INTERNET DRAFT Jung-Soo Park Expires: January 2002 Yong-Jin Kim ETRI Sung-Woo Park Hannam University July 2001 Stateless address autoconfiguration in Mobile Ad Hoc Networks using site-local address 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 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 obsolete by other documents at anytime. 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 The concept of IPv6 stateless address autoconfiguration (SAA) lends itself easily to a mobile ad hoc network where no administrative configurations are available. However, the SAA designed to operate on a single link is not directly applicable to the mobile ad hoc network with multi-hop paths. In this document, we extend the current SAA to overcome this limitation by using the IPv6 site- local address. Table of Contents: 1. Introduction 2. Scope of Work 3. Protocol Overview 3.1 Address Generation 3.2 DAD JPark, Kim, SPark Expires January 2002 [Page 1] INTERNET-DRAFTUse of Site-Local Address in Mobile Ad Hoc Networks July 2001 4. Security Considerations References 1. Introduction A mobile ad hoc network is a network that is built on the fly without any pre-established infrastructure. For a node to participate in communication over the network, the first thing to do is to obtain an IP address. However, since there exists no centralized administration in the mobile ad hoc network, each node has to be configured on its own. IPv6 enables a node to autoconfigure itself with an IP address in two different ways: stateful or stateless. The stateless address autoconfiguration (SAA) provides a useful way to assign IP addresses to nodes in the network with no configuration servers. In the SAA [1], each node generates a link-local address and performs the duplicate address detection (DAD) to verify the uniqueness of that address. The DAD is based on the Neighbor Discovery Protocol (NDP) [2] in which messages are exchanged only among neighbors. That is, all the messages used in NDP are link-local scoped. We find it difficult to apply the SAA directly in the mobile ad hoc network due to the mismatch between the address scope and the network topology. A mobile ad hoc network typically consists of mobile nodes connected by wireless links. Each node is conceived as a host-enabled router and forwards datagrams at the IP layer. Depending on the transmission range of wireless links, a communication path may span more than a single hop. In this case, using link-local addresses will violate the definition of the term "link-local" by which the transmission of datagrams must be confined to a single link. Fortunately, IPv6 defines another level of the local-scoped address called the "site-local" address. IP datagrams with the site-local scope could reach anywhere inside a site without putting any restrictions on the intermediate nodes. Even though there has been no rigorous definition yet about the site, we see that the area covered by the mobile ad hoc network usually fits well with that of the site. Accordingly, it would be appropriate to use the site- local address to deliver IP datagrams along the multi-hop paths within the mobile ad hoc network (site). The accompanied DAD also needs to be consistent with the multi-hop environments. 2. Scope of Work JPark, Kim, SPark Expires January 2002 [Page 2] INTERNET-DRAFTUse of Site-Local Address in Mobile Ad Hoc Networks July 2001 A mobile ad hoc network may or may not connect to the external IP- based networks such as Internet. This document deals with the situation where the mobile ad hoc network operates in isolation from the outside world. Connecting to the Internet needs further study and is currently out of scope in this document. From the topology point of view, one of main features of the mobile ad hoc network is the dynamically changing connectivity. This happens due to either the unreliable wireless channels or the node mobility. Some nodes can be occasionally disconnected from the rest of the network and re-connected after a while. Recovering from this type of network partitioning may require additional procedures but is out of scope in this document. 3. Protocol Overview 3.1 Address Generation By the assumption of the isolated operation, we allow each node to generate a local-scoped address and use it inside the mobile ad hoc network. In IPv6, there are two types of local-scoped addresses: link- local and site-local. Since we would like to view the mobile ad hoc network as a single site, the use of site-local addresses is preferred. As specified in [3], a site-local address is composed of four fields: 10-bit site-local format prefix (FEC0::/10), 38-bit all zeros, 16-bit subnet ID, and 64-bit interface ID. The first 48 bits are fixed and the interface ID is determined by the link layer address. To construct a complete site-local address, each node randomly generates its own subnet ID within a permissible range. By doing this, every node may have different subnet ID from each other. As a matter of fact, the subnet ID makes no sense since it does not offer any type of route aggregation. Thus, the subnet ID is simply considered as the extension of interface ID and can be renumbered later by the gateway when connected to the Internet. Recently, there have been some arguments for treating the mobile ad hoc network as a single subnet. This makes it easy to connect to the Internet via route aggregation, but forces each node to forward datagrams below the IP level. In this case, the well-known subnet ID can be defined and used by nodes. 3.2 DAD Once a site-local address has been generated, its uniqueness must JPark, Kim, SPark Expires January 2002 [Page 3] INTERNET-DRAFTUse of Site-Local Address in Mobile Ad Hoc Networks July 2001 be checked out before being assigned to the interface. DAD is such a procedure that detects the duplicate addresses that might be present in the network. The DAD can be done with the aid of the underlying routing protocol. A lot of different routing protocols are being considered for implementation in the mobile ad hoc network. We believe that it would be better to have the DAD independent from the variety of the routing protocols. Alternatively, the DAD may utilize the existing NDP as in [1]. The DAD is performed via two NDP messages: Neighbor Solicitation (NS) and Neighbor Advertisement (NA). Recall that all the IP addresses used in NDP messages are link-local scoped. On the other hand, the mobile ad hoc network requires the NS/NA messages be broadcast to all network nodes along the multi-hop path. One possible way to do this is to have each node forward selectively the DAD-related messages even though those messages are link-local scoped. However, rather than apply different forwarding rules to messages with the link-local scope, we modify the address scope of the current NS/NA messages for DAD in the mobile ad hoc network. If needed, new types of ICMP messages can be defined for the same purpose. With NS messages, the destination IP address of the NS message must be changed as follows. First, the address scope is changed from link-local to site-local. Next, instead of using solicited-node multicast address, all nodes multicast address is used. This prevents some nodes more than one hop away from missing NS messages. The resulting destination IP address of the NS message will be the well-known site-local all nodes multicast address (FF05::1). Considering that each node acts as a router, the site- local all routers multicast address (FF05::2) may be also used. In the current SAA, NA messages are already broadcast to all nodes. We only need to change the scope of the destination IP address from link- local to site-local. With no doubt, the NS/NA messages may be excessively flooded over the site due to the transmission characteristics of wireless links. Some mechanisms must be prepared to avoid this kind of broadcast storm problems. Each node can maintain a cache entry that keeps the addresses for which NS/NA messages has been sent. The broadcast identifier can be used to discard the redundant NS/NA messages. 4. Security Considerations TBD. References JPark, Kim, SPark Expires January 2002 [Page 4] INTERNET-DRAFTUse of Site-Local Address in Mobile Ad Hoc Networks July 2001 [1] S. Thomson and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC2462, December 1998. [2] T. Narten, El. Nordmark and W. Simpson, "Neighbor Discovery for IP version 6 (IPv6), RFC2461, December 1998. [3] R. Hinden and S. Deering, "IP version 6 Addressing Architecture", RFC2373, July 1998. Authors Addresses Jung-Soo Park ETRI PEC 161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea Tel: +82 42 860 6514 Fax: +82 42 861 5404 E-mail: jspark@pec.etri.re.kr Yong-Jin Kim ETRI PEC 161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea Tel: +82 42 860 6564 Fax: +82 42 861 5404 E-mail: yjkim@pec.etri.re.kr Sung-Woo Park Dept. of Information and Communication Eng. Hannam University 133 Ojung-Dong, Daeduk-Gu, Taejon 306-791, Korea Tel: +82 42 639 7398 Fax: +82 42 629 7843 E-mail: swpark@eve.hannam.ac.kr JPark, Kim, SPark Expires January 2002 [Page 5]