INTERNET DRAFT Yong-Geun Hong Expires: May 2002 Yong-Jin Kim ETRI Min-Tae Hwang Changwon Nat'l Univ. November 2001 Autoconfiguration of IPv4 Link-Local Addresses in Multilink 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 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 This document describes a RPM(Router Proxy for Multilink) protocol for proxy DAD(Duplication Address Detection) and proxy ARP(Address Resolution Protocol)in multilink networks using IPv4 link-local addresses. Herein we consider the multilink network dangled to a single router as a single subnet, not as multiple subnets. Each host generates an IPv4 link-local address automatically and checks its duplication using DAD procedure. To check the address duplication over all links the gateway router uses the proxy DAD function. The router searches for link-local address lookup table whether the desired address is already in use in the other links. The router received an ARP request broadcasts messages as a proxy DAD. During the proxy DAD function, the link-local address lookup table is made. Also the router uses the proxy ARP function to support the inter link communication. The proxy ARP in the router replies to the request after looking up the lookup table and broadcasts an ARP request packet only to the link that the receiver host is located in for address resolution. Hong, Kim, Hwang Expires May 2002 [Page 1] INTERNET-DRAFT RPM(Router Proxy for Multilink) November 2001 Table of Contents: 1. Introduction 2. Example of Multilink Network 3. Operations of RPM(Router Proxy for Multilink) Protocol 3.1 Selecting an IPv4 Link-Local Address 3.2 Duplicate Address Detection over Multilink 3.3 Finding Router's Link-Local Address 3.4 Intra Link Communication 3.5 Inter Link Communication 4. Other Considerations References 1. Introduction It is possible for home networks to include multiple links. This issue can arise, for example, in the case of a home network supporting IEEE 802.11 wireless as well as IEEE 1394 and Ethernet. In multilink small networks connected by a single router, it is desirable for the people to be able to use IP application software without the inconvenience of having to manually configure static IP addresses or set up a DHCP server. Therefore the use of zero configuration address is especially valuable in environments where no other configuration mechanism is available. In this document we describe a RPM(Router Proxy for Multilink) protocol for proxy DAD and proxy ARP in multilink networks using IPv4 link-local addresses. Hosts in multilink network automatically configure their interfaces with an IPv4 link-local addresses in the 169.254/16 range[1]. It will be desirable to consider the multilink networks connected by a single router as a single subnet, not as multiple subnets. Therefore we extend the normal DAD procedure[1] to prove the uniqueness of their own link-local address to the whole links, not confining to a single link. To check the address duplication over all links the gateway router uses the proxy DAD function. The router searches for link-local address lookup table whether the desired address is already in use in the other links. The router received an ARP request broadcasts messages as a proxy DAD. During the proxy DAD function, the link-local address lookup table is made. Also we describe the inter link communication using IPv4 link-local address with the help of a router's ARP proxy. The proxy ARP in the router replies to the request after looking up the lookup table and broadcasts an ARP request packet only to the link that the receiver host is located in for address resolution. Hong, Kim, Hwang Expires May 2002 [Page 2] INTERNET-DRAFT RPM(Router Proxy for Multilink) November 2001 2. Example of Multilink Network Figure 1 shows an example of multilink network model. OUTSIDE : Multilink Host-A Host-B : network | | : +---+-----------+----- USB : | : +--------+ | Host-C Host-D : | |---+ | | ------+ Router |==========+====+=====+=== Ethernet : | |**** | : +--------+ * Host-E : * : ****+***********+***** IEEE1394 : | | : Host-F Host-G : Figure 1 Example of Multilink Network Several home networking technologies, such as HomePNA(Home Phoneline Networking Alliances), IEEE 802.11 wireless LAN, IrDA, PLC(Powerline Communication), etc., are possible to be connected to the router. The router helps the inter link communication. 3. Operations of RPM(Router Proxy for Multilink) Protocol The RPM protocol uses some proxy functions in the router, such as a proxy DAD to support the DAD procedure over multiple links and a proxy ARP to support the inter link communication, in order to emulate the multilink network as a single subnet to obey the non-forwarding rule. The non-forwarding rule means that hosts may assume that all 169.254/16 destination addresses are on-link and directly reachable. 3.1 Selecting an IPv4 Link-Local Address The selection, defense and delivery of IPv4 link-local address within a link can be borrowed from the document[1]. When a host wishes to configure a link-local address, it selects an address using a random (or pseudo-random) number generator with a uniform distribution in the range from 169.254.1.0 to 169.254.254.255. Hong, Kim, Hwang Expires May 2002 [Page 3] INTERNET-DRAFT RPM(Router Proxy for Multilink) November 2001 3.2 Duplicate Address Detection over Multilink In order to probe the uniqueness of the selected address, the host broadcasts an ARP request for the desired address. On a network such as Ethernet that supports ARP, address collision detection is done using ARP probe[1]. When the link-local address is already in use in the same link, the reply message notifies the address confliction. Then the host tries again to generate another link-local address. To check address collision over all links, the router searches for the link-local address lookup table whether the desired address is already in use in the other links. The router received an ARP request may broadcast messages to each attached link in the multilink, except one from which the ARP request was just received. So the router acts as a proxy DAD. If the link-local address is already in use in the other link, the router send a reply message to the originating host of the ARP request. Then the originating host knows it and tries again to generate another link-local address. If not, the originating host may use the desired address. In this case the router adds the link local address to the link-local address lookup table in the appropriate entry. The router creates and maintains the link-local address lookup table. Figure 2 shows an example of link-local address lookup table. +---------------+---------------+---------------+ | Link 1 | Link 2 | Link 3 | +---------------+---------------+---------------+ | 169.254.1.11 | 169.254.3.234 | 169.254.2.123 | +---------------+---------------+---------------+ | 169.254.2.151 | 169.254.9.8 | 169.254.1.5 | +---------------+---------------+---------------+ | : | 169.254.2.111 | : | + +---------------+ + | | : | | +---------------+---------------+---------------+ Figure 2. Example of Link-Local Address Lookup Table 3.3 Finding Router's Link-Local Address At a multilink network, the router has multiple interfaces and each interface has a unique link-local address. The host which wants to know the router's link-local address generates a RS(Router Solicitation) message. And the router sends a reply message to the originating host. Hong, Kim, Hwang Expires May 2002 [Page 4] INTERNET-DRAFT RPM(Router Proxy for Multilink) November 2001 Then the host gets the router's link-local address. Also, a router may send RA(Router Advertisement) messages periodically through each interface. The hosts received this RA message know the router's link-local address. 3.4 Intra Link Communication We don't describe this operation in this document. See [1]. 3.5 Inter Link Communication In the multilink network environment, the link layer address used in one link is different from that of the other links, when the implementation technologies(e.g. USB, IEEE 1394, Ethernet) are different each other. Therefore the inter link communication by using ARP broadcasting for address resolution is not possible. We describe the proxy ARP in the router to support the inter link communication. A host which wants to communicate with the hosts on the other links broadcasts an ARP request on the same link. In this case the proxy ARP in the router replies to the request after looking up the lookup table when the receiver's link-local address is in the table. Then the originating host knows the receiver's link layer address, herein the router's link layer address, and sends a packet to the router. The router broadcasts an ARP request packet only to the link that the receiver host is located in for address resolution. Then the receiver replies its link layer address to the router and the router sends the received packet to the receiver host. Figure 3 shows a procedure of inter link communication. Sender host Router Receiver host | :: | | ARP request :: | |-------------------------->:: | | Lookup Table | | ARP reply :: ARP request | |<--------------------------::------------------------->| | :: ARP reply | | IP packet send ::<-------------------------| |-------------------------->:: ARP request(optional) | | ::------------------------->| | :: ARP reply(optional) | | ::<-------------------------| | :: IP packet send | | ::------------------------->| | Link 1 :: Link 2 | Figure 3 Procedure of inter link communication Hong, Kim, Hwang Expires May 2002 [Page 5] INTERNET-DRAFT RPM(Router Proxy for Multilink) November 2001 4. Other Considerations The router must dynamically update the link-local address lookup table when a host is down or going up. To consider a multilink network in IPv6, see [2]. The security condition between links is not concerned in this document. References [1] Stuart Cheshire, "Dynamic Configuration of IPv4 Link-Local Addresses", , 2001. [2] Dave Thaler, "Multi-link Subnets Support in IPv6", , 2001. Authors Addresses Yong-Geun Hong, Yong-Jin Kim ETRI PEC 161 Gajeong-Dong, Yuseong-Gu, Daejon 305-350, Korea Tel : +82 42 860 6557 Fax : +82 42 861 5404 E-mail : {yghong, yjkim}@pec.etri.re.kr Min-Tae Hwang Changwon National University 9 Sarim-Dong, Changwon, 641-773, Korea Tel : +82 55 279 7632 Fax : +82 55 279 7639 E-mail : mthwang@sarim.changwon.ac.kr Hong, Kim, Hwang Expires January 2002 [Page 6]