The length of the prefix of an IPv6 link-local address ranges from 10 to 127
draft-petrescu-6man-ll-prefix-len-06

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6MAN Working Group                                           A. Petrescu
Internet-Draft                                                 CEA, LIST
Intended status: Standards Track                       December 17, 2018
Expires: June 20, 2019

The length of the prefix of an IPv6 link-local address ranges from 10 to
                                  127
                  draft-petrescu-6man-ll-prefix-len-06

Abstract

   A rejected Errata to RFC4291 "IPv6 Addr Archi" on the topic of link-
   local addresses 'needs' a draft.  This is an answer to that need.

   The length of the prefix of an IPv6 link-local address is variable.
   The minimal value is 10 decimal.  The maximum value is 127 decimal.

Status of This Memo

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   This Internet-Draft will expire on June 20, 2019.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Definitions and Statements  . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Context . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Example of use of LL Prefix Length 32 . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  ChangeLog  . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Definitions and Statements

   The prefix of an IP address is formed by the n leftmost bits of the
   address.  (in a left-to-right writing system).

   The prefix of an IP address is used for goals such as: identify the
   type of an IPv6 address (link-local, global, others), identify the
   belonging of an IP address to a particular subnetwork, assist the
   forwarding (or not forwarding) decisions, and others.

   The minimal length of the prefix of an IPv6 link-local address (the
   value of n) is equal to 10 decimal.  The maximum is 127.

   The prefix of an IPv6 link-local address is represented textually as
   "fe80::/n", where n MAY be any value between 10 and 127.

   Regardless of the prefix length, the leftmost 10 bits of an IPv6
   link-local address MUST be set to binary 1111111010 (hexadecimal
   fe80).

   The illustration of an IPv6 link-local address is:

     | leftmost |         Subnet ID and Interface ID
     | 10 bits  |                 118 bits                             |
     +----------+------------------------------------------------------+
     |1111111010+          Bits that MAY be either 0 or 1              |
     +----------+------------------------------------------------------+

                   Figure 1: The IPv6 link-local address

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   Examples: fe80::1/10, fe80:1::1/32 and fe80::1:1/64 are all IPv6
   link-local addresses; their prefix lengths are 10, 32 and 64
   respectively.  Each such IPv6 address has the leftmost 10 bits equal
   to binary 1111111010.

   The Difficulty: the number binary 1111111010 can not be written in
   hexadecimal without specifying the number of significant bits
   (fe80::/10); yet that does not make it a 'prefix'.  Converting
   1111111010 to hexadecimal leads to 3FA (because in a left-to-right
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