RFC 1924 (rfc1924) - Page 1 of 6

A Compact Representation of IPv6 Addresses

Alternative Format: Original Text Document
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Network Working Group                                             R. Elz
Request for Comments: 1924                       University of Melbourne
Category: Informational                                     1 April 1996


               A Compact Representation of IPv6 Addresses

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

1. Abstract

   IPv6 addresses, being 128 bits long, need 32 characters to write in
   the general case, if standard hex representation, is used, plus more
   for any punctuation inserted (typically about another 7 characters,
   or 39 characters total).  This document specifies a more compact
   representation of IPv6 addresses, which permits encoding in a mere 20
   bytes.

2. Introduction

   It is always necessary to be able to write in characters the form of
   an address, though in actual use it is always carried in binary.  For
   IP version 4 (IP Classic) the well known dotted quad format is used.
   That is, 10.1.0.23 is one such address.  Each decimal integer
   represents a one octet of the 4 octet address, and consequently has a
   value between 0 and 255 (inclusive).  The written length of the
   address varies between 7 and 15 bytes.

   For IPv6 however, addresses are 16 octets long [IPv6], if the old
   standard form were to be used, addresses would be anywhere between 31
   and 63 bytes, which is, of course, untenable.

   Because of that, IPv6 had chosen to represent addresses using hex
   digits, and use only half as many punctuation characters, which will
   mean addresses of between 15 and 39 bytes, which is still quite long.
   Further, in an attempt to save more bytes, a special format was
   invented, in which a single run of zero octets can be dropped, the
   two adjacent punctuation characters indicate this has happened, the
   number of missing zeroes can be deduced from the fixed size of the
   address.

   In most cases, using genuine IPv6 addresses, one may expect the
   address as written to tend toward the upper limit of 39 octets, as
   long strings of zeroes are likely to be rare, and most of the other



Elz                          Informational
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