Exchange 2010 and SLD / Disjoint / Discontiguous Namespaces

Published Oct 27 2009 01:43 PM 13.5K Views

This is an update to the blog post Next version of Exchange and Single Label Domain (SLD) policy under review.

In response to customer feedback, the Exchange team has updated their testing matrix and has determined that Exchange Server 2010 will be supported on Single Label Domains (SLD), Disjoint Namespaces, and Discontiguous Namespaces. This post contains a brief description of each of these scenarios and special considerations. If you intend to install Exchange 2010 into one of these environments you need to read the documentation about the applicable subject.

In adding support for these types of topologies, there is an underlying requirement for DNS to be properly installed and configured. Before proceeding with any deployment defined here, clients and servers must be able to reliably resolve DNS queries for a given resource in the appropriate namespace.

Single Label Domains

Single-label DNS names are DNS names that do not contain a suffix such as .com, .corp, .net, or .org. For example contoso would be an SLD while,, or contoso.local would not be an SLD.

Not a recommended configuration

While Exchange 2010 is supported with SLDs, the Exchange product team's view is that SLDs are not a recommended configuration, and may not be supported by future Exchange versions. Other Microsoft or third party applications that you want to run in your environment may not be supported on an SLD. This could have an adverse effect on your environment. While we will allow installation of Exchange 2010 in an SLD, we strongly recommend that you take steps to move your organization out of this configuration.

Disjoint Namespaces

A disjoint namespace scenario is one in which the primary DNS suffix of a computer does not match the DNS domain name where that computer resides. The computer with the primary DNS suffix that does not match is said to be disjoint. Another disjoint namespace scenario occurs if the NetBIOS domain name of a domain controller does not match the DNS domain name.

Exchange 2010 and Disjoint Namespaces

In Microsoft Exchange 2010, there are three supported scenarios for deploying Exchange in a domain that has a disjoint namespace. The supported scenarios are as follows:

  • Scenario 1   The primary DNS suffix of the domain controller is not the same as the DNS domain name. Computers that are members of the domain can be either disjoint or not disjoint.
  • Scenario 2   A member computer in an Active Directory domain is disjoint, even though the domain controller is not disjoint.
  • Scenario 3   The NetBIOS domain name of the domain controller is not the same as the subdomain of the DNS domain name of that domain controller.

For more information on Exchange 2010 and disjoint namespaces see Understanding Disjoint Namespace Scenarios.

Special Considerations

Discontiguous Namespaces

A discontiguous namespace, also referred to as non-contiguous namespace, is one in which the domains in a forest are not defined hierarchically. If the domains in a forest have discontiguous DNS names, they form separate domain trees within the forest. An Active Directory forest can have one or more domain trees. An example of a multi-tree forest would be a forest containing the domains, and Note: and in the same forest would be an invalid configuration. This is because they would both be using a NetBIOS name of contoso in their respective domains. In the case of discontiguous DNS namespaces, each domain must still register a unique legacy NetBIOS domain name.

Special Considerations

For discontiguous namespaces, DNS must be configured such that Exchange servers are able to resolve all domain names in the environment. It is also a requirement that msds-allowedDNSSuffixes be configured within the Active Directory environment for all namespaces used within the forest. For instructions on configuring this, please see the Tech Net article "Understanding DNS Client Settings."

Exchange 2010 System Requirements

For more information on Exchange 2010 System Requirements please see the Tech Net article "Exchange 2010 System Requirements"

- Ed Beck

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Scenario 3   The NetBIOS domain name of the domain controller is not the same as the subdomain of the DNS domain name of that domain controller.

There is not a lot of information on what to do to rectify this problem, or how it will affect the user. If our domain is "" and our netbios domain name is "sls" how does this affect our clients?

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I have the same question as Mr. Falk. We have the domain "", however our NetBIOS name is "Neptune". It's not very clear if this is a problem that needs to be fixed or not for Exchange 2010 or the releases after that. We currently use AD 2003 and Exchange 2003.
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Mr. Falk and Mr. Sloan,
Thank you for asking this question, it pointed out something we need to fix in our docs.
The NetBIOS name does not have any effect in this scenario. You’ll be fine.
Please take a look at the “Scenario 3” section of Understanding Disjoint Namespace Scenarios with Exchange 2007 ( The diagram shows a NetBIOS name that has no relation to the domain names in the example.  

The documents should be the same for Exchange 2010 as Exchange 2007. We’re updating our Exchange 2010 document to include this information.
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I have an SLD. I have been working on a plan to migrate to a new forest/domain because of the previous warnings about SLD.

We have chosen a disjoint namespace, since the desired netbios name is taken by our SLD.

Is there any reason I would want to change the domain name now before I start migrating? I have never heard of a reason to have the dns subdomain name match the netbios name.
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Hi Paul, from an Exchange point of view, there is no reason to have the NetBIOS name match the domain name.
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Dear Sir,

One of our user has changed Exchange 2007 OWA to basic we want to convert OWA experience from basic to premium please help us.

Martand Mishra
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martandmishra - have them check if they accidentaly turned on accessibility options? That'll do it... Otehrwise - please post to Exchange forums?
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