IETF MIPSHOP Working Group Internet Draft Youngjun Park Kyungjoo Suh Document: draft-park-mipshop-nhmds-01.txt Samsung Electronics Expires: July 2004 January 2004 Non-hierarchical MAP Discovery and Selection in HMIPv6 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [i]. 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 memo introduces an alternative dynamic MAP (Mobility Anchor Point) discovery and selection procedure for HMIPv6 (Hierarchical Mobile IPv6). A new dynamic MAP discovery method is defined in order to change the size of MAP domain. Subsequent MAP selection algorithm enables to locate MAP on the closest and highest level of hierarchical structure of routers. Addressed method is beneficial not only for the performance of localized mobility management but also for the location privacy. Also it gives flexible domain designing capability to the operators. Park and Suh Expires - July 2004 [Page 1] MAP discovery and selection in HMIPv6 January 2004 Conventions used in this document 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 [ii]. Table of Contents 1. Introduction...................................................3 2. Overview.......................................................3 2.1. MAP Discovery and Selection...............................3 2.2. MAP Domain Notification...................................3 3. MAP Discovery and Selection....................................5 3.1. MAP Operations............................................5 3.2. Router Operations.........................................7 3.3. Mobile Node Operations....................................8 4. Compatibility Considerations..................................10 Security Considerations..........................................10 References.......................................................10 Author's Addresses...............................................11 Park and Suh Expires - July 2004 [Page 2] MAP discovery and selection in HMIPv6 January 2004 1 Introduction HMIPv6 is suggested to reduce signalling overhead of MIPv6. By introducing a MAP as the local mobility agent, overhead incurred by binding updates to home agent and correspondent node can be decreased. In HMIPv6, a dynamic MAP discovery and a MAP selection are used by mobile nodes to locate MAPs [vi]. Alternative MAP discovery algorithm and MAP selection criteria are introduced in this memo. Suggested MAP discovery algorithm helps finding the closest MAP on the highest level of the hierarchy of routers. In addition, a method to change the boundary of the MAP domain is suggested. 2 Overview In HMIPv6, a mobile node must carry out binding updates to both home agent and correspondent node whenever serving MAP is changed. Binding update to the distant home agent and correspondent node produces packet reception latency and this latency results in the loss of packets from correspondent node. Therefore the performance of HMIPv6 is determined by the time a mobile node can be served by a single MAP continuously. A mobile node can use HMIPv6 when it can locate MAP at the visited network. MAP discovery is the process by which mobile node can find the remote MAP. MAPs and routers are in charge of MAP discovery. Each MAP propagates its MAP option to the neighbor routers and each router distributes received MAP options to other routers. If the domain of each MAP is wider, the less HMIPv6 mobile node changes serving MAP. But at the same time, traffic and computational load of each MAP and local binding signalling latency will increase. Otherwise, MAP has smaller load and mobile node can update local binding quickly, but MAP service discontinuity increases. Two cases have trade-off. The coverage of MAP is determined by the MAP option propagation method. In the dynamic MAP discovery [vi], MAP option is distributed only to the lower level routers. Therefore, MAP domain is bounded to the routers located below the MAP. In this memo, two MAP options are used to achieve adjustable MAP domain; modified MAP option and DOMAIN option. Differs from the original MAP option, proposed MAP options are distributed to the whole subnet even to the higher level routers. MAP domain boundary is determined not by distribution scheme, but by another option message which indicates the highest router of MAP domain. Park and Suh Expires - July 2004 [Page 3] MAP discovery and selection in HMIPv6 January 2004 2.1. MAP Discovery and Selection The basic idea of the proposed method is to introduce the concept of direction to the hierarchy of routers. New value "Upward" is defined to represent the number of times MAP option is delivered from the router located on lower level to the router located on higher level. "Distance" of original MAP option represents the number of times MAP option is delivered from a router to another router. The relative height of MAP to the recipient of MAP option can be calculated by the difference between "Distance" and "Upward". Proposed MAP dynamic discovery method distributes MAP options to the whole subnet. MAP and the intermediate routers forward MAP options to all the neighbor routers. Routers receiving MAP options calculate and modify the value of "Distance" and "Upward". The operation continues until MAP option is delivered to mobile node. Upon reception of MAP option, mobile node must select one MAP to perform local binding update. Basic criterion of proposed MAP selection is to select the closest MAP on the highest level in a given MAP domain. Delivered "Distance" and "Upward" values are used in determining optimal MAP. 2.2. MAP Domain Notification Mobile node requests local binding to particular MAP when it moves in corresponding MAP domain. The MAP domain is a logical area which consists of routers and access routers. To provide adjustable MAP domain, MAP generates and sends DOMAIN option in this memo. DOMAIN option conveys information about the boundary router of MAP domain. When the boundary router receives this option, it limits MAP service up to itself. Park and Suh Expires - July 2004 [Page 4] MAP discovery and selection in HMIPv6 January 2004 3 MAP Discovery and Selection 3.1 MAP Operations 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 | Dist | Pref |R|I|P|V| Upward| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Global IP Address for MAP + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: New MAP option message format 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 | Dist | Level |Resrvd | Upward| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Global IP Address for MAP + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: New DOMAIN option message format Park and Suh Expires - July 2004 [Page 5] MAP discovery and selection in HMIPv6 January 2004 Fields: Upward A 4 bit unsigned integer indicating the number of times MAP option has been forwarded to a higher level router. When a router receives a MAP option sent from the lower level, it increase "Upward" by two before distributing MAP option to other routers. Level A 4 bit unsigned integer indicating the hierarchical level of a router. The router indicated by this value becomes the highest router of new MAP domain. 32-bit zeros This field is used to distinguish DOMAIN option from MAP option. A valid MAP option has non-zero "Valid lifetime" value. When a router receives MAP option whose "Valid lifetime" is zero, such MAP options are considered as DOMAIN option. The basic process of a MAP is similar to that of dynamic MAP discovery method described in HMIPv6 [vi]. MAP serves as the local home agent for mobile nodes in a visited network. To announce essential information for local binding update such as subnet prefix, MAP generates and propagates MAP options in the router advertisement. All MAPs must be configured so that they can send its MAP option onto all the interfaces. No manually configured hierarchical forwarding path is needed. "Distance" field has default initial value one for all MAPs. This field indicates the logical distance between the MAP and mobile node. Thus, "Distance" value increases by one whenever the MAP option passes a router. "Upward" field has default initial value zero for all MAPs. This field indicates the relative height of the mobile node to the MAP in the hierarchy. "Upward" value increases by two whenever the MAP option is delivered upward from the lower level router to the higher level router. "Preference" field may be configured by operators and can be changed by policy or performance based decisions. Definition and usage of other fields including R, I, P, and V flags are identical with the description of HMIPv6. After propagating its MAP option in router advertisement, MAP waits for a mobile node to send local binding update. Upon reception of local binding update, MAP checks validity of remaining lifetime of RCoA provided by the mobile node. If the local binding update is Park and Suh Expires - July 2004 [Page 6] MAP discovery and selection in HMIPv6 January 2004 acceptable, MAP sends binding acknowledgement to the mobile node including type 2 routing header with the RCoA. When a MAP needs to change its domain, it generates and sends DOMAIN option. The differences of DOMAIN option from MAP option are 1) The "Valid lifetime" of MAP option has non-zero value, 2) MAP option is sent periodically, but DOMAIN option is sent only when a MAP changes its domain, and 3) the recipients of MAP option are all the routers and mobile nodes in the subnet, but DOMAIN option targets only the router which located on the highest level of new MAP domain. MAP domain is identified by the router located on highest level of MAP domain. The value "Level" represents the relative height of target router to the MAP. For example, if MAP wants to limit MAP domain to the routers located on two level higher than it, MAP sends DOMAIN option with "Level" = 2. If "Level" = 0, the highest router of MAP domain is MAP itself, so new MAP domain is routers located below the MAP. This domain is identical to the MAP domain of original dynamic MAP discovery. 3.2 Router Operations Upon receiving router advertisement including MAP option, a router inspects the list of MAP options included in the advertisement. The router must check whether newly received MAP option is duplicated one. If "Global IP address for MAP" field of newly received MAP option is identical with the MAP option received before, two MAP options are duplicated. Identical MAP options may have different propagation paths because they are distributed via all the interfaces of all the routers. In this case, two MAP options from same MAP may have different "Distance" or "Upward" values. In addition, "Preference" value may be changes by network operators by the policy or performance reason. Thus duplicated MAP options may have different values. The Router checks if two options have same "Distance", "Upward", and "Preference" values. The router computes the difference between "Distance" and "Upward" for all the duplicated MAP options and accepts the MAP option which has smallest difference. After accepting a unique MAP option for a MAP, the router examines the value of "Valid lifetime" If the value is zero, received MAP option is DOMAIN option. Then the router computes and compares the value of (Upward - Distance + 1) with the value of "Level". If the value of (Upward - Distance + 1) is equal to the value of "Level" the router finds itself the highest router of the MAP domain. From then, when a MAP option from the MAP which sent DOMAIN option, the router forwards MAP option to the routers located on the lower Park and Suh Expires - July 2004 [Page 7] MAP discovery and selection in HMIPv6 January 2004 level. Also the router changes the value of "Preference" to zero and forward MAP option to the routers located on the higher level. Resultantly, when the routers and mobile nodes outside the new MAP domain receive MAP option propagated by this router, they do not request local binding update to the MAP. For all subtraction operations, the values below zero are considered as zero. If the value of (Upward - Distance + 1) is less than the value of "Level" the router forwards DOMAIN options to the neighbor routers. If received option is not a DOMAIN option but a MAP option, router changes the values of "Distance" and "Upward" and retransmits MAP option via all the interfaces. The modifications of these values are classified into three cases: (1) If the MAP option is sent from the routers on the higher levels, then the router must increase "Distance" value by one. (2) If the MAP option is sent from the routers on the lower level, then the router must increase both "Distance" value by one and "Upward" value by two. (3) If the MAP option is sent from the router on the same level, then the router must not modify any value in the MAP option. If the router can not determine the level of router from which MAP option is sent, the received router must not change any value in the MAP option. A router sends MAP option in its router advertisement after it adjusts "Distance" and "Upward" values. 3.3 Mobile Node Operations After moving from an access router to new access router, mobile node listens for router advertisement. If received router advertisement contains information about new access router, mobile node can determine its movement and configures its LCoA by stateless or stateful address autoconfiguration [iii]. If no router advertisement has been received, a mobile node can send router solicitation to new access router in order to invoke router advertisement [v]. Mobile node inspects the MAP option extension included in the router advertisement. First, it checks the value of "Valid lifetime" field. Because DOMAIN option has meaning only to the intermediate routers, mobile node ignores received MAP option if the value is zero. Park and Suh Expires - July 2004 [Page 8] MAP discovery and selection in HMIPv6 January 2004 For MAP options with non-zero "Valid lifetime", if either "Distance" field or "Upward" field of previous MAP has changed, the mobile node determines that it may change MAP. If previous MAP does not exist in the list of MAPs mobile node received, mobile node decides to select new MAP. MAP selection procedure of mobile node has three steps. First, mobile node tries to find the MAP located on the highest level. Second, mobile node tries to find the closest MAP if two or more MAPs are selected in the previous step. Last, mobile node selects possible previous MAP or random MAP in the case more than one MAP are selected in the second step. To find the MAP located on the highest level, mobile node estimates the level of each Map. The level of MAP can be defined as the difference between "Distance" and "Upward" value as described in the section 2. Mobile node arranges MAPs in descendent order of difference and selects the MAP which has largest difference. If two or more MAPs have the largest difference in common, the mobile node arranges these MAPs in ascending order of "Distance". The mobile node selects one has smallest "Distance" value among these MAPs. If more than one MAP still remain as candidates after above two steps, mobile node tries to select the previous MAP where it already has local binding. Selecting previous MAP well meets the context of MAP selection because mobile node should be lazy in releasing existing binding [vi]. But, if previous MAP does not exist in the lists of MAPs, mobile node chooses random MAP from remaining candidates. For all of above cases, mobile node must confirm that "Preference" value of selected MAP is not zero. After selecting new MAP, mobile node must perform local binding update. If selected MAP is previous one, mobile node must perform local binding update to the previous MAP by using new LCoA and old RCoA. Binding update to neither home agent nor correspondent node is needed when previous MAP is reselected. Otherwise, the mobile node must configure new RCoA by using prefix extracted from the MAP option. Mobile node must perform local binding update to the new MAP by using new LCoA and new RCoA. Upon granting binding acknowledgement, mobile node sends binding update to home agent and to correspondent node respectively. Park and Suh Expires - July 2004 [Page 9] MAP discovery and selection in HMIPv6 January 2004 4 Compatibility Considerations The MAP option and addressed in this memo is completely compatible with HMIPv6 mobile node which uses original dynamic MAP discovery and selection. The "Upward" field is the last four bits of fourth octet and these bits are defined as "Reserved" in HMIPv6 [vi]. Other fields have the same meaning and value with those of the MAP option used in dynamic MAP discovery. DOMAIN option is not defined to be passed to mobile node. But all zero-valued "Valid lifetime" of DOMAIN option makes mobile node ignore the option when mobile node receives DOMAIN option . When a HMIPv6 mobile node gains a connection to new access router, it will eventually receive the MAP option described in the section 3.1. If the mobile node is not capable of MAP selection described in the section 3.3, it can select the MAP as defined in dynamic MAP discovery and operate with appropriate MAP. Security Considerations A strong authentication is needed between MAPs and mobile nodes especially when mobile nodes have local bindings to remote MAPs. Detailed security problems will be considered in the next version of this memo. References [i] S. Brandner, "The Internet Standards Process - Revision 3", RFC 2026. [ii] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [iii] S. Thomson and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462. [iv] T. Narten, E. Nordmark and W. Simpson, "Neighbor Discovery for IP Version 6",RFC 2461. [v] D. Johnson, C. Perkins and J. Arkko, "Mobility Support in IPv6", draft-ietf-mobileip-ipv6-24. Park and Suh Expires - July 2004 [Page 10] MAP discovery and selection in HMIPv6 January 2004 [vi] H. Soliman, C. Castelluccia, K. El-Malki and L. Bellier, "Hierarchical Mobile IPv6 mobility management", draft-ietf- mobileip-hmipv6-08. (work in progress) Author's Addresses Questions about this memo can be directed to: Youngjun Park Samsung Electronics Co., Ltd. Dong Suwon P.O.BOX 105 416 Maetan-3Dong, Youngtong-Gu, Suwon-City, Gyeonggi-Do, Korea, 442-600 Email: youngjun74.park@samsung.com Kyungjoo Suh Email: joo.suh@samsung.com Park and Suh Expires - July 2004 [Page 11]