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Versions: 00                                                            
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
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Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.









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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.

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   (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.

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   (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.







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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

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