INTERNET DRAFT Yong-Geun Hong Expires: January 2002 Jung-soo Park Min-kyo In Yong-jin Kim ETRI July 2001 Multicast Address Allocation using IPv4 Link-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 In this document, we describe a method by which a host automatically allocates multicast addresses using IPv4 link local address without any address allocation server. These multicast addresses do not collide with other multicast addresses in a local scope. Table of Contents: 1. Introduction 2. IPv4 Multicast Address Allocation 2.1 The IPv4 Local Scope Multicast Address 2.2 Multicast Address Generation using IPv4 Link-local Address 3 Consideration of Variable Network 3.1 Intra-domain Network 3.2 Inter-domain Network Hong, Park, In, Kim Expires January 2002 [Page 1] INTERNET-DRAFTMulticast Address Allocation using IPv4 Link-local AddressJuly 2001 3.3 Consideration for Joining to a Global Network 4. Limitations References 1. Introduction IPv4 addresses in the 169.254/16 ranges are used for link-local communication. These are valuable in networking where no other configuration and administration is available. We call this networking Zero configuration networking. The zero configuration network don't need any centralized administration. Networks where zeroconf protocols apply can include (but are not limited to) environments where no DHCP, MADCAP, or DNS servers are present. There are two methods for allocating an IP multicast address. Firstly, it can be allocated by using a multicast address allocation server. Secondly, it can be allocated without the server. The former allocates a hierarchical multicast address by using a MAAs server, or MADCAP server to guarantee the global uniqueness of the allocated address. The latter is a method where a host chooses a multicast address by its own way in the well-known multicast address range, and then checks the duplication of the address. In this document, we deal with the latter case that servers do not exist. While the latter method has the advantage of no need to use any server, it can cause a significant address resolution delay and increased traffic. In this document, we will describe multicast address allocation method without the delay and increased traffic within a local scope network. 2. IPv4 Multicast Address Allocation Typically, an IP address is used to identify a node within a network. A port number is used to identify a data stream between endpoints. Therefore, the host address and port number can be used as an identifier that differentiates sessions in a specific area. 2.1 The IPv4 Local Scope Multicast Address Originally the address space 239.255.0.0/16 was defined as being Hong, Park, In, Kim Expires January 2002 [Page 2] INTERNET-DRAFTMulticast Address Allocation using IPv4 Link-local AddressJuly 2001 used in the IPv4 local scope multicast address, and that expanded to the reserved ranges of 239.254.0.0/16 and 239.253.0.0/16. If the demand of IPv4 local multicast scope is increased, the local multicast scope will be further extended. In this document, we consider two important issues. The first one is keeping the status of IP multicast address allocation. The second one is that the packet with a multicast address specified in local scope should not forward to outside networks. So we must define the routing policy at the border router such as "Administratively Scoped IP Multicast"[1]. With this routing policy, we can easily deal with the situations such as inter-domain networking and joining to a global network. 2.2 Multicast Address Generation using IPv4 Link-local Address In this document, a multicast address in the local scope is made from the combination of IPv4 link-local address (169.254.x.x) and multicast address prefix. The multicast address consists of two upper octets of an IPv4 local scope multicast address and two lower octets of a link-local address, as shown in figure 1. Host IP Address (link-local address) Port number +-------------+ +------+ |169.254.c.d | | u.v | +-------------+ +------+ | | | | V V +------------------------------------------------------+ | +--------------+ (1) +---------+ (2) | | | 239.255.c.d | | | | | | 239.254.c.d | | (u.v) | | | | 239.253.c.d | | | | | +--------------+ +---------+ | +------------------------------------------------------+ Multicast Address subspace port number Figure 1: Extended multicast address subspace formation using IPv4 link-local address To make a multicast address in local scope, two upper octets are selected among [239.255/16, 239.254/16, 239.253/16] according to the above definition and two lower octets are generated by the copy the two lower octets of link-local address. Until now, the number of available multicast address is 3, and if Hong, Park, In, Kim Expires January 2002 [Page 3] INTERNET-DRAFTMulticast Address Allocation using IPv4 Link-local AddressJuly 2001 the local multicast scope is extended, the number of available multicast addresses is also increased. Keeping the status of address allocation has some advantages, e.g., when a multicast address is needed, it can choose unique one without any bothersome jobs. And we can use two octets port number of link-local address to identify a multicast session address. The link-local address that is used for multicast address is unique in local scope by the mechanism of address collision detection [2]. So the generated multicast address is also unique in the local scope. We don't have to worry about the collision of the multicast address to other hosts. Within a host, it solves the collision of multicast address by keeping the status of address allocatioion. For example, let us assume a host has an IP address of 169.254.190.121, and it can choose individual multicast addresses of 239.255.190.121, 239.254.190.121 and 239.253.190.121. Also, it can choose two octets-port numbers to identify the endpoint of the session. These three multicast address spaces with port numbers are unique in the local scope. 3 Consideration of Variable Network 3.1 Intra-domain Network All nodes in an Intra-domain network must perform DAD (Duplicate Address Detection) procedure. Throughout the DAD procedure, a host can guarantee the uniqueness of the address in the local scope. For example in figure 2. The hosts A, B and C receive packets that have the multicast address 'a', and hosts C, D and E receive packets of the multicast address 'e'. Host C can receive packets of multicast address 'a' and 'e' concurrently. In the case, there is no collision of multicast addresses and host C is not confused. A B C D E | | | | | | | | | | |(a) |(a) |(a,e) |(e) |(e) ------+-----------+----------+---------+--------+--- Network Address 169.254.x.x Figure 2: Intra-domain Network Hong, Park, In, Kim Expires January 2002 [Page 4] INTERNET-DRAFTMulticast Address Allocation using IPv4 Link-local AddressJuly 2001 3.2 Inter-domain Network The IPv4 local scope multicast address can only be used in a local area and cannot be forwarded to external networks by the routing policy at the boarder router. If two isolated domains meet together and form an inter-domain network, the packet should not be delivered to neighbor domain. So, even though two multicast addresses generated at each domain are the same, that causes no problem because of the limited delivery. The inter-domain issue is out of scope. 3.3 Consideration for Joining to a Global Network The multicast address, which is allocated by the proposed scheme, would be recommended to use in the isolated network. But it is possible for the isolated network to join to a global network with connection to a public network. At that time the proposed scheme don't have any problems because the multicast address, which has a local scope, is not allowed to be forwarded to the external network through the border router. 4. Limitations In this paper, we only deal with link-local range. Thus, global range is out of scope of this document. To provide multicast services through the Internet, MAAs and MADCAP servers can be used. References [1] D. Meyer. "Administratively Scoped IP Multicast", [RFC 2365], Jul. 1998. [2] Stuart Cheshire, Apple Computer, Bernard Aboba and Mircrosoft, "draft-ietf-zeroconf-IPv4-linklocal-03.txt", Mar. 2001 Authors Addresses Yung-geun Hong Hong, Park, In, Kim Expires January 2002 [Page 5] INTERNET-DRAFTMulticast Address Allocation using IPv4 Link-local AddressJuly 2001 ETRI PEC 161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea Tel : +82 42 860 6557 Fax : +82 42 861 5404 E-mail : yghong@etri.re.kr 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 : pjs@etri.re.kr Min-kyo In ETRI PEC 161 Kajong-Dong, Yusong-Gu, Taejon 305-600, Korea Tel : +82 42 860 6489 Fax : +82 42 861 5404 E-mail : mkin@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 : kimyj@etri.re.kr Hong, Park, In, Kim Expires January 2002 [Page 6]