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Keywords: [--------|e], Routing, Mail, EMail, Message, Handling, System, X.400
Network Working Group S. Kille
Request for Comments: 1801 ISODE Consortium
Category: Experimental June 1995
X.400-MHS use of the X.500 Directory to support X.400-MHS Routing
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. This memo does not specify an Internet standard of any
kind. Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Table of Contents
1 Introduction 3
2 Goals 3
3 Approach 5
4 Direct vs Indirect Connection 6
5 X.400 and RFC 822 8
6 Objects 9
7 Communities 10
8 Routing Trees 11
8.1 Routing Tree Definition . . . . . . . 12
8.2 The Open Community Routing Tree . . . . . 12
8.3 Routing Tree Location . . . . . . . 13
8.4 Example Routing Trees . . . . . . . 13
8.5 Use of Routing Trees to look up Information . . 13
9 Routing Tree Selection 14
9.1 Routing Tree Order . . . . . . . . 14
9.2 Example use of Routing Trees . . . . . . 15
9.2.1 Fully Open Organisation . . . . . 15
9.2.2 Open Organisation with Fallback . . . 15
9.2.3 Minimal-routing MTA . . . . . . 16
9.2.4 Organisation with Firewall . . . . . 16
9.2.5 Well Known Entry Points . . . . . 16
9.2.6 ADMD using the Open Community for Advertising 16
9.2.7 ADMD/PRMD gateway . . . . . . . 17
10 Routing Information 17
10.1 Multiple routing trees . . . . . . . 20
10.2 MTA Choice . . . . . . . . . . 22
10.3 Routing Filters . . . . . . . . . 25
10.4 Indirect Connectivity . . . . . . . 26
11 Local Addresses (UAs) 27
11.1 Searching for Local Users . . . . . . 30
12 Direct Lookup 30
13 Alternate Routes 30
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13.1 Finding Alternate Routes . . . . . . . 30
13.2 Sharing routing information . . . . . . 31
14 Looking up Information in the Directory 31
15 Naming MTAs 33
15.1 Naming 1984 MTAs . . . . . . . . . 35
16 Attributes Associated with the MTA 35
17 Bilateral Agreements 36
18 MTA Selection 38
18.1 Dealing with protocol mismatches . . . . . 38
18.2 Supported Protocols . . . . . . . . 39
18.3 MTA Capability Restrictions . . . . . . 39
18.4 Subtree Capability Restrictions . . . . . 40
19 MTA Pulling Messages 41
20 Security and Policy 42
20.1 Finding the Name of the Calling MTA . . . . 42
20.2 Authentication . . . . . . . . . 42
20.3 Authentication Information . . . . . . 44
21 Policy and Authorisation 46
21.1 Simple MTA Policy . . . . . . . . 46
21.2 Complex MTA Policy . . . . . . . . 47
22 Delivery 49
22.1 Redirects . . . . . . . . . . 49
22.2 Underspecified O/R Addresses . . . . . . 50
22.3 Non Delivery . . . . . . . . . . 51
22.4 Bad Addresses . . . . . . . . . 51
23 Submission 53
23.1 Normal Derivation . . . . . . . . 53
23.2 Roles and Groups . . . . . . . . . 53
24 Access Units 54
25 The Overall Routing Algorithm 54
26 Performance 55
27 Acknowledgements 55
28 References 56
29 Security Considerations 57
30 Author's Address 58
A Object Identifier Assignment 59
B Community Identifier Assignments 60
C Protocol Identifier Assignments 60
D ASN.1 Summary 61
E Regular Expression Syntax 71
List of Figures
1 Location of Routing Trees . . . . . . 12
2 Routing Tree Use Definition . . . . . . 14
3 Routing Information at a Node . . . . . 17
4 Indirect Access . . . . . . . . . 25
5 UA Attributes . . . . . . . . . 27
6 MTA Definitions . . . . . . . . . 33
7 MTA Bilateral Table Entry . . . . . . 36
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8 Bilateral Table Attribute . . . . . . 37
9 Supported MTS Extensions . . . . . . . 39
10 Subtree Capability Restriction . . . . . 40
11 Pulling Messages . . . . . . . . . 41
12 Authentication Requirements . . . . . . 43
13 MTA Authentication Parameters . . . . . 45
14 Simple MTA Policy Specification . . . . . 46
15 Redirect Definition . . . . . . . . 48
16 Non Delivery Information . . . . . . . 50
17 Bad Address Pointers . . . . . . . . 52
18 Access Unit Attributes . . . . . . . 53
19 Object Identifier Assignment . . . . . . 59
20 Transport Community Object Identifier Assignments 60
21 Protocol Object Identifier Assignments . . . 61
22 ASN.1 Summary . . . . . . . . . 61
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.
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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
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.
This has indirect impact on the routing approaches used.
o Interact sensibly with ADMD services.
o Be global in scope
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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.
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.
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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 [19]. 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, 17] 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.
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.
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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
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
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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.
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 message routing. It is
important that this can be integrated with RFC 822 based routing, as
many MTAs will work in both communities. This routing document is
written with this problem in mind, and some work to verify this has
been done. support for RFC 822 routing using the same basic
infrastructure is defined in a companion document [13]. 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.
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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 [11]. The list of objects
used in this specification is:
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
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the UA. It will identify which MTAs are able to access the UA.
(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.)
Role Some organisational function. For example:
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
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.
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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 [15]. 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 Countries and US States.
---------------------------------------------------------------------
routingTreeRoot OBJECT-CLASS ::= {
SUBCLASS OF {routingInformation|subtree}
ID oc-routing-tree-root}
Figure 1: Location of Routing Trees
---------------------------------------------------------------------
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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" [15]. 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:
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
[15] in order to generate a Distinguished Name.
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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.
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.
---------------------------------------------------------------------
routingTreeList ATTRIBUTE ::= {
WITH SYNTAX RoutingTreeList
SINGLE VALUE
ID at-routing-tree-list}
RoutingTreeList ::= SEQUENCE OF RoutingTreeName
RoutingTreeName ::= DistinguishedName
Figure 2: Routing Tree Use Definition
---------------------------------------------------------------------
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:
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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
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.
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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).
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 it is important to
support cleanly.
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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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
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
KIND auxiliary
MAY CONTAIN {
subtreeInformation|
routingFilter|
routingFailureAction|
mTAInfo|
accessMD| 10
nonDeliveryInfo|
badAddressSearchPoint|
badAddressSearchAttributes}
ID oc-routing-information}
-- No naming attributes as this is not a
-- structural object class
subtreeInformation ATTRIBUTE ::= { 20
WITH SYNTAX SubtreeInfo
SINGLE VALUE
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ID at-subtree-information}
SubtreeInfo ::= ENUMERATED {
all-children-present(0),
not-all-children-present(1) }
routingFilter ATTRIBUTE ::= { 30
WITH SYNTAX RoutingFilter
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), 50
next-tree-only(1),
next-tree-first(2),
stop(3) }
mTAInfo ATTRIBUTE ::= {
WITH SYNTAX MTAInfo
ID at-mta-info}
MTAInfo ::= SEQUENCE { 60
name DistinguishedName,
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), 70
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preferred-access(5),
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
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).
The value all-children-present simply means that all of the child
entries are present, and that this can be used to determine
invalid addresses. There are no implications about the presence
of routing information. Thus it is possible to verify an entire
address, but only to route on one of the higher level components.
For example, consider the node:
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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 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 the use of X.500 and handling of errors is discussed in
Section 14. The routing decision works by examining a series of
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entries (nodes) in one or more routing trees. This information is
summarised in Figure 3. 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
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:
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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:
o The manager for the node of the tree shall place it there. This
is a formality, but critical in terms of overall authority.
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, which is
defined in Figure 3. 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 MTA's 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
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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.
ae-info 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.
The structure of information within ae-info is as follows:
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 below.
ae-attributes Attributes from the AEs entry.
Information in the mta-attributes and ae-info is present as a
performance optimisation, so that routing choices can be made with a
much smaller number of directory operations. Using this information,
whose presence is optional, is equivalent to looking up the
information in the MTA. If this information is present, it shall be
maintained to be the same as that information stored in the MTA
entry. Despite this maintenence requirement, use of this performance
optimisation data is optional, and the information may always be
looked up from the MTA entry.
Note: It has been suggested that substantial performance optimisation
will be achieved by caching, and that the performance gained
from maintaining these attributes does not justify the effort
of maintaining the entries. If this is borne out by
operational experience, this will be reflected in future
versions of this specification.
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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:
protocolInformation
applicationContext
mhs-deliverable-content-length
responderAuthenticationRequirements
initiatorAuthenticationRequirements
responderPullingAuthenticationRequirements
initiatorPullingAuthenticationRequirements
initiatorP1Mode
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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 attributes 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.
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.
When present, the procedures of analysing the routing filters shall
be followed before other actions. The routing filter overrides
mTAInfo and accessMD attributes, which means that the routing filter
must be considered first. Only in the event that no routing filters
match shall the mTAInfo and accessMD attributes be considered. 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.
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dda-key If the attribute is domain defined, then this parameter may
be used to identify the key.
accessMD ATTRIBUTE ::= {
SUBTYPE OF distinguishedName
ID at-access-md}
Figure 4: Indirect Access
---------------------------------------------------------------------
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 distinguished name specifies the entry which holds routing
information for the filter. It shall be an entry with object
class routingInformation, which can be used to determine the MTA
or MTA choice. All of the attributes from this entry should be
used, as if they had been directly returned from the current entry
(i.e., the procedure recurses). The current entry does not set
defaults.
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.
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. It shall be an
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entry with object class routingInformation, which can be used to
determine the MTA or MTA choice and route according to the
information retrieve to this access MD. All of the attributes from
this entry should be used, as if they had been directly returned from
the current entry (i.e., the procedure recurses). The current entry
does not set defaults.
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 due to directory security restrictions, the routing algorithm
shall continue as if no MTA information was located in the routing
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:
---------------------------------------------------------------------
routedUA OBJECT-CLASS ::= {
SUBCLASS OF {routingInformation}
KIND auxiliary
MAY CONTAIN {
-- from X.402
mhs-deliverable-content-length|
mhs-deliverable-content-types|
mhs-deliverable-eits|
mhs-message-store| 10
mhs-preferred-delivery-methods|
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
-- defined here
supportedExtensions|
redirect|
supportingMTA|
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
---------------------------------------------------------------------
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 MTS extensions supported by the MTA, which affect
delivery.
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
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possible and useful for several MTAs to be able to deliver to a
single UA. This attribute is a subtype of mTAInfo, and it defines
access information for an MTA which is able to deliver to the UA.
There may also be an mTAInfo attribute in the entry.
Components of the supportingMTA attribute are interpreted in the
same manner as mtaInfo is for routing, with one exception. The
values of the Route Weight are interpreted in the following
manner:
o 0. A preferred MTA for delivery.
o 5. A backup MTA.
o 10. A backup MTA, which is not presferred.
The supportingMTA attribute shall be present, unless the address
is being non-delivered or redirected, in which case it may be
omitted.
redirect The redirect attribute controls redirects, as described in
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)).
Misconfiguration of the supportingMTA attribute could have serious
operational and possibly security problems, although for the most
part no worse than general routing configuration problems. An MTA
using this attribute may choose to perform certain sanity checks,
which might be to verify the routing tree or subtree that the entry
resides in.
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
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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.
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.
Note: This performance optimisation has a management overhead, and
further experience is needed to determine if the effort
justifies the performance improvement.
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
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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
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:
Entry Found Information from the entry (node) is returned and shall
be examined. The routing process continues or terminates, based
on this information.
Entry Not Found Return information on the length of best possible
match to the routing algorithm.
Temporary Reject The MTA shall stop the calculation, and repeat the
request later. Repeated temporary rejects should be handled in a
similar manner to the way the local MTA 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. The
routing calculation should be stopped and the message
non-delivered.
The algorithm proceeds by a series of directory read operations. If
the read operation is successful, the Entry Found procedure should be
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followed. Errors from the lookup (directory read) shall be handled
in terms of the above procedures as follows. The following handling
is used when following a routing tree:
AttributeError This leads to a Permanent Reject.
NameError Entry Not Found is used. The matched parameter is used to
determine the number of components of the name that have matched
(possibly zero). The read may then repeated with this name.
This is the normal case, and allows the "best" entry in the
routingn tree to be located with two reads.
Referral The referral shall be followed, and then the procedure
recurses.
SecurityError Entry Not Found is used. Return a match length of one
less than the name provided.
ServiceError This leads to a Temporary Reject.
There will be cases where the algorithm moves to a name outside of
the routing tree being followed (Following an accessMD attribute, or
a redirect or a matched routing filter). The handling will be the
same as above, except:
NameError This leads to a Permanent Reject.
SecurityError This leads to a Permanent Reject.
When reading objects which of not of object class routingInformation,
the following error handling is used:
AttributeError This leads to a Permanent Reject.
NameError This leads to a Permanent Reject.
Referral The referral shall be followed, and then the procedure
recurses.
SecurityError In the case of an MTA, treat as if it is not possible
to route to this MTA. In other cases, this leads to a Permanent
Reject.
ServiceError This leads to a Temporary Reject.
The algorithm specifies the object class of entries which are read.
If an object class does not match what is expected, this shall lead
to a permanent reject.
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15. Naming MTAs
MTAs need to be named in the DIT, but the name does not have routing
significance. The MTA name 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 ::= {
SUBCLASS OF {application-process}
KIND auxiliary 20
MAY CONTAIN {
mTAWillRoute|
globalDomainID|
routingTreeList|
localAccessUnit|
accessUnitsUsed
}
ID oc-mta-application-process}
mTA OBJECT CLASS ::= { -- Application Entity 30
SUBCLASS OF {mhs-message-transfer-agent}
KIND structural
MAY CONTAIN {
mTAName|
globalDomainID| -- per AE variant
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responderAuthenticationRequirements|
initiatorAuthenticationRequirements|
responderPullingAuthenticationRequirements|
initiatorPullingAuthenticationRequirements|
initiatorP1Mode| 40
responderP1Mode|
polledMTAs|
protocolInformation|
respondingRTSCredentials|
initiatingRTSCredentials|
callingPresentationAddress|
callingSelectorValidity|
bilateralTable|
mTAWillRoute|
mhs-deliverable-content-length| 50
routingTreeList|
supportedMTSExtensions|
mTAsAllowedToPoll
}
ID oc-mta}
Figure 6: MTA Definitions
---------------------------------------------------------------------
In X.400 (1984), 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) the Distinguished Name shall 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.
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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.
The situation considered so far is where an MTA supports one
application context (protocol). The MTA is represented in the
directory by a single directory entry, having no subordinate
applicationEntity entries. This name is considered to be the name of
the MTA and its Application Process Title. The MTA has no
Application Entity Qualifier, and so this is also the Application
Entity Title. In the case where an MTA supports more than one
application context, the Application Process Title is exactly the
same as above, but it also has one or more subordinate
applicationEntity entries. Each of these subordinate entries is
associated with a single application context. The relative
distinguished name of the subordinate applicationEntity entry is the
Application Entity Qualifier of the Application Entity Title. The
Application Entity Title is the distinguished name of the
applicationEntity. The term MTA Name is used to refer to the
Application Process Title.
15.1 Naming 1984 MTAs
Some simplifications are necessary for 1984 MTAs, and only one naming
approach may be used. This is because Directory Names are not
carried in the protocol, and so it must be possible to derive the
name algorithmically from parameters carried. 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.
globalDomainID Section 15.
protocolInformation Section 18.1.
applicationContext Section 18.2.
mhs-deliverable-content-length Section 18.3.
responderAuthenticationRequirements Section 20.2.
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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.
---------------------------------------------------------------------
mTABilateralTableEntry OBJECT-CLASS ::=
SUBCLASS OF {mTA| distinguishedNameTableEntry}
ID oc-mta-bilateral-table-entry}
Figure 7: MTA Bilateral Table Entry
---------------------------------------------------------------------
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
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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 [15].
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.
---------------------------------------------------------------------
bilateralTable ATTRIBUTE ::= {
WITH SYNTAX SEQUENCE OF DistinguishedName
SINGLE VALUE
ID at-bilateral-table}
Figure 8: Bilateral Table Attribute
---------------------------------------------------------------------
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
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present. Other MTA attributes (e.g., presentation address) may be
present for one of two reasons:
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.
Note: For some bilateral connections there is a need control various
other functions, such as trace stripping and originator address
manipulation. For now, this is left to implementation specific
extensions. This is expected to 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.
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---------------------------------------------------------------------
supportedMTSExtensions ATTRIBUTE ::= {
SUBTYPE OF objectIdentifier
ID at-supported-mts-extensions}
Figure 9: Supported MTS Extensions
---------------------------------------------------------------------
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.
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.
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---------------------------------------------------------------------
restrictedSubtree OBJECT-CLASS ::= {
SUBCLASS OF {top}
KIND auxiliary
MAY CONTAIN {
subtreeDeliverableContentLength|
subtreeDeliverableContentTypes|
subtreeDeliverableEITs}
ID oc-restricted-subtree}
10
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 20
ID at-subtree-deliverable-eits}
Figure 10: Subtree Capability Restriction
---------------------------------------------------------------------
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
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 setting defaults in the subtree.
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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
---------------------------------------------------------------------
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
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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 derived from the AP-Title and AE-Qualifier in
the A-Associate. For X.400(84), it will not be possible to derive a
global name from the bind. The MTA Name exchanged in the RTS Bind
will provide a key into the private bilateral agreement table (or
tables), where the connection information can be verified. Thus for
X.400(1984) it will only be possible to have bilateral inbound links
or no authentication of the calling MTA.
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.
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If an attribute is omitted, no checks are required. If multiple
checks are required, then each of the relevant bits shall be set.
The attribute is single value, which implies that the MTA must set a
single authentication policy.
---------------------------------------------------------------------
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
responderPullingAuthenticationRequirements 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
---------------------------------------------------------------------
The values of the authentication requirements mean:
mta-name-present That an RTS level MTA parameter shall be present for
logging purposes.
aet-present That a distinguished name application entity title shall
be provided at the ACSE level.
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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 or multilateral
agreements. 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
applied. Note that in some cases, MTA information will be split
across a private and public entry.
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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
---------------------------------------------------------------------
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 shall default to a zero-length OCTET
STRING.
Note: Future versions of this specification may 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.
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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.
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.
21.2 Complex MTA Policy
MTAs will generally have a much more complex policy mechanism, such
as that provided by PP MTA [10]. 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:
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
o Use of charging and non-charging nets
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.
MTAs may apply more complex routing policies. However, this shall
not lead to the rejection of messages which might otherwise be
correctly routed on the published policy information. Policies
relating to submission do not need to be public. They can be private
to the MTA.
---------------------------------------------------------------------
redirect ATTRIBUTE ::= {
WITH SYNTAX Redirect
SINGLE VALUE
ID at-redirect}
Redirect ::= SEQUENCE OF SEQUENCE {
or-name ORName,
reason RedirectionReason, -- from X.411
filter CHOICE { 10
min-size [1] INTEGER,
max-size [2] INTEGER,
content [3] ContentType,
eit [4] ExternalEncodedInformationType } OPTIONAL
}
Figure 15: Redirect Definition
---------------------------------------------------------------------
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22. Delivery
22.1 Redirects
There is a need to specify redirects in the Directory. 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. A mechanism is given to allow conditional
(filtered) redirects for different types of messages. This allow
small messages, large messages, or messages containing specific EITs
or content to be redirected. The definitions are given in Figure 15.
Redirection is specified by the redirect attribute. If present, this
attribute shall be processed before supportingMTA and
nonDeliveryInfo. These two attributes shall only be considered if it
is determined that no redirection applies. The redirect attribute is
a sequence of elements which are considered in the order specified.
Each element is examined in turn. The first element which applies is
used, and no further elements are examined. Use of an element for
redirection, shall follow the X.400 procedures for redirection, and
an element shall not be used if prevented by a service control. If
the redirect attribute is processed and no redirection is generated,
processing shall continue irrespective of service controls. If non-
delivery is intended in this event, this shall be achieved by use of
the nonDeliveryInfo attribute.
The components have the following interpretations:
or-name This X.400 O/R Name is for use in the redirection. This O/R
Name will contain an optional directory name and optional O/R
address. One or both of the must be present. If the O/R Address
element is present, the Directory Name, if present, is for
information only. and is to be placed in the X.400 redirection.
If the O/R address element is absent, the Directory Name shall be
present and shall be looked up to determine the O/R address of the
redirected recipient. The O/R Address of the intended recipient
will either be present or derived by lookup. Routing shall be
done on the basis of this O/R Address.
reason This is the reason information to be placed in the X.400
redirect, and it shall take one of the following values of
RedirectReason defined in X.411:
recipient-assigned-alternate-recipient;
recipient-MD-assigned-alternate-recipient; or alias. It shall not
have the value originator-requested-alternate-recipient.
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
filter If filter is absent, the redirect is mandoatory and shall be
followed. If the filter is present, use of the redirect under
consideration depends on the type of filter as follows:
min-size Follow redirect if the message (MT content) is larger
than min-size (measured in kBytes).
max-size Follow redirect if the message (MT content) is smaller
than max-size (measured in kBytes).
content Follow redirect if message content is of type content.
eit Follow redirect if the encoded information types registered
in the envelope contain eit.
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.
---------------------------------------------------------------------
nonDeliveryInfo ATTRIBUTE ::= {
WITH SYNTAX NonDeliveryReason
SINGLE VALUE
ID at-non-delivery-info}
NonDeliveryReason ::= SEQUENCE {
reason INTEGER (0..ub-reason-codes),
diagnostic INTEGER (0..ub-diagnostic-codes) OPTIONAL,
supplementaryInfo PrintableString OPTIONAL } 10
Figure 16: Non Delivery Information
---------------------------------------------------------------------
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
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
is to be rejected as ambiguous, an entry shall be created in the DIT,
and forced non-delivery specified for this reason.
Note: It is also possible to handle this situation by searching. An
MTA conforming to this specification may handle underspecified
addresses in this manner. The choice of mechanism will be
reviewed after operational experience with both approaches.
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. If a nonDeliveryInfo attribute is present, any
supportingMTA attribute shall be ignored and the message non-
delivered.
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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---------------------------------------------------------------------
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
---------------------------------------------------------------------
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 AlternativeAddressInformation
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) in X.400(1988).
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.
Note: It might be useful to allow control of search type, and also
single level vs subtree. This issue is for further study.
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
---------------------------------------------------------------------
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 UnitAttributes
---------------------------------------------------------------------
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.
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.
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
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.
Note 1: This mechanism might be used to replace the routefilter
mechanism of the MTS routing. Comments are solicited.
Note 2: It has been proposed to add a more powerful filter mechanism.
Comments are solicited.
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.
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
further. (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.) 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 supports, as described in Section 18.2.
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
(Note that this could be an RFC 822 protocol, as well as an
X.400 protocol.)
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
in [12].
26. Performance
The routing algorithm has been 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 memo is the central document of a series of specifications [14,
15, 16], and to other work in progress. 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
Kille Experimental [Page 55]
RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
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.
28. 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,
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] Eppenberger, U., "Routing Coordination for X.400 MHS Services
Within a Multi Protocol / Multi Network Environment Table Format
V3 for Static Routing", RFC 1465, SWITCH, May 1993.
[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] Kille, S., "Encoding Network Addresses to support operation over
non-OSI lower layers", RFC 1277, Department of Computer Science,
University College London, November 1991.
[10] S.E. Kille. Implementing X.400 and X.500: The PP and QUIPU
Systems. Artech House, 1991. ISBN 0-89006-564-0.
[11] Kille, S., "A Representation of Distinguished Names
(OSI-DS 23 (v5))", RFC 1485, Department of Computer Science,
University College London, January 1992.
Kille Experimental [Page 56]
RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
[12] Kille, S., Mhs use of X.500 directory to support mhs content
conversion, Work in Progress, July 1993.
[13] Kille, S., "Use of the X.500 directory to support routing for
RFC 822 and related protocols", Work in Progress, July 1993.
[14] Kille, S., "Representing tables and subtrees in the X.500
directory", Work in Progress, September 1994.
[15] Kille, S., "Representing the O/R Address hierarchy in the X.500
directory information tree", Work in Progress, September 1994.
[16] Kille, S., "Use of the X.500 directory to support mapping
between X.400 and RFC 822 addresses", Work in Progress,
September 1994.
[17] Lauder, P., Kummerfeld, R., and A. Fekete. Hierarchical network
routing. In Tricomm 91, 1991.
[18] CCITT recommendations X.400 / ISO 10021, April 1988. CCITT
SG 5/VII / ISO/IEC JTC1, Message Handling: System and Service
Overview.
[19] 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.
29. Security Considerations
Security issues are not discussed in this memo.
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
30. Author's Address
Steve Kille
ISODE Consortium
The Dome
The Square
Richmond
TW9 1DT
England
Phone: +44-81-332-9091
EMail: S.Kille@ISODE.COM
X.400: I=S; S=Kille; O=ISODE Consortium; P=ISODE;
A=Mailnet; C=FI;
DN: CN=Steve Kille,
O=ISODE Consortium, C=GB
UFN: S. Kille, ISODE Consortium, GB
Kille Experimental [Page 58]
RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
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 8}
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-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-redirect OBJECT IDENTIFIER ::= {at 46}
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}40
at-responder-p1-mode OBJECT IDENTIFIER ::= {at 24}
at-responder-pulling-authentication-requirements
OBJECT IDENTIFIER ::= {at 25}
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
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 47}
at-polled-mtas OBJECT IDENTIFIER ::= {at 37}
at-bilateral-table OBJECT IDENTIFIER {at 45}
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
-----------------------------------------------------------------------
B Community Identifier Assignments
-----------------------------------------------------------------------
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+RFC1006
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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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
C Protocol Identifier Assignments
-----------------------------------------------------------------------
mail-protocol OBJECT-IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1)
private(4)n 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
-----------------------------------------------------------------------
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
KIND auxiliary
MAY CONTAIN {
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
subtreeInformation|
routingFilter|
routingFailureAction|
mTAInfo|
accessMD|
nonDeliveryInfo| 30
badAddressSearchPoint|
badAddressSearchAttributes}
ID oc-routing-information}
-- No naming attributes as this is not a
-- structural object class
subtreeInformation ATTRIBUTE ::= {
WITH SYNTAX SubtreeInfo 40
SINGLE VALUE
ID at-subtree-information}
SubtreeInfo ::= ENUMERATED {
all-children-present(0),
not-all-children-present(1) }
routingFilter ATTRIBUTE ::= {
WITH SYNTAX RoutingFilter 50
ID at-routing-filter}
RoutingFilter ::= SEQUENCE{
attribute-type OBJECT-IDENTIFIER,
weight RouteWeight,
dda-key String OPTIONAL,
regex-match IA5String OPTIONAL,
node DistinguishedName }
60
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), 70
next-tree-first(2),
stop(3) }
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
mTAInfo ATTRIBUTE ::= {
WITH SYNTAX MTAInfo
ID at-mta-info}
MTAInfo ::= SEQUENCE {
name DistinguishedName, 80
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), 90
backup(10)} (0..20)
accessMD ATTRIBUTE ::= {
SUBTYPE OF distinguishedName
ID at-access-md}
routedUA OBJECT-CLASS ::= {
SUBCLASS OF {routingInformation}
KIND auxiliary
MAY CONTAIN { 100
-- from X.402
mhs-deliverable-content-length|
mhs-deliverable-content-types|
mhs-deliverable-eits|
mhs-message-store|
mhs-preferred-delivery-methods|
-- defined here
supportedExtensions|
redirect|
supportingMTA| 110
userName|
nonDeliveryInfo}
ID oc-routed-ua}
supportedExtensions ATTRIBUTE ::= {
SUBTYPE OF objectIdentifier
ID at-supported-extensions}
supportingMTA ATTRIBUTE ::= {
SUBTYPE OF mTAInfo 120
ID at-supporting-mta}
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
userName ATTRIBUTE ::= {
SUBTYPE OF distinguishedName
ID at-user-name}
mTAName ATTRIBUTE ::= {
SUBTYPE OF name
WITH SYNTAX DirectoryString{ub-mta-name-length}
SINGLE VALUE 130
ID at-mta-name}
-- 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 140
-- to enable trace to be written
mTAApplicationProcess OBJECT-CLASS ::= {
SUBCLASS OF {application-process}
KIND auxiliary
MAY CONTAIN {
mTAWillRoute|
globalDomainID|
routingTreeList|
localAccessUnit| 150
accessUnitsUsed
}
ID oc-mta-application-process}
mTA OBJECT CLASS ::= { -- Application Entity
SUBCLASS OF {mhs-message-transfer-agent}
KIND structural
MAY CONTAIN {
mTAName|
globalDomainID| -- per AE variant 160
responderAuthenticationRequirements|
initiatorAuthenticationRequirements|
responderPullingAuthenticationRequirements|
initiatorPullingAuthenticationRequirements|
initiatorP1Mode|
responderP1Mode|
polledMTAs|
protocolInformation|
respondingRTSCredentials|
initiatingRTSCredentials| 170
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RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
callingPresentationAddress|
callingSelectorValidity|
bilateralTable|
mTAWillRoute|
mhs-deliverable-content-length|
routingTreeList|
supportedMTSExtensions|
mTAsAllowedToPoll
}
ID oc-mta} 180
mTABilateralTableEntry OBJECT-CLASS ::=
SUBCLASS OF {mTA| distinguishedNameTableEntry}
ID oc-mta-bilateral-table-entry}
bilateralTable ATTRIBUTE ::= {
WITH SYNTAX SEQUENCE OF DistinguishedName
SINGLE VALUE
ID at-bilateral-table}
190
supportedMTSExtensions ATTRIBUTE ::= {
SUBTYPE OF objectIdentifier
ID at-supported-mts-extensions}
restrictedSubtree OBJECT-CLASS ::= {
SUBCLASS OF {top}
KIND auxiliary
MAY CONTAIN {
subtreeDeliverableContentLength|
subtreeDeliverableContentTypes| 200
subtreeDeliverableEITs}
ID oc-restricted-subtree}
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} 210
subtreeDeliverableEITs ATTRIBUTE ::= {
SUBTYPE OF mhs-deliverable-eits
ID at-subtree-deliverable-eits}
initiatorP1Mode ATTRIBUTE ::= {
WITH SYNTAX P1Mode
Kille Experimental [Page 65]
RFC 1801 X.400-MHS Routing using X.500 Directory June 1995
SINGLE VALUE
ID at-initiator-p1-mode} 220
responderP1Mode ATTRIBUTE ::= {
WITH SYNTAX P1Mode
SINGLE VALUE
ID at-responder-p1-mode}
P1Mode ::= ENUMERATED {
push-only(0),
pull-only(1),
twa(2) } 230
polledMTAs ATTRIBUTE ::= {
WITH SYNTAX PolledMTAs
ID at-polled-mtas}
PolledMTAs ::= SEQUENCE {
mta DistinguishedName,
poll-frequency INTEGER OPTIONAL --frequency in minutes
}
240
mTAsAllowedToPoll ATTRIBUTE ::= {
SUBTYPE OF distinguishedName
ID at-mtas-allowed-to-poll}
responderAuthenticationRequirements ATTRIBUTE ::= {
WITH SYNTAX AuthenticationRequirements
SINGLE VALUE
ID at-responder-authentication-requirements}
250
initiatorAuthenticationRequirements ATTRIBUTE ::= {
WITH SYNTAX AuthenticationRequirements
SINGLE VALUE
ID at-initiator-authentication-requirements}
responderPullingAuthenticationRequirements ATTRIBUTE ::= {
WITH SYNTAX AuthenticationRequirements
SINGLE VALUE
ID at-responder-pulling-authentication-requirements}
260
initiatorPullingAuthenticationRequirements ATTRIBUTE ::= {
WITH SYNTAX AuthenticationRequirements
SINGLE VALUE
ID at-initiator-pulling-authentication-requirements}
AuthenticationRequirements ::= BITSTRING {
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mta-name-present(0),
aet-present(1),
aet-valid(2),
network-address(3), 270
simple-authentication(4),
strong-authentication(5),
bilateral-agreement-needed(6)}
respondingRTSCredentials ATTRIBUTE ::= {
WITH SYNTAX RTSCredentials
SINGLE VALUE
ID at-responding-rts-credentials}
280
initiatingRTSCredentials ATTRIBUTE ::= {
WITH SYNTAX RTSCredentials
SINGLE VALUE
ID at-initiating-rts-credentials}
RTSCredentials ::= SEQUENCE {
request [0] MTAandPassword OPTIONAL,
response [1] MTAandPassword OPTIONAL }
290
MTAandPassword ::= SEQUENCE {
MTAName,
Password } -- MTAName and Password
-- from X.411
callingPresentationAddress ATTRIBUTE ::= {
SUBTYPE OF presentationAddress
MULTI VALUE 300
ID at-calling-presentation-address}
callingSelectorValidity ATTRIBUTE ::= {
WITH SYNTAX CallingSelectorValidity
SINGLE VALUE
ID at-calling-selector-validity}
CallingSelectorValidity ::= ENUMERATED {
all-selectors-fixed(0),
tsel-may-vary(1), 310
all-selectors-may-vary(2) }
mTAWillRoute ATTRIBUTE ::= {
WITH SYNTAX MTAWillRoute
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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, 320
to-excludes [3] SET OF ORAddressPrefix OPTIONAL }
ORAddressPrefix ::= DistinguishedName
redirect ATTRIBUTE ::= {
WITH SYNTAX Redirect
SINGLE VALUE
ID at-redirect}
Redirect ::= SEQUENCE OF SEQUENCE { 330
or-name ORName,
reason RedirectionReason, -- from X.411
filter CHOICE {
min-size [1] INTEGER,
max-size [2] INTEGER,
content [3] ContentType,
eit [4] ExternalEncodedInformationType } OPTIONAL
}
nonDeliveryInfo ATTRIBUTE ::= { 340
WITH SYNTAX NonDeliveryReason
SINGLE VALUE
ID at-non-delivery-info}
NonDeliveryReason ::= SEQUENCE {
reason INTEGER (0..ub-reason-codes),
diagnostic INTEGER (0..ub-diagnostic-codes) OPTIONAL,
supplementaryInfo PrintableString OPTIONAL }
badAddressSearchPoint ATTRIBUTE ::= { 350
SUBTYPE OF distinguishedName
ID at-bad-address-search-point}
badAddressSearchAttributes ATTRIBUTE ::= {
WITH SYNTAX AttributeType
ID at-bad-address-search-attributes}
alternativeAddressInformation EXTENSION
AlternativeAddressInformation
::= id-alternative-address-information 360
-- X.400(92) continues to use MACRO notation
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AlternativeAddressInformation ::= SET OF SEQUENCE {
distinguished-name DistinguishedName OPTIONAL,
or-address ORAddress OPTIONAL,
other-useful-info SET OF Attribute }
localAccessUnit ATTRIBUTE ::= {
WITH SYNTAX AccessUnitType
ID at-local-access-unit} 370
AccessUnitType ::= ENUMERATED {
fax (1),
physical-delivery (2),
teletex (3),
telex (4) }
accessUnitsUsed ATTRIBUTE ::= {
WITH SYNTAX SelectedAccessUnit
ID at-access-units-used} 380
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)}
routing OBJECT IDENTIFIER ::= {mhs-ds 3}
390
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}
oc-routing-information OBJECT IDENTIFIER ::= {oc 3}
oc-restricted-subtree OBJECT IDENTIFIER ::= {oc 4}
oc-routed-ua OBJECT IDENTIFIER ::= {oc 8} 400
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}
at-bad-address-search-point OBJECT IDENTIFIER ::= {at 5}
at-calling-selector-validity OBJECT IDENTIFIER ::= {at 7} 410
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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 ::= {at 14}
at-local-access-unit OBJECT IDENTIFIER ::= {at 15}
at-redirect OBJECT IDENTIFIER ::= {at 46}
at-mta-info OBJECT IDENTIFIER ::= {at 40} 420
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 ::= {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} 430
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}
at-transport-community OBJECT IDENTIFIER ::= {at 34}
at-user-name OBJECT IDENTIFIER ::= {at 35}
at-non-delivery-info OBJECT IDENTIFIER ::= {at 47}
at-polled-mtas OBJECT IDENTIFIER ::= {at 37}
at-bilateral-table OBJECT IDENTIFIER {at 45} 440
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)
private(4) enterprises(1) isode-consortium (453) ts-communities (4)}
450
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+RFC1006
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)
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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)} 460
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)
END
Figure 22: ASN.1 Summary
-----------------------------------------------------------------------
E Regular Expression Syntax
This appendix defines a form of regular expression for pattern
matching. This pattern matching is derived from commonly available
regular expression software including UNIX egrep(1) 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, cancelling the special nature
of the character.
. 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
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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 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 (hyphen), 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 regular expression, followed by an asterisk (*) matches zero
or more occurrences of the regular expression. For example,
[a-z][a-z]* matches any string of one or more lower case
letters.
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+ A regular expression, followed by a plus character (+) matches
one or more occurrences of the regular expression. For
example, [a-z]+ matches any string of one or more lower case
letters.
? A regular expression, followed by a question mark (?) matches
zero or one occurrences of the regular expression. For
example, ^[a-z]?[0-9]* matches a string starting with an
optional lower case letter, followed by zero or more digits.
{m}
{m,}
{m,n}
A regular expression, followed by {m}, {m,}, or {m,n} matches
a range of occurrences of the regular expression. The values
of m and n must be non-negative integers less than 256; {m}
matches exactly m occurrences; {m,} matches at least m
occurrences; {m,n} matches any number of occurrences between m
and n inclusive. Whenever a choice exists, the regular
expression matches as many occurrences as possible.
| Alternation: two regular expressions separated by `|' or
NEWLINE match either a match for the first or a match for the
second.
(...)
A regular expression enclosed between the character sequences
( and ) matches whatever the unadorned RE matches.
The order of precedence of operators at the same parenthesis level
is `[ ]' (character classes), then `*' `+' `?' '{m,n}' (closures),
then concatenation, then `|' (alternation) and NEWLINE.
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