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Versions: 02 05 RFC 1801

Network Working                                             S.E. Kille
Group                                                 ISODE Consortium
INTERNET-DRAFT                                               June 1994
                                               Expires:  December 1994
                                                                 File:
                                draft-ietf-mhsds-routdirectory-05.txt,ps




             MHS use of Directory to support MHS Routing





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 specifies an approach for X.400 Message Handling Systems
to perform application level routing using the OSI Directory [20, 1].
Use of the directory in this manner is fundamental to enabling large
scale deployment of X.400.
This draft document will be submitted to the RFC editor as a protocol
standard.  Distribution of this memo is unlimited.  Please send
comments to the author or to the discussion group
<mhs-ds@mercury.udev.cdc.com>.



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Contents

1   Introduction                                                     6

2   Goals                                                            6


3   Approach                                                         9

4   Direct vs Indirect Connection                                    9


5   X.400 and RFC 822                                               12

6   Objects                                                         12

7   Communities                                                     14


8   Routing Trees                                                   15
    8.1    Routing Tree Definition   .   .   .   .   .   .   .      16
    8.2    The Open Community Routing Tree   .   .   .   .   .      16

    8.3    Routing Tree Location     .   .   .   .   .   .   .      17
    8.4    Example Routing Trees     .   .   .   .   .   .   .      17

    8.5    Use of Routing Trees to look up Information   .   .      18

9   Routing Tree Selection                                          19
    9.1    Routing Tree Order    .   .   .   .   .   .   .   .      19

    9.2    Example use of Routing Trees  .   .   .   .   .   .      20
        9.2.1    Fully Open Organisation     .   .   .   .   .      20
        9.2.2    Open Organisation with Fallback     .   .   .      20

        9.2.3    Minimal-routing MTA     .   .   .   .   .   .      20
        9.2.4    Organisation with Firewall  .   .   .   .   .      21
        9.2.5    Well Known Entry Points     .   .   .   .   .      21

        9.2.6    ADMD using the Open Community for Advertising      21
        9.2.7    ADMD/PRMD gateway   .   .   .   .   .   .   .      22


10  Routing Information                                             22

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    10.1   Multiple routing trees    .   .   .   .   .   .   .      26
    10.2   MTA Choice    .   .   .   .   .   .   .   .   .   .      27
    10.3   Routing Filters   .   .   .   .   .   .   .   .   .      30

    10.4   Indirect Connectivity     .   .   .   .   .   .   .      32

11  Local Addresses (UAs)                                           33
    11.1   Searching for Local Users     .   .   .   .   .   .      34


12  Direct Lookup                                                   35

13  Alternate Routes                                                35

    13.1   Finding Alternate Routes  .   .   .   .   .   .   .      35
    13.2   Sharing routing information   .   .   .   .   .   .      35

14  Looking up Information in the Directory                         36


15  Naming MTAs                                                     37
    15.1   Naming 1984 MTAs  .   .   .   .   .   .   .   .   .      39


16  Attributes Associated with the MTA                              39

17  Bilateral Agreements                                            41

18  MTA Selection                                                   42

    18.1   Dealing with protocol mismatches  .   .   .   .   .      42
    18.2   Supported Protocols   .   .   .   .   .   .   .   .      43
    18.3   MTA Capability Restrictions   .   .   .   .   .   .      43

    18.4   Subtree Capability Restrictions   .   .   .   .   .      43

19  MTA Pulling Messages                                            44

20  Security and Policy                                             44

    20.1   Finding the Name of the Calling MTA   .   .   .   .      44
    20.2   Authentication    .   .   .   .   .   .   .   .   .      45

    20.3   Authentication Information    .   .   .   .   .   .      46

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21  Policy and Authorisation                                        47
    21.1   Simple MTA Policy     .   .   .   .   .   .   .   .      47
    21.2   Complex MTA Policy    .   .   .   .   .   .   .   .      48


22  Delivery                                                        49
    22.1   Redirects     .   .   .   .   .   .   .   .   .   .      49
    22.2   Underspecified O/R Addresses  .   .   .   .   .   .      50

    22.3   Non Delivery  .   .   .   .   .   .   .   .   .   .      50
    22.4   Bad Addresses     .   .   .   .   .   .   .   .   .      50


23  Submission                                                      51
    23.1   Normal Derivation     .   .   .   .   .   .   .   .      51
    23.2   Roles and Groups  .   .   .   .   .   .   .   .   .      52


24  Access Units                                                    52

25  The Overall Routing Algorithm                                   53

26  Performance                                                     54


27  Acknowledgements                                                54

28  Security Considerations                                         56


29  Author's Address                                                56

A   Object Identifier Assignment                                    58

B   Community Identifier Assignments                                60


C   Protocol Identifier Assignments                                 61

D   ASN.1 Summary                                                   62


E   Regular Expression Syntax                                       73


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    E.1    Pseudo Code   .   .   .   .   .   .   .   .   .   .      75












































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List of Figures

    1      Location of Routing Trees     .   .   .   .   .   .      17
    2      Routing Tree Use Definition   .   .   .   .   .   .      19

    3      Routing Information at a Node     .   .   .   .   .      24
    4      Indirect Access   .   .   .   .   .   .   .   .   .      32
    6      MTA Definitions   .   .   .   .   .   .   .   .   .      38

    19     Object Identifier Assignment  .   .   .   .   .   .      59
    22     ASN.1 Summary     .   .   .   .   .   .   .   .   .      72

    5      UA Attributes     .   .   .   .   .   .   .   .   .      76
    7      MTA Bilateral Table Entry     .   .   .   .   .   .      76
    8      Bilateral Table Attribute     .   .   .   .   .   .      77

    9      Supported MTS Extensions  .   .   .   .   .   .   .      77
    10     Subtree Capability Restriction    .   .   .   .   .      77
    11     Pulling Messages  .   .   .   .   .   .   .   .   .      78

    12     Authentication Requirements   .   .   .   .   .   .      79
    13     MTA Authentication Parameters     .   .   .   .   .      80
    14     Simple MTA Policy Specification   .   .   .   .   .      81

    15     Redirect Definition   .   .   .   .   .   .   .   .      81
    16     Non Delivery Information  .   .   .   .   .   .   .      82
    17     Bad Address Pointers  .   .   .   .   .   .   .   .      82

    18     Access Unit Attributes    .   .   .   .   .   .   .      83
    20     Transport Community Object Identifier Assignments        83

    21     Protocol Object Identifier Assignments    .   .   .      84

List of Tables


    1      Possible target end to end delays     .   .   .   .       7








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1  Introduction

MHS Routing is the problem of controlling the path of a message as it
traverses one or more MTAs to reach its destination recipients.
Routing starts with a recipient O/R Address, and parameters associated
with the message to be routed.  It is assumed that this is known a
priori, or is derived at submission time as described in Section 23.

The key problem in routing is to map from an O/R Address onto an MTA
(next hop).  This shall be an MTA which in some sense is ``nearer'' to
the destination UA. This is done repeatedly until the message can be
directly delivered to the recipient UA. There are a number of things
which need to be considered to determine this.  These are discussed in
the subsequent sections.  A description of the overall routing process
is given in Section 25.


2  Goals

Application level routing for MHS is a complex procedure, with many
requirements.  The following goals for the solution are set:

 o  Straightforward to manage.  Non-trivial configuration of routing
    for current message handling systems is a black art, often
    involving gathering and processing many tables, and editing
    complex configuration files.  Many problems are solved in a very
    ad hoc manner.  Managing routing for MHS is the most serious
    headache for most mail system managers.

 o  Economic, both in terms of network and computational resources.

 o  Robust.  Errors and out of date information shall cause minimal
    and localised damage.

 o  Deal with link failures.  There needs to be some ability to choose
    alternative routes.  In general, it is desirable that the routing
    approach be redundant.

 o  Load sharing.  Information on routes shall allow ``equal'' routes
    to be specified, and thus facilitate load sharing.

 o  Support format and protocol conversion



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_____________________________________________________________
|______________|High_Priority_|Normal_Priority_|Low_Priority_|_
|50%_max_delay_|0.5_hour______|1_hour__________|12_hours_____|
|98%_max_delay_|3_hours_______|12_hours________|24_hours_____|
|max_delay_____|6_hours_______|72_hours________|96_hours_____|

             Table 1:  Possible target end to end delays

 o  Dynamic and automatic.  There shall be no need for manual
    propagation of tables or administrator intervention.

 o  Policy robust.  It shall not allow specification of policies which
    cause undesirable routing effects.

 o  Reasonably straightforward to implement.

 o  Deal with X.400, RFC 822, and their interaction.

 o  Extensible to other mail architectures

 o  Recognise existing RFC 822 routing, and coexist smoothly.

 o  Improve RFC 822 routing capabilities.  This is particularly
    important for RFC 822 sites not in the SMTP Internet.

 o  Deal correctly with different X.400 protocols (P1, P3, P7), and
    with 1984, 1988 and 1992 versions.

 o  Support X.400 operation over multiple protocol stacks (TCP/IP,
    CONS, CLNS) and in different communities.

 o  Messages shall be routed consistently.  Alternate routing
    strategies, which might introduce unexpected delay, shall be used
    with care (e.g.  routing through a protocol converter due to
    unavailability of an MTA).

 o  Delay between message submission and delivery shall be minimised.
    Table 1 indicates the sort of target which might be aimed for.
    The figures are illustrative of the sort of target which might be
    set.  They are better than achieved in most current Research
    Networks.  The long tail-offs on Normal and Low priority recognise
    the fact that some end systems will not get 24 hour operator
    coverage (whereas any MTAs providing ADMD service will usually be
    required to so this).  In the case of a high and normal priority


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    messages, it is a target that a non-delivery notification be
    returned within the suggested time.

 o  Interact sensibly with ADMD services.

 o  Be global in scope

 o  Routing strategy shall deal with a scale of order of magnitude
    1,000,000 -- 100,000,000 MTAs.

 o  Routing strategy shall deal with of order 1,000,000 -- 100,000,000
    Organisations.

 o  Information about alterations in topology shall propagate rapidly
    to sites affected by the change.

 o  Removal, examination, or destruction of messages by third parties
    shall be difficult.  This is hard to quantify, but ``difficult''
    shall be comparable to the effort needed to break system security
    on a typical MTA system.

 o  As with current Research Networks, it is recognised that
    prevention of forged mail will not always be possible.  However,
    this shall be as hard as can be afforded.

 o  Sufficient tracing and logging shall be available to track down
    security violations and faults.

 o  Optimisation of routing messages with multiple recipients, in
    cases where this involves selection of preferred single recipient
    routes.

The following are not initial goals:


 o  Advanced optimisation of routing messages with multiple
    recipients, noting dependencies between the recipients to find
    routes which would not have been chosen for any of the single
    recipients.

 o  Dynamic load balancing.  The approach does not give a means to
    determine load.  However, information on alternate routes is
    provided, which is the static information needed for load
    balancing.

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3  Approach

A broad problem statement, and a survey of earlier approaches to the
problem is given in the COSINE Study on MHS Topology and Routing [8].
The interim (table-based) approach suggested in this study, whilst not
being followed in detail, broadly reflects what the research X.400
(GO-MHS) community is doing.  The evolving specification of the RARE
table format is defined in [5].  This document specifies the envisaged
longer term approach.
Some documents have made useful contributions to this work:


 o  A paper by the editor on MHS use of directory, which laid out the
    broad approach of mapping the O/R Address space on to the DIT [7].

 o  Initial ISO Standardisation work on MHS use of Directory for
    routing [21].  Subsequent ISO work in this area has drawn from
    earlier drafts of this specification.

 o  The work of the VERDI Project [3].

 o  Work by Kevin Jordan of CDC [6].

 o  The routing approach of ACSNet [4, 19] paper.  This gives useful
    ideas on incremental routing, and replicating routing data.

 o  A lot of work on network routing is becoming increasingly
    relevant.  As the MHS routing problem increases in size, and
    network routing increases in sophistication (e.g., policy based
    routing), the two areas have increasing amounts in common.  For
    example, see [2].


4  Direct vs Indirect Connection

Two extreme approaches to routing connectivity are:


1.  High connectivity between MTAs.  An example of this is the way the
    Domain Name Server system is used on the DARPA/NSF Internet.
    Essentially, all MTAs are fully interconnected.

2.  Low connectivity between MTAs.  An example of this is the UUCP
    network.

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In general an intermediate approach is desirable.  Too sparse a
connectivity is inefficient, and leads to undue delays.  However, full
connectivity is not desirable, for the reasons discussed below.
A number of general issues related to relaying are now considered.
The reasons for avoiding relaying are clear.  These include.


 o  Efficiency.  If there is an open network, it is desirable that it
    be used.

 o  Extra hops introduce delay, and increase the (very small)
    possibility of message loss.  As a basic principle, hop count
    shall be minimised.

 o  Busy relays or Well Known Entry points can introduce high delay
    and lead to single point of failure.

 o  If there is only one hop, it is straightforward for the user to
    monitor progress of messages submitted.  If a message is delayed,
    the user can take appropriate action.

 o  Many users like the security of direct transmission.  It is an
    argument often given very strongly for use of SMTP.

Despite these very powerful arguments, there are a number of reasons
why some level of relaying is desirable:


 o  Charge optimisation.  If there is an expensive network/link to be
    traversed, it may make sense to restrict its usage to a small
    number of MTAs.  This would allow for optimisation with respect to
    the charging policy of this link.

 o  Copy optimisation.  If a message is being sent to two remote MTAs
    which are close together, it is usually optimal to send the
    message to one of the MTAs (for both recipients), and let it pass
    a copy to the other MTA.

 o  To access an intermediate MTA for some value added service.  In
    particular for:

    --  Message Format Conversion

    --  Distribution List expansion

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 o  Dealing with different protocols.  The store and forward approach
    allows for straightforward conversion.  Relevant cases include:

    --  Provision of X.400 over different OSI Stacks (e.g.
        Connectionless Network Service).

    --  Use of a different version of X.400.

    --  Interaction with non-X.400 mail services

 o  To compensate for inadequate directory services:  If tables are
    maintained in an ad hoc manner, the manual effort to gain full
    connectivity is too high.

 o  To hide complexity of structure.  If an organisation has many
    MTAs, it may still be advantageous to advertise a single entry
    point to the outside world.  It will be more efficient to have an
    extra hop, than to (widely) distribute the information required to
    connect directly.  This will also encourage stability, as
    organisations need to change internal structure much more
    frequently than their external entry points.  For many
    organisations, establishing such firewalls is high priority.

 o  To handle authorisation, charging and security issues.  In
    general, it is desirable to deal with user oriented authorisation
    at the application level.  This is essential when MHS specific
    parameters shall be taken into consideration.  It may well be
    beneficial for organisations to have a single MTA providing access
    to the external world, which can apply a uniform access policy
    (e.g.  as to which people are allowed access).  This would be
    particularly true in a multi-vendor environment, where different
    systems would otherwise have to enforce the same policy --- using
    different vendor-specific mechanisms.


In summary there are strong reasons for an intermediate approach.
This will be achieved by providing mechanisms for both direct and
indirect connectivity.  The manager of a configuration will then be
able to make appropriate choices for the environment.
Two models of managing large scale routing have evolved:

1.  Use of a global directory/database.  This is the approach proposed
    here.


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2.  Use of a routing table in each MTA, which is managed either by a
    management protocol or by directory.  This is coupled with means
    to exchange routing information between MTAs.  This approach is
    more analogous to how network level routing is commonly performed.
    It has good characteristics in terms of managing links and dealing
    with link related policy.  However, it assumes limited
    connectivity and does not adapt well to a network environment with
    high connectivity available.


5  X.400 and RFC 822

This document defines mechanisms for X.400 routing.  It is important
that this can be integrated with RFC 822 base routing, as many MTAs
will work in both communities.  This routing document is written with
this problem in mind, and support for RFC 822 routing using the same
basic infrastructure is defined in a companion document [12].  In
addition support for X.400/RFC 822 gatewaying is needed, to support
interaction.  Directory based mechanisms for this are defined in [16].
The advantages of the approach defined by this set of specifications
are:


 o  Uniform management for sites which wish to support both protocols.

 o  Simpler management for gateways.

 o  Improved routing services for RFC 822 only sites.

For sites which are only X.400 or only RFC 822, the mechanisms
associated with gatewaying or with the other form of addressing are
not needed.


6  Objects

It is useful to start with a manager's perspective.  Here is the set
of object classes used in this specification.  It is important that
all information entered relates to something which is being managed.
If this is achieved, configuration decisions are much more likely to
be correct.  In the examples, distinguished names are written using
the String Syntax for Distinguished Names [10].  The list of objects
used in this specification is:


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User An entry representing a single human user.  This will typically
    be named in an organisational context.  For example:

     CN=Edgar Smythe,
     O=Zydeco Services, C=GB


    This entry would have associated information, such as telephone
    number, postal address, and mailbox.

MTA A Message Transfer Agent.  In general, the binding between
    machines and MTAs will be complex.  Often a small number of MTAs
    will be used to support many machines, by use of local approaches
    such as shared filestores.  MTAs may support multiple protocols,
    and will identify separate addressing information for each
    protocol.
    To achieve support for multiple protocols, an MTA is modelled as
    an Application Process, which is named in the directory.  Each MTA
    will have one or more associated Application Entities.  Each
    Application Entity is named as a child of the Application Process,
    using a common name which conveniently identifies the Application
    Entity relative to the Application Process.  Each Application
    Entity supports a single protocol, although different Application
    Entities may support the same protocol.  Where an MTA only
    supports one protocol or where the addressing information for all
    of the protocols supported have different attributes to represent
    addressing information (e.g., P1(88) and SMTP) the Application
    Entity(ies) may be represented by the single Application Process
    entry.

User Agent (Mailbox) This defines the User Agent (UA) to which mail
    may be delivered.  This will define the account with which the UA
    is associated, and may also point to the user(s) associated with
    the UA. It will identify which MTAs1 are able to access the UA.

Role Some organisational function.  For example:

----------------------------
    1. In the formal X.400 model, there will be a single MTA
delivering to a UA. In many practical configurations, multiple MTAs
can deliver to a single UA. This will increase robustness, and is
desirable.



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     CN=System Manager, OU=Sales,
     O=Zydeco Services, C=GB


    The associated entry would indicate the occupant of the role.

Distribution Lists There would be an entry representing the
    distribution list, with information about the list, the manger,
    and members of the list.


7  Communities

There are two basic types of agreement in which an MTA may participate
in order to facilitate routing:


Bilateral Agreements An agreement between a pair of MTAs to route
    certain types of traffic.  This MTA pair agreement usually
    reflects some form of special agreement and in general bilateral
    information shall be held for the link at both ends.  In some
    cases, this information shall be private.

Open Agreements An agreement between a collection of MTAs to behave
    in a cooperative fashion to route traffic.  This may be viewed as
    a general bilateral agreement.

It is important to ensure that there are sufficient agreements in
place for all messages to be routed.  This will usually be done by
having agreements which correspond to the addressing hierarchy.  For
X.400, this is the model where a PRMD connects to an ADMD, and the
ADMD provides the inter PRMD connectivity, by the ability to route to
all other ADMDs.  Other agreements may be added to this hierarchy, in
order to improve the efficiency of routing.  In general, there may be
valid addresses, which cannot be routed to, either for connectivity or
policy reasons.

We model these two types of agreements as communities.  A community is
a scope in which an MTA advertises its services and learns about other
services.  Each MTA will:

1.  Register its services in one or more communities.



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2.  Look up services in one or more communities.

In most cases an MTA will deal with a very small number of communities
--- very often one only.  There are a number of different types of
community.


The open community This is a public/global scope.  It reflects
    routing information which is made available to any MTA which
    wishes to use it.

The local community This is the scope of a single MTA. It reflects
    routing information private to the MTA. It will contain an MTA's
    view of the set of bilateral agreements in which it participates,
    and routing information private and local to the MTA.

Hierarchical communities A hierarchical community is a subtree of the
    O/R Address tree.  For example, it might be a management domain,
    an organisation, or an organisational unit.  This sort of
    community will allow for firewalls to be established.  A community
    can have complex internal structure, and register a small subset
    of that in the open community.

Closed communities A closed community is a set of MTAs which agrees
    to route amongst themselves.  Examples of this might be ADMDs
    within a country, or a set of PRMDs representing the same
    organisation in multiple countries.

Formally, a community indicates the scope over which a service is
advertised.  In practice, it will tend to reflect the scope of
services offered.  It does not make sense to offer a public service,
and only advertise it locally.  Public advertising of a private
service makes more sense, and this is shown below.  In general, having
a community offer services corresponding to the scope in which they
are advertised will lead to routing efficiency.  Examples of how
communities can be used to implement a range of routing policies are
given in Section 9.2.


8  Routing Trees

Communities are a useful abstract definition of the routing approach
taken by this specification.  Each community is represented in the


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directory as a routing tree.  There will be many routing trees
instantiated in the directory.  Typically, an MTA will only be
registered in and make use of a small number of routing trees.  In
most cases, it will register in and use the same set of routing trees.

8.1  Routing Tree Definition


Each community has a model of the O/R address space.  Within a
community, there is a general model of what to do with a given O/R
Address.  This is structured hierarchically, according to the O/R
address hierarchy.  A community can register different possible
actions, depending on the depth of match.  This might include
identifying the MTA associated with a UA which is matched fully, and
providing a default route for an O/R address where there is no match
in the community --- and all intermediate forms.
The name structure of a routing tree follows the O/R address
hierarchy, which is specified in a separate document [14].  Where
there is any routing action associated with a node in a routing tree,
the node is of object class routingInformation, as defined in
Section 10.

8.2  The Open Community Routing Tree


The routing tree of the open community starts at the root of the DIT.
This routing tree also serves the special function of instantiating
the global O/R Address space in the Directory.  Thus, if a UA wishes
to publish information to the world, this hierarchy allows it to do
so.
The O/R Address hierarchy is a registered tree, which may be
instantiated in the directory.  Names at all points in the tree are
valid, and there is no requirement that the namespace is instantiated
by the owner of the name.  For example, a PRMD may make an entry in
the DIT, even if the ADMD above it does not.  In this case, there will
be a ``skeletal'' entry for the ADMD, which is used to hang the PRMD
entry in place.  The skeletal entry contains the minimum number of
entries which are needed for it to exist in the DIT (Object Class and
Attribute information needed for the relative distinguished name).
This entry may be placed there solely to support the subordinate
entry, as its existence is inferred by the subordinate entry.  Only
the owner of the entry may place information into it.  An analogous
situation in current operational practice is to make DIT entries for


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_______________________________________________________________________

routingTreeRoot OBJECT-CLASS ::= {
    SUBCLASS OF {routingInformation|subtree}
    ID oc-routing-tree-root}

_________________Figure_1:__Location_of_Routing_Trees__________________


Countries and US States.


8.3  Routing Tree Location

All routing trees follow the same O/R address hierarchy.  Routing
trees other than the open community routing tree are rooted at
arbitrary parts of the DIT. These routing trees are instantiated using
the subtree mechanism defined in the companion document ``Representing
Tables and Subtrees in the Directory'' [14].  A routing tree is
identified by the point at which it is rooted.  An MTA will use a list
of routing trees, as determined by the mechanism described in
Section 9.  Routing trees may be located in either the organisational
or O/R address structured part of the DIT. All routing trees, other
than the open community routing tree, are rooted by an entry of object
class routingTreeRoot, as defined in Figure 1.


8.4  Example Routing Trees

Consider routing trees with entries for O/R Address:


 P=ABC; A=XYZMail; C=GB;


In the open community routing tree, this would have a distinguished
name of:


 PRMD=ABC, ADMD=XYZMail, C=GB


Consider a routing tree which is private to:



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 O=Zydeco Services, C=GB


They might choose to label a routing tree root ``Zydeco Routing
Tree'', which would lead to a routing tree root of:


 CN=Zydeco Routing Tree, O=Zydeco Services, C=GB


The O/R address in question would be stored in this routing tree as:


 PRMD=ABC, ADMD=XYZMail
 C=GB, CN=Zydeco Routing Tree,
 O=Zydeco Services, C=GB


8.5  Use of Routing Trees to look up Information


Lookup of an O/R address in a routing tree is done as follows:

1.  Map the O/R address onto the O/R address hierarchy described in
    [14] in order to generate a Distinguished Name.

2.  Append this to the Distinguished Name of the routing tree, and
    then look up the whole name.

3.  Handling of errors will depend on the application of the lookup,
    and is discussed later.


Note that it is valid to look up a null O/R Address, as the routing
tree root may contain default routing information for the routing
tree.  This is held in the root entry of the routing tree, which is a
subclass of routingInformation.  The open community routing tree does
not have a default.
Routing trees may have aliases into other routing trees.  This will
typically be done to optimise lookups from the first routing tree
which a given MTA uses.  Lookup needs to take account of this.




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_______________________________________________________________________

routingTreeList ATTRIBUTE ::= {
        WITH SYNTAX RoutingTreeList
        SINGLE VALUE
        ID at-routing-tree-list}

RoutingTreeList ::= SEQUENCE OF RoutingTreeName

RoutingTreeName ::= DistinguishedName

________________Figure_2:__Routing_Tree_Use_Definition_________________


9  Routing Tree Selection


The list of routing trees which a given MTA uses will be represented
in the directory.  This uses the attribute defined in Figure 2.
This attribute defines the routing trees used by an MTA, and the order
in which they are used.  Holding these in the directory eases
configuration management.  It also enables an MTA to calculate the
routing choice of any other MTA which follows this specification,
provided that none of its routing trees have access restrictions.
This will facilitate debugging routing problems.


9.1  Routing Tree Order

The order in which routing trees are used will be critical to the
operation of this algorithm.  A common approach will be:

1.  Access one or more shared private routing trees to access private
    routing information.

2.  Utilise the open routing tree.

3.  Fall back to a default route from one of the private routing
    trees.


Initially, the open routing tree will be very sparse, and there will
be little routing information in ADMD level nodes.  Access to many
services will only be via ADMD services, which in turn will only be


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accessible via private links.  For most MTAs, the fallback routing
will be important, in order to gain access to an MTA which has the
right private connections configured.
In general, for a site, UAs will be registered in one routing tree
only, in order to avoid duplication.  They may be placed into other
routing trees by use of aliases, in order to gain performance.  For
some sites, Users and UAs with a 1:1 mapping will be mapped onto
single entries by use of aliases.


9.2  Example use of Routing Trees

Some examples of how this structure might be used are now given.  Many
other combinations are possible to suit organisational requirements.

9.2.1  Fully Open Organisation


The simplest usage is to place all routing information in the open
community routing tree.  An organisation will simply establish O/R
addresses for all of its UAs in the open community tree, each
registering its supporting MTA. This will give access to all systems
accessible from this open community.

9.2.2  Open Organisation with Fallback

In practice, some MTAs and MDs will not be directly reachable from the
open community (e.g., ADMDs with a strong model of bilateral
agreements).  These services will only be available to
users/communities with appropriate agreements in place.  Therefore it
will be useful to have a second (local) routing tree, containing only
the name of the fallback MTA at its root.  In many cases, this
fallback would be to an ADMD connection.

Thus, open routing will be tried first, and if this fails the message
will be routed to a single selected MTA.

9.2.3  Minimal-routing MTA

The simplest approach to routing for an MTA is to deliver messages to
associated users, and send everything else to another MTA (possibly
with backup).



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An organisation using MTAs with this approach will register its users
as for the fully open organisation.  A single routing tree will be
established, with the name of the organisation being aliased into the
open community routing tree.  Thus the MTA will correctly identify
local users, but use a fallback mechanism for all other addresses.

9.2.4  Organisation with Firewall

An organisation can establish an organisation community to build a
firewall, with the overall organisation being registered in the open
community.  This is an important structure, which cannot be achieved
easily with current technology (e.g., DNS with MX records).


 o  Some MTAs are registered in the open community routing tree to
    give access into the organisation.  This will include the O/R tree
    down to the organisational level.  Full O/R Address verification
    will not take place externally.

 o  All users are registered in a private (organisational) routing
    tree.

 o  All MTAs in the organisation are registered in the organisation's
    private routing tree, and access information in the organisation's
    community.  This gives full internal connectivity.

 o  Some MTAs in the organisation access the open community routing
    tree.  These MTAs take traffic from the organisation to the
    outside world.  These will often be the same MTAs that are
    externally advertised.

9.2.5  Well Known Entry Points


Well known entry points will be used to provide access to countries
and MDs which are oriented to private links.  A private routing tree
will be established, which indicates these links.  This tree would be
shared by the well known entry points.

9.2.6  ADMD using the Open Community for Advertising


An ADMD uses the open community for advertising.  It advertises its
existence and also restrictive policy.  This will be useful for:

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 o  Address validation

 o  Advertising the mechanism for a bilateral link to be established

9.2.7  ADMD/PRMD gateway

An MTA provides a gateway from a PRMD to an ADMD. It is important to
note that many X.400 MDs will not use the directory.  This is quite
legitimate.  This technique can be used to register access into such
communities from those that use the directory.


 o  The MTA registers the ADMD in its local community (private link)

 o  The MTA registers itself in the PRMD's community to give access to
    the ADMD.


10  Routing Information

Routing trees are defined in the previous section, and are used as a
framework to hold routing information.  Each node, other than a
skeletal one, in a routing tree has information associated with it,
which is defined by the object class routingInformation in Figure 3.
This structure is fundamental to the operation of this specification,
and_it_is_recommended_that_it_be_studied_with_care.____________________


routingInformation OBJECT-CLASS ::= {
    SUBCLASS OF top
    MAY CONTAIN {
        subtreeInformation|
        routingFilter|
        routingFailureAction|
        mTAInfo|
        accessMD|
        nonDeliveryInfo|                                            10
        badAddressSearchPoint|
        badAddressSearchAttributes}
    ID oc-routing-information}
                -- No naming attributes as this is not a
                -- structural object class



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subtreeInformation ATTRIBUTE ::= {
    WITH SYNTAX SubtreeInfo                                         20
    SINGLE VALUE
    ID at-subtree-information}

SubtreeInfo ::= ENUMERATED {
    all-children-present(0),
    not-all-children-present(1) }


routingFilter ATTRIBUTE ::= {
    WITH SYNTAX RoutingFilter                                       30
    ID at-routing-filter}


RoutingFilter ::= SEQUENCE{
        attribute-type OBJECT-IDENTIFIER,
        weight RouteWeight,
        dda-key String OPTIONAL,
        regex-match IA5String OPTIONAL,
        node DistinguishedName }
                                                                    40
String ::= CHOICE {PrintableString, TeletexString}

routingFailureAction ATTRIBUTE ::= {
    WITH SYNTAX RoutingFailureAction
    SINGLE VALUE
    ID at-routing-failure-action}

RoutingFailureAction ::= ENUMERATED {
            next-level(0),
            next-tree-only(1),                                      50
            next-tree-first(2),
            stop(3)  }


mTAInfo ATTRIBUTE ::= {
    WITH SYNTAX MTAInfo
    ID at-mta-info}

MTAInfo ::= SEQUENCE {
            name DistinguishedName,                                 60

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            weight [1] RouteWeight DEFAULT preferred-access,
            mta-attributes [2] SET OF Attribute OPTIONAL,
            ae-info  SEQUENCE OF SEQUENCE {
                aEQualifier PrintableString,
                ae-weight RouteWeight DEFAULT preferred-access,
                ae-attributes SET OF Attribute OPTIONAL} OPTIONAL
}

RouteWeight ::= INTEGER  {endpoint(0),
                preferred-access(5),                                70
                backup(10)} (0..20)

_______________Figure_3:__Routing_Information_at_a_Node________________

For example, information might be associated with the (PRMD) node:


 PRMD=ABC, ADMD=XYZMail, C=GB


If this node was in the open community routing tree, then the
information represents information published by the owner of the PRMD
relating to public access to that PRMD. If this node was present in
another routing tree, it would represent information published by the
owner of the routing tree about access information to the referenced
PRMD. The attributes associated with a routingInformation node provide
the following information:


Implicit That the node corresponds to a partial or entire valid O/R
    address.  This is implicit in the existence of the entry.

Object Class If the node is a UA. This will be true if the node is of
    object class routedUA. This is described further in Section 11.
    If it is not of this object class, it is an intermediate node in
    the O/R Address hierarchy.

routingFilter A set of routing filters, defined by the routingFilter
    attribute.  This attribute provides for routing on information in
    the unmatched part of the O/R Address.  This is described in
    Section 10.3.

subtreeInformation Whether or not the node is authoritative for the
    level below is specified by the subtreeInformation attribute.  If

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    it is authoritative, indicated by the value all-children-present,
    this will give the basis for (permanently) rejecting invalid O/R
    Addresses.  The attribute is encoded as enumerated, as it may be
    later possible to add partial authority (e.g., for certain
    attribute types).  If this attribute is missing, the node is
    assumed to be non-authoritative (not-all-children-present).
    For example, consider the node:

     MHS-O=Zydeco, PRMD=ABC, ADMD=XYZMail, C=GB


    An organisation which has a bilateral agreement with this
    organisation has this entry in its routing tree, with no children
    entries.  This is marked as non-authoritative.  There is a second
    routing tree maintained by Zydeco, which contains all of the
    children of this node, and is marked as authoritative.  When
    considering an O/R Address

     MHS-G=Random + MHS-S=Unknown, MHS-O=Zydeco,
     PRMD=ABC, ADMD=XYZMail, C=GB


    only the second, authoritative, routing tree can be used to
    determine that this address is invalid.  In practice, the manager
    configuring the non-authoritative tree, will be able to select
    whether an MTA using this tree will proceed to full verification,
    or route based on the partially verified information.

mTAInfo A list of MTAs and associated information defined by the
    mTAInfo attribute.  This information is discussed further in
    Sections 15 and 18.  This information is the key information
    associated with the node.  When a node is matched in a lookup, it
    indicates the validity of the route, and a set of MTAs to connect
    to.  Selection of MTAs is discussed in Sections 18 and
    Section 10.2.

routingFailureAction An action to be taken if none of the MTAs can be
    used directly (or if there are no MTAs present) is defined by the
    routingFailureAction attribute.  Use of this attribute and
    multiple routing trees is described in Section 10.1.

accessMD The accessMD attribute is discussed in Section 10.4.  This
    attribute is used to indicate MDs which provide indirect access to


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    the part of the tree that is being routed to.

badAddressSearchPoint/badAddressSearchAttributes The
    badAddressSearchPoint and badAddressSearchAttributes are discussed
    in Section 17.  This attribute is for when an address has been
    rejected, and allows information on alternative addresses to be
    found.

10.1  Multiple routing trees


A routing decision will usually be made on the basis of information
contained within multiple routing trees.  This section describes the
algorithms relating to use of multiple routing trees.  Issues relating
to use of X.500 and handling of errors is discussed in Section14.
The routing decision works by examining a series of entries (nodes) in
one or more routing trees.  Each entry may contain information on
possible next-hop MTAs.  When an entry is found which enables the
message to be routed, one of the routing options determined at this
point is selected, and a routing decision is made.  It is possible,
that further entries may be examined, in order to determine other
routing options.  This sort of heuristic is not discussed here.
When a single routing tree is used, the longest possible match based
on the O/R address to be routed to is found.  This entry, and then
each of its parents in turn is considered, ending with the routing
tree root node (except in the case of the open routing tree, which
does not have such a node).  When multiple routing trees are
considered, the basic approach is to treat them in a defined order.
This is supplemented by a mechanism whereby if a matched node cannot
be used directly, the routing algorithm will have the choice to move
up a level in the current routing tree, or to move on to the next
routing tree with an option to move back to the first tree later.
This option to move back is to allow for the common case where a tree
is used to specify two things:


1.  Routing information private to the MTA (e.g., local UAs or routing
    info for bilateral links).

2.  Default routing information for the case where other routing has
    failed.

The actions allow for a tree to be followed, for the private


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information, then for other trees to be used, and finally to fall back
to the default situation.  For very complex configurations it might be
necessary to split this into two trees.  The options defined by
routingFailureAction, to be used when the information in the entry
does not enable a direct route, are:

next-level Move up a level in the current routing tree.  This is the
    action implied if the attribute is omitted.  This will usually be
    the best action in the open community routing tree.

next-tree-only Move to the next tree, and do no further processing on
    the current tree.  This will be useful optimisation for a routing
    tree where it is known that there is no useful additional routing
    information higher in the routing tree.

next-tree-first Move to the next tree, and then default back to the
    next level in this tree when all processing is completed on
    subsequent trees.  This will be useful for an MTA to operate in
    the sequence:

    1.  Check for optimised private routes

    2.  Try other available information

    3.  Fall back to a local default route

stop This address is unroutable.  No processing shall be done in any
    trees.


For the root entry of a routing tree, the default action and
next-level are interpreted as next-tree-only.

10.2  MTA Choice


This section considers how the choice between alternate MTAs is made.
First, it is useful to consider the conditions why an MTA is entered
into a node of the routing tree are:

 o  The manager for the node of the tree shall place it there.  This
    is a formality, but critical in terms of overall authority.



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 o  The MTA manager shall agree to it being placed there.  For a well
    operated MTA, the access policy of the MTA will be set to enforce
    this.

 o  The MTA will in general (for some class of message) be prepared to
    route to any valid O/R address in the subtree implied by the
    address.  The only exception to this is where the MTA will route
    to a subset of the tree which cannot easily be expressed by making
    entries at the level below.  An example might be an MTA prepared
    to route to all of the subtree, with certain explicit exceptions.

Information on each MTA is stored in an mTAInfo attribute.  This
attribute contains:


name The Distinguished Name of the MTA (Application Process)

weight A weighting factor (Route Weight) which gives a basis to
    choose between different MTAs.  This is described in Section 10.2.

mta-attributes Attributes from the MTAs entry.  Information on the
    MTA will always be stored in the MTA's entry.  The MTA is
    represented here as a structure, which enables some of this entry
    information to be represented in the routing node.  This is
    effectively a maintained cache, and can lead to considerable
    performance optimisation.  For example if ten MTAs were
    represented at a node, another MTA making a routing decision might
    need to make ten directory reads in order to obtain the
    information needed.  If any attributes are present here, all of
    the attributes needed to make a routing decision shall be
    included, and also all attributes at the Application Entity level.

Where an MTA supports a single protocol only, or the protocols it
supports have address information that can be represented in
non-conflicting attributes, then the MTA may be represented as an
application process only.  In this case, the ae-info structure which
gives information on associated application entities may be omitted,
as the MTA is represented by a single application entity which has the
same name as the application process.  In other cases, the names of
all application entities shall be included.  A weight is associated
with each application entity to allow the MTA to indicate a preference
between its application entities.



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ae-qualifier A printable string (e.g.  ``x400-88''), which is the
    value of the common name of the relative distinguished name of the
    application entity.  This can be used with the application process
    name to derive the application entity title.

ae-weight A weighting factor (Route Weight) which gives a basis to
    choose between different Application Entities (not between
    different MTAs).  This is described in Section 10.2.

ae-attributes Attributes from the AEs entry.

Route weighting is a mechanism to distinguish between different route
choices.  A routing weight may be associated with the MTA in the
context of a routing tree entry.  This is because routing weight will
always be context dependent.  This will allow machines which have
other functions to be used as backup MTAs.  The Route Weight is an
integer in range 0--20.  The lower the value, the better the choice of
MTA. Where the weight is equal, and no other factors apply, the choice
between the MTAs shall be random to facilitate load balancing.  If the
MTA itself is in the list, it shall only route to an MTA of lower
weight.  The exact values will be chosen by the manager of the
relevant part of the routing tree.  For guidance, three fixed points
are given:


 o  0.  For an MTA which can deliver directly to the entire subtree
    implied by the position in the routing tree.

 o  5.  For an MTA which is preferred for this point in the subtree.

 o  10.  For a backup MTA.

When an organisation registers in multiple routing trees, the route
weight used is dependent on the context of the subtree.  In general it
is not possible to compare weights between subtrees.  In some cases,
use of route weighting can be used to divert traffic away from
expensive links.

Attributes present in an MTA Entry are defined in various parts of
this specification.  A summary and pointers to these sections is given
in Section 16.
Attributes that are available in the MTA entry and will be needed for
making a routing choice are:


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protocolInformation

applicationContext

mhs-deliverable-content-length

responderAuthenticationRequirements

initiatorAuthenticationRequirements

responderPullingAuthenticationRequirements

initiatorPullingAuthenticationRequirements

initiatorP1Mode

responderP1Mode

polledMTAs Current MTA shall be in list if message is to be pulled.

mTAsAllowedToPoll

supportedMTSExtensions

If any MTA attributes are present in the mTAInfo attribute, all of the
attribute that may affect routing choice shall be present.  Other
attributes may be present.  A full list of MTA attributes, with
summaries of their descriptions are given in Section 16, with a formal
definition in Figure 6 on Page 37.


10.3  Routing Filters

This attribute provides for routing on information in the unmatched
part of the O/R Address, including:


 o  Routing on the basis of an O/R Address component type

 o  Routing on the basis of a substring match of an O/R address
    component.  This might be used to route X121 addressed faxes to an
    appropriate MTA.



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When present, the procedures of analysing the routing filters shall be
followed before other actions.  The routing filter overrides mTAInfo
and accessMD attributes.  The components of the routingFilter
attribute are:

attribute-type This gives the attribute type to be matched, and is
    selected from the attribute types which have not been matched to
    identify the routing entry.  The filter applies to this attribute
    type.  If there is no regular expression present (as defined
    below), the filter is true if the attribute is present.  The value
    is the object identifier of the X.500 attribute type (e.g.,
    at-prmd-name).

weight This gives the weight of the filter, which is encoded as a
    Route Weight, with lower values indicating higher priority.  If
    multiple filters match, the weight of each matched filter is used
    to select between them.  If the weight is the same, then a random
    choice shall be made.

dda-key If the attribute is domain defined, then this parameter may
    be used to identify the key.

regex-match This string is used to give a regular expression match on
    the attribute value.  The syntax for regular expressions is
    defined in Appendix E.

node This defines where to get routing information for the filter.
    It will be an entry with object class routingInformation, which
    can be used to determine the MTA or MTA choice.


An example of use of routing filters is now given, showing how to
route on X121 address to a fax gateway in Germany.  Consider the
routing point.

  PRMD=ABC, ADMD=XYZMail, C=GB



The entry associated would have two routing filters:

1.  One with type x121 and no regular expression, to route a default
    fax gateway.


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_______________________________________________________________________

accessMD ATTRIBUTE ::= {
        SUBTYPE OF distinguishedName
        ID at-access-md}

______________________Figure_4:__Indirect_Access_______________________


2.  One with type x121 and a regular expression ^9262 to route all
    German faxes to a fax gateway located in Germany with which there
    is a bilateral agreement.  This would have a lower weight, so that
    it would be selected over the default fax gateway.


10.4  Indirect Connectivity

In some cases a part of the O/R Address space will be accessed
indirectly.  For example, an ADMD without access from the open
community might have an agreement with another MD to provide this
access.  This is achieved by use of the accessMD attribute defined in
Figure 4.  If this attribute is found, the routing algorithm shall
read the entry pointed to by this distinguished name and route
according to the information retrieved, in order to route to this
access MD.

The attribute is called an MD, as this is descriptive of its normal
use.  It might point to a more closely defined part of the O/R Address
space.
It is possible for both access MD and MTAs to be specified.  This
might be done if the MTAs only support access over a restricted set of
transport stacks.  In this case, the access MD shall only be routed to
if it is not possible to route to any of the MTAs.
This structure can also be used as an optimisation, where a set of
MTAs provides access to several parts of the O/R Address space.
Rather than repeat the MTA information (list of MTAs) in each
reference to the MD, a single access MD is used as a means of grouping
the MTAs.  The value of the Distinguished Name of the access MD will
probably not be meaningful in this case (e.g., it might be the name
``Access MTA List'', within the organisation.)

If the MTA routing is unable to access the information in the Access
MD dues to directory security restrictions, the routing algorithm
shall continue as if no MTA information was located in the routing


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entry.


11  Local Addresses (UAs)

Local addresses (UAs) are a special case for routing:  the endpoint.
The definition of the routedUA object class is given in Figure 5.
This identifies a User Agent in a routing tree.  This is needed for
several reasons:

1.  To allow UAs to be defined without having an entry in another part
    of the DIT.

2.  To identify which (leaf and non-leaf) nodes in a routing tree are
    User Agents.  In a pure X.400 environment, a UA (as distinct from
    a connecting part of the O/R address space) is simply identified
    by object class.  Thus an organisation entry can itself be a UA. A
    UA need not be a leaf, and can thus have children in the tree.

3.  To allow UA parameters as defined in X.402 (e.g., the
    mhs-deliverable-eits) to be determined efficiently from the
    routing tree, without having to go to the user's entry.

4.  To provide access to other information associated with the UA, as
    defined below.


The following attributes are defined associated with the UA.

supportedExtensions

supportingMTA The MTAs which support a UA directly are noted in the
    SupportingMTA attribute, which may be multi-valued.  In the X.400
    model, only one MTA is associated with a UA. In practice, it is
    possible and useful for several MTAs to be able to deliver to a
    single UA. This attribute is a subtype of MTAinfo, as it is
    possible for an MTA to be registered to route to a UA, without it
    actually being able to deliver messages to it.
    This attribute shall be present, unless the address is being
    non-delivered or redirected.

mandatoryRedirect/filteredRedirect The attributes mandatoryRedirect
    and filteredRedirect control redirects, as described in


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    Section 22.1.

userName The attribute userName points to the distinguished Name of
    the user, as defined by the mhs-user in X.402.  The pointer from
    the user to the O/R Address is achieved by the mhs-or-addresses
    attribute.  This makes the UA/User linkage symmetrical.

nonDeliveryInfo The attribute nonDeliveryInfo mandates non-delivery
    to this address, as described in Section 22.3.

When routing to a UA, an MTA will read the supportingMTA attribute.
If it finds its own name present, it will know that the UA is local,
and invoke appropriate procedures for local delivery (e.g.,
co-resident or P3 access information).  The cost of holding these
attributes for each UA at a site will often be reduced by use of
shared attributes (as defined in X.500(93)).

The linkage between the UA and User entries was noted above.  It is
also possible to use a single entry for both User and UA, as there is
no conflict between the attributes in each of the objects.  In this
case, the entries shall be in one part of the DIT, with aliases from
the other.  Because the UA and User are named with different
attributes, the aliases shall be at the leaf level.

11.1  Searching for Local Users

The approach defined in this specification performs all routing by use
of reads.  This is done for performance reasons, as it is a reasonable
expectation that all DSA implementations will support a high
performance read operation.  For local routing only, an MTA in
cooperation with the provider of the local routing tree may choose to
use a search operation to perform routing.  The major benefit of this
is that there will not be a need to store aliases for alternate names,
and so the directory storage requirement and alias management will be
reduced.  The difficulty with this approach is that it is hard to
define search criteria that would be effective in all situations and
well supported by all DUAs.  There are also issues about determining
the validity of a route on the basis of partial matches.







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12  Direct Lookup

Where an O/R address is registered in the open community and has one
or more ``open'' MTAs which support it, this will be optimised by
storing MTA information in the O/R address entry.  In general, the
Directory will support this by use of attribute inheritance or an
implementation will optimise the storage or repeated information, and
so there will not be a large storage overhead implied.  This is a
function of the basic routing approach.
As a further optimisation of this case, the User's distinguished name
entry may contain the mTAInfo attribute.  This can be looked up from
the distinguished name, and thus routing on submission can be achieved
by use of a single read.


13  Alternate Routes


13.1  Finding Alternate Routes

The routing algorithm selects a single MTA to be routed to.  It could
be extended to find alternate routes to a single MTA with possibly
different weights.  How far this is done is a local configuration
choice.  Provision of backup routing is desirable, and leads to robust
service, but excessive use of alternate routing is not usually
beneficial.  It will often force messages onto convoluted paths, when
there was only a short outage on the preferred path.
It is important to note that this strategy will lead to picking the
first acceptable route.  It is important to configure the routing
trees so that the first route identified will also be the best route.


13.2  Sharing routing information

So far, only single addresses have been considered.  Improving routing
choice for multiple addresses is analogous to dealing with multiple
routes.  This section defines an optional improvement.  When multiple
addresses are present, and alternate routes are available, the
preferred routes may be chosen so as to maximise the number of
recipients sent with each message.

Specification of routing trees can facilitate this optimisation.
Suppose there is a set of addresses (e.g., in an organisation) which


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have different MTAs, but have access to an MTA which will do local
switching.  If each address is registered with the optimal MTA as
preferred, but has the ``hub'' MTA registered with a higher route
weight, then optimisation may occur when a message is sent to multiple
addresses in the group.


14  Looking up Information in the Directory

The description so far has been abstract about lookup of information.
This section considers how information is looked up in the Directory.
Consider that an O/R Address is presented for lookup, and there is a
sequence of routing trees.  At any point in the lookup sequence, there
is one of a set of actions that can take place:

Handle MTA Info Information from the node shall be examined.  If
    suitable information is found, one of the following is done:

     o  Use the information and finish the routing process

     o  Continue the routing process in order to find more options to
        choose from

Unroutable Address Potentially valid address, which cannot be routed

Bad Address Return the failure to the routing algorithm

Temporary Reject Try again later.  The MTA shall handle this in a
    similar manner to the way it would handle the failure to connect
    to a remote MTA.

Permanent Reject Administrative error on the directory which may be
    fixed in future, but which currently prevents routing.


Editor's Note: Add information on what to do and which diagnostic
    codes and handling of failed lookups.

Errors from the lookup (directory read) shall be handled as follows:


AttributeError This leads to a permanent reject.



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NameError The matched parameter is used to determine the number of
    components of the name that have matched (possibly zero).  The
    read is then repeated with this name.  This is the normal case,
    and allows the ``best'' entry in the routing tree to be located
    with two reads.

Referral The referral shall be followed.

SecurityErrror Strip one component of the O/R address and continue.

ServiceError This leads to a temporary reject (see above).


15  Naming MTAs

MTAs need to be named in the DIT, but the name does not have routing
significance, it is simply a unique key.  Attributes associated with
naming MTAs are given in Figure 6.  This figure also gives a list of
attributes, which may be present in the MTA entry.  The use of most of
these is explained in subsequent sections.  The mTAName and
globalDomainID attributes are needed to define the information that an
MTA places in trace information.  As noted previously, an MTA is
represented as an Application Process, with one or more Application
Entities.______________________________________________________________


mTAName ATTRIBUTE ::= {
    SUBTYPE OF name
    WITH SYNTAX DirectoryString{ub-mta-name-length}
    SINGLE VALUE
    ID at-mta-name}
                        -- used for naming when
                        -- MTA is named in O=R Address Hierarchy

globalDomainID ATTRIBUTE ::= {                                      10
    WITH SYNTAX GlobalDomainIdentifier
    SINGLE VALUE
    ID at-global-domain-id}
                        -- both attributes present when MTA
                        -- is named outside O=R Address Hierarchy
                        -- to enable trace to be written

mTAApplicationProcess OBJECT CLASS ::= {


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    SUBCLASS OF {application-process}
    MAY CONTAIN {                                                   20
        mTAWillRoute|
        globalDomainID|
        routingTreeList|
        accessMD|
        localAccessUnit|
        accessUnitsUsed
    }
    ID oc-mta-application-process}

mTA OBJECT CLASS ::= {   -- Application Entity                      30
    SUBCLASS OF {mhs-message-transfer-agent}
    MAY CONTAIN {
        mTAName|
        globalDomainID|         -- per AE variant
        responderAuthenticationRequirements|
        initiatorAuthenticationRequirements|
        responderPullingAuthenticationRequirements|
        initiatorPullingAuthenticationRequirements|
        initiatorP1Mode|
        responderP1Mode|                                            40
        polledMTAs|
        protocolInformation|
        respondingRTSCredentials|
        initiatingRTSCredentials|
        callingPresentationAddress|
        callingSelectorValidity|
        bilateralTable|
        mTAWillRoute|
        mhs-deliverable-content-length|
        routingTreeList|                                            50
        supportedMTSExtensions|
        mTAsAllowedToPoll
        }
    ID oc-mta}

______________________Figure_6:__MTA_Definitions_______________________

In X.400, MTAs are named by MD and a single string.  This style of
naming is supported, with MTAs named in the O/R Address tree relative
to the root of the DIT (or possibly in a different routing tree).  The
mTAName attribute is used to name MTAs in this case.  For X.400(88) it


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is assumed that the Distinguished Name may be passed as an AE Title.
MTAs may be named with any other DN, which can be in the O/R Address
or Organisational DIT hierarchy.  There are several reasons why MTAs
might be named differently.


 o  The flat naming space is inadequate to support large MDs.  MTA
    name assignment using the directory would be awkward.

 o  An MD does not wish to register its MTAs in this way (essentially,
    it prefers to give them private names in the directory).

 o  An organisation has a policy for naming application processes,
    which does not fit this approach.

In this case, the MTA entry shall contain the correct information to
be inserted in trace.  The mTAName and globalDomainID attributes are
used to do this.  They are single value.  For an MTA which inserts
different trace in different circumstances, a more complex approach
would be needed.
An MD may choose to name its MTAs outside of the O/R address
hierarchy, and then link some or all of them with aliases.  A pointer
from this space may help in resolving information based on MTA Trace.


15.1  Naming 1984 MTAs

Some simplifications are necessary for 1984 MTAs, and only one naming
approach may be used.  In X.400, MTAs are named by MD and a single
string.  This style of naming is supported, with MTAs named in the O/R
Address tree relative to the root of the DIT (or possibly in a
different routing tree).  The MTAName attribute is used to name MTAs
in this case.


16  Attributes Associated with the MTA


This section lists the attributes which may be associated with an MTA
as defined in Figure 6, and gives pointers to the sections that
describe them.

mTAName Section 15.


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globalDomainID Section 15.

protocolInformation Section 18.1.

applicationContext Section 18.2.

mhs-deliverable-content-length Section 18.3.

responderAuthenticationRequirements Section 20.2.

initiatorAuthenticationRequirements Section 20.2.

responderPullingAuthenticationRequirements Section 20.2.

initiatorPullingAuthenticationRequirements Section 20.2.

initiatorP1Mode Section 19.

responderP1Mode Section 19.

polledMTAs Section 19.

mTAsAllowedToPoll Section 19.

respondingRTSCredentials Section 20.3.

initiatingRTSCredentials Section 20.3.

callingPresentationAddress Section 20.3.

callingSelectorValidity Section 20.3.

bilateralTable Section 17.

mTAWillRoute Section 21.

routingTreeList Section 9.

supportedMTSExtensions Section 18.3.






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17  Bilateral Agreements

Each MTA has an entry in the DIT. This will be information which is
globally valid, and will be useful for handling general information
about the MTA and for information common to all connections.  In many
cases, this will be all that is needed.  This global information may
be restricted by access control, and so need not be globally
available.  In some cases, MTAs will maintain bilateral and
multilateral agreements, which hold authentication and related
information which is not globally valid.  This section describes a
mechanism for grouping such information into tables, which enables an
MTA to have bilateral information or for a group of MTAs to share
multilateral information.  The description is for bilateral
information, but is equally applicable to multilateral agreements.
For the purpose of a bilateral agreement, the MTA is considered to be
an application entity.  This means that when this is distinct from the
application process, that the agreements are protocol specific.

A bilateral agreement is represented by one entry associated with each
MTA participating in the bilateral agreement.  For one end of the
bilateral agreement, the agreement information will be keyed by the
name of the MTA at the other end.  Each party to the agreement will
set up the entry which represents its half of the agreed policy.  The
fact that these correspond is controlled by the external agreement.
In many cases, only one half of the agreement will be in the
directory.  The other half might be in an ADMD MTA configuration file.
MTA bilateral information is stored in a table, as defined in [14].
An MTA has access to a sequence of such tables, each of which controls
agreements in both directions for a given MTA. Where an MTA is
represented in multiple tables, the first agreement shall be used.
This allows an MTA to participate in multilateral agreements, and to
have private agreements which override these.  The definition of
entries in this table are defined in Figure 7.  This table will
usually be access controlled so that only a single MTA or selected
MTAs which appear externally as one MTA can access it.
Each entry in the table is of the object class
distinguishedNameTableEntry, which is used to name the entry by the
distinguished name of the MTA. In some cases discussed in
Section 20.1, there will also be aliases of type textTableEntry.  The
MTA attributes needed as a part of the bilateral agreement (typically
MTA Name/Password pairs), as described in Section 20.3, will always be
present.  Other MTA attributes (e.g., presentation address) may be
present for one of two reasons:


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1.  As a performance optimisation

2.  Because the MTA does not have a global entry

Every MTA with bilateral agreements will define a bilateral MTA table.
When a connection from a remote MTA is received, its Distinguished
Name is used to generate the name of the table entry.  For 1984, the
MTA Name exchanged at the RTS level is used as a key into the table.
The location of the bilateral tables used by the MTA and the order in
which they are used are defined by the bilateralTable attribute in the
MTA entry, which is defined in Figure 8.

All of the MTA information described in Section 16 may be used in the
bilateral table entries.  This will allow bilateral control of a wide
range of parameters.

Editor's Note: Need to add in control for various ghastly things such
    as trace stripping and originator munging.  Whilst this is needed,
    it is perhaps best swept under the carpet and left to
    implementation specific extensions.  This area will be reviewed in
    light of implementation experience.


18  MTA Selection


18.1  Dealing with protocol mismatches

MTAs may operate over different stacks.  This means that some MTAs
cannot talk directly to each other.  Even where the protocols are the
same, there may be reasons why a direct connection is not possible.
An environment where there is full connectivity over a single stack is
known as a transport community [9].  The set of transport communities
supported by an MTA is specified by use of the protocolInformation
attribute defined in X.500(93).  This is represented as a separate
attribute for the convenience of making routing decisions.
A community is identified by an object identifier, and so the
mechanism supports both well known and private communities.  A list of
object identifiers corresponding to well known communities is given in
Appendix B.





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18.2  Supported Protocols

It is important to know the protocol capabilities of an MTA. This is
done by the application context.  There are standard definitions for
the following 1988 protocols.


 o  P3 (with and without RTS, both user and MTS initiated)

 o  P7 (with and without RTS).

 o  P1 (various modes).  Strictly, this is the only one that matters
    for routing.

In order to support P1(1984) and P1(1988) in X.410 mode, application
contexts which define these protocols are given in Appendix C.  This
context is for use in the directory only, and would never be exchanged
over the network.
For routing purposes, a message store which is not co-resident with an
MTA is represented as if it had a co-resident MTA and configured with
a single link to its supporting MTA.

In cases where the UA is involved in exchanges, the UA will be of
object class mhs-user-agent, and this will allow for appropriate
communication information to be registered.

18.3  MTA Capability Restrictions


In addition to policy restrictions, described in Section 21, an MTA
may have capability restrictions.  The maximum size of MPDU is defined
by the standard attribute mhs-deliverable-content-length.  The
supported MTS extensions are defined by a new attribute specified in
Figure 9.
It may be useful to define other capability restrictions, for example
to enable routing of messages around MTAs with specific deficiencies.
It has been suggested using MTA capabilities as an optimised means of
expressing capabilities of all users associated with the MTA. This is
felt to be undesirable.


18.4  Subtree Capability Restrictions



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In many cases, users of a subtree will share the same capabilities.
It is possible to specify this by use of attributes, as defined in
Figure 10.  This will allow for restrictions to be determined in cases
where there is no entry for the user or O/R Address.  This will be a
useful optimisation in cases where the UA capability information is
not available from the directory, either for policy reasons or because
it is not there.  This information may also be present in the domain
tree (RFC 822).
This shall be implemented as a collective attribute, so that it is
available to all entries in the subtree below the entry.  This can
also be used for default setting in the subtree.


19  MTA Pulling Messages

Pulling messages between MTAs, typically by use of two way alternate,
is for bilateral agreement.  It is not the common case.  There are two
circumstances in which it can arise.


1.  Making use of a connection that was opened to push messages.

2.  Explicitly polling in order to pull messages

Attributes to support this are defined in Figure 11.  These attributes
indicate the capabilities of an MTA to pull messages, and allows a
list of polled MTAs to be specified.  If omitted, the normal case of
push-only is specified.  In the MTA Entry, the polledMTAs attribute
indicates MTAs which are to be polled and the mTAsAllowedToPoll
attribute indicates MTAs that may poll the current MTA.


20  Security and Policy


20.1  Finding the Name of the Calling MTA

A key issue for authentication is for the called MTA to find the name
of the calling MTA. This is needed for it to be able to look up
information on a bilateral agreement.
Where X.400(88) is used, the name is available as a distinguished name
from the AE-Title provided in the A-Associate.  For X.400(84), it will
not be possible to derive a global name from the bind.  The MTA Name


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exchanged in the RTS Bind will provide a key into the private
bilateral agreement table (or tables).  Thus for X.400(1984) it will
only be possible to have bilateral inbound links or no authentication
of the calling MTA.

Editor's Note CDC use a search here, as a mechanism to use a single
    table and an 88/84 independent access.  This may be considered for
    general adoption.  It appears to make the data model cleaner,
    possibly at the expense of some performance.  This will be
    considered in the light of implementation experience.


20.2  Authentication

The levels of authentication required by an MTA will have an impact on
routing.  For example, if an MTA requires strong authentication, not
all MTAs will be able to route to it.  The attributes which define the
authentication requirements are defined in Figure 12.

The attributes specify authentication levels for the following cases:

Responder These are the checks that the responder will make on the
    initiator's credentials.

Initiator These are the checks that the initiator will make on the
    responders credentials.  Very often, no checks are needed ---
    establishing the connection is sufficient.

Responder Pulling These are responder checks when messages are
    pulled.  These will often be stronger than for pushing.

Initiator Pulling For completeness.


If an attribute is omitted, no checks are required.  If multiple
checks are required, then each of the relevant bits shall be set.  If
there are alternative acceptable checks, then multiple values of the
attribute are used.
The values of the authentication requirements mean:


mta-name-present That an RTS level MTA parameter shall be present for
    logging purposes.


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aet-present That a distinguished name application entity title shall
    be provided at the ACSE level

aet-valid As for aet-present, and that the AET be registered in the
    directory.  This may be looked up as a part of the validation
    process.  If mta-name-present is set, the RTS value of mta and
    password shall correspond to those registered in the directory.

network-address This can only be used for the responder.  The AET
    shall be looked up in the directory, and the
    callingPresentationAddress attribute matched against the calling
    address.  This shall match exactly at the network level.  The
    validity of selectors will be matched according to the
    callingSelectorValidity attribute.

simple-authentication All MTA and password parameters needed for
    simple authentication shall be used.  This will usually be in
    conjunction with a bilateral agreement.

strong-authentication Use of strong authentication.

bilateral-agreement-needed This means that this MTA will only accept
    connections in conjunction with a bilateral agreement.  This link
    cannot be used unless such an agreement exists.

These attributes may also be used to specify UA/MTA authentication
policy.  They may be resident in the UA entry in environments where
this information cannot be modified by the user.  Otherwise, it will
be present in an MTA table (represented in the directory).

An MTA could choose to have different authentication levels related to
different policies (Section 21).  This is seen as too complex, and so
they are kept independent.  The equivalent function can always be
achieved by using multiple Application Entities with the application
process.

20.3  Authentication Information

This section specifies connection information needed by P1.  This is
essentially RTS parameterisation needed for authentication.  This is
defined in Figure 13.  Confidential bilateral information is implied
by these attributes, and this will be held in the bilateral
information agreement.  This shall have appropriate access control


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applied.  Note that in some cases, MTA information will be split
across a private and public entry.
The parameters are:


Initiating Credentials The credentials to be used when the local MTA
    initiates the association.  It gives the credentials to insert
    into the request, and those expected in the response.

Responding Credentials The credentials to be used when the remote MTA
    initiates the association.  It gives the credential expected in
    the request, and those to be inserted into the response.

Remote Presentation Address Valid presentation addresses, which the
    remote MTA may connect from.

If an MTA/Password pair is omitted.  The MTA shall default to the
local MTA Name, and the password to a zero length OCTET STRING.


Note: It may be useful to add more information here relating to
    parameters required for strong authentication.


21  Policy and Authorisation

21.1  Simple MTA Policy


The routing trees will generally be configured in order to identify
MTAs which will route to the destination.  A simple means is
identified to specify an MTA's policy.  This is defined in Figure 14.
If this attribute is omitted, the MTA shall route all traffic to the
implied destinations from the context of the routing tree for any MTAs
that have valid access to the routing tree.
The multi-valued attribute gives a set of policies which the MTA will
route.  O/R Addresses are represented by a prefix, which identifies a
subtree.  A distinguished name encoding of O/R Address is used.  There
are three components:

from This gives a set of O/R addresses which are granted permission
    by this attribute value.  If omitted, ``all'' is implied.



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to This gives the set of acceptable destinations.  If omitted,
    ``all'' is implied.

from-excludes This defines (by prefix) subtrees of the O/R address
    tree which are explicitly excluded from the ``from'' definition.
    If omitted, there are no exclusions.

to-excludes This defines (by prefix) subtrees of the O/R address tree
    which are explicitly excluded from the ``to'' definition.  If
    omitted, there are no exclusions.

This simple policy will suffice for most cases.  In particular, it
gives sufficient information for most real situations where a policy
choice is forced, and the application of this policy would prevent a
message being routed.

This simple prefixing approach does not deal explicitly with alias
dereferencing.  The prefixes refer to O/R addresses where aliases have
been dereferenced.  To match against these prefixes, O/R addresses
being matched need to be ``normalised'' by being looked up in the
directory to resolve alias values.  If the lookup fails, it shall be
assumed that the provided address is already normalised.  This means
that policy may be misinterpreted for parts of the DIT not referenced
in the directory.
The originator refers to the MTS originator, and the recipient to the
MTS recipient, following any list expansion or redirect.
This simple policy does not apply to delivery reports.  Any advertised
route shall work for delivery reports, and it does not makes sense to
regulate this on the basis of the sender.


Editor's Note: It would be useful to include some examples here.

21.2  Complex MTA Policy


MTAs will generally have a much more complex policy mechanism, such as
that provided by PP [17].  Representing this as a part of the routing
decision is not done here, but may be addressed in future versions.
Some of the issues which need to be tackled are:

 o  Use of charging and non-charging nets



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 o  Policy dependent on message size

 o  Different policy for delivery reports.

 o  Policy dependent on attributes of the originator or
    recipient(e.g., mail from students)

 o  Content type and encoded information types

 o  The path which the message has traversed to reach the MTA

 o  MTA bilateral agreements

 o  Pulling messages

 o  Costs.  This sort of policy information may also be for
    information only.

Where an MTA applies more complex policies, it is highly undesirable
that they lead to non-routablity of messages for MTAs routing using
the published information.

Policies relating to submission do not need to be public.  They can be
private to the MTA.

22  Delivery


22.1  Redirects

There is a need to specify redirects in the Directory.  This will be
done at the O/R Address level (i.e., in a routing tree).  This will be
useful for alternate names where an equivalent name (synonym) defined
by an alias is not natural.  An example where this might be
appropriate is to redirect mail to a new O/R address where a user had
changed organisation.  The definitions are given in Figure 15.

Mandatory redirects are specified by the mandatoryRedirect attribute.
A filtered redirect is provided, to allow small messages, large
messages, or messages containing specific EITs or content to be
redirected.  Message size is measured in kBytes.  Where multiple
elements are contained in the FilteredRedirect structure, they are
treated as having a ``logical or'' relationship.


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When a delivery report is sent to an address which would be
redirected, X.400 would ignore the redirect.  This means that every
O/R address would need to have a valid means of delivery.  This would
seem to be awkward to manage.  Therefore, the redirect shall be
followed, and the delivery report delivered to the redirected address.
These redirects are handled directly by the MTA. Redirects can also be
initiated by the UA, for example in the context of a P7 interaction.


22.2  Underspecified O/R Addresses

X.400 requires that some underspecified O/R Addresses are handled in a
given way (e.g., if a surname is given without initials or given
name).  Where an underspecified O/R Address is to be treated as if it
were another O/R Address, an alias shall be used.  If the O/R Address
is to be rejected as ambiguous, and entry shall be created in the DIT,
and forced non-delivery specified for this reason.

22.3  Non Delivery


It is possible for a manager to define an address to non-deliver with
specified reason and diagnostic codes.  This might be used for a range
of management purposes.  The attribute to do this is defined in
Figure 16.

22.4  Bad Addresses


If there is a bad address, it is desirable to do a directory search to
find alternatives.  This is a helpful user service and may be
supported.  This function is invoked after address checking has
failed, and where this is no user supplied alternate recipient.  This
function would be an MTA-chosen alternative to administratively
assigned alternate recipient.
Attributes to support handling of bad addresses are defined in
Figure 17.  The attributes are:


badAddressSearchPoint This gives the point (or list of points) from
    which to search.

badAddressSearchAttributes This gives the set of attribute types to
    search on.  The default is common name.

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Searches are always single level, and always use approximate match.
If a small number of matches are made, this is returned to the
originator by use of the per recipient AlternativeAddresssInformation
in the delivery report (DR). This shall be marked non-critical, so
that it will not cause the DR to be discarded (e.g., in downgrading to
X.400(1984)).  This attribute allows the Distinguished Name and O/R
Address of possible alternate recipients to be returned with the
delivery report.  There is also the possibility to attach extra
information in the form of directory attributes.  Typically this might
be used to return attributes of the entry which were matched in the
search.  A summary of the information shall also be returned using the
delivery report supplementary information filed (e.g., ``your message
could not be delivered to smith, try J. Smith or P. Smith''), so that
the information is available to user agents not supporting this
extension.  Note the length restriction of this field is 256
(ub-supplementary-info-length).
If the directory search fails, or there are no matches returned, a
delivery report shall be returned as if this extra check had not been
made.


Editor's Note: It might be useful to allow control of search type,
    and also single level vs subtree.  This issue is for further
    study.


23  Submission

A message may be submitted with Distinguished Name only.  If the MTA
to which the message is submitted supports this service, this section
describes how the mapping is done.

23.1  Normal Derivation


The Distinguished Name is looked up to find the attribute
mhs-or-addresses.  If the attribute is single value, it is
straightforward.  If there are multiple values, one O/R address shall
be selected at random.






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23.2  Roles and Groups

Some support for roles is given.  If there is no O/R address, and the
entry is of object class role, then the roleOccupant attribute shall
be dereferenced, and the message submitted to each of the role
occupants.  Similarly, if the entry is of object class group, where
the groupMember attribute is used.


24  Access Units

Attributes needed for support of Access Units, as defined in
X.400(88), are defined in Figure 18.

The attributes defined are:

localAccessUnit This defines the list of access units supported by
    the MTA.

accessUnitsUsed This defines which access units are used by the MTA,
    giving the type and MTA. An O/R Address filter is provided to
    control which access unit is used for a given recipient.  For a
    filter to match an address, all attributes specificed in the
    filter shall match the given address.  This is specified as an O/R
    Address, so that routing to access units can be filtered on the
    basis of attributes not mapped onto the directory (e.g., postal
    attributes).  Where a remote MTA is used, it may be necessary to
    use source routing.


Editor's Note 1: This mechanism might be used to replace the
    routefilter mechanism of the MTS routing.  Comments are solicited.

Editor's Note 2: It has been proposed to add a more powerful filter
    mechanism.  Comments are solicited.

Editor's Note 3: The utility of this specification as a mechanism to
    route faxes and other non MHS messages has been noted, but not
    explored.  Comments as to how and if this should be developed are
    solicited.

These three issues are for further study.



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25  The Overall Routing Algorithm

Having provided all the pieces, a summary of how routing works can be
given.
The core of the X.400 routing is described in Section 10.  A sequence
of routing trees are followed.  As nodes of the routing tree are
matched, a set of MTAs will be identified for evaluation as possible
next hops.  If all of these are rejected, the trees are followed
further2.  A set of MTAs is evaluated on the following criteria:


 o  If an MTA is the local MTA, deliver locally.

 o  Supported protocols.  The MTA shall support a protocol that the
    current MTA supports3, as described in Section 18.2.

 o  The protocols shall share a common transport community, as
    described in Section 18.1.

 o  There shall be no capability restrictions in the MTA which
    prevents transfer of the current message, as described in
    Section 18.3.

 o  There shall be no policy restrictions in the MTA which prevents
    transfer of the current message, as described in Section 21.

 o  The authentication requirements of the MTA shall be met by the
    local MTA, as described in Section 20.2.

 o  If the authentication (Section 20.2) indicates that a bilateral
    agreement is present, the MTA shall be listed in the local set of
    bilateral agreements, as described in Section 17.

 o  In cases where the recipient UA's capabilities can be determined,
    there should either be no mismatch, or there shall be an ability
    to use local or remote reformatting capabilities, as described

----------------------------
    2. It might be argued that the trees should be followed to find
alternate routes in the case that only one MTA is acceptable.  This is
not proposed.
    3. Note that this could be an RFC 822 protocol, as well as an
X.400 protocol.


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    in[11].


26  Performance

The routing algorithm has beed designed with performance in mind.  In
particular, care has been taken to use only the read function, which
will in general be optimised.  Routing trees may be configured so that
routing decisions can be made with only two directory reads.  More
complex configurations will not require a substantially larger number
of operations.


27  Acknowledgements

This INTERNET--DRAFT is the central document of a series of
specifications [13, 14, 16, 18, 12, 15, 11].  The acknowledgements for
all of this work is given here.  Previous work, which significantly
influenced these specifications is described in Section 3.  This lead
to an initial proposal by the editor, which was subsequently split
into eight documents.

Work on this specifications has been done by the IETF MHS-DS working
group.  Special credit is given to the joint chairs of this group:
Harald Alvestrand (Uninett) and Kevin Jordan (CDC). Credit is given to
all members of the WG. Those who have made active contribution
include:  Piete Brooks (Cambridge University); Allan Cargille
(University of Wisconsin); Jim Craigie (JNT); Dennis Doyle (SSS); Urs
Eppenberger (SWITCH); Peter Furniss; Christian Huitema (Inria); Marko
Kaittola (Dante); Sylvain Langlois (EDF); Lucy Loftin (AT&T GIS);
Julian Onions (NEXOR); Paul-Andre Pays (Inria); Colin Robbins (NEXOR);
Michael Roe (Cambridge University); Jim Romaguera (Netconsult);
Michael Storz (Leibniz Rechenzentrum); Mark Wahl (ISODE Consortium);
Alan Young (ISODE Consortium).
This work was partly funded by the COSINE Paradise project.


References

 [1] The Directory --- overview of concepts, models and services,
     1993. CCITT X.500 Series Recommendations.

 [2] J.N. Chiappa. A new IP routing and addressing architecture,


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INTERNET--DRAFT         MHS Routing using Directory          June 1994


     1991.

 [3] A. Consael, M. Tschicholz, O. Wenzel, K. Bonacker, and M. Busch.
     DFN-Directory nutzung durch MHS, April 1990. GMD Report.

 [4] P. Dick-Lauder, R.J. Kummerfeld, and K.R. Elz. ACSNet - the
     Australian alternative to UUCP. In EUUG Conference, Paris, pages
     60--69, April 1985.

 [5] U. Eppenberger. Routing coordination for an X.400 MHS service
     within a multi protocol / multinetwork environment. RFC 1465.

 [6] K.E. Jordan. Using X.500 directory services in support of X.400
     routing and address mapping, November 1991. Private Note.

 [7] S.E. Kille. MHS use of directory service for routing.  In IFIP
     6.5 Conference on Message Handling, Munich, pages 157--164.
     North Holland Publishing, April 1987.

 [8] S.E. Kille. Topology and routing for MHS.  COSINE Specification
     Phase 7.7, RARE, 1988.

 [9] S.E. Kille. Encoding network addresses to support operation over
     non-OSI lower layers. Request for Comments RFC 1277, Department
     of Computer Science, University College London, November 1991.

[10] S.E. Kille. A string representation of distinguished name.
     Request for Comments in preparation, Department of Computer
     Science, University College London, January 1992.

[11] S.E. Kille. Mhs use of directory to support mhs content
     conversion, July 1993. Internet Draft.

[12] S.E. Kille. Use of the directory to support routing for RFC 822
     and related protocols, July 1993. Internet Draft.

[13] S.E. Kille. Representing tables and subtrees in the directory,
     June 1994. Internet Draft.

[14] S.E. Kille. Representing the O/R Address hierarchy in the
     directory information tree, June 1994. Internet Draft.

[15] S.E. Kille. A simple profile for MHS use of directory, March
     1994. Internet Draft.

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[16] S.E. Kille. Use of the directory to support mapping between
     X.400 and RFC 822 addresses, June 1994. Internet Draft.

[17] S.E. Kille and J.P. Onions. The PP manual, December 1991.
     Version 6.0.

[18] S.E. Kille and C.J. Robbins. MHS use of the directory to support
     distribution lists, March 1994. Internet Draft.

[19] P. Lauder, R.J. Kummerfeld, and A. Fekete. Hierarchical network
     routing. In Tricomm 91, 1991.

[20] CCITT recommendations X.400 / ISO 10021, April 1988. CCITT
     SG 5/VII / ISO/IEC JTC1, Message Handling:  System and Service
     Overview.

[21] Zen and the ART of navigating through the dark and murky regions
     of the message transfer system:  Working document on MTS
     routing, September 1991. ISO SC 18 SWG Messaging.


28  Security Considerations

Security considerations are not discussed in this INTERNET--DRAFT.


29  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;

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    DN: CN=Steve Kille,
    O=ISODE Consortium, C=GB

    UFN: S. Kille, ISODE Consortium, GB









































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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)}

routing OBJECT IDENTIFIER ::= {mhs-ds 3}

oc OBJECT IDENTIFIER ::= {routing 1}
at OBJECT IDENTIFIER ::= {routing 2}
id OBJECT IDENTIFIER ::= {routing 3}

                                                                    10
oc-mta OBJECT IDENTIFIER ::= {oc 1}
oc-mta-bilateral-table-entry OBJECT IDENTIFIER ::= {oc 2}
oc-routing-information OBJECT IDENTIFIER ::= {oc 3}
oc-restricted-subtree OBJECT IDENTIFIER ::= {oc 4}
oc-routed-ua OBJECT IDENTIFIER ::= {oc 5}
oc-routing-tree-root OBJECT IDENTIFIER ::= {oc 6}
oc-mta-application-process OBJECT IDENTIFIER ::= {oc 7}

at-access-md OBJECT IDENTIFIER ::= {at 1}
at-access-units-used OBJECT IDENTIFIER ::= {at 2}                   20
at-subtree-information OBJECT IDENTIFIER ::= {at 3}
at-bad-address-search-attributes OBJECT IDENTIFIER ::= {at 4}
at-bad-address-search-point OBJECT IDENTIFIER ::= {at 5}

at-calling-selector-validity OBJECT IDENTIFIER ::= {at 7}

at-filtered-redirect OBJECT IDENTIFIER ::= {at 38}
at-global-domain-id OBJECT IDENTIFIER ::= {at 10}
at-initiating-rts-credentials OBJECT IDENTIFIER ::= {at 11}
at-initiator-authentication-requirements OBJECT IDENTIFIER ::= {at 12}30
at-initiator-p1-mode OBJECT IDENTIFIER ::= {at 13}
at-initiator-pulling-authentication-requirements OBJECT IDENTIFIER ::= {at 14}
at-local-access-unit OBJECT IDENTIFIER ::= {at 15}
at-mandatory-redirect OBJECT IDENTIFIER ::= {at 16}
at-mta-info OBJECT IDENTIFIER ::= {at 40}
at-mta-name OBJECT IDENTIFIER ::= {at 19}

at-mta-will-route OBJECT IDENTIFIER ::= {at 21}
at-calling-presentation-address OBJECT IDENTIFIER ::= {at 22}


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at-responder-authentication-requirements OBJECT IDENTIFIER ::= {at 23}40
at-responder-p1-mode OBJECT IDENTIFIER ::= {at 24}
at-responder-pulling-authentication-requirements OBJECT IDENTIFIER ::= {at 25}
at-responding-rts-credentials OBJECT IDENTIFIER ::= {at 26}
at-routing-failure-action OBJECT IDENTIFIER ::= {at 27}
at-routing-filter OBJECT IDENTIFIER ::= {at 28}
at-routing-tree-list OBJECT IDENTIFIER ::= {at 29}
at-subtree-deliverable-content-length OBJECT IDENTIFIER ::= {at 30}
at-subtree-deliverable-content-types OBJECT IDENTIFIER ::= {at 31}
at-subtree-deliverable-eits OBJECT IDENTIFIER ::= {at 32}
at-supporting-mta OBJECT IDENTIFIER ::= {at 33}                     50
at-transport-community OBJECT IDENTIFIER ::= {at 34}
at-user-name OBJECT IDENTIFIER ::= {at 35}
at-non-delivery-info OBJECT IDENTIFIER ::= {at 36}
at-polled-mtas  OBJECT IDENTIFIER ::= {at 37}
at-bilateral-table OBJECT IDENTIFIER {at 41}
at-supported-extension OBJECT IDENTIFIER {at 42}
at-supported-mts-extension OBJECT IDENTIFIER {at 43}
at-mtas-allowed-to-poll OBJECT IDENTIFIER {at 44}

id-alternative-address-information OBJECT IDENTIFIER ::= {id 1}     60

_______________Figure_19:__Object_Identifier_Assignment________________






















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B  Community Identifier Assignments












































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C  Protocol Identifier Assignments












































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D  ASN.1 Summary
_______________________________________________________________________
MHS-DS-Definitions
DEFINITIONS ::=
BEGIN

 -- assign OID to module
 -- define imports and exports

routingTreeRoot OBJECT-CLASS ::= {
    SUBCLASS OF {routingInformation|subtree}
    ID oc-routing-tree-root}                                        10

routingTreeList ATTRIBUTE ::= {
        WITH SYNTAX RoutingTreeList
        SINGLE VALUE
        ID at-routing-tree-list}

RoutingTreeList ::= SEQUENCE OF RoutingTreeName

RoutingTreeName ::= DistinguishedName
                                                                    20
routingInformation OBJECT-CLASS ::= {
    SUBCLASS OF top
    MAY CONTAIN {
        subtreeInformation|
        routingFilter|
        routingFailureAction|
        mTAInfo|
        accessMD|
        nonDeliveryInfo|
        badAddressSearchPoint|                                      30
        badAddressSearchAttributes}
    ID oc-routing-information}
                -- No naming attributes as this is not a
                -- structural object class



subtreeInformation ATTRIBUTE ::= {
    WITH SYNTAX SubtreeInfo
    SINGLE VALUE                                                    40
    ID at-subtree-information}


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SubtreeInfo ::= ENUMERATED {
    all-children-present(0),
    not-all-children-present(1) }


routingFilter ATTRIBUTE ::= {
    WITH SYNTAX RoutingFilter
    ID at-routing-filter}                                           50


RoutingFilter ::= SEQUENCE{
        attribute-type OBJECT-IDENTIFIER,
        weight RouteWeight,
        dda-key String OPTIONAL,
        regex-match IA5String OPTIONAL,
        node DistinguishedName }

String ::= CHOICE {PrintableString, TeletexString}                  60

routingFailureAction ATTRIBUTE ::= {
    WITH SYNTAX RoutingFailureAction
    SINGLE VALUE
    ID at-routing-failure-action}

RoutingFailureAction ::= ENUMERATED {
            next-level(0),
            next-tree-only(1),
            next-tree-first(2),                                     70
            stop(3)  }


mTAInfo ATTRIBUTE ::= {
    WITH SYNTAX MTAInfo
    ID at-mta-info}

MTAInfo ::= SEQUENCE {
            name DistinguishedName,
            weight [1] RouteWeight DEFAULT preferred-access,        80
            mta-attributes [2] SET OF Attribute OPTIONAL,
            ae-info  SEQUENCE OF SEQUENCE {
                aEQualifier PrintableString,
                ae-weight RouteWeight DEFAULT preferred-access,
                ae-attributes SET OF Attribute OPTIONAL} OPTIONAL

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}

RouteWeight ::= INTEGER  {endpoint(0),
                preferred-access(5),
                backup(10)} (0..20)                                 90

accessMD ATTRIBUTE ::= {
        SUBTYPE OF distinguishedName
        ID at-access-md}

routedUA OBJECT-CLASS ::= {
    SUBCLASS OF {routingInformation}
    MAY CONTAIN {
                        -- from X.402
        mhs-deliverable-content-length|                            100
        mhs-deliverable-content-types|
        mhs-deliverable-eits|
        mhs-message-store|
        mhs-preferred-delivery-methods|
                        -- defined here
        supportedExtensions|
        mandatoryRedirect|
        supportingMTA|
        filteredRedirect|
        userName|                                                  110
        nonDeliveryInfo}
    ID oc-routed-ua}

supportedExtensions ATTRIBUTE ::= {
    SUBTYPE OF objectIdentifier
    ID at-supported-extensions}

supportingMTA ATTRIBUTE ::= {
    SUBTYPE OF mtaInfo
    ID at-supporting-mta}                                          120

userName ATTRIBUTE ::= {
    SUBTYPE OF distinguishedName
    ID at-user-name}

mTAName ATTRIBUTE ::= {
    SUBTYPE OF name
    WITH SYNTAX DirectoryString{ub-mta-name-length}
    SINGLE VALUE

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    ID at-mta-name}                                                130
                        -- used for naming when
                        -- MTA is named in O=R Address Hierarchy

globalDomainID ATTRIBUTE ::= {
    WITH SYNTAX GlobalDomainIdentifier
    SINGLE VALUE
    ID at-global-domain-id}
                        -- both attributes present when MTA
                        -- is named outside O=R Address Hierarchy
                        -- to enable trace to be written           140

mTAApplicationProcess OBJECT CLASS ::= {
    SUBCLASS OF {application-process}
    MAY CONTAIN {
        mTAWillRoute|
        globalDomainID|
        routingTreeList|
        accessMD|
        localAccessUnit|
        accessUnitsUsed                                            150
    }
    ID oc-mta-application-process}

mTA OBJECT CLASS ::= {   -- Application Entity
    SUBCLASS OF {mhs-message-transfer-agent}
    MAY CONTAIN {
        mTAName|
        globalDomainID|         -- per AE variant
        responderAuthenticationRequirements|
        initiatorAuthenticationRequirements|                       160
        responderPullingAuthenticationRequirements|
        initiatorPullingAuthenticationRequirements|
        initiatorP1Mode|
        responderP1Mode|
        polledMTAs|
        protocolInformation|
        respondingRTSCredentials|
        initiatingRTSCredentials|
        callingPresentationAddress|
        callingSelectorValidity|                                   170
        bilateralTable|
        mTAWillRoute|
        mhs-deliverable-content-length|

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        routingTreeList|
        supportedMTSExtensions|
        mTAsAllowedToPoll
        }
    ID oc-mta}

mTABilateralTableEntry OBJECT-CLASS ::=                            180
    SUBCLASS OF {mTA| distinguishedNameTableEntry}
    ID oc-mta-bilateral-table-entry}

bilateralTable ATTRIBUTE ::= {
        WITH SYNTAX SEQUENCE OF DistinguishedName
        SINGLE VALUE
        ID at-bilateral-table}

supportedMTSExtensions ATTRIBUTE ::= {
    SUBTYPE OF objectIdentifier                                    190
    ID at-supported-mts-extensions}

restrictedSubtree OBJECT-CLASS ::= {
        SUBCLASS OF {top}
        MAY CONTAIN {
                subtreeDeliverableContentLength|
                subtreeDeliverableContentTypes|
                subtreeDeliverableEITs}
        ID oc-restricted-subtree}
                                                                   200
subtreeDeliverableContentLength ATTRIBUTE ::= {
        SUBTYPE OF mhs-deliverable-content-length
        ID at-subtree-deliverable-content-length}

subtreeDeliverableContentTypes ATTRIBUTE ::= {
        SUBTYPE OF mhs-deliverable-content-types
        ID at-subtree-deliverable-content-types}

subtreeDeliverableEITs ATTRIBUTE ::= {
        SUBTYPE OF mhs-deliverable-eits                            210
        ID at-subtree-deliverable-eits}


initiatorP1Mode ATTRIBUTE ::= {
    WITH SYNTAX P1Mode
    SINGLE VALUE
    ID at-initiator-p1-mode}

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responderP1Mode ATTRIBUTE ::= {
    WITH SYNTAX P1Mode                                             220
    SINGLE VALUE
    ID at-responder-p1-mode}

P1Mode ::= ENUMERATED {
    push-only(0),
    pull-only(1),
    twa(2) }

polledMTAs ATTRIBUTE ::= {
    WITH SYNTAX PolledMTAs                                         230
    ID at-polled-mtas}

PolledMTAs ::= SEQUENCE {
        mta DistinguishedName,
        poll-frequency INTEGER OPTIONAL --frequency in minutes
        }

mTAsAllowedToPoll ATTRIBUTE ::= {
        SUBTYPE OF distinguishedName
        ID at-mtas-allowed-to-poll}                                240


responderAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE
   ID at-responder-authentication-requirements}

initiatorAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE                                                    250
   ID at-initiator-authentication-requirements}

repsonderPullingAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE
   ID at-responder-pulling-authentication-requirements}

initiatorPullingAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE                                                    260
   ID at-initiator-pulling-authentication-requirements}

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AuthenticationRequirements ::= BITSTRING {
    mta-name-present(0),
    aet-present(1),
    aet-valid(2),
    network-address(3),
    simple-authentication(4),
    strong-authentication(5),
    bilateral-agreement-needed(6)}                                 270

respondingRTSCredentials ATTRIBUTE ::= {
        WITH SYNTAX RTSCredentials
        SINGLE VALUE
        ID at-responding-rts-credentials}


initiatingRTSCredentials ATTRIBUTE ::= {
        WITH SYNTAX RTSCredentials
        SINGLE VALUE                                               280
        ID at-initiating-rts-credentials}


RTSCredentials ::= SEQUENCE {
        request [0] MTAandPassword OPTIONAL,
        response [1] MTAandPassword OPTIONAL }


MTAandPassword ::= SEQUENCE {
        MTAName,                                                   290
        Password }              -- MTAName and Password
                                -- from X.411


callingPresentationAddress ATTRIBUTE ::= {
        SUBTYPE OF presentationAddress
        MULTI VALUE
        ID at-calling-presentation-address}

callingSelectorValidity ATTRIBUTE ::= {                            300
        WITH SYNTAX CallingSelectorValidity
        SINGLE VALUE
        ID at-calling-selector-validity}

CallingSelectorValidity ::= ENUMERATED {

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        all-selectors-fixed(0),
        tsel-may-vary(1),
        all-selectors-may-vary(2) }

mTAWillRoute ATTRIBUTE ::= {                                       310
    WITH SYNTAX MTAWillRoute
    ID at-mta-will-route}

MTAWillRoute ::= SEQUENCE {
        from [0]        SET OF ORAddressPrefix OPTIONAL,
        to [1]          SET OF ORAddressPrefix OPTIONAL,
        from-excludes [2]       SET OF ORAddressPrefix OPTIONAL,
        to-excludes [3]         SET OF ORAddressPrefix OPTIONAL }

ORAddressPrefix ::= DistinguishedName                              320

mandatoryRedirect ATTRIBUTE ::= {
        SUBTYPE OF  distinguishedName
        SINGLE VALUE
        ID at-mandatory-redirect}

filteredRedirect ATTRIBUTE ::= {
        WITH SYNTAX FilteredRedirect
        SINGLE VALUE
        ID at-filtered-redirect}                                   330

FilteredRedirect ::= SEQUENCE {
        redirect-to DistinguishedName,
        SEQUENCE {
                min-size [1] INTEGER,
                max-size [2] INTEGER,
                content [3] ContentType,
                eit [4] ExternalEncodedInformationType }
        }
                                                                   340



nonDeliveryInfo ATTRIBUTE ::= {
        WITH SYNTAX NonDeliveryReason
        ID at-non-delivery-info}

NonDeliveryReason ::= SEQUENCE {
        reason INTEGER (0..ub-reason-codes),

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        diagnostic INTEGER (0..ub-diagnostic-codes),               350
        supplementaryInfo PrintableString }

badAddressSearchPoint ATTRIBUTE ::= {
        SUBTYPE OF distinguishedName
        ID at-bad-address-search-point}

badAddressSearchAttributes ATTRIBUTE ::= {
        WITH SYNTAX AttributeType
        ID at-bad-address-search-attributes}
                                                                   360
alternativeAddressInformation EXTENSION
        AlternativeAddressInformation
        ::= id-alternative-address-information
                -- X.400(92) continues to use MACRO notation

AlternativeAddressInformation ::= SET OF SEQUENCE {
        distinguished-name DistinguishedName OPTIONAL,
        or-address ORAddress OPTIONAL,
        other-useful-info SET OF Attribute }
                                                                   370
localAccessUnit ATTRIBUTE ::= {
        WITH SYNTAX AccessUnitType
        ID at-local-access-unit}

AccessUnitType ::= ENUMERATED {
        fax (1),
        physical-delivery (2),
        teletex (3),
        telex (4) }
                                                                   380
accessUnitsUsed ATTRIBUTE ::= {
        WITH SYNTAX SelectedAccessUnit
        ID at-access-units-used}

SelectedAccessUnit ::= SEQUENCE {
        type AccessUnitType,
        providing-MTA DistinguishedName,
        filter SET OF ORAddress OPTIONAL }
mhs-ds OBJECT-IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1) private(4)
          enterprises(1) isode-consortium (453) mhs-ds (7)}        390

routing OBJECT IDENTIFIER ::= {mhs-ds 3}


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oc OBJECT IDENTIFIER ::= {routing 1}
at OBJECT IDENTIFIER ::= {routing 2}
id OBJECT IDENTIFIER ::= {routing 3}


oc-mta OBJECT IDENTIFIER ::= {oc 1}
oc-mta-bilateral-table-entry OBJECT IDENTIFIER ::= {oc 2}          400
oc-routing-information OBJECT IDENTIFIER ::= {oc 3}
oc-restricted-subtree OBJECT IDENTIFIER ::= {oc 4}
oc-routed-ua OBJECT IDENTIFIER ::= {oc 5}
oc-routing-tree-root OBJECT IDENTIFIER ::= {oc 6}
oc-mta-application-process OBJECT IDENTIFIER ::= {oc 7}

at-access-md OBJECT IDENTIFIER ::= {at 1}
at-access-units-used OBJECT IDENTIFIER ::= {at 2}
at-subtree-information OBJECT IDENTIFIER ::= {at 3}
at-bad-address-search-attributes OBJECT IDENTIFIER ::= {at 4}      410
at-bad-address-search-point OBJECT IDENTIFIER ::= {at 5}

at-calling-selector-validity OBJECT IDENTIFIER ::= {at 7}

at-filtered-redirect OBJECT IDENTIFIER ::= {at 38}
at-global-domain-id OBJECT IDENTIFIER ::= {at 10}
at-initiating-rts-credentials OBJECT IDENTIFIER ::= {at 11}
at-initiator-authentication-requirements OBJECT IDENTIFIER ::= {at 12}
at-initiator-p1-mode OBJECT IDENTIFIER ::= {at 13}
at-initiator-pulling-authentication-requirements OBJECT IDENTIFIER ::=4{at214}0
at-local-access-unit OBJECT IDENTIFIER ::= {at 15}
at-mandatory-redirect OBJECT IDENTIFIER ::= {at 16}
at-mta-info OBJECT IDENTIFIER ::= {at 40}
at-mta-name OBJECT IDENTIFIER ::= {at 19}

at-mta-will-route OBJECT IDENTIFIER ::= {at 21}
at-calling-presentation-address OBJECT IDENTIFIER ::= {at 22}
at-responder-authentication-requirements OBJECT IDENTIFIER ::= {at 23}
at-responder-p1-mode OBJECT IDENTIFIER ::= {at 24}
at-responder-pulling-authentication-requirements OBJECT IDENTIFIER ::=4{at325}0
at-responding-rts-credentials OBJECT IDENTIFIER ::= {at 26}
at-routing-failure-action OBJECT IDENTIFIER ::= {at 27}
at-routing-filter OBJECT IDENTIFIER ::= {at 28}
at-routing-tree-list OBJECT IDENTIFIER ::= {at 29}
at-subtree-deliverable-content-length OBJECT IDENTIFIER ::= {at 30}
at-subtree-deliverable-content-types OBJECT IDENTIFIER ::= {at 31}
at-subtree-deliverable-eits OBJECT IDENTIFIER ::= {at 32}

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at-supporting-mta OBJECT IDENTIFIER ::= {at 33}
at-transport-community OBJECT IDENTIFIER ::= {at 34}
at-user-name OBJECT IDENTIFIER ::= {at 35}                         440
at-non-delivery-info OBJECT IDENTIFIER ::= {at 36}
at-polled-mtas  OBJECT IDENTIFIER ::= {at 37}
at-bilateral-table OBJECT IDENTIFIER {at 41}
at-supported-extension OBJECT IDENTIFIER {at 42}
at-supported-mts-extension OBJECT IDENTIFIER {at 43}
at-mtas-allowed-to-poll OBJECT IDENTIFIER {at 44}

id-alternative-address-information OBJECT IDENTIFIER ::= {id 1}

ts-communities OBJECT-IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1)4private(4)50
          enterprises(1) isode-consortium (453) ts-communities (4)}


tc-cons OBJECT IDENTIFIER ::= {ts-communities 1}        -- OSI CONS
tc-clns OBJECT IDENTIFIER ::= {ts-communities 2}        -- OSI CLNS
tc-internet OBJECT IDENTIFIER ::= {ts-communities 3}    -- Internet + RFC 1006
tc-int-x25 OBJECT IDENTIFIER ::= {ts-communities 4}     -- International X.25
                                                        -- Without CONS
tc-ixi OBJECT IDENTIFIER ::= {ts-communities 5}         -- IXI (Europe)
tc-janet OBJECT IDENTIFIER ::= {ts-communities 6}       -- Janet (UK)460

mail-protocol OBJECT-IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1) private(4)
          enterprises(1) isode-consortium (453) mail-protocol (5)}

ac-p1-1984 OBJECT IDENTIFIER ::= {mail-protocol 1}      -- p1(1984)
ac-smtp  OBJECT IDENTIFIER ::= {mail-protocol 2}        -- SMTP
ac-uucp OBJECT IDENTIFIER ::= {mail-protocol 3}         -- UUCP Mail
ac-jnt-mail OBJECT IDENTIFIER ::= {mail-protocol 4}     -- JNT Mail (UK)
ac-p1-1988-x410 OBJECT IDENTIFIER ::= {mail-protocol 5} -- p1(1988) in X.410 mode
ac-p3-1984 OBJECT IDENTIFIER ::= {mail-protocol 6}      -- p3(1984)470
END

______________________Figure_22:__ASN.1_Summary________________________









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E  Regular Expression Syntax

This appendix defines a form of regular expression for pattern
matching.  This pattern matching is derived from the UNIX ed(1)
command.  The matching is modified to be case insensitive.



    A regular expression (RE) specifies a set of character strings to
    match against - such as ``any string containing digits 5 through 9''.
    A member of this set of strings is said to be matched by the regular
    expression.

    Where multiple matches are present  in  a  line,  a  regular
    expression  matches  the  longest  of  the leftmost matching
    strings.

    Regular expressions can  be  built  up  from  the  following
    ``single-character'' RE's:


     c    Any ordinary character not listed below.   An  ordinary
          character matches itself.

     \    Backslash.  When followed by a special  character,  the
          RE  matches  the  "quoted" character.  A backslash fol-
          lowed by one of ( or  )  represents  an
          operator in a regular expression, as described below.

     .    Dot.  Matches any single character.

     ^    As the leftmost character, a caret (or circumflex) con-
          strains the RE to match the leftmost portion of a string.
          A match of this type  is  called  an  "anchored  match"
          because  it  is  "anchored"  to a specific place in the
          string.  The ^ character loses its special meaning if  it
          appears in any position other than the start of the RE.

     $    As the rightmost character, a  dollar  sign  constrains
          the RE to match the rightmost portion of a string.  The $
          character loses its special meaning if  it  appears  in
          any position other than at the end of the RE.

     ^RE$ The construction ^RE$ constrains the RE  to  match  the

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          entire string.

     [c...]
          A nonempty string of  characters,  enclosed  in  square
          brackets  matches  any  single character in the string.
          For example, [abcxyz] matches any single character from
          the  set  `abcxyz'.   When  the  first character of the
          string is a caret (^), then the RE matches any  charac-
          ter  except those in the remainder of the string.  For
          example, `[^45678]' matches any  character except  `45678'.
          A  caret  in  any  other position is interpreted as an
          ordinary character.

     []c...]
          The  right  square  bracket  does  not  terminate   the
          enclosed  string if it is the first character (after an
          initial `^', if any), in the bracketed string.  In this
          position it is treated as an ordinary character.

     [l-r]
          The minus sign, between  two  characters,  indicates  a
          range  of  consecutive  ASCII characters to match.  For
          example, the range `[0-9]' is equivalent to the  string
          `[0123456789]'.   Such a bracketed string of characters
          is known as a character class.  The `-' is  treated  as
          an  ordinary  character  if  it  occurs first (or first
          after an initial ^) or last in the string.

     The following rules and special characters  allow  for  con-
     structing RE's from single-character RE's:

          A concatenation of RE's matches a concatenation of text
          strings,  each  of which is a match for a successive RE
          in the search pattern.

     *    A single-character RE,  followed  by  an  asterisk  (*)
          matches   zero  or  more  occurrences  of  the  single-
          character RE. Such a pattern is called a closure.   For
          example,  [a-z][a-z]* matches any string of one or more
          lower case letters.

     \(...\)
          An RE enclosed between the character sequences  \(  and
          \) matches whatever the unadorned RE matches, but saves

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          the string matched by the enclosed  RE  in  a  numbered
          substring  register.  There can be up to nine such sub-
          strings in an RE,  and  parenthesis  operators  can  be
          nested.

     \n   Match the contents of the nth substring  register  from
          the  current RE. This provides a mechanism for extract-
          ing matched substrings.  For  example,  the  expression
          ^\(..*\)\1$  matches  a string consisting entirely of two
          adjacent non-null appearances of the same string.  When
          nested  parenthesized  substrings  are  present,  n  is
          determined by counting occurrences of \( starting  from
          the left.





E.1  Pseudo Code


This section describes the routing algorithm in pseudo-code and gives
examples of its use.
To be supplied.





















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_______________________________________________________________________

routedUA OBJECT-CLASS ::= {
    SUBCLASS OF {routingInformation}
    MAY CONTAIN {
                        -- from X.402
        mhs-deliverable-content-length|
        mhs-deliverable-content-types|
        mhs-deliverable-eits|
        mhs-message-store|
        mhs-preferred-delivery-methods|                             10
                        -- defined here
        supportedExtensions|
        mandatoryRedirect|
        supportingMTA|
        filteredRedirect|
        userName|
        nonDeliveryInfo}
    ID oc-routed-ua}

supportedExtensions ATTRIBUTE ::= {                                 20
    SUBTYPE OF objectIdentifier
    ID at-supported-extensions}

supportingMTA ATTRIBUTE ::= {
    SUBTYPE OF mtaInfo
    ID at-supporting-mta}

userName ATTRIBUTE ::= {
    SUBTYPE OF distinguishedName
    ID at-user-name}                                                30

_______________________Figure_5:__UA_Attributes________________________


_______________________________________________________________________

mTABilateralTableEntry OBJECT-CLASS ::=
    SUBCLASS OF {mTA| distinguishedNameTableEntry}
    ID oc-mta-bilateral-table-entry}

_________________Figure_7:__MTA_Bilateral_Table_Entry__________________



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_______________________________________________________________________


bilateralTable ATTRIBUTE ::= {
        WITH SYNTAX SEQUENCE OF DistinguishedName
        SINGLE VALUE
        ID at-bilateral-table}

_________________Figure_8:__Bilateral_Table_Attribute__________________

_______________________________________________________________________

supportedMTSExtensions ATTRIBUTE ::= {
    SUBTYPE OF objectIdentifier
    ID at-supported-mts-extensions}


_________________Figure_9:__Supported_MTS_Extensions___________________

_______________________________________________________________________

restrictedSubtree OBJECT-CLASS ::= {
        SUBCLASS OF {top}
        MAY CONTAIN {
                subtreeDeliverableContentLength|
                subtreeDeliverableContentTypes|
                subtreeDeliverableEITs}
        ID oc-restricted-subtree}

subtreeDeliverableContentLength ATTRIBUTE ::= {                     10
        SUBTYPE OF mhs-deliverable-content-length
        ID at-subtree-deliverable-content-length}

subtreeDeliverableContentTypes ATTRIBUTE ::= {
        SUBTYPE OF mhs-deliverable-content-types
        ID at-subtree-deliverable-content-types}

subtreeDeliverableEITs ATTRIBUTE ::= {
        SUBTYPE OF mhs-deliverable-eits
        ID at-subtree-deliverable-eits}                             20



______________Figure_10:__Subtree_Capability_Restriction_______________


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_______________________________________________________________________

initiatorP1Mode ATTRIBUTE ::= {
    WITH SYNTAX P1Mode
    SINGLE VALUE
    ID at-initiator-p1-mode}

responderP1Mode ATTRIBUTE ::= {
    WITH SYNTAX P1Mode
    SINGLE VALUE
    ID at-responder-p1-mode}                                        10

P1Mode ::= ENUMERATED {
    push-only(0),
    pull-only(1),
    twa(2) }

polledMTAs ATTRIBUTE ::= {
    WITH SYNTAX PolledMTAs
    ID at-polled-mtas}
                                                                    20
PolledMTAs ::= SEQUENCE {
        mta DistinguishedName,
        poll-frequency INTEGER OPTIONAL --frequency in minutes
        }

mTAsAllowedToPoll ATTRIBUTE ::= {
        SUBTYPE OF distinguishedName
        ID at-mtas-allowed-to-poll}


_____________________Figure_11:__Pulling_Messages______________________








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_______________________________________________________________________

responderAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE
   ID at-responder-authentication-requirements}

initiatorAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE
   ID at-initiator-authentication-requirements}                     10

repsonderPullingAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE
   ID at-responder-pulling-authentication-requirements}

initiatorPullingAuthenticationRequirements ATTRIBUTE ::= {
   WITH SYNTAX AuthenticationRequirements
   SINGLE VALUE
   ID at-initiator-pulling-authentication-requirements}             20

AuthenticationRequirements ::= BITSTRING {
    mta-name-present(0),
    aet-present(1),
    aet-valid(2),
    network-address(3),
    simple-authentication(4),
    strong-authentication(5),
    bilateral-agreement-needed(6)}

_______________Figure_12:__Authentication_Requirements_________________








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_______________________________________________________________________

respondingRTSCredentials ATTRIBUTE ::= {
        WITH SYNTAX RTSCredentials
        SINGLE VALUE
        ID at-responding-rts-credentials}


initiatingRTSCredentials ATTRIBUTE ::= {
        WITH SYNTAX RTSCredentials
        SINGLE VALUE                                                10
        ID at-initiating-rts-credentials}


RTSCredentials ::= SEQUENCE {
        request [0] MTAandPassword OPTIONAL,
        response [1] MTAandPassword OPTIONAL }


MTAandPassword ::= SEQUENCE {
        MTAName,                                                    20
        Password }              -- MTAName and Password
                                -- from X.411


callingPresentationAddress ATTRIBUTE ::= {
        SUBTYPE OF presentationAddress
        MULTI VALUE
        ID at-calling-presentation-address}

callingSelectorValidity ATTRIBUTE ::= {                             30
        WITH SYNTAX CallingSelectorValidity
        SINGLE VALUE
        ID at-calling-selector-validity}

CallingSelectorValidity ::= ENUMERATED {
        all-selectors-fixed(0),
        tsel-may-vary(1),
        all-selectors-may-vary(2) }


______________Figure_13:__MTA_Authentication_Parameters________________



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_______________________________________________________________________

mTAWillRoute ATTRIBUTE ::= {
    WITH SYNTAX MTAWillRoute
    ID at-mta-will-route}

MTAWillRoute ::= SEQUENCE {
        from [0]        SET OF ORAddressPrefix OPTIONAL,
        to [1]          SET OF ORAddressPrefix OPTIONAL,
        from-excludes [2]       SET OF ORAddressPrefix OPTIONAL,
        to-excludes [3]         SET OF ORAddressPrefix OPTIONAL }   10

ORAddressPrefix ::= DistinguishedName

_____________Figure_14:__Simple_MTA_Policy_Specification_______________


_______________________________________________________________________

mandatoryRedirect ATTRIBUTE ::= {
        SUBTYPE OF  distinguishedName
        SINGLE VALUE
        ID at-mandatory-redirect}

filteredRedirect ATTRIBUTE ::= {
        WITH SYNTAX FilteredRedirect
        SINGLE VALUE
        ID at-filtered-redirect}                                    10

FilteredRedirect ::= SEQUENCE {
        redirect-to DistinguishedName,
        SEQUENCE {
                min-size [1] INTEGER,
                max-size [2] INTEGER,
                content [3] ContentType,
                eit [4] ExternalEncodedInformationType }
        }
                                                                    20



___________________Figure_15:__Redirect_Definition_____________________



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_______________________________________________________________________


nonDeliveryInfo ATTRIBUTE ::= {
        WITH SYNTAX NonDeliveryReason
        ID at-non-delivery-info}

NonDeliveryReason ::= SEQUENCE {
        reason INTEGER (0..ub-reason-codes),
        diagnostic INTEGER (0..ub-diagnostic-codes),
        supplementaryInfo PrintableString }

_________________Figure_16:__Non_Delivery_Information__________________





_______________________________________________________________________

badAddressSearchPoint ATTRIBUTE ::= {
        SUBTYPE OF distinguishedName
        ID at-bad-address-search-point}

badAddressSearchAttributes ATTRIBUTE ::= {
        WITH SYNTAX AttributeType
        ID at-bad-address-search-attributes}

alternativeAddressInformation EXTENSION                             10
        AlternativeAddressInformation
        ::= id-alternative-address-information
                -- X.400(92) continues to use MACRO notation

AlternativeAddressInformation ::= SET OF SEQUENCE {
        distinguished-name DistinguishedName OPTIONAL,
        or-address ORAddress OPTIONAL,
        other-useful-info SET OF Attribute }


___________________Figure_17:__Bad_Address_Pointers____________________




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_______________________________________________________________________


localAccessUnit ATTRIBUTE ::= {
        WITH SYNTAX AccessUnitType
        ID at-local-access-unit}

AccessUnitType ::= ENUMERATED {
        fax (1),
        physical-delivery (2),
        teletex (3),
        telex (4) }                                                 10

accessUnitsUsed ATTRIBUTE ::= {
        WITH SYNTAX SelectedAccessUnit
        ID at-access-units-used}

SelectedAccessUnit ::= SEQUENCE {
        type AccessUnitType,
        providing-MTA DistinguishedName,
        filter SET OF ORAddress OPTIONAL }

__________________Figure_18:__Access_Unit_Attributes___________________



_______________________________________________________________________

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


tc-cons OBJECT IDENTIFIER ::= {ts-communities 1}        -- OSI CONS
tc-clns OBJECT IDENTIFIER ::= {ts-communities 2}        -- OSI CLNS
tc-internet OBJECT IDENTIFIER ::= {ts-communities 3}    -- Internet + RFC 1006
tc-int-x25 OBJECT IDENTIFIER ::= {ts-communities 4}     -- International X.25
                                                        -- Without CONS10
tc-ixi OBJECT IDENTIFIER ::= {ts-communities 5}         -- IXI (Europe)
tc-janet OBJECT IDENTIFIER ::= {ts-communities 6}       -- Janet (UK)


____Figure_20:__Transport_Community_Object_Identifier_Assignments______



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_______________________________________________________________________

mail-protocol OBJECT-IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1) private(4)
          enterprises(1) isode-consortium (453) mail-protocol (5)}

ac-p1-1984 OBJECT IDENTIFIER ::= {mail-protocol 1}      -- p1(1984)
ac-smtp  OBJECT IDENTIFIER ::= {mail-protocol 2}        -- SMTP
ac-uucp OBJECT IDENTIFIER ::= {mail-protocol 3}         -- UUCP Mail
ac-jnt-mail OBJECT IDENTIFIER ::= {mail-protocol 4}     -- JNT Mail (UK)
ac-p1-1988-x410 OBJECT IDENTIFIER ::= {mail-protocol 5} -- p1(1988) in X.410 mode
ac-p3-1984 OBJECT IDENTIFIER ::= {mail-protocol 6}      -- p3(1984) 10


__________Figure_21:__Protocol_Object_Identifier_Assignments___________

















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