RFC 2460                   IPv6 Specification              December 1998


   It is hoped that those experiments will eventually lead to agreement
   on what sorts of traffic classifications are most useful for IP
   packets.  Detailed definitions of the syntax and semantics of all or
   some of the IPv6 Traffic Class bits, whether experimental or intended
   for eventual standardization, are to be provided in separate
   documents.

   The following general requirements apply to the Traffic Class field:

      o  The service interface to the IPv6 service within a node must
         provide a means for an upper-layer protocol to supply the value
         of the Traffic Class bits in packets originated by that upper-
         layer protocol.  The default value must be zero for all 8 bits.

      o  Nodes that support a specific (experimental or eventual
         standard) use of some or all of the Traffic Class bits are
         permitted to change the value of those bits in packets that
         they originate, forward, or receive, as required for that
         specific use.  Nodes should ignore and leave unchanged any bits
         of the Traffic Class field for which they do not support a
         specific use.

      o  An upper-layer protocol must not assume that the value of the
         Traffic Class bits in a received packet are the same as the
         value sent by the packet's source.



























 
RFC 2460                   IPv6 Specification              December 1998


8. Upper-Layer Protocol Issues

8.1 Upper-Layer Checksums

   Any transport or other upper-layer protocol that includes the
   addresses from the IP header in its checksum computation must be
   modified for use over IPv6, to include the 128-bit IPv6 addresses
   instead of 32-bit IPv4 addresses.  In particular, the following
   illustration shows the TCP and UDP "pseudo-header" for IPv6:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                         Source Address                        +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Destination Address                      +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Upper-Layer Packet Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      zero                     |  Next Header  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      o  If the IPv6 packet contains a Routing header, the Destination
         Address used in the pseudo-header is that of the final
         destination.  At the originating node, that address will be in
         the last element of the Routing header; at the recipient(s),
         that address will be in the Destination Address field of the
         IPv6 header.