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Network Working Group                                           S. KilleRequest for Comments: 1838                              ISODE ConsortiumCategory: Experimental                                       August 1995Use of the X.500 Directory to support mapping between X.400andRFC 822 AddressesStatus of this Memo   This memo defines an Experimental Protocol for the Internet   community.  This memo does not specify an Internet standard of any   kind.  Discussion and suggestions for improvement are requested.   Distribution of this memo is unlimited.Abstract   This document defines how to use directory to support the mapping   between X.400 O/R Addresses and mailboxes defined inRFC 1327 [2].1.  X.400/RFC 822 MappingsRFC 1327 defines an algorithm for maintaining a global mapping   between X.400 andRFC 822 addresses directory [2].RFC 1327 also   defines a table based mechanism for maintaining this mapping.  There   is substantial benefit to maintaining this mapping within the   directory.  In particular, this will lead to an approach for managing   the mapping which is both distributed and scalable.   Mechanisms for representing O/R Address and Domain hierarchies within   the DIT are defined in [1,5].  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 the currently deployed table-based       approach.   3.  It handles the issues of "missing components" in a natural       manner.Kille                         Experimental                      [Page 1]

RFC 1838RFC 822/X.400 Mapping by X.500          August 1995          An alternative approach which is not taken is to locate the          information in the routing subtrees.  The benefits of this          would be:        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.   There are three mappings, which are represented by two subtrees   located under:   OU=X.400/RFC 822 Mapping,  O=Internet   These subtree roots are of object class subtree, and use the   mechanism for representing subtrees defined in [4].   X.400 toRFC 822 This table gives the equivalence mapping from X.400       toRFC 822.  There is an O/R Address tree under this.  An example       entry is:       PRMD=UK.AC, ADMD=Gold 400, C=GB, CN=X.400 toRFC 822,       OU=X.400/RFC 822 Mapping,  O=InternetRFC 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=X.400/RFC 822 Mapping,  O=Internet   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                         Experimental                      [Page 2]

RFC 1838RFC 822/X.400 Mapping by X.500          August 19952.  Omitted Components   InRFC 1327, it is possible to have omitted components in O/R   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., at-prmd-   name).  This mechanism is for use only within the X.400 toRFC 822   subtree and for the at-associated-or-address attribute.-----------------------------------------------------------------------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}    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}                                        30             Figure 1:  ObjectClasses forRFC 1327 mappingsKille                         Experimental                      [Page 3]

RFC 1838RFC 822/X.400 Mapping by X.500          August 1995-----------------------------------------------------------------------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 O/R Address Component3.  Mapping from X.400 toRFC 822   As an example, consider the mapping from the O/R Address:   P=UK.AC; A=Gold 400; C=GB   This would be keyed by the directory entry:   PRMD=UK.AC, ADMD=Gold 400, C=GB, CN=X.400 toRFC 822,   OU=X.400/RFC 822 Mapping,  O=Internet   and return the mapping from the associatedDomain attribute, which   gives the domain which this O/R address maps to.  This attribute is   used to define authoritative mappings, which are placed in the open   community tree.  The manager of anRFC 1327 mapping shall make the   appropriate entry.   Functionally, mapping takes place exactly according toRFC 1327.  The   longest match is found by the following algorithm.   1.  Take the O/R Address, and derive a directory name.  This will be       the O/R Address as far as the lowest OU.   2.  Look up the entire name derived from theRFC 1327 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 attribute in the matched entry.Kille                         Experimental                      [Page 4]

RFC 1838RFC 822/X.400 Mapping by X.500          August 1995   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:   AC.UK   Is represented in the DIT as:   DomainComponent=AC, DomainComponent=UK,  CN=RFC 822 to X.400,   OU=X.400/RFC 822 Mapping,  O=Internet   This has associated with it the attribute associatedORAddress encoded   as a distinguished name with a value:   PRMD=UK.AC, ADMD=Gold 400, C=GB   The "table 3" mapping defined inRFC 1327 [2] 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 O/R 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   toRFC 1327.  The longest match is found by the following algorithm.   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 O/R   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 O/R Address   defined by this attribute.  If multiple associatedX400GatewayKille                         Experimental                      [Page 5]

RFC 1838RFC 822/X.400 Mapping by X.500          August 1995   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.  Acknowledgements   Acknowledgements for work on this document are given in [3].References   [1] Kille, S. "X.500 and Domains",RFC 1279,       Department of Computer Science, University College London,       November 1991.   [2] Kille, S., "Mapping between X.400(1988)/ISO 10021 andRFC 822",RFC 1327, Department of Computer Science, University College       London, May 1992.   [3] Kille, S., "MHS Use of the X.500 Directory to Support MHS       Routing",RFC 1801, ISODE Consortium, June 1995.   [4] Kille, S., "Representing Tables and Subtrees in the X.500       Directory",RFC 1837, ISODE Consortium, August 1995.   [5] Kille, S., "Representing the O/R Address Hierarchy in the X.500       Directory Information Tree",RFC 1836, ISODE Consortium, August       1995.6.  Security Considerations   Security issues are not discussed in this memo.Kille                         Experimental                      [Page 6]

RFC 1838RFC 822/X.400 Mapping by X.500          August 19957.  Author's Address   Steve Kille   ISODE Consortium   The Dome   The Square   Richmond   TW9 1DT   England   Phone:  +44-81-332-9091   Internet EMail:  S.Kille@ISODE.COM   X.400:  I=S; S=Kille; O=ISODE Consortium; P=ISODE;   A=Mailnet; C=FI;   UFN: S. Kille, ISODE Consortium, GBKille                         Experimental                      [Page 7]

RFC 1838RFC 822/X.400 Mapping by X.500          August 1995A  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}              10oc-x400-to-rfc822-mapping OBJECT IDENTIFIER ::= {oc 2}oc-omitted-or-address-component OBJECT IDENTIFIER ::= {oc 3}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}Figure 3:  Object Identifier AssignmentKille                         Experimental                      [Page 8]