assigned HA. 11. Change Log Version 2 is totally revamped from earlier version. The most notable changes are: Removed references to directed HA/assigned HA. There is no HA redirection in the network to incorporate the feedback from Pete McCann. The single entity is currently called Assigned HA. Added a new error code for HA rejection when dst IP is unicast and HA address is unicast and these two addresses are different. The HA receiving RRQ rejects the RRQ and puts another HA in RRP and its source address in RRP. Also, when this new error code is used for HA redirection, a new HA address is suggested in a new extension 12. Intellectual Property Rights The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed Kulkarni, Patel, Leung Expires July 8, 2004 [Page 18] Internet Draft Dynamic HA Assignment 8 January 2004 to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights, which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 13. Acknowledgements The authors would like to thank Pete McCann for suggestions on security considerations and definition of ALL-ZERO-ONE-ADDR. Thanks to Kuntal Chowdhury for extensive review and comments on this draft. Also thanks to Henrik Levkowetz for detailed reviews and suggestions. The authors would like to thank Mike Andrews, Madhavi Chandra and Yoshi Tsuda for their review and suggestions. 14. References [1] C. Perkins, "IP Mobility Support for IPv4", RFC 3344, August 2002. [2] P. Calhoun and C. Perkins, "Mobile IP Network Access Identifier Extension for IPv4", RFC 2794, March 2000. [3] D. Senie, "Changing the Default for Directed Broadcasts in Routers", RFC 2644, August 1999. [4] S. Alexander and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997. [5] C. Perkins and P. Calhoun, "Mobile IPv4 Challenge/Response Extensions", RFC 3012, November 2000. [6] H. Levkowetz and S. Vaarala, "Mobile IP Traversal of Network Address Translation (NAT) Devices", RFC 3519, July 803. [7] C. Perkins and P. Calhoun, "AAA Registration Keys for Mobile IP", draft-ietf-mobileip-aaa-key-13.txt, 22 June 2003. [8] Jari Arkko, et. al., ôThoughts on bootstrapping mobility securelyö as presented at 57th IETF in Vienna, Austria, 16th July, 2003 Kulkarni, Patel, Leung Expires July 8, 2004 [Page 19] Internet Draft Dynamic HA Assignment 8 January 2004 Authors' Addresses Milind Kulkarni Cisco Systems Inc. 170 W. Tasman Drive, San Jose, CA 95134 USA Email: mkulkarn@cisco.com Phone:+1 408-527-8382 Alpesh Patel Cisco Systems Inc. 170 W. Tasman Drive, San Jose, CA 95134 USA Email: alpesh@cisco.com Phone:+1 408-853-9580 Kent Leung Cisco Systems Inc. 170 W. Tasman Drive, San Jose, CA 95134 USA Email: kleung@cisco.com Phone: +1 408-526-5030 Full Copyright Statement Copyright (C) The Internet Society (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. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 20] Internet Draft Dynamic HA Assignment 8 January 2004 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Kulkarni, Patel, Leung Expires July 8, 2004 [Page 21]