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6MAN Working Group                                           A. Petrescu
Internet-Draft                                                 CEA, LIST
Intended status: Standards Track                      September 24, 2018
Expires: March 28, 2019


                The length of the IPv6 link-local prefix
                  draft-petrescu-6man-ll-prefix-len-01

Abstract

   The length of the IPv6 link-local prefix is 64 decimal.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on March 28, 2019.

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Table of Contents

   1.  Statement . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Context . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  ChangeLog  . . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Statement

   The length of the IPv6 link-local prefix is 64 decimal.

   The IPv6 link-local prefix is represented textually "fe80::/64".

   The illustration of the IPv6 link-local prefix is:


     |
     |    64 bits, the link-local prefix  |          64 bits           |
     +----------+-------------------------+----------------------------+
     |1111111010000000000000...00000000000|       interface ID         |
     +----------+-------------------------+----------------------------+


                   Figure 1: The IPv6 link-local prefix

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   prefix: a contiguous string of bits valid for forwarding operations
   and for subnet formation.

   textual representation of a prefix: e.g. fe80::/64.

   n leading bits: the first n bits in a string of bits read from left
   to right in a writing system that is read left-to-right.  E.g. the 10
   leading bits of the fe80::/64 textual representation of the IPv6
   link-local prefix are 1111111010.





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3.  Context

   The RFC "IPv6 Address Archi" illustrates the format of the link-local
   addresses.  From the illustration it MAY be understood that the
   length of the link-local prefix is 10 bits of value 1111111010 and 54
   0 bits.

   IANA lists the "IPv6 prefix", and "Address Block", to be "fe80::/10"
   on its website.  It is possible that in the future the IETF could
   decide to use the bits 11-53.

   The RFC 2464 "IPv6-over-Ethernet" states that the prefix for link-
   local addresses is "fe80::/64".

   RFC 6874, "Representing IPv6 Zone Identifiers in Address Literals and
   Uniform Resource Identifiers" specifies the link-local addresses to
   be under prefix "fe80::/1".

   Several knowledgeable interpretations state that, generally speaking,
   the prefix length of link-local addresses is 10, but it is 64 in the
   particular case of Stateless Address-Autoconfiguration (SLAAC).  In
   this latter case, the prefix is named a "subnet prefix", or "prefix
   on a link", and it is "fe80::/64".

   Implementations of an IPv6 stack in a particular operating system
   allow for the manual configuration of both prefix lengths 64 and 10
   for link-local addresses.  In another operating system the prefix
   length for link-local addresses can not be explicitely specified by
   the end user, but may be indirectly derived from two distinct textual
   formats by using an unspecified rule.

   Misconfigurations and lack of interoperability MAY arise between
   computers that use mixed prefix lengths for link-local addresses.

   A memo describes the use of IPv6 link-local addresses in
   applications.  The filename of the Internet Draft is draft-smith-
   ipv6-link-locals-apps-00.

   Historical note: earlier, the link-local prefix fe80::/10 and site-
   local prefix fec0::/10 were grouped into a common fe80::/9.  If bits
   10-64 were 0 then the prefix was a link-local, otherwise a site-
   local.  The site-local addresses were later deprecated by RFC 3879.

4.  Security Considerations

   The clarification of the definition of the prefix length of the IPv6
   link-local prefix at IANA is: call it 'leading bits' and not
   'prefix', or state that the IPv6 prefix length of link-local



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   addresses is 10 decimal.  This clarification has beneficial impact in
   the algorithm implementation for calculation of the opaque and stable
   Interface Identifiers for IPv6 link-local addresses.  It also
   positively impacts some implementations of IPv6 forwarding.

5.  IANA Considerations

   IANA is requested to change the name of the column head in the table
   that depicts the "Internet Protocol Version 6 Address Space".  The
   name should be "The n leading bits of an address" instead of "IPv6
   Prefix".

   The desired effect of this change is that the IPv6 link-local prefix
   be "fe80::/64" and that the 10 leading bits of this prefix be
   1111111010.  A second effect is that the textual representation
   "fe80::/10" as an IPv6 link-local prefix should disappear from that
   IANA page, because it is wrong.

6.  Contributors

   Listed from 6man WG discussion.

7.  Acknowledgements

   The following persons are acknowledged for the discussion that is
   reflected in this draft.  Not all points are reflected.  Some points
   are copied almost entirely.

   Ole Troan, Scott Timothy Morizot, Brian Carpenter, Fred Baker, Mark
   Smith, Peter Occil, Philip Homburg, Albert Manfredi, _–3/4
   ’BAE, Fernando Gont, Christian Huitema.

8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

Appendix A.  ChangeLog

   The changes are listed in reverse chronological order, most recent
   changes appearing at the top of the list.








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Author's Address

   Alexandre Petrescu
   CEA, LIST
   CEA Saclay
   Gif-sur-Yvette , Ile-de-France   91190
   France

   Phone: +33169089223
   Email: Alexandre.Petrescu@cea.fr









































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