INTERNET-DRAFT Pyungsoo Kim Expires: June 2003 Soohong Daniel Park Youngkeun Kim Samsung Electronics December 2002 Efficient and Fast Discovery of Slave Home Agent's Address Status of This Memo This document is an Internet-Draft and is subject to 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 This document proposes a new mechanism in Mobile IPv6, which allows a mobile node to discover promptly a suitable slave home agent's address on its home link when the mobile node may not know a master home agent's address due to some reasons. To implement the proposed mechanism, new Binding Update/Acknowledgement messages are defined. The proposed mechanism might be more efficient and general, and faster than the existing Home Agent Address Discovery in [1]. Kim, Park, Kim Expires June 2003 [Page 1] Internet Draft Discovery of slave HA's address Dec 2002 Table of Contents 1. Introduction......................................................2 2. Terminology.......................................................4 3. Efficient and Fast Discovery of Slave Home Agent's Address........4 3.1. New Binding Update/Acknowledgement Message Formats...........4 3.1.1. New Binding Update Message Format.......................4 3.1.2. New Binding Acknowledgement Message Format..............5 3.2. Operation Procedure..........................................6 4. Advantages........................................................8 5. Authors' Addresses................................................8 1. Introduction In Mobile IPv6, after deciding to change its primary care-of address, a mobile node sends a Binding Update to its home agent and receives a Binding Acknowledgment from its home agent in order to register the care-of address. Then, the mobile node needs to send a Binding Update to its home agent periodically according to the lifetime. However, sometimes, the mobile node may not know the address of a home agent for it. For example, the home agent of the mobile node has been broken, or repaired, or reconfigured while the mobile node has been away from home, such that the home agent has been replaced by a different router serving this role. In this case, the mobile node may attempt to discover a suitable home agent's address on its home link. To do so, in [1] the mobile node sends a Home Agent Address Discovery Request message to the Mobile IPv6 Home-Agents anycast address [2] for its home IP subnet prefix. Then, the home agent on its home link that receives this request message will return a Home Agent Address Discovery Reply message, giving the Home Agent List which has all home agents' addresses operating on the home link. Figure 1 shows the message flow for the existing mechanism in [1]. However, in the existing mechanism [1], the mobile node might select generally the most preferred home agent address or the one of more preferred ones from the Home Agent List. This means that one or a few home agent addresses could be sufficient for the mobile node which discovers a suitable home agent's address. Therefore, it is somewhat inefficient that the mobile node receives the Home Agent List with all home agents' addresses operating on the home link. In addition, in the existing mechanism, it is recommended that the home agent's preference is configured manually by a system administrator. Therefore, it could be noted that the preference order in the Home Agent List will not be varied frequently. In this document, an efficient and general mechanism will be proposed newly for the mobile node to discover promptly a suitable home agent's address on its home link. Hereafter, a home agent which is now doing binding will be called the "master home agent" and the home agent which can do binding in future will be called the "slave home agent". Kim, Park, Kim Expires June 2003 [Page 2] Internet Draft Discovery of slave HA's address Dec 2002 Firstly, new Binding Update/Acknowledgment messages are defined to implement the proposed mechanism. Then, using these messages, the mobile node performs the Binding Update/Acknowledgment to register the care-of address or to renew binding periodically according to the lifetime. When the mobile node registers the care-of address in the first Binding Update/Acknowledgment, the mobile node sends a newly defined Binding Update message with the request of a slave home agent's address to the master home agent. Then, the master home agent will reply a newly defined Binding Acknowledgment message with only one or a few slave home agents' addresses according to preference. Then, the mobile node might select the most preferred slave home agent's address or the one of slave home agents' addresses. The proposed mechanism provides several advantages over the existing mechanism in [1]. The proposed mechanism can omit the Home Agent Address Discovery Request/Reply used in the existing one. This means the proposed mechanism can provide the faster discovery of the slave home agent's address than the existing one. The omission of the Home Agent Address Discovery Request/Reply might reduce amount of traffic when there are many mobile nodes that are now doing binding with the master home agent. In addition, the proposed mechanism requires only one or a few slave home agents' addresses while the existing one requires all slave home agents' addresses. This means the proposed mechanism can be more efficient than the existing one. Moreover, the proposed mechanism can be implemented as the existing one according to setting bit or status code, which means the generality of the proposed mechanism. Current Other MN HA HAs 1st |--------------BU (normally)------------->| | BU/BACK | | | |<------------BACK (normally)-------------| | | | | Before |--------------BU (normally)------------->| | Expiration| | | |<------------BACK (normally)-------------| | | : | | | : | | Before |--------------BU (normally)------------->| | Expiration| | | |<--------ICMP Error (Unreachable) | | | | | |-------Discovery Request (Anycast)------>| | | | | Select |<--Discovery Reply (all HAs' addresses)--| | HA address| Current | HA 1st |------------------BU (normally)------------------>| BU/BACK | | |<----------------BACK (normally)------------------| Figure 1 : Message flow for existing mechanism Kim, Park, Kim Expires June 2003 [Page 3] Internet Draft Discovery of slave HA's address Dec 2002 2. Terminology Mobile Node A Mobile IPv6 host capable of moving its point of attachment to the Internet. Home Agent A router on a mobile node's home link with which the mobile node has registered its current care-of address. Master Home Agent A home agent that is now doing binding. Slave Home Agent A home agent that can do binding in future. 3. Efficient and Fast Discovery of Slave Home Agent's Address In this document, an efficient and general mechanism will be proposed newly for the mobile node to discover promptly a suitable home agent's address on its home link. Hereafter, a home agent which is now doing binding will be called the "master home agent" and the home agent which can do binding in future will be called the "slave home agent". 3.1. New Binding Update/Acknowledgement Message Formats Firstly, new Binding Update/Acknowledgment messages are defined to implement the proposed mechanism. Then, using these messages, the mobile node performs the Binding Update/Acknowledgment to register the care-of address or to renew binding periodically according to the lifetime. 3.1.1. New Binding Update Message Format The Binding Update (BU) message is used by a mobile node to notify other nodes of a new care-of address for itself. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence # | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |A|H|S|D|L|R| Reserved | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Mobility options . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Slave Request (R) The Slave Request (R) bit is set by the sending mobile node to request a Binding Acknowledgement with one or a few slave home agents' addresses. Other Fields Their definitions can be shown in [1]. Kim, Park, Kim Expires June 2003 [Page 4] Internet Draft Discovery of slave HA's address Dec 2002 3.1.2. New Binding Acknowledgement Message Format The Binding Acknowledgement (BACK) is used to acknowledge receipt of a Binding Update. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Status |Reser'd| Number| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence # | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Addresses of slave HAs (Preference Ordering) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Mobility Options . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Status 8-bit unsigned integer indicating the disposition of the Binding Update. The following Status codes are defined newly or additionally: 0 accepts Binding Update, but will not reply slave home agents' addresses. 1 accepts Binding Update, and will reply slave home agents' addresses. Number The number of slave home agents' addresses. The maximum value is 8. However, this value is usually set by 1 because it might be general that the mobile node selects the most preferred slave home agent's address. Addresses of slave HAs A list of one or a few slave home agents' addresses on the home link for the mobile node. These addresses are ordered according to the preference of slave home agents. Note that the preference of slave home agents are recommended to be configured manually by a system administrator as shown in the existing mechanism [1]. Other Fields Their definitions can be shown in [1]. Kim, Park, Kim Expires June 2003 [Page 5] Internet Draft Discovery of slave HA's address Dec 2002 3.2. Operation Procedure In Mobile IPv6, after deciding to change its primary care-of address, a mobile node sends a Binding Update to its master home agent and receives a Binding Acknowledgment from its home agent in order to register the care-of address. In this time, if the mobile node wants to request a suitable slave home agent's address, the Slave Request (R) bit is set in the Binding Update message. The master home agent node that receives this request message will reply a newly defined Binding Acknowledgment message to the mobile node. Assume the master home agent accepts the Binding Update. In this time, if the master home agent wants to reply one or a few slave home agents' addresses according to the preference, Status code is set by 1 in the Binding Acknowledgment message. Note that the preference of slave home agents are recommended to be configured manually by a system administrator as shown in the existing mechanism [1], which could mean that the preference order will not be varied frequently. The mobile node that receives this reply message checks the Status code firstly. If Status code is 1, the mobile node selects and caches the most preferred slave home agent's address or the one of slave home agents' addresses. As mentioned previously, the mobile node might select and cache usually the most preferred slave home agent's address After then, if the mobile node wants the services of the master home agent beyond the current registration period (the lifetime), the mobile node sends a new Binding Update to it well before the expiration of this period, even if it is not changing its primary care-of address. In this case, the Binding Update/Acknowledgment is operated normally. That is, the Slave Request (R) bit in the Binding Update message must be cleared. However, sometimes, the mobile node may not know the address of a master home agent for it. For example, the master home agent has been broken, or repaired, or reconfigured while the mobile node has been away from home, such that the master home agent has been replaced by a different router serving this role. In this time, the mobile node can acquire the most preferred slave home agent's address which was cached before. The selected slave home agent becomes the new master home agent for the mobile node. Then, the mobile node repeats above procedure. Figure 2 shows the message flow for the proposed mechanism. The proposed mechanism can be equivalent to the existing one according to setting the Slave Request (R) bit or Status code. For example, if the mobile node doesn't want to request a suitable slave home agent's address, the Slave Request (R) bit is cleared in the Binding Update message. In addition, regardless of the Slave Request (R) bit, if the master home agent wants to reply one or a few slave home agents' addresses according to the preference, Status code is set by 0 in the Binding Acknowledgment message. Figure 3 shows the message flow for the proposed mechanism in this case. This means the generality of the proposed mechanism. Kim, Park, Kim Expires June 2003 [Page 6] Internet Draft Discovery of slave HA's address Dec 2002 Master Slave MN HA HAs 1st |--------------BU (R is set)------------->| | BU/BACK | | | |<------------BACK (Status=1)-------------| | | | | Before |--------------BU (normally)------------->| | Expiration| | | |<------------BACK (normally)-------------| | | : | | | : | | Before |--------------BU (normally)------------->| | Expiration| | | |<--------ICMP Error (Unreachable) | | Select | Master HA address| HA |-------------BU (R is set or cleared)------------>| 1st | | BU/BACK |<-----------BACK (Status=1 or Status=0)-----------| Figure 2 : Message flow for proposed mechanism Master Slave MN HA HAs 1st |------------BU (R is cleared)----------->| | BU/BACK | | | |<------------BACK (Status=0)-------------| | | | | Before |--------------BU (normally)------------->| | Expiration| | | |<------------BACK (normally)-------------| | | : | | | : | | Before |--------------BU (normally)------------->| | Expiration| | | |<--------ICMP Error (Unreachable) | | | | | |-------Discovery Request (Anycast)------>| | | | | Select |<--Discovery Reply (all HAs' addresses)--| | HA address| Master | HA 1st |-------------BU (R is set or cleared)------------>| BU/BACK | | |<-----------BACK (Status=1 or Status=0)-----------| Figure 3 : Message flow for proposed mechanism equivalent to existing mechanism Kim, Park, Kim Expires June 2003 [Page 7] Internet Draft Discovery of slave HA's address Dec 2002 4. Advantages The proposed mechanism provides several advantages over the existing mechanism in [1]. The proposed mechanism can omit the Home Agent Address Discovery Request/Reply used in the existing one. This means the proposed mechanism can provide the faster discovery of the slave home agent's address than the existing one. The omission of the Home Agent Address Discovery Request/Reply might reduce amount of traffic when there are many mobile nodes that are now doing binding with the master home agent. In addition, the proposed mechanism requires only one or a few slave home agents' addresses while the existing one requires all slave home agents' addresses. This means the proposed mechanism can be more efficient than the existing one. Moreover, the proposed mechanism can be equivalent to the existing one according to setting bit or status code, which means the generality of the proposed mechanism. 5. References [1] D. Johnson, C. Perkins and J. Arkko, Mobility Support in IPv6, draft-ietf-mobileip-ipv6-19.txt, Oct 2002 [2] D. Johnson and S. Deering. Reserved IPv6 Subnet Anycast Addresses. Request for Comments (Proposed Standard) 2526, Internet Engineering Task Force, March 1999. 6. Authors' Addresses Pyungsoo Kim Samsung Electronics Digital Media R&D Center 416, Maetan-3Dong,Paldal-Gu, Suwon City, Gyeonggi-Do,Korea Phone: +82-31-200-4635 Email:kimps@samsung.com Soohong Daniel Park Samsung Electronics Digital Media R&D Center 416, Maetan-3Dong,Paldal-Gu, Suwon City, Gyeonggi-Do,Korea Phone: +82-31-200-3728 Email:soohong.park@samsung.com Youngkeun Kim Samsung Electronics Digital Media R&D Center 416, Maetan-3Dong,Paldal-Gu, Suwon City, Gyeonggi-Do,Korea Phone: +82-31-200-3772 Email:ykksam@samsung.com Kim, Park, Kim Expires June 2003 [Page 8]