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Versions: 00 01 02 RFC 2164

Network Working                                             S.E. Kille
Group                                                       Isode Ltd.
INTERNET-DRAFT                                           February 1997
Obsoletes:  RFC 1838                             Expires:  August 1997
                                                                 File:
                                     draft-ietf-mixer-directory-02.txt





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






Status of this Memo
This document is an Internet Draft.  Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups.  Note that other groups may also distribute
working documents as Internet Drafts.

Internet Drafts are draft documents valid for a maximum of six months.
Internet Drafts may be updated, replaced, or obsoleted by other
documents at any time.  It is not appropriate to use Internet Drafts
as reference material or to cite them other than as a ``working
draft'' or ``work in progress.''
Please check the I-D abstract listing contained in each Internet Draft
directory to learn the current status of this or any other Internet
Draft.
Abstract

This document defines how to use an X.500 or LDAP directory to support
the mapping between X.400 OR Addresses and mailboxes defined in MIXER
(RFC 1327bis) [5].
This draft document will be submitted to the RFC editor as a protocol
standard.  Distribution of this memo is unlimited.



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1  MIXER X.400/RFC 822 Mappings

MIXER (RFC 1327bis) defines an algorithm for use of a set of global
mapping between X.400 and RFC 822 addresses [5].  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 [1, 3].  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:


     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


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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 [2].


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.

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.,


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_______________________________________________________________________
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[5] 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

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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 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:



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PRMD=Isode, ADMD=Mailnet, C=FI

The X.400 gateway mapping defined in MIXER[5] 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.


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


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_______________________________________________________________________
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.


6  Acknowledgements


Acknowledgements for work on this document are given in [4].

References

[1] S.E. Kille. X.500 and domains.  Request for Comments RFC 1279,
    Department of Computer Science, University College London,
    November 1991.

[2] S.E. Kille. Representing tables and subtrees in the X.500
    directory. Request for Comments RFC 1837, Isode Ltd., August
    1995.

[3] S.E. Kille. Representing the O/R Address hierarchy in the X.500
    directory information tree. Request for Comments RFC 1836, Isode
    Ltd., August 1995.

[4] S.E. Kille. X.400-MHS use of the X.500 directory to support
    X.400-MHS routing. Request for Comments RFC 1801, Isode Ltd.,
    June 1995.



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[5] S.E. Kille. MIXER (Mime Internet X.400 Enhanced Relay):  Mapping
    between X.400 and RFC 822/MIME. Request for Comments RFC 1327bis,
    Isode Ltd., February 1997.


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.


8  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.COM








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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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