NEMO Working Group H. Cho Internet-Draft E. K. Paik Expires: July 13, 2004 Seoul National University January 13, 2004 Hierarchical Mobile Router Advertisement for nested mobile networks 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. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document describes needs for hierarchical mobile router advertisement for nested mobile networks. When ingress and egress interfaces of a Mobile Router are both wireless, the MR cannot distinguish the Router Advertisement of the parent MR from the RA of the child MR. To maintain hierarchical information of wireless nested mobile networks, RA message needs to be extended to deliver additional information for hierarchy. Cho, Paik July 13, 2004 [Page 1] INTERNET-DRAFT Hierarchical Mobile Router Advertisement Jan. 13, 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terms and Abbreviations. . . . . . . . . . . . . . . . . . . 3 3. Router Advertisement (RA) Confliction problem .br in nested mobile networks. . . . . . . . . . . . . . . . . 3 4. Hierarchical Mobile Router Advertisement (HMRA). . . . . . . 4 4.1. Router Advertisement Message Format. . . . . . . . . . . . 4 4.2. Hierarchy management . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations. . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 References. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction This document proposes the Router Advertisement mechanism called Hierarchical Mobile Router Advertisement (HMRA) for nested mobile networks. Mobile network is a network that the entire network moves as a single unit and includes one or more mobile routers (MRs) that connect it to the global Internet [1]. Mobile routers use Mobile IPv6 protocol to broadcast Router Advertisement message. Mobile Network Nodes (MNNs) under an MR can configure their address and know the connectivity to the MR by listening the RA. Personal Area Network (PAN) and Vehicle Area Network (VAN) connected to the Internet are examples of mobile network. Furthermore, PANs in a vehicle are also possible and this situation is referred to as a nested mobile network. Nested mobile networks contain MRs that are not directly attached to the Internet (i.e. connected to the Internet via another MR). In the case of nested mobile network, MRs also use Mobile IPv6 RA mechanism. MRs have ingress and egress interfaces, and each interface can be wired or wireless. If an MR uses wired ingress interface, the RA of the MR is delivered to only nodes connected by wire. But if an MR uses wireless ingress interfaces, all nodes in its coverage receive the RA of the MR. So when a parent MR has wireless egress interface and a child MR has wireless egress interface, the parent MR can listen to the RA of the child MR. This situation is called "RA Confliction". Cho, Paik July 13, 2004 [Page 2] INTERNET-DRAFT Hierarchical Mobile Router Advertisement Jan. 13, 2004 2. Terms and Abbreviations Age Age is defined as decreasing value by the distance from AR. Visiting Mobile Node (VMN) A mobile node (MN), either a host or a router who can move topologically with respect to the MR and whose home link doesn't belong to the mobile network. A VMN that gets attached to a foreign link within the mobile network obtains an address on that link. [2] 3. Router Advertisement (RA) Confliction problem When egress and ingress interfaces of an MR are both wireless, nested mobile networks have Router Advertisement (RA) confliction problem. When MRs form nested mobile networks, an MR receives RA of the child MR as well as the parent MR for the open characteristics of wireless interface. But the MR cannot distinguish which MR is its parent. Figure 1 shows the RA confliction problem. With existing RA scheme [3], MR2 receives both RAs of MR1 and MR3. So MR2 may think it is under MR3. And in this situation if MR2 wants to send data to the outside of mobile network, the packets cannot be routed correctly. +-----+ | AR | Age = max_age max_age max_age max_age +-----+ | +-----+ | MR1 | Age = 0 max_age-1 max_age-1 max_age-1 +-----+ | +-----+ | MR2 | Age = 0 0 max_age-2 max_age-2 +-----+ | +-----+ | MR3 | Age = 0 0 0 max_age-3 +-----+ Figure 1. RA Confliction problem RA confliction problem occurs since MRs and ARs broadcast RA messages simultaneously. Thus, additional information is needed in RA message for the management of hierarchy between MRs. Cho, Paik July 13, 2004 [Page 3] INTERNET-DRAFT Hierarchical Mobile Router Advertisement Jan. 13, 2004 4. Hierarchical Mobile Router Advertisement (HMRA) To solve the RA confliction problem of nested mobile networks this document proposes hierarchical architecture of RA, HMRA. HMRA is based on the information of hierarchy. For the purpose of hierarchical management, we employ a field for age in the RA message. Initially Access Router (AR) has age of maximum value and MRs have age of zero. The maximum value of age means the maximum depth of hierarchy. When an MR receives an RA with an age value, the MR compares received age with its own age. So if the received age is less than or equal to its own age, the MR just ignores the RA. And if received age is bigger than its own age, the MR sets its own age to smaller age than the received age by one. So each MR can construct the parent-child relationship by using this age information. When an MR moved to other network, we can know the movement by the change of Care-of Address (CoA). So whenever an MR changes its point of attachment, the MR re-initializes its age to zero and re- calculates its age again using new RA. 4.1. Router Advertisement Message Format Figure 2 shows the RA message format with age field. 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 | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cur Hop Limit |M|O| Age |Rsvd | Router Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reachable Time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Retrans Timer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+- Figure 2. Router Advertisement message with "Age" field ICMP Fields: Type 134 Code 0 Checksum The ICMP checksum. See [4]. Cho, Paik July 13, 2004 [Page 4] INTERNET-DRAFT Hierarchical Mobile Router Advertisement Jan. 13, 2004 Cur Hop Limit 8-bit unsigned integer. The default value that should be placed in the Hop Count field of the IP header for outgoing IP packets. A value of zero means unspecified (by this router). M 1-bit "Managed address configuration" flag. When set, hosts use the administered (stateful) protocol for address autoconfiguration in addition to any addresses autoconfigured using stateless address autoconfiguration. The use of this flag is described in [5]. O 1-bit "Other stateful configuration" flag. When set, hosts use the administered (stateful) protocol for autoconfiguration of other (non-address) information. The use of this flag is described in [5]. Age 3-bit "Age" field for HMRA. Initially Access Router has age of maximum value and MRs have age of zero. Rsvd A 3-bit unused field. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. Router Lifetime 16-bit unsigned integer. The lifetime associated with the default router in units of seconds. The maximum value corresponds to 18.2 hours. A Lifetime of 0 indicates that the router is not a default router and SHOULD NOT appear on the default router list. Reachable Time 32-bit unsigned integer. The time, in milliseconds, that a node assumes a neighbor is reachable after having received a reachability confirmation. A value of zero means unspecified (by this router). Retrans Timer 32-bit unsigned integer. The time, in milliseconds, between retransmitted Neighbor Solicitation messages. A value of zero means unspecified (by this router). 4.2. Hierarchy management When an MR moves to the same level of other nested mobile network, the MR sets its age to zero and listens RA from neighbor MRs. If Cho, Paik July 13, 2004 [Page 5] INTERNET-DRAFT Hierarchical Mobile Router Advertisement Jan. 13, 2004 the MR receives RA from the child MR before it receives from the parent MR, the MR thinks that the child MR is the parent. But after the MR receives RA of the parent MR, the MR corrects its age. When an N-level MR moves to an (N-1)-level mobile network, the MR receives bigger or the same age of RA from neighbor MRs. In this case re-initializing of age is not necessary. The MR just ignores the RA of the same age and accepts the RA of bigger age and set its age to smaller age than received age by one. When an N-level MR moves to an (N+1)-level mobile network, the MR sets its age to zero and listens to RA from the neighbor MRs. The next procedures are the same as the two cases above. 5. Security Considerations When a malicious MR broadcast RA with the maximum age, hierarchy of nested mobile network can be confused. 6. Acknowledgements This work was supported in part by the Brain Korea 21 project of the Ministry of Education, and in part by the National Research Laboratory project of the Ministry of Science and Technology, Korea. The authors would like to thank people who have given valuable comments on various nested mobile network issues on the mailing list. References [1] Vijay Devarapalli, Ryuji Wakikawa, Alexandru Petrescu, and Pascal Thubert, "Nemo Basic Support Protocol", draft-ietf-nemo-basic-support-01.txt, September 2003, work in progress. [2] Thierry Ernst, and Hong-Yon Lach, "Network Mobility Support Terminology", draft-ietf-nemo-terminology-00.txt, May 2003, work in progress. [3] T. Narten, E. Nordmark, and W. Simpson, "Neighbor Discovery for IP Version 6", RFC2461, December 1998. [4] Conta, A. and S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", Cho, Paik July 13, 2004 [Page 6] INTERNET-DRAFT Hierarchical Mobile Router Advertisement Jan. 13, 2004 RFC 2463, December 1998. [5] Thomson, S. and T. Narten, "IPv6 Address Autoconfiguration", RFC 2462, December 1998. Authors' Addresses Hosik Cho Multimedia and Computer Communications Lab. Seoul National University ENG4190, School of Electronic Engineering and Computer Science Seoul National University Seoul 151-744, Korea Phone: +82 2 880 1832 Fax: +82 2 872 2045 EMail: hscho@mmlab.snu.ac.kr Eun Kyoung Paik Multimedia and Computer Communications Lab. Seoul National University ENG4190, School of Electronic Engineering and Computer Science Seoul National University Seoul 151-744, Korea Phone: +82 2 880 1832 Fax: +82 2 872 2045 EMail: eun@mmlab.snu.ac.kr Cho, Paik July 13, 2004 [Page 7]