Network Working Group                                         S. Kille
Request for Comments: 2164                                  Isode Ltd.
Obsoletes: 1838                                           January 1998
Category: Standards Track



   Use of an X.500/LDAP directory to support MIXER address mapping

Status of this Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (1998).  All Rights Reserved.

1  MIXER X.400/RFC 822 Mappings

  MIXER (RFC 2156) defines an algorithm for use of a set of global
  mapping between X.400 and RFC 822 addresses [4].  This specification
  defines how to represent and maintain these mappings (MIXER
  Conformant Global Address Mappings of MCGAMs) in an X.500 or LDAP
  directory.  Mechanisms for representing OR Address and Domain
  hierarchies within the DIT are defined in [5, 2].  These techniques
  are used to define two independent subtrees in the DIT, which contain
  the mapping information.  The benefits of this approach are:

  1.  The mapping information is kept in a clearly defined area which
      can be widely replicated in an efficient manner.  The tree is
      constrained to hold only information needed to support the
      mapping.  This is important as gateways need good access to the
      entire mapping.

  2.  It facilitates migration from a table-based approach.

  3.  It handles the issues of "missing components" in a natural
      manner.

         An alternative approach which is not taken is to locate the
         information in the routing subtrees.  The benefits of this
         would be:





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       o  It is the "natural" location, and will also help to
          ensure correct administrative authority for a mapping
          definition.

       o  The tree will usually be accessed for routing, and so it
          will be efficient for addresses which are being routed.

         This is not done, as the benefits of the approach proposed are
         greater.

  MCGAMs are global.  A MIXER gateway may use any set of MCGAMs.  A key
  use of the directory is to enable MIXER gateways to share MCGAMs and
  to share the effort of maintaining and publishing MCGAMs.  This
  specification and MIXER also recognise that there is not a single
  unique location for publication of all MCGAMs.  This specification
  allows for multiple sets of MCGAMs to be published.  Each set of
  MCGAMs is published under a single part of the directory.  There are
  four mappings, which are represented by two subtrees located under
  any part of the DIT. For the examples the location defined below is
  used:


  OU=MIXER MCGAMs, O=Zydeco Plc,  C=GB

  These subtree roots are of object class subtree, and use the
  mechanism for representing subtrees defined in [1].


  X.400 to RFC 822 This table gives the equivalence mapping from X.400
      to RFC 822.  There is an OR Address tree under this.  An example
      entry is:

      PRMD=Isode, ADMD=Mailnet, C=FI, CN=X.400 to RFC 822,
      OU=MIXER MCGAMs, O=Zydeco Plc,  C=GB

  RFC 822 to X.400 There is a domain tree under this.  This table holds
      the equivalence mapping from RFC 822 to X.400, and the gateway
      mapping defined in RFC 1327.  An example entry is:

      DomainComponent=ISODE, DomainComponent=COM,
      CN=RFC 822 to X.400,
      OU=MIXER MCGAMs, O=Zydeco Plc,  C=GB

  The values of the table mapping are defined by use of two new object
  classes, as specified in Figure 1.  The objects give pointers to the
  mapped components.





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2  Omitted Components

  In MIXER, it is possible to have omitted components in OR Addresses
  on either side of the mapping.  A mechanism to represent such omitted
  components is defined in Figure 2.  The attribute at-or-address-
  component-type is set to the X.500 attribute type associated with the
  omitted component (e.g.,


rFC822ToX400Mapping OBJECT-CLASS ::= {
   SUBCLASS OF {domain-component}
   MAY CONTAIN {
       associatedORAddress|
       associatedX400Gateway}
   ID oc-rfc822-to-x400-mapping}

x400ToRFC822Mapping OBJECT-CLASS ::= {
   SUBCLASS OF {top}
   MAY CONTAIN {                                                   10
       associatedDomain|
       associatedInternetGateway}
   ID oc-x400-to-rfc822-mapping}

associatedORAddress ATTRIBUTE ::= {
   SUBTYPE OF distinguishedName
   SINGLE VALUE
   ID at-associated-or-address}

                                                                   20
associatedX400Gateway ATTRIBUTE ::= {
   SUBTYPE OF mhs-or-addresses
   MULTI VALUE
   ID at-associated-x400-gateway}

associatedDomain ATTRIBUTE ::= {
   SUBTYPE OF name
   WITH SYNTAX caseIgnoreIA5String
   SINGLE VALUE
   ID at-associated-domain}                                        30

associatedInternetGateway ATTRIBUTE ::= {
   SUBTYPE OF name
   WITH SYNTAX caseIgnoreIA5String
   MULTI VALUE
   ID at-associated-internet-gateway}


             Figure 1:  Object Classes for MIXER mappings



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omittedORAddressComponent OBJECT-CLASS ::=
       SUBCLASS OF {top}
       MUST Contain {
               oRAddressComponentType
       }
       ID oc-omitted-or-address-component}


oRAddressComponentType ATTRIBUTE ::= {
       SUBTYPE OF  objectIdentifier                                10
       SINGLE VALUE
       ID at-or-address-component-type}

               Figure 2:  Omitted OR Address Component


  at-prmd-name).  This mechanism is for use only within the X.400 to
  RFC 822 subtree and for the at-associated-or-address attribute.

3  Mapping from X.400 to RFC 822

  As an example, consider the mapping from the OR Address:


  P=Isode; A=Mailnet; C=FI

  This would be keyed by the directory entry:

  PRMD=Isode, ADMD=Mailnet, C=FI, CN=X.400 to RFC 822,
  OU=MIXER MCGAMs, O=Zydeco Plc,  C=GB

  and return the mapping from the associatedDomain attribute, which
  gives the domain which this OR address maps to.  This attribute is
  used to define authoritative mappings, which are placed in the open
  community tree.  The manager of an MCGAM shall make the appropriate
  entry.

  The Internet gateway mapping defined in MIXER[4] is provided by the
  associatedInternetGateway attribute.  This value may identify
  multiple possible associated gateways.  This information is looked up
  at the same time as mapped OR addresses.  In effect, this provides a
  fallback mapping, which is found if there is no equivalence mapping.
  Because of the nature of the mapping an OR Address will map to either
  a gateway or a domain, but not both.  Thus, there shall never be both







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  an associatedDomain and associatedInternetGateway attribute present
  in the same entry.  Functionally, mapping takes place exactly
  according to MIXER. The longest match is found by the following
  algorithm.

  1.  Take the OR Address, and derive a directory name.  This will be
      the OR Address as far as the lowest OU.

  2.  Look up the entire name derived from the MIXER key in the in the
      X.400 to RFC 822 subtree.  This lookup will either succeed, or it
      will fail and indicate the longest possible match, which can then
      be looked up.

  3.  Check for an associatedDomain or associatedInternetGateway
      attribute in the matched entry.

  The mapping can always be achieved with two lookups.  Because of the
  availability of aliases, some of the table mappings may be
  simplified.  In addition, the directory can support mapping from
  addresses using the numeric country codes.

4  Mapping from RFC 822 to X.400

  There is an analogous structure for mappings in the reverse
  direction.  The domain hierarchy is represented in the DIT according
  to RFC 1279.  The domain:

  ISODE.COM

  Is represented in the DIT as:

  DomainComponent=ISODE, DomainComponent=COM,  CN=RFC 822 to X.400,
  OU=MIXER MCGAMs, O=Zydeco Plc,  C=GB

  This has associated with it the attribute associatedORAddress encoded
  as a distinguished name with a value: PRMD=Isode, ADMD=Mailnet, C=FI

  The X.400 gateway mapping defined in MIXER[4] is provided by the
  associatedX400Gateway attribute.  This value may identify multiple
  possible associated gateways.  This information is looked up at the
  same time as mapped OR addresses.  In effect, this provides a
  fallback mapping, which is found if there is no equivalence mapping.
  Because of the nature of the mapping a domain will map to either a
  gateway or a domain, but not both.  Thus, there shall never be both
  an associatedX400Gateway and associatedORAddress attribute present in
  the same entry.  Functionally, mapping takes place exactly according
  to MIXER. The longest match is found by the following algorithm.




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  1.  Derive a directory name from the domain part of the RFC 822
      address.

  2.  Look up this name in the RFC 822 to X.400 subtree to find the
      mapped value (either associatedORAddress or
      associatedX400Gateway.).  If the lookup fails, the error will
      indicate the longest match, which can then be looked up.

  If associatedORAddress is found, this will define the mapped OR
  Address.  The mapping can always be achieved with two lookups.  If an
  associatedX400Gateway is present, the address in question will be
  encoded as a domain defined attribute, relative to the OR Address
  defined by this attribute.  If multiple associatedX400Gateway
  attributes are found, the MTA may select the one it chooses to use.

  Because of the availability of aliases, some of the table mappings
  may be simplified.  In addition, the directory can support mapping
  from addresses using the numeric country codes.

5  Gateway Selection of MCGAMs

  The directory information to support identification of MCGAMs is
  given in Figure 3.  A MIXER gateway simply identifies the an ordered
  lists of MCGAM collections that it will use for lookup.  These are
  referenced by name.  A gateway is not required to use any MCGAMs.
  Where MCGAMs are accessed from multiple sources, it is recommended
  that all of the sources be accessed in order to determine the MCGAM
  which gives the


mixerGateway OBJECT-CLASS ::=
       KIND auxiliary
       SUBCLASS OF {mhs-message-transfer-agent}
       MUST Contain {
               mcgamTables
       }
       ID oc-mixer-gateway}


mcgamTables ATTRIBUTE ::= {                                         10
       WITH SYNTAX SEQUENCE OF DistinguishedName
       SINGLE VALUE
       ID at-mcgam-tables}

            Figure 3:  Object Classes for MCGAM selection


best match.



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6  Acknowledgements

  Acknowledgements for work on this document are given in [3].

References

  [1] Kille, S., "Representing tables and subtrees in the X.500
      directory", RFC 1837, August 1995.

  [2] Kille, S., "Representing the O/R Address hierarchy in the X.500
      directory information tree," RFC 1836, August 1995.

  [3] Kille, S., " X.400-MHS use of the X.500 directory to support
      X.400-MHS routing," RFC 1801, June 1995.

  [4] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay):
      Mapping between X.400 and RFC 822/MIME," RFC 2156, January 1998.

  [5] Kille, S., Wahl, M., Grimsatd, A., Huber, R., and S. Sataluri,
      "Using Domains in LDAP/X.500 Distinguished Names", RFC 2247,
      January 1998.

7  Security Considerations

  This document specifies a means by which the X.500/LDAP directory
  service can direct the translation between X.400 and Internet mail
  addresses.  This can indirectly affect the routing of messages across
  a gateway between X.400 and Internet Mail.  A succesful attack on
  this service could cause incorrect translation of an originator
  address (thus "forging" the originator address), or incorrect
  translation of a recipient address (thus directing the mail to an
  unauthorized recipient, or making it appear to an authorized
  recipient, that the message was intended for recipients other than
  those chosen by the originator).  When cryptographic authentication
  is available for directory responses, clients shall employ those
  mechanisms to verify the authenticity and integrity of those
  responses.














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8  Author's Address

  Steve Kille
  Isode Ltd.
  The Dome
  The Square
  Richmond
  TW9 1DT
  England

  Phone:  +44-181-332-9091
  Internet EMail:  [email protected]







































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A  Object Identifier Assignment


mhs-ds OBJECT IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1) private(4)
         enterprises(1) isode-consortium (453) mhs-ds (7)}

mapping OBJECT IDENTIFIER ::= {mhs-ds 4}

oc OBJECT IDENTIFIER ::= {mapping 1}
at OBJECT IDENTIFIER ::= {mapping 2}


oc-rfc822-to-x400-mapping OBJECT IDENTIFIER ::= {oc 1}              10
oc-x400-to-rfc822-mapping OBJECT IDENTIFIER ::= {oc 2}
oc-omitted-or-address-component OBJECT IDENTIFIER ::= {oc 3}
oc-mixer-gateway ::= {oc 4}

at-associated-or-address OBJECT IDENTIFIER ::= {at 6}
at-associated-x400-gateway OBJECT IDENTIFIER ::= {at 3}
at-associated-domain OBJECT IDENTIFIER ::= {at 4}
at-or-address-component-type OBJECT IDENTIFIER ::= {at 7}
at-associated-internet-gateway OBJECT IDENTIFIER ::= {at 8}
at-mcgam-tables ::= {at 9}                                          20


               Figure 4:  Object Identifier Assignment

























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Full Copyright Statement

  Copyright (C) The Internet Society (1998).  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any
  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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