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rfc:rfc1026

Network Working Group S.E. Kille Request for Comments 1026 University College London

                                                         September 1987
                       Addendum to RFC 987
               (Mapping between X.400 and RFC-822)

Status of this Memo

 This RFC suggest a proposed protocol for the Internet community, and
 requests discussion and suggestions for improvements.  Distribution
 of this memo is unlimited.
 This document specifies a number of additions and corrections to
 RFC-987, aka Mailgroup Note 19.
 The addendum carries equal weight to the original specification,
 which must be used when this mapping is performed on the Internet or
 in the UK Academic Community.  This mapping may also be used within
 the RARE community in Europe.  This specification may be modified in
 the light of implementation experience, but no substantial changes
 are expected.

1. Errata

  1. In section 4.6.4, replace ".." with ".".
  1. In section 4.2.4, replace three references to 4.3.1 by

4.2.1, and one reference to 4.2.2 by 4.1.2.

  1. In section 5.2, replace "1 mailbox" with "1#mailbox",

"1 msg-id" with "1#msg-id" and "1 encoded-type" with

      "1#encoded-type".

2. Component Ordering

 In most cases, ordering of O/R name components is not significant for
 the mappings specified by this document.  However, Organisational
 Units and Domain Defined Attributes are specified as SEQUENCE, in
 P1.ORName, and so their order may be significant.  This specification
 needs to take account of this in two ways:
 1)   To allow consistent mapping into the domain hierarchy
 2)   To ensure preservation of order over multiple mappings.

Kille [Page 1] RFC 1026 September 1987

There are three places where an order must be specified:

 1)   On the text encoding (std-orname) of P1.ORName as used in the
      local-part of an RFC-822 address, the most significant component
      must be on the RHS.  This applies only to those components which
      may have multiple values (Organisational Unit, and Domain
      Defined Attributes).  Other attributes may be presented in any
      order. Note that in dmn-orname specified in Appendix F, this
      ordering is already implied by the current ordering
      requirements.
 2)   For the Organisational Units (OU) in P1.ORName, the first OU in
      the SEQUENCE is the most signicicant.  This follows the
      "natural" hierarchy of the specification of P1.ORName, where the
      most significant components are defined first.
 3)   For the Domain Defined Attributes in P1.ORName, the First Domain
      Defined Attribute in the SEQUENCE is the most significant.
 Note that although the ordering defined in 2) and 3) is mandatory for
 this mapping, there are NO implications on ordering significance
 within X.400.
 3.  Extensions To Deal with Omitted Components
 Implementation of RFC-987 has proved to be a little inflexible for
 some naming strategies.  In particular, there are some difficulties
 where Organisation or PRMD is omitted:
 The following sentence of RFC-987 should be removed: 4.2.1 (Page 27):
 "If one of the hierarchical components is omitted ....  tuple).".
 The strategy proposed is to introduce the concept of explicit missing
 components to the symmetrical mapping described in 4.2.1.
 Essentially, a domain may be associated with an omitted attribute in
 conjuction with several present ones.  When performing the
 algorithmic insertion of components lower in the hierarchy, the
 omitted value should be skipped.  For example, if "GMD.DFN" is
 associated with "C=DE", "ADMD=DBP", "PRMD=GMD", and omitted
 organisation, then "ZI.GMD.DFN" is mapped with "C=DE", "ADMD=DBP",
 "PRMD=GMD", "OU=ZI".  It should be noted that attributes may have
 null values, and that this is treated separately from omitted
 attributes (whilst it would be bad practice to treat these two cases
 differently, they must be allowed for in practice).

Kille [Page 2] RFC 1026 September 1987

 To allow the mapping of null organisations to be represented in the
 specification of Appendix F, the dmn-orname syntax is extended, so
 that values may be given the symbol "@" (not a printable string
 character). This corresponds to an omitted attribute. The new
 definition is:
         dmn-orname      = dmn-part *( "." dmn-part )
         dmn-part        = attribute "$" value
         attribute       = standard-type
                         / "~" dmn-printablestring
         value           = dmn-printablestring
                         / "@"
         dmn-printablestring
                         = *( dmn-char / dmn-pair )
         dmn-char        = <ps-delim, and any ps-char except ".">
         dmn-pair        = "."
 Appendix F - Format of address mapping tables
 A new Appendix F is defined as follows:
 There is a need to specify the association between the domain and
 X.400 namespaces described in 4.2.1.  This is defined as a table
 syntax, but the syntax is defined in a manner which makes it suitable
 for use with domain nameservices (such as the Internet Domain
 nameservers or the UK NRS).  The mapping is not symmetric, and so a
 separate table is specified for each direction.  If multiple matches
 are possible, the longest possible match should be used.
 Various restrictions are placed on the usage of dmn-orname:
 1)   Only C, ADMD, PRMD, O, and OU may be used.
 2)   There must be a strict ordering of all components, with the most
      significant components on the RHS.
 3)   No components may be omitted from the hierarchy, although the
      hierarchy may terminate at any level.  If the mapping is to an
      omitted component, the "@" syntax is used.
 For domain -> X.400:
         domain-syntax "#" dmn-orname "#"
 Note that the trailing "#" is used for clarity, as the dmn-orname
 syntax can lead to values with trailing blanks.
         For example:
         AC.UK#PRMD$DES.ADMD$BT.C$UK#
         XEROX.COM#O$Xerox.ADMD$ATT.C$US#

Kille [Page 3] RFC 1026 September 1987

         HMI.DBP.DFN#O$@.PRMD$HMI.ADMD.DBP.C$DE#
 For X.400 -> domain:
         dmn-orname "#" domain-syntax "#"

Kille [Page 4]

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