CHAPTER 16
MESSAGE ROUTING ADMINISTRATION
Microsoft Exchange 2000 Server cares about it. Install as many Exchange 2000 servers
in you local area network (LAN) as you like, add all servers to the same routing group,
place mailboxes on them, and your users will be able to send each other messages in an
instant.
Lesson 1:
Routing Group Planning
A routing group is a collection of Exchange 2000 servers that typically share a permanent,
reliable, high-bandwidth network connection. In a particular routing group, all servers
communicate directly with each other using SMTP. SMTP, in turn, can work efficiently
over all types of network connections, including demand dial-up links with limited
bandwidths and high latencies.
Multiple Routing Groups Scenarios
The primary reason for multiple routing groups in an Exchange 2000 organization is
control and optimization of the flow of messages between servers. Between routing groups,
on the other hand, message transfer relies on messaging connectors. Connector parameters,
such as connection times, determine how messages are transferred.
NOTE: All SMTP virtual servers of a particular Exchange 2000 server must belong to
the same routing group.
Single Routing Group Scenario
Organizations operating a homogeneous LAN-like environment will find that deployment
of a single routing group sufficient and advantageous. By default, one routing group called
First Routing Group exists, and all servers are added to it during their installation.
In a single routing group environment, connectors are merely used to connect to foreign
systems. To give an example, you can use the SMTP Connector to establish an access
point to the Internet. The server running the SMTP Connector is called a bridgehead
server. All inbound and outbound messages must be transferred to the bridgehead server
before they are delivered.
======================================================================
winexc16.html PAGE 2 2002/06/29
The following are some advantages of single routing group organizations:
Direct access to public folders. Routing groups define the boundaries of direct public
folders access.
Easiest Message routing administration. It is not necessary to manage the routing topology
manually. Connectors installed on bridgehead servers in the routing group are available to
all users in the routing group.
Efficient routing of messages. Message delivery from server to server is direct and
immediate without a need for intermediate bridgehead servers (single-hop routing).
SMTP-based message transfer. SMTP is the transport protocol used between Exchange
2000 servers for message transfer in the same routing group.
Reasons for Multiple Routing Groups
If an organization relies on wide area network (WAN) connections, it will be desirable
to control network communication. WAN connections may generate transmission costs,
may have low bandwidth, may not be permanently available, and may operate unreliably.
Multiple routing groups enable you to minimize the consumption of network bandwidth.
Messaging connectors between routing groups can also help minimize transmission costs.
You may queue messages and transfer them in batches at specified connection times
when transmission charges are minimal.
NOTE: It is possible to place all servers in one administrative group for global
administration but still maintain multiple routing groups for optimized message transfer.
If “dial-up” you may want to schedule it at different times).
The following are reasons for implementing multiple routing groups:
======================================================================
winexc16.html PAGE 3 2002/06/29
Hierarchical Routing Group Arrangement
I this approach, a central group of hub servers controls the entire message transfer
between subordinated groups, known as spokes. Multiple hub servers share the workload
and provide redundancy for well-defined message paths between all locations.
NOTE: The new directory architecture and the implementation of the link stat algorithm
help to overcome many of the deployment issues found in earlier versions of Exchange
Server.
Full-Mesh Routing Group Arrangement
Message routing always involves an additional hop, or transfer of a message to a hub server.
If there are connectors installed you will stop the single point of failure.
Based on link state information, Exchange 2000 Server is able to gain a complete overview
of connector availability in the organization, which allows for optimal message routing.
Mixed Routing Group Arrangement
The full-mesh architecture is a headache to trouble-shoot.
Managing Routing Groups
You can use Exchange System Manager to create routing groups, move servers between
them, rename routing groups, or delete them. Moving server between routing groups is as
easy as a simple drag-and-drop operation. Connectors associated with a particular server,
such as an X.400 Connectors, are moved along with the server.
NOTE: The default First Routing Group is not displayed unless you explicitly enable it via
the Display Routing Groups check box (in the General tab of the organization object (for
example, Blue Sky Airlines [Exchange]). If you display administrative groups in addition,
you will find this routing group under First Administrative Group. All administrators of the
First Administrative Group are routing administrators by default.
======================================================================
winexc16.html PAGE 4 2002/06/29
Dedicated Routing Group Management
Delegate Access permissions for this administrative group can be members of the routing
groups. The routing group topology is independent of the administrative group arrangement.
Exercise Summary:
different routing groups.
recipients. NDRs provide information about delivery problems, suggest possible options
to resolve them, and indicate the servers that could not transfer the messages further.
Lesson 2:
Connecting Routing Groups
Exchange 2000 Server provides numerous messaging connectors, but not all can be used
to link routing groups together. Only the Routing Group Connector (RGC), SMTP
Connector, and X.400 Connector are able to fulfill the requirements. For load balancing
and fault tolerance, configure multiple bridgehead servers between two routing groups.
Routing Group Connector
The RGC is the easiest connector to install and more powerful than the others. It provides
a high level of fault tolerance because it supports multiple source and destination bridgehead
servers. Multiple bridgeheads can guarantee message delivery even if a particular server is
shut down. In native Exchange 2000 Server environments, the RGC transfers messages in
transport-neutral encapsulation format (TNEF) based on SMTP.
Connectors only go one-way!
TIP Although messages are transferred in TNEF and not in plain text, messages are not
encrypted between bridgehead servers. Experienced intruders will be able to disclose the
message content. To encrypt the server-to-server communication, use IP Security (IPSec)
tunnels. Microsoft Windows 2000 Server supports IPSec.
======================================================================
winexc16.html PAGE 5 2002/06/29
Local and Remote Messaging Bridgeheads
It is important to note that the RGC is able to try any SMTP virtual server in the local and
remote routing group without message rerouting.
Remote bridgehead servers are specified in the Remote Bridgehead tab. Multiple bridgehead
provide load balancing and fault tolerance, whereas single bridgeheads allow you to implement
servers with dedicated purposes in your organization. If DNS cannot provide a valid IP
address, NetBIOS name resolution is attempted.
This allows for Backward compatibility.
Direction of Message Transfer
When you create an RGC, Exchange System Manager can retrieve most configuration
parameters from the local instance to configure the opposing connector automatically for
you.
Configuration Settings
To create a new RPG, expand the desired routing group, right-click on Connectors, point
to New, and then select Routing Group Connector.
The following are the Routing Group Connector Properties:
routing group that receive messages directly from this connector.
a separate activation schedule for these messages.
details of topology.
======================================================================
winexc16.html PAGE 6 2002/06/29
Exercise Summary:
unidirectionally, you have to configure a separate connector in every routing group.
SMTP Connector:
The primary purpose of the SMTP connector is to connect an Exchange 2000 organization
to foreign SMTP systems, such as SMTP hosts on the Internet or other Exchange 2000
organizations. The SMTP connector can also be used instead of an RGC to provide
messaging connectivity between routing groups in a single Exchange 2000 environment.
TIP It is advantageous to configure an SMTP Connector to provide Internet connectivity.
RGC Versus SMTP Connector
Both the RGC and SMTP Connector use SMTP for message transfer. The RGC is easier
to maintain, but the SMTP Connector give you more control over your routing configuration.
Consider the configuration of an SMTP Connector instead of an RGC in the following situations:
specific account information for authentication.
an earlier version of Exchange Server, or to another Exchange 2000 organization.
on a remote STMP virtual server.
======================================================================
winexc16.html PAGE 7 2002/06/29
DNS and Smart Host Configurations
When connecting to the Internet, the SMTP Connector is able to look up external DNS
servers for mail exchanger (MX) records that correspond to Internet domain names
specified in recipient addresses.
In the address space tab, of the connector to the Internet, define an address space of type
SMTP with an address of *. For the connector to the downstream domain, on the other
hand, specify the corresponding smart host, and, in the Address Space tab, define a
detailed address space, such as SMTP: downstream-domain.com.
As mentioned, parameters or an SMTP Connector have higher priority than the settings
of SMTP virtual servers. By default, Exchange 2000 Server attempts to locate the
remote SMTP host using DNS until you change the delivery options of the SMTP
virtual server.
SMTP Connectors Between Routing
Groups
DNS cannot be used when an SMTP Connector is used to link routing groups together
because messages are transferred within the same e-mail domain.
Retrieving Mail Through ETRN
Modern Extended STMP (ESMTP) systems, including Exchange 2000 Server, support the
ETRN command, which is used to signal remote ESMTP server to send its queued messages
to the local host. The remote ESMTP server must be configured to receive and hold
messages on behalf of the local destination domain. Messages will be requested based
on fully qualified domain names (FQDNs), such as Bluesky-inc-10.com.
The SMTP Connector supports the ETRN command completely.
Configuration Settings
To create an SMTP Connector, expand the desired routing group, right-click Connectors,
point to New, and then select SMTP Connector.
The following are the SMTP Connector Properties dialog box tabs:
Address Space. Use this tab to identify the SMTP domains that this connector is supposed
to transfer messages to.
======================================================================
winexc16.html PAGE 8 2002/06/29
Advanced. Use this tab to configure outbound security, to specify whether to send a
HELO instead of a EHLO command to the remote SMTP host (which can be useful
if the remote SMTP host does not support ESMTP), and to specify whether to issue an
ETRN or TURN command when connecting to remote hosts for message retrieval.
Connected Routing Groups. Use this tab to specify the names of remote routing groups that
can be reached through this SMTP Connector.
Content Restrictions. Use this tab to specify which type of messages can traverse the
connector
according to priority (High,
or Non-System Messages), and message size (Allowed Size).
Delivery Options. The SMTP connector allows you to queue mail for remotely triggered
delivery.
Delivery Restrictions. By default, messages are accepted form everyone.
Details. Use this tab to specify an administrative note for informative purposes.
General. In addition, you can select the Do Not Allow Public Folder Referrals check box to
prevent Outlook 2000 users from accessing public folder resources in the remote routing group.
Exercise Summary:
The configuration of an SMTP Connector differs from an RGC in that you have to specify the
emote bridgehead server in the form of an SMTP host. Because the SMTP Connector may
be used to connect to foreign SMTP systems, you must specify the remote routing group
X.400 Connector
This is particularly the case if your messaging backbone relies on X.400 and connects different
e-mail systems together. Using an X.400 Connector, you can connect Exchange 2000 Server
to any foreign X.400 system and to earlier versions of Exchange Server and Exchange 2000
Server in different routing groups or organizations. Backwards compatibility.
Microsoft Exchange Message Transfer Agent Service
Exchange 2000 Server supports the X.400 standard through its Microsoft Exchange Message
Transfer Agent (MTA) Stacks service, which corresponds to an MTA of the 1988
conformance year.
======================================================================
winexc16.html PAGE 9 2002/06/29
MTA Transport Stacks
The MTA service of Exchange 2000 Server is able to utilize TCP/IP or X.25 for communications
by means of an MTZ transport stack, which must be added to the server before you can configure
an X.400 connector.
The TCP/IP transport stack allows you to establish X.400 connections over the Internet and virtual
private networks (VPNs). TSAP, SSAP, and PSAP correspond to the text boxes labeled T
Selector, S Selector, and P Selector.
With X.25 you need extra equipment, such as PAD.
The X.25 protocol, on the other hand, can be used to communicate with remote X.400 systems
using a packet switching network. This is usually the case when connecting to the public X.400
provider. The X.122 Address is the most important configuration parameter for X.25, yet all
other settings, such as Call, User Data and Facilities Data, must be specified precisely as well.
Configuring the X.400 Connector
As soon as the MTA transport stack has been installed, X.400 Connectors can be configured.
This is a complex tasks, especially when connecting to a foreign X.400 system.
Connect Request Information
The name and password of the local MTA can be determined in the properties of the X.400
object underneath the server’s Protocol container.
IMPORTANT: The MTA password is case-sensitive. If it is misspelled, connections cannot
be established.
Transport Stack Configuration
The transport stack configuration, accomplished using the Stack tab, does not refer to the
configuration of the local computer.
======================================================================
winexc16.html PAGE 10 2002/06/29
Overriding Local Information
Especially when connecting to a public X.400 network, you may be forced to override the name
and password of the local MTA. The public X.400 carrier provides the required information for
you to use.
NOTE: When using the X.400 Connector over an on-demand dial-up connection, it may be
advisable to increase the Maximum Transfer Retries to a value of 5.
Connecting Routing Groups
Over extremely unreliable, low-bandwidth network links, it might be a good idea to use X.400
Connectors between routing groups. X.400 has the advantage of supporting graceful recovery
of transfer associations.
Advanced Configuration Issues
In the Advanced tab, you can specify X.400 features that should be enabled when connecting the
organization to a foreign X.400 system.
NOTE: Exchange 2000 Server supports the 1988 X.400 standard. As the X.400 standard
demands, MTAs of the 1992 conformance year must fall back to the 1988 conformance year
for communication with 1988 MTAs.
A.400 Addressing:
A = Adm Domain
P = Primary Domain
O = Organization
CN = Container
S = Surname
I = Initials
G = Given name
When connecting to a remote Exchange MTA, make sure the Allow Exchange Contents
check box is selected to send messages in native format without the overhead of message
conversion.
======================================================================
winexc16.html PAGE 11 2002/06/29
The following are the X.400 Connector Properties dialog box tabs:
Address Space. Use this tab to define the type and format or routing addresses. Costs values
are associated with address spaces to optimize the routing.
Advanced. Use this tab to specify X.400 message formats and transfer procedures when sending
messages to a remote X.400 system or Exchange 2000 Server.
Connected Routing Groups. Use this tab to specify the names of remote routing groups that can be
reached through this X.400 Connector.
Content Restrictions. Use this tab to specify which type of messages can traverse the connector
according
to priority (High,
Delivery Restrictions. By default, messages are accepted from the everyone group.
Details. Use this tab to specify an administrative note for informative purposes.
General. You can also specify whether remote clients support the Messaging Application
Programming Interface (MAPI) and whether to allow public folder referrals.
Override. Use this tab to override default X.400 attributes of the local MTA.
Schedule. Use this tab to set the communication schedule. There are 15 minutes intervals.
Stack. Use this tab to specify required address information, such as remote host name or
IP address (or X.121 address), and service access points for the remote system.
Exercise Summary:
It requires careful configuration of MTAs, X.400 transport stacks, and X.400
Connector components on both ends of the communication link.
Exchange 2000 Server and Earlier Versions in the Same Site
or Routing Group
Within the same site or routing group, X.400 over remote Procedure call (RPC) is used for
server-to-server communication between Exchange 2000 Server and earlier versions of
Exchange Server.
Before you can add Exchange 2000 Server to an existing Exchange Server organization, you
need to deploy the Active Directory Connector (ADC). Among other things, ADC in
conjunction with SRS, replicates connector and routing information from the existing
organization with Active Directory Service, which allows Exchange 2000 Server to discover
and route messages to existing Exchange 5.5 connectors.
======================================================================
winexc16.html PAGE 12 2002/06/29
Gateway Address Routing Table (GWART)
GWART is used for message routing. Exchange 2000 Server relies on connector
configurations stored in the configuration naming context of the Active Directory directory
service and link state information instead.
Communication Using Messaging Connectors
The RGC of Exchange 2000 Server provides features similar to the Site Connector of
Exchange Server 5.5.
The SMTP Connector is the counterpart of the Internet Mail Service in earlier versions of
Exchange Server. Consequently, if you want to transfer messages to a remote site via
SMTP, configure a dedicated SMTP Connector as you would to connect to another
remote routing group.
Connectors over Dial-UP Connections
When configuring the various main messaging connectors, you will find that direct support
for dial-up connections is missing. A Dynamic Remote Access Service (RAS) Connector
is not available, nor does any Exchange 2000 connector provide a Dial-Up Connections tab.
Lesson 3:
Link Status Information
When you create multiple routing groups and link them together, you establish a system
of message pathways across your organization. Basically a routing table.
Message Routing
Message routing refers to the process of directing messages to their destinations through
SMTP virtual server connections, messaging connectors, or gateways. The routing
process begins when a message is passed to the SMTP transport engine.
======================================================================
winexc16.html PAGE 13 2002/06/29
If a message is destined for a local recipient, it is transferred to the Information Store
service, which delivers the message to the recipient’s mailbox.
If the connector resides on a bridgehead server in the local routing group, the message is transferred
to that bridgehead first.
NOTE: The routing information, maintained in the Active Directory configuration naming context,
is replicated throughout the Active Directory forest and available to all Exchange 2000 Servers.
Address Spaces
Exchange 2000 Server determines possible connectors for a particular message by comparing the
recipient’s address with available address space information associated with each connector.
Assigning Cost Values to Connectors
Cost values determine which connector is preferred for message transfer. The cost value can
range from 1 to 100, and the connector that owns the address space with the lowest cost value
is tried first. If messages cannot pass this connector, the next available connector is tried. If
you assign the same cost value to multiple address spaces on different connectors, Exchange
000 Server selects a random connector to provide a simple form of load balancing. Always
default to the cheapest connector.
Connector Selection
If more than one connector is available to deliver a message, the list of all potential connectors
must be reduced to one that will be used to transfer the message.
Message Rerouting
If a connector is temporarily unavailable, Exchange 2000 Server will reroute messages over
alternate routes (if they exist). For instance, if an RGC has unsuccessfully attempted to transfer
a message to its remote bridgehead servers three times, it is marked as unavailable, and other
possible connectors may be chosen for message transfer.
======================================================================
winexc16.html PAGE 14 2002/06/29
NOTE: Exchange Development Kit (EDK) gateway and connectors to foreign messaging
systems are always considered available. Exchange 2000 Server considers the message
delivered when it reaches the connector’s message queue. Rerouting is not performed, even
if the EDK connector cannot deliver the message.
Rerouting and Activation Schedules
If a connector is currently active, its state is known as Active Now. Active Connectors
are the first choice. If the connector is currently not active but scheduled to connect at a
later time, its state is called Will Become Active In The Future.
Link state information eliminates problems with message looping between servers because each
Exchange 2000 server can determine the availability of every connector in the organization.
NOTE: There are only two possible states for any given link (up or down). LSI also includes
connector costs for efficient message routing. However, retry counts for activation schedules
are not included in link state information.
Every Exchange 2000 server maintains an LST containing information about the current state
of each connector. The LST is a small, in-memory database, and each entry (routing group,
connector, server) in the database requires approximately 32 bytes of memory.
To propagate the link state information to all servers in an organization, a link propagation protocol
known as link state algorithm (LSA) is used. LSA is based on the Open Shortest Path First
(OSPF) protocol.
======================================================================
winexc16.html PAGE 15 2002/06/29
Changing the Routing Group Master
The master server is normally the first server in a routing group. If this server fails or is taken offline,
link state information is no longer propagated within the routing group.
NOTE: After a connector is tagged as unavailable, the original bridgehead server continues to retry
the connection at 60-second intervals even if no messages are awaiting transfer. As soon as a
connection can be established, the connector is considered available again, and the bridgehead
notifies the local routing group master about the link state change.
Chapter Summary:
permanent, reliable high-bandwidth network connection. In a particular routing
group, all servers communicate directly with each other using SMTP.
SMTP Connectors, or X.400 Connectors.
It is advisable to rely on X.400 Connectors only for the purpose of building messaging
bridges for foreign X.400 systems.
Between routing groups, link state information is transferred by means of RGCs.
Message loops and ping-pong effects can be prevented efficiently using link states.