INFORMATIONAL

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 2 . Introduction 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 [Page 1]

RFC 1924 A Compact Representation of IPv6 Addresses 1 April 1996 3 . Current formats AddrSpec] specifies that the preferred text representation of IPv6 addresses is in one of three conventional forms. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the hexadecimal values of the eight 16-bit pieces of the address. Examples: FEDC:BA98:7654:3210:FEDC:BA98:7654:3210 (39 characters) 1080:0:0:0:8:800:200C:417A (25 characters) The second, or zero suppressed, form allows "::" to indicate multiple groups of suppressed zeroes, hence: 1080:0:0:0:8:800:200C:417A may be represented as 1080::8:800:200C:417A a saving of just 5 characters from this typical address form, and still leaving 21 characters. In other cases the saving is more dramatic, in the extreme case, the address: 0:0:0:0:0:0:0:0 that is, the unspecified address, can be written as :: This is just 2 characters, which is a considerable saving. However such cases will rarely be encountered. Elz Informational [Page 2]

RFC 1924 A Compact Representation of IPv6 Addresses 1 April 1996 4 . The New Encoding Format 4.1 . Why 85? 4.2 . The Character Set Elz Informational [Page 3]

RFC 1924 A Compact Representation of IPv6 Addresses 1 April 1996 5 . Converting an IPv6 address to base 85. Elz Informational [Page 4]

RFC 1924 A Compact Representation of IPv6 Addresses 1 April 1996 6 . Additional Benefit 7 . Implementation Issues 8 . Security Considerations Elz Informational [Page 5]