The Free On-line Dictionary of Computing (30 December 2018):

Internet Protocol version 6
IPv6

    (IPv6, IPng, IP next generation) The
   most viable candidate to replace the current Internet
   Protocol.  The primary purpose of IPv6 is to solve the
   problem of the shortage of IP addresses.

   The following features have been purposed: 16-byte addresses
   instead of the current four bytes; embedded encryption - a
   32-bit Security Association ID (SAID) plus a variable length
   initialisation vector in packet headers; user
   authentication (a 32-bit SAID plus variable length
   authentication data in headers); autoconfiguration
   (currently partly handled by Dynamic Host Configuration
   Protocol); support for delay-sensitive traffic - a 24 bit
   flow ID field in headers to denote voice or video, etc.

   One possible solution is based on the TUBA protocol (RFC
   1347, 1526, 1561) which is itself based on the OSI
   Connectionless Network Protocol (CNLP).  Another is TP/IX
   (RFC 1475) which changes TCP and UDP headers to give a
   64-bit IP address, a 32-bit port number, and a 64-bit
   sequence number.

   RFC 1550 is a white paper on IPng.

   IPv6.org (http://ipv6.org/).

   ["Doubts About IPng could create TCP/IP chaos", Johna Till
   Johnson, Data Communications, Nov 1994].

   (2004-06-17)