6man Working Group Yu hua bing Internet-Draft Ruijie Networks, China Intended status: Standards Track Expiration: August 28, 2011 February 28, 2011 IPv6 Stateless Address Autoconfiguration With Prefixes Longer Than 64 draft-yhb-6man-slaac-improvement-00 Abstract IPv6 stateless address autoconfiguration described by RFC4862 only supports 64-bit prefixes. This approach can't be deployed in the sites with prefixes longer than 64. We have no right to require that the sites MUST use 64-bit prefixes. This document tries to implement stateless address autoconfiguration with prefixes longer than 64. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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Yu hua bing Expires August 2011 [Page 1] Internet-Draft IPv6 Stateless Address Autoconfiguration February 2011 Table of Contents 1. Introduction ....................................................2 2. Protocol Specification ..........................................2 2.1. Router Advertisement Processing ............................2 2.2. ISATAP Tunnel ..............................................4 2.3. Analysis of Duplicate Address Possiblity ...................4 3. References ......................................................5 3.1. Normative References .......................................5 3.2. Informative References .....................................5 1. Introduction The IPv6 stateless address autoconfiguration described by RFC4862 requires no manual configuration of hosts and no additional servers, so it is welcomed by a lot of users. But it has a detect that some users complain about: The sum of the prefix length and interface identifier length MUST equal 128 bits. RFC4291 specifies that for all unicast addresses, except those that start with the binary value 000, Interface IDs are required to be 64 bits long. It means the prefix length MUST be 64, and this approach can't be deployed in the sites with prefixes longer than 64. A 64-bit prefix can generate at most 2^64 IPv6 addresses. In fact, any LAN can't run out of so many IPv6 addresses, and only a very small part of IPv6 addresses are used, so it is a serious waste. Some sites do not need 64-bit prefixes. We have no right to require that the sites MUST use 64-bit prefixes. If the prefix of the site is longer than 64, or if the prefix is 64 bits long, and the site is divided into several subnets, then the stateless address autoconfiguration cannot be used and the convenience it will bring cannot be shared. So we scream for stateless address autoconfiguration with prefixes longer than 64. The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC2119]. 2. Protocol Specification 2.1. Router Advertisement Processing When a host receives a valid router advertisement, execute the following steps for each Prefix-Information option in the router advertisement: (1) If the Autonomous flag is not set, silently ignore the Prefix Information option. Yu hua bing Expires August 2011 [Page 2] Internet-Draft IPv6 Stateless Address Autoconfiguration February 2011 (2) If the prefix is a link-local prefix, silently ignore the Prefix Information option. (3) If the preferred lifetime is greater than the valid lifetime, silently ignore the Prefix Information option. A node MAY wish to log a system management error in this case. (4) If the prefix length is less than (128 - length of interface ID) or more than 126, the Prefix Information option MUST be ignored. An implementation MAY wish to log a system management error in this case. (5) If the prefix advertised overlaps with the prefix of an address configured by stateless autoconfiguration already in the list of addresses associated with the interface, and the former is not equal to the latter, the Prefix Information option MUST be ignored. An implementation MAY wish to log a system management error in this case. (6) If the receiving interface is not ISATAP tunnel interface, the Valid Lifetime is not 0, host ID is configured (the host ID greater than 0 and less than 2 ^ (128 - prefix length) is valid), an address is formed by combining the advertised prefix with the host ID as follows: | N bits | 128 - N bits | +---------------------------------------+------------------------+ | link prefix | host ID | +----------------------------------------------------------------+ A host MUST allow the host ID to be configured by system management. If the host ID configured on the host is invalid, an address can't be formed. A node MUST log a system management error in this case. (7) If the receiving interface is Ethernet, and the Valid Lifetime is not 0, do with the Prefix-Information option as follows: (7.1) If the prefix length is 64, an address is formed by combining the advertised prefix with the interface identifier. (7.2)If the prefix length is greater than 64 and is not greater than 80, an address is formed by combining the advertised prefix with the MAC address of the interface as follows: | N bits | (80 - N) bits | 48 bits | +------------------------------+---------------+-----------------+ | link prefix | reserved | MAC address | +----------------------------------------------------------------+ The middle (80 - N) bits are reserved for future use, now it MUST be zero. Yu hua bing Expires August 2011 [Page 3] Internet-Draft IPv6 Stateless Address Autoconfiguration February 2011 (7.3) If the prefix length is greater than 80, a random number between 0 and 2 ^ (128 - prefix length) is generated, and an address is formed by combining the advertised prefix with the random number as follows: | N bits | 128 - N bits | +---------------------------------------+------------------------+ | link prefix | random number | +----------------------------------------------------------------+ (8) If the receiving interface is not Ethernet, execute step d in section 5.5.3 of RFC4862. (9) If the advertised prefix is equal to the prefix of an address configured by stateless autoconfiguration in the list, execute step e in section 5.5.3 of RFC4862. 2.2. ISATAP Tunnel Besides Ethernet, stateless address autoconfiguration is often used on an ISATAP tunnel. But, it is a pity that the ISATAP tunnel can't support stateless address autoconfiguration with prefixes longer than 64 because of ISATAP interface identifier. 2.3. Analysis of Duplicate Address Possibility On the Ethernet, if the prefix length is not less than 64 and not greater than 80,use the MAC address to form the IPv6 address. The possibility that the IPv6 address is duplicate is very low, because the possibility that the MAC address is duplicate is very low. If the prefix length is greater than 80, it is more convenient for users to use the random number to form the IPv6 address, but the IPv6 address is possibly duplicate. Suppose there are M hosts on the link,the prefix length is N, if all hosts run stateless address autoconfiguration almost at the same time, for each host, duplicate address possibility P is (M-1)/(2^(128-N)-1). In order to ensure each host runs stateless address autoconfiguration successfully, P SHOULD be less than 1/1000. For example, there are 1000 hosts on the link, if it is required that P should be less than 1/1000, N should be less than 108.If stateless address autoconfiguration fails for the first time, it is a good idea to try more times. Another choice is that the network administrator assigns host IDs to each host. The first benefit is that the IPv6 addresses can be fully used, for example, on the link with 1000 hosts, the 118-bit prefix is enough. The second benefit is that duplicate address possibility is very low, almost zero. Yu hua bing Expires August 2011 [Page 4] Internet-Draft IPv6 Stateless Address Autoconfiguration February 2011 3. References 3.1. Normative References [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. 3.2. Informative References [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [RFC4941] T. Narten,R. Draves and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, September 2007. [RFC5214] F. Templin,T. Gleeson and D. Thaler, "Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, March 2008. Authors' Addresses Yu hua bing Ruijie Networks Fuzhou Fujian China Email: yhb@ruijie.com.cn Yu hua bing Expires August 2011 [Page 5]