RFC 883                                                    November 1983
                         Domain Names - Implementation and Specification


   Conventions

      The domain system has several conventions dealing with low-level,
      but fundamental, issues.  While the implementer is free to violate
      these conventions WITHIN HIS OWN SYSTEM, he must observe these
      conventions in ALL behavior observed from other hosts.

             ********** Data Transmission Order **********

      The order of transmission of the header and data described in this
      document is resolved to the octet level.  Whenever a diagram shows
      a group of octets, the order of transmission of those octets is
      the normal order in which they are read in English.  For example,
      in the following diagram the octets are transmitted in the order
      they are numbered.

                                    
                    0                   1           
                    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |       1       |       2       |
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |       3       |       4       |
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |       5       |       6       |
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Transmission Order of Bytes

      Whenever an octet represents a numeric quantity the left most bit
      in the diagram is the high order or most significant bit.  That
      is, the bit labeled 0 is the most significant bit.  For example,
      the following diagram represents the value 170 (decimal).

                                    
                            0 1 2 3 4 5 6 7 
                           +-+-+-+-+-+-+-+-+
                           |1 0 1 0 1 0 1 0|
                           +-+-+-+-+-+-+-+-+

                          Significance of Bits

      Similarly, whenever a multi-octet field represents a numeric
      quantity the left most bit of the whole field is the most
      significant bit.  When a multi-octet quantity is transmitted the
      most significant octet is transmitted first.






 

RFC 883                                                    November 1983
                         Domain Names - Implementation and Specification


                  ********** Character Case **********

      All comparisons between character strings (e.g. labels, domain
      names, etc.) are done in a case-insensitive manner.

      When data enters the domain system, its original case should be
      preserved whenever possible.  In certain circumstances this cannot
      be done.  For example, if two domain names x.y and X.Y are entered
      into the domain database, they are interpreted as the same name,
      and hence may have a single representation.  The basic rule is
      that case can be discarded only when data is used to define
      structure in a database, and two names are identical when compared
      in a case insensitive manner.

      Loss of case sensitive data must be minimized.  Thus while data
      for x.y and X.Y may both be stored under x.y, data for a.x and B.X
      can be stored as a.x and B.x, but not A.x, A.X, b.x, or b.X.  In
      general, this prevents the first component of a domain name from
      loss of case information.

      Systems administrators who enter data into the domain database
      should take care to represent the data they supply to the domain
      system in a case-consistent manner if their system is
      case-sensitive.  The data distribution system in the domain system
      will ensure that consistent representations are preserved.