Mixed Mode and Native Mode Concepts
An
Exchange Server 2003 organization can operate in one of two modes:
native mode or mixed mode. Native mode offers full Exchange Server 2003
functionality, while mixed mode offers limited Exchange Server 2003
functionality but the benefit of interoperability between Exchange
Server 2003 and Exchange Server 5.5. When you install Exchange Server
2003, your Exchange organization operates in mixed mode by default.
This default setting ensures past and future interoperability with
previous versions of Exchange. For example, you have the ability to
install a server running Exchange Server 5.5 at a future date, even if
no servers running Exchange Server 5.5 exist in the organization at the
time of installation. You might encounter such a situation if your
organization acquires another organization that is still running
Exchange Server 5.5.
The
concept of mixed mode and native mode organizations is similar to the
concept of mixed mode and native mode domains in Active Directory.
These are called modes in Windows 2000 Server and functional levels
in Windows Server 2003, but the terms refer to the same thing. The
similarity exists in terms of limiting new features that won’t work on
previous product versions versus exposing all of the new functionality.
What mode you choose has tradeoffs between functionality and backwards
compatibility. No direct relationship exists between the mode of the
domain and the mode of an Exchange organization. With Exchange Server
2003, you can select native mode and mixed mode only at an
organizational level.
Tip
When
an organization is in native mode, you only have servers running
Exchange 2000 Server and Exchange Server 2003. Servers running Exchange
2000 Server and Exchange Server 2003 can coexist in native mode, so be
aware of this when you come across scenarios where servers running
Exchange 2000 Server are thrown into the mix. |
A
comparison of the benefits and limitations of each mode is useful in
demonstrating the importance of the choice of mode for your Exchange
Server 2003 organization. A particular benefit or limitation may be the
deciding factor in your deployment plan, as to whether you need to
convert to native mode as soon as possible in order to take advantage
of native mode features, or whether you should stay in mixed mode to
support previous versions of Exchange Server, previous applications, or
connectors.
Mixed Mode Benefits and Limitations
The
ability to operate an Exchange organization in mixed mode exists for
backward compatibility with previous versions of Exchange Server and
other software that relies on it. The differences between mixed mode
and native mode are primarily concerned with the concept of
administrative groups and routing groups. Mixed mode exists mainly to
bridge the gap between Exchange Server 5.5 sites and Exchange 2000
Server and Exchange Server 2003 organizations by forcing Exchange 2000
Server and Exchange Server 2003 to operate within the boundaries of
Exchange Server 5.5 sites. Administrative groups and routing groups
cannot be managed independently in mixed mode. In other words,
administrative groups and routing groups are mapped directly to sites
and therefore do not have the flexibility that they have when the
Exchange organization is operating in native mode.
Benefits of Mixed Mode
Running
your Exchange organization in mixed mode ensures future
interoperability between Exchange Server 2003 and previous versions of
Exchange. The benefits of operating in mixed mode include the following:
Interoperability between servers running Exchange Server 2003 and Exchange Server 5.5.
Routing between Exchange Server 2003 and Exchange Server 5.5 is seamless.
Exchange
Server 2003 can use existing Exchange Server 5.5 connectors and
gateways to connect to foreign e-mail systems and route e-mail messages.
Both
Exchange Server 5.5 objects (users, custom recipients, and distribution
lists) and Exchange Server 2003 objects (users, contacts, and groups)
can be managed from Active Directory.
Public
folders replicated between Exchange Server 2003 and Exchange Server 5.5
can be securely accessed from clients on either system.
You have the option to install servers running Exchange Server 5.5 at a later date.
All
Exchange Server 5.5 directory service objects such as servers and
connectors are replicated to Exchange Server 2003 and are displayed in
the Exchange System Manager console.
Limitations of Mixed Mode
When
your Exchange organization is operating in mixed mode, there are
limitations and issues you must consider, such as the following:
Exchange Server 5.5 sites are mapped directly to administrative groups.
Administrative
groups are mapped directly to Exchange Server 5.5 sites, which means
that you cannot create administrative groups independent of the routing
infrastructure.
You can only move mailboxes between servers that are in the same administrative group.
Routing
group membership must consist only of servers installed in the
administrative group that is defined with the routing group.
You
can move servers between routing groups, but all members of all routing
groups must be members of the same administrative group.
Exchange 5.5 system objects present read-only properties when viewed from Exchange System Manager.
Some
commands may not always function as you would expect them to due to
interaction between older and newer components and management tools.
For example, you cannot view the resource tables of an Exchange Server
5.5 server’s database with Exchange System Manager.
In
an Exchange Server 5.5 site, not only are all servers managed as a
single group, but all servers have reliable, high-speed connectivity
for sending messages to one another. However, when an Exchange Server
2003 organization is in mixed mode and Exchange 5.x
sites are mapped one-to-one with administrative groups, you can
subdivide the routing structure for the servers running Exchange Server
2003 in the collection using routing groups. A server cannot belong to
a routing group that is held under a different administrative group. |
|
Because
of the limitations of mixed mode, most organizations opt to convert to
native mode unless they have a specific need to support Exchange Server
5.5 servers and sites.
Native Mode Advantages
Once
an Exchange organization is converted from mixed mode to native mode,
the organization is no longer interoperable with systems running
Exchange Server 5.5. Exchange organizations operating in native mode
can contain servers running both Exchange 2000 Server and Exchange
Server 2003, and you can convert an Exchange organization to native
mode only when all of the Exchange servers in it are running Exchange
2000 Server and Exchange Server 2003.
Convert your Exchange organization to native mode if the following apply:
You
do not have any servers running Exchange Server 5.5 in your
organization (you’ve either migrated or decommissioned all of them or
never had any to begin with).
You
have no plans to add servers running Exchange Server 5.5 to your
organization in the future, such as a result of a merger or the
acquisition of a company with servers running Exchange Server 5.5.
Your organization will never require interoperability with servers running Exchange Server 5.5.
Your organization does not use any connectors or gateway applications that run only on Exchange Server 5.5.
Important
Once
you convert from mixed mode to native mode, the organization is no
longer interoperable with Exchange Server 5.5 systems. That isn’t to
say that you won’t be able to send or receive e-mail with Exchange
Server 5.5 servers, but you won’t be able to have seamless integration
in the same Exchange organization. It is important to note that
converting to native mode is a one-time, one-way operation that cannot
be reversed at a later date. |
Advantages of Native Mode
Running
an Exchange organization in native mode gives you the full
functionality and flexibility of Exchange Server 2003 when you manage
your messaging system.
Greater
flexibility for defining routing groups and administrative groups.
Since administrative groups are not tied to Exchange Server 5.5 sites,
you can utilize the full functionality of the administrative group
model.
The ability to move mailboxes between servers in different administrative groups.
The
ability to configure administrative and routing groups independent of
each other since they are no longer connected to fit the site model.
Query-based
distribution groups (QDGs) can be created only in a native-mode
Exchange organization.
If
routing bridgehead pairs are upgraded to Exchange Server 2003 in a
native-mode organization, they will use 8BITMIME data transfers instead
of converting down to 7-bit. This equates to considerably less traffic
over WAN connections when compared to Routing Group Connectors.
Converting to Native Mode
Converting
to native mode is accomplished through Exchange System Manager, by
right-clicking on the organization name at the top of the window and
clicking Properties. This brings up the property sheet shown in Figure 1.
As shown in Figure 1,
there is a Change Mode button on the General tab. The button will be
unavailable if you are in native mode, but if you are in the default
mixed mode, you can click the button to change the mode. When you do,
you will receive a warning message that advises you that once the
operation is complete, you will not be able to convert back to mixed
mode.
