Mobile IP Working Group Milind Kulkarni INTERNET-DRAFT Alpesh Patel Category: Standards Track Kent Leung Date : 28 June 2004 Cisco Systems Inc. Mobile IPv4 Dynamic Home Agent Assignment draft-ietf-mip4-dynamic-assignment-02.txt Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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. This Internet-Draft will expire on December 28, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract Mobile IPv4 [1] 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 December 28, 2004 [Page 1] Internet Draft Dynamic HA Assignment 28 June 2004 Table of Contents 1. Introduction.................................................3 2. Requirements Terminology.....................................3 3. Problem Statement............................................4 3.1 Scope.......................................................5 3.2 Dynamic Home Agent Discovery in Mobile IPv4.................5 3.3 NAI usage and dynamic HA assignment.........................5 3.4 Dynamic HA extension........................................6 3.4.1 Requested HA extension....................................6 3.4.2 Redirected HA extension...................................7 4. Messaging mechanism for dynamic HA assignment/redirection....7 4.1 Messaging for dynamic HA assignment.........................7 4.1.1 Example with Message Flow Diagram.........................8 4.2 Messaging for HA redirection................................9 4.2.1 Example with Message Flow Diagram........................10 5. Mobility Agent Considerations...............................12 5.1 Mobile Node Considerations.................................12 5.1.1 MN using FA CoA..........................................12 5.1.2 MN using Collocated CoA..................................13 5.1.3 Refreshing Assigned HA Address on Mobile Node............13 5.2 Foreign Agent Considerations...............................14 5.3 Home Agent Considerations..................................14 5.3.1 Assigned Home Agent Considerations.......................15 6. Requested Home Agent Selection..............................16 7. Error Values................................................17 8. IANA Considerations.........................................17 9. Security Considerations.....................................18 10. Backward Compatibility Considerations......................19 11. Change Log from previous versions..........................19 12. Acknowledgements...........................................20 13. Normative References.......................................20 Authors' Addresses.............................................20 Intellectual Property Statement................................21 Kulkarni, Patel, Leung Expires December 28, 2004 [Page 2] Internet Draft Dynamic HA Assignment 28 June 2004 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 [2] when requesting a dynamically assigned HA. MN requests a dynamically assigned HA by setting the HA field in the initial Registration Request to ALL-ZERO-ONE-ADDR (defined in section 2). If the request is accepted, the HA field in successful Registration Reply contains the HA 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 extension). If the RRQ is rejected with Redirected HA extension or if the MN wishes to register at a specific HA, MN can put the HA address in the Requested HA extension in Registration Request. The HA address in Requested HA extension is a hint to the network where the MN may be anchored. The HA field is set to ALL-ZERO-ONE-ADDRESS for dynamic HA assignment. The messaging mechanism is defined in this document so that the MN can request and receive a dynamic HA address in Mobile IP messages. However, the mechanism by which the network selects an HA for assignment to the MN is outside the scope of this document. For example, the selection may be made by any network node that receives the registration request (or information about the registration request), such as a Foreign Agent, AAA server, or Home Agent. The node that selects the HA may select one based on a number of criteria, including but not limited to HA load-balancing, geographical proximity, administrative policy etc.. 2. Requirements Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [6]. The Mobile IP related terminology described in RFC 3344 [1] is used in this document. In addition, the following terms are used: 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 Kulkarni, Patel, Leung Expires December 28, 2004 [Page 3] Internet Draft Dynamic HA Assignment 28 June 2004 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 6. 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 extension). AAA server: Authentication, Authorization and Accounting Server. DNS: Domain Name System. DHCP: Dynamic Host Configuration Protocol. MN: Mobile Node as defined in Mobile IPv4 [1]. HA: Home Agent as defined in Mobile IPv4 [1]. FA: Foreign Agent as defined in Mobile IPv4 [1]. 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: Kulkarni, Patel, Leung Expires December 28, 2004 [Page 4] Internet Draft Dynamic HA Assignment 28 June 2004 - 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 a home agent that is close to the mobile node it can drastically reduce the latency between the home agent and mobile node. - 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. 3.1 Scope This specification does not address the problem of distributing a security association between the MN and HA, and it can either be statically preconfigured or dynamically distributed using other mechanisms [7]. The draft introduces the terms Requested/Assigned/Redirected HA (section 6). 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 Mobile IPv4 Mobile IPv4 [1] 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 Kulkarni, Patel, Leung Expires December 28, 2004 [Page 5] Internet Draft Dynamic HA Assignment 28 June 2004 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 is compatible with the procedures documented in the NAI specification [2]. 3.4 Dynamic HA extension The Dynamic HA extension, shown in figure 1, contains the address of the HA. This is a generic extension and can be used in Registration Request and Reply messages. It is a skippable extension. 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 | Sub-Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HA-Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: The Dynamic HA address Extension Type DYNAMIC-HA-ADDRESS (skippable) (to be assigned by IANA) is the type, which specifies the dynamic HA address. Sub-Type Defines the use of this extension as: sub-type 1 = Requested HA extension 2 = Redirected HA extension Length Indicates the length of the extension not including the type, sub-type and length fields. Length is always 4 bytes. HA-Address Address of the Home Agent. 3.4.1 Requested HA extension The Requested HA extension is a Dynamic HA extension of subtype 1. MN may include the Requested HA extension in the registration request as a hint to the network where it wishes to be anchored. This extension contains the address of the HA. A valid unicast IP address MUST be used as HA address in this extension. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 6] Internet Draft Dynamic HA Assignment 28 June 2004 In absence of an FA, the RRQ is forwarded to this HA. In presence of an FA, FA MUST forward RRQ to the HA address in this extension. 3.4.2 Redirected HA extension The Redirected HA extension is a Dynamic HA extension of subtype 2. The Redirected HA extension, contains the address of the HA where the MN should attempt the next registration. The HA receiving a 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 this extension. The Redirected HA extension MUST be included in Registration Reply when the reply code is REDIRECT-HA-REQ. 4. Messaging mechanism for dynamic HA assignment/redirection This specification presents two alternatives for home agent assignment. The two alternatives are: (a) Dynamic HA assignment (described in section 4.1) and (b) HA redirection (described in section 4.2). 4.1 Messaging for dynamic HA assignment The following sequence of events occurs when the Requested HA accepts the Registration Request and returns a Registration Reply to the mobile node. 1. MN sets the Home Agent address field in the Registration Request to ALL-ZERO-ONE-ADDR. If the MN is aware of the HA address, it can add that address in the Requested HA extension in Registration Request. 2. The MN (if using collocated CoA) or FA (if using FA CoA) sends the Registration Request to the "Requested HA". If the Requested HA extension is present, Requested HA is specified in the "HA Address" of this extension. 3. "Requested HA" is the home agent, which processes the Registration Request in accordance with Mobile IPv4 [1] 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. (Note that the "Assigned HA" will be same as the "Requested HA"). 5. Subsequent Registration Request messages for renewal are sent to the Assigned HA. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 7] Internet Draft Dynamic HA Assignment 28 June 2004 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 alternative is best described with the help of a message flow diagram and description. 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 dynamic HA assignment 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 | +-----------------------------------------------------------+ If the MN is aware of an HA address, it can add that address in the Requested HA extension in Registration Request as a hint. That extension is not shown above. 2. The FA sends the Registration Request to the Requested HA. The Registration Request looks as follows: Kulkarni, Patel, Leung Expires December 28, 2004 [Page 8] Internet Draft Dynamic HA Assignment 28 June 2004 +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA | +-----------------------------------------------------------+ (If MN includes the Requested HA extension, the FA copies that extension. The FA then forwards the Registration Request, along with the Requested HA extension, to the HA address specified in Requested HA extension.) 3. HA processes the Registration Request in accordance with Mobile IPv4 [1] and the messaging defined in this document. HA 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). +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | |Assigned| Src IP of | | Assigned HA |FA CoA/| | HA | the RRQ | | | | +-----------------------------------------------------------+ 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. Note that the Assigned HA is the same as the Requested HA. 4.2 Messaging for HA redirection This section describes the events that occur when the Requested HA does not accept the Registration Request and redirects the mobile node to another HA (aka Redirected HA) instead. 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". If the MN is aware of an HA address, it can add that address in the Requested HA extension in Registration Request. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 9] Internet Draft Dynamic HA Assignment 28 June 2004 3. When HA receives the Registration Request, 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 IP address of the HA that is the target of the redirection is specified in Redirected HA 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 extension. The MN then sends a Registration Request to Redirected HA, unless it has already received a redirection response from this HA while processing this Registration Request. 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 HA redirection 1. MN sets the Home Agent address field in the Registration Request to ALL-ZERO-ONE-ADDR address. Since MN is using FA CoA in this example, it sends the Registration Request to the FA. The Registration Request looks as follows: Kulkarni, Patel, Leung Expires December 28, 2004 [Page 10] Internet Draft Dynamic HA Assignment 28 June 2004 +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | MN | FA | | ALL-ZERO-ONE-ADDR |FA CoA | +-----------------------------------------------------------+ If the MN is aware of an HA address, it can add that address in the Requested HA extension in Registration Request as a hint. That extension is not shown above. 2. The FA sends the Registration Request to the Requested HA. If Requested HA extension is present, Requested HA is the HA address in this extension. The Registration Request looks as follows: +-----------------------------------------------------------+ | 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 Mobile IPv4 [1] and the messaging defined in this document. If the 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 Redirected HA in the Redirected HA extension. HA then sends Registration Reply reject to the FA, which looks as follows: +-----------------------------------------------------------+ | Src IP=| Dest IP = | MN HoA | HA Address = | CoA = | | | Src IP of | | HA |FA CoA | | HA | the RRQ | | | | +-----------------------------------------------------------+ | Redirected HA 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 extension ... | +-----------------------------------------------------------+ 5. If MN can authenticate the Reply, MN extracts the HA address from Redirected HA extension. The MN then sends Registration Request to Redirected HA, unless it has already received a redirection response from this HA while processing the Registration Request. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 11] Internet Draft Dynamic HA Assignment 28 June 2004 5. Mobility Agent Considerations 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. Since MN uses NAI extension, the Home Address field is set to 0.0.0.0. While dynamic HA assignment is in progress and MN has not successfully anchored at a Home Agent, mobile node MUST set the Home Agent field in the Registration Request to 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 Mobile IPv4 [1] or Mobile IPv4 Challenge/Response Extensions [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 [7]. 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 requesting dynamic HA assignment, it MUST set the home agent address field in the Registration Request to 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. Assigned HA address is the same as Requested HA address. 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 Kulkarni, Patel, Leung Expires December 28, 2004 [Page 12] Internet Draft Dynamic HA Assignment 28 June 2004 Redirected HA extension. MN MUST put the Redirected HA in the HA address of the Requested HA extension. In some cases, for the first Registration Request MN may want to hint to the network to be anchored at a specific HA and the MN MUST put that address in the HA address of the Requested HA extension. If the Registration Request contains the Requested HA extension, the HA address in that extension must match the destination IP of the Request. 5.1.2 MN using Collocated CoA Mobile Node in collocated CoA mode requesting dynamic HA assignment MUST set the home agent address field in the Registration Request to ALL-ZERO-ONE-ADDR. The destination IP address of the Registration Request is the Requested HA. Some ideas on how 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 Assigned HA will be same as Requested HA. 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 for the duration of the Mobile IP session, 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 extension. MN MUST put the Redirected HA in the HA address of the Requested HA extension. In some cases, for the first Registration Request MN may want to hint to the network to be anchored at a specific HA and the MN MUST put that address in the HA address of the Requested HA extension. While requesting dynamic HA assignment in collocated CoA mode, Requested HA extension must always be included. 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 by not including the Requested HA extension. 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. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 13] Internet Draft Dynamic HA Assignment 28 June 2004 Alternately, MN may save the Assigned HA address and use it in the Requested HA extension along with ALL-ZERO-ONE-ADDR address in Registration Request. 5.2 Foreign Agent Considerations When the mobile node is using foreign agent CoA or MN using CCoA finds R bit is set in the FA advertisement, 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 and it doesn't contain the Requested HA extension, FA obtains the Requested HA address to forward the Registration Request. Some ideas on how 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. If the MN has included the Requested HA extension, FA MUST forward Registration Request to the address in this extension. If the HA address in this extension is not a routable unicast address, FA MUST reject request with error code NONZERO-HA-REQD. If the Registration Request contains the Requested HA extension, the HA address in that extension must match the destination IP of the Request. Backward compatibility issues related to the mobility agents are addressed in section 10. 5.3 Home Agent Considerations Home Agent can process an incoming Registration Request in one of the following two ways: 1. 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. 2. Home Agent receiving the Registration Request with HA field set to ALL-ZERO-ONE-ADDR MAY reject the request even if successfully authenticated and suggest an alternate HA address in Reply. In such a case, the HA puts its own address in HA field of Reply and sets the Reply code to REDIRECT-HA-REQ and adds the Redirected HA extension. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 14] Internet Draft Dynamic HA Assignment 28 June 2004 If the Registration Request contains the Requested HA extension, the HA address in that extension must match the destination IP of the Request. If it does not match, the Requested HA must reject the Registration Request with error code 136. 5.3.1 Assigned Home Agent Considerations The HA that processes the incoming Registration Request fully in accordance with Mobile IPv4 [1] and this specification becomes the Assigned HA. The Registration Request terminates at the Assigned HA. The Assigned HA creates one mobility binding per MN 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. Dest IP Addr HA field Processing at Assigned HA ------------ ------------ ---------------------------------- Unicast non-unicast Mobile IPv4 [1]: There is no change in handling for this case from (Must be Mobile IPv4. It is mentioned here equal to the for reference only. HA receiving HA denies the registration the RRQ) with error code 136 and sets HA field to its own IP address in the reply as per section 3.8.3.2 in [1]. ALL-ZERO- ONE-ADDR New Behavior: Accept the RRQ as 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: If authentication is successful, reject RRQ with a new Kulkarni, Patel, Leung Expires December 28, 2004 [Page 15] Internet Draft Dynamic HA Assignment 28 June 2004 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 extension. Table 1: Registration Request handling at Assigned HA 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, Mobile IPv4 [1] 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 Mobile IPv4 [1] 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 other reasons. HA puts its own address in HA field of the Registration Reply message and puts the address of the redirected HA in the Redirected HA extension. If HA accepts the Request, HA field in the Registration 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 Mobile IPv4 [1]. 6. Requested Home Agent Selection When dynamic HA assignment is requested, the destination IP address of the Registration Request is the Requested HA. This address MUST be a unicast IP address. If the MN has included a Requested HA extension in Registration Request, the HA address in this extension is the Requested HA. Some example methods by which the MN or the FA may select the Requested HA are briefly described below: Kulkarni, Patel, Leung Expires December 28, 2004 [Page 16] Internet Draft Dynamic HA Assignment 28 June 2004 DHCP: MN performs DHCP to obtain an IP address on the visited network. The Requested HA is learned from the DHCP Mobile IP 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 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 sends the Registration Request to the configured address. 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 Reregister with redirected HA. 8. IANA Considerations Kulkarni, Patel, Leung Expires December 28, 2004 [Page 17] Internet Draft Dynamic HA Assignment 28 June 2004 The code value NONZERO-HA-REQD is a Mobile IP response code [1] taken from the range of values associated with rejection by the foreign agent (i.e. value in the range 64-127). The code value REDIRECT-HA-REQ is a Mobile IP response code [1] taken from the range of values associated with rejection by the home agent (i.e. value in the range 128-192). The Dynamic HA extension is assigned from the range of values associated with skippable extensions at the home agent (i.e. value in the range 128-255). IANA should record the values as defined in Section 7 and 3.4. 9. Security Considerations This specification assumes that a security configuration has been preconfigured between the MN and the HA or is configured along with the initial RRQ/RRP as per [7]. This specification does not change or degrade the security model established in Mobile IPv4 [1]. Mobile Nodes are often connected to the network via wireless link, which may be more prone to passive eavesdropping, replay attacks. Such an attack might lead to bogus registrations or redirection of traffic or denial of service. As per the messaging in this draft, the Assigned Home Agent will process the incoming Registration Request as per Mobile IPv4 [1]. Hence the Assigned Home Agent will have same security concerns as that of the Home Agent in Mobile IPv4 [1]. They are addressed in Section 5 "Security Considerations" of Mobile IPv4 [1]. The Registration Request and Registration Reply messages are protected by a valid authenticator as specified in Mobile IPv4 [1]. 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 MN-HA Authentication Extension. 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 Mobile IPv4 [1] and RFC-3012. The MN Kulkarni, Patel, Leung Expires December 28, 2004 [Page 18] Internet Draft Dynamic HA Assignment 28 June 2004 also authenticates the Registration Reply from the Assigned HA, thus the existing trust model in Mobile IPv4 [1] is maintained. 10. Backward Compatibility Considerations In this section, we examine concerns that may arise when using this specification in a mixed environment where some nodes implement the specification and others do not. In each of the examples below, we consider the case where one node is a "Legacy" node which does not implement the specification in the context of other nodes which do. 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 from previous versions Changes from revision 1 to 2: 1. Editorial changes suggested by the WG, the chair's reviews and idnits. Changes from revision 0 to 1: 1. Added subtype field in Redirected HA Address Extension. 2. Aligned the HA address at 4-byte world boundary. 3. The case of handling unicast HA field is removed in section 5.3.1. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 19] Internet Draft Dynamic HA Assignment 28 June 2004 12. Acknowledgements The authors would like to thank Pete McCann for thorough review, 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. 13. Normative 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] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [7] C. Perkins and P. Calhoun, "AAA Registration Keys for Mobile IP", draft-ietf-mip4-aaa-key-06.txt, June 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 Kulkarni, Patel, Leung Expires December 28, 2004 [Page 20] Internet Draft Dynamic HA Assignment 28 June 2004 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 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Copyright Statement Kulkarni, Patel, Leung Expires December 28, 2004 [Page 21] Internet Draft Dynamic HA Assignment 28 June 2004 Copyright (C) The Internet Society (2003). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Kulkarni, Patel, Leung Expires December 28, 2004 [Page 22]