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Network Working Group                                         S. KilleRequest for Comments: 2164                                  Isode Ltd.Obsoletes:1838                                           January 1998Category: Standards TrackUse of an X.500/LDAP directory to support MIXER address mappingStatus 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 andRFC 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:Kille                       Standards Track                     [Page 1]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 1998        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 toRFC 822 This table gives the equivalence mapping from X.400       toRFC 822.  There is an OR Address tree under this.  An example       entry is:       PRMD=Isode, ADMD=Mailnet, C=FI, CN=X.400 toRFC 822,       OU=MIXER MCGAMs, O=Zydeco Plc,  C=GBRFC 822 to X.400 There is a domain tree under this.  This table holds       the equivalence mapping fromRFC 822 to X.400, and the gateway       mapping defined inRFC 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.Kille                       Standards Track                     [Page 2]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 19982  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}                                                                    20associatedX400Gateway 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}                                        30associatedInternetGateway ATTRIBUTE ::= {    SUBTYPE OF name    WITH SYNTAX caseIgnoreIA5String    MULTI VALUE    ID at-associated-internet-gateway}              Figure 1:  Object Classes for MIXER mappingsKille                       Standards Track                     [Page 3]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 1998omittedORAddressComponent 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 toRFC 822 subtree and for the at-associated-or-address attribute.3  Mapping from X.400 toRFC 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 toRFC 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 bothKille                       Standards Track                     [Page 4]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 1998   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 toRFC 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 fromRFC 822 to X.400   There is an analogous structure for mappings in the reverse   direction.  The domain hierarchy is represented in the DIT according   toRFC 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.Kille                       Standards Track                     [Page 5]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 1998   1.  Derive a directory name from the domain part of theRFC 822       address.   2.  Look up this name in theRFC 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 themixerGateway 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 selectionbest match.Kille                       Standards Track                     [Page 6]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 19986  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 andRFC 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.Kille                       Standards Track                     [Page 7]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 19988  Author's Address   Steve Kille   Isode Ltd.   The Dome   The Square   Richmond   TW9 1DT   England   Phone:  +44-181-332-9091   Internet EMail:  S.Kille@ISODE.COMKille                       Standards Track                     [Page 8]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 1998A  Object Identifier Assignmentmhs-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}              10oc-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 AssignmentKille                       Standards Track                     [Page 9]

RFC 2164         X.500/LDAP Directory to Support MIXER      January 1998Full 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.Kille                       Standards Track                    [Page 10]