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Distributed Transaction Coordinator

Updated: January 12, 2011

Applies To: Windows Server 2003 with SP1

What does Distributed Transaction Coordinator do?

The Distributed Transaction Coordinator (DTC) service coordinates transactions that update two or more transaction-protected resources, such as databases, message queues, files systems, and so on. These transaction-protected resources may be on a single computer or distributed across many networked computers.

Who does this feature apply to?

  • Users of any computers that participate in DTC transactions, either directly or through other computers.

  • System administrators of networks that use DTC components to perform transactions across networks.

What new functionality is added to this feature in Windows Server 2003 Service Pack 1?

Securing all network communication by default

Detailed description

In Windows Server 2003 Service Pack 1, DTC provides the administrator with greater control over the network communication between computers. By default, all network communication is disabled.

In order to manipulate the communication settings, the DTC security settings properties page has been enhanced. To see the page, use the following procedure:

To open the DTC security settings properties page

  1. Open the Component Services snap-in Microsoft Management Console (MMC).

  2. In the console tree, click the Computers folder.

  3. In the results pane, right click My Computer and then click Properties.

  4. Click the MSDTC tab, and then click Security Configuration.

The table below defines the new fields in the property page, along with the registry keys affected for the different settings. All the registry keys related to MSDTC are located in the following registry key:

MyComputer\HKEY_LOCAL_MACHINE\Software\Microsoft\MSDTC

CautionCaution
Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on the computer. These registry keys might not be supported in future releases.

The following table tells you where to find the MSDTC key specific values.

 

Setting Description Corresponding registry value

Network DTC Access

Determines whether DTC on the local computer is allowed to access the network. This setting must be enabled in combination with one of the other settings to enable network DTC transactions.

Default setting: Off

Security\NetworkDtcAccess

0 = Off

1 = On

Allow inbound

Allows a distributed transaction that originates from a remote computer to run on this computer.

Default setting: Off

To enable this setting you must set the following registry key values to 1:

Security\NetworkDtcAccess

Security\NetworkDtcAccessTransactions

Security\NetworkDtcAccessInbound

To disable this setting, you only need to set the following registry key value to 0:

Security\NetworkDtcAccessInbound

Allow Outbound

Allows the local computer to initiate a transaction and run it on a remote computer.

To enable this setting, you need to set the following registry key values to 1:

Security\NetworkDtcAccess

Security\NetworkDtcAccessTransactions

Security\NetworkDtcAccessOutbound

To disable this setting, you only need to set the following registry key value to 0:

Security\NetworkDtcAccessOutbound

Mutual Authentication Required

Adds support for mutual authentication in future versions and is the highest secured communication mode. In the current versions of Windows and Windows Server, it is functionally equivalent to the Incoming Caller Authentication Required setting. This is the recommended transaction mode for clients running Windows XP SP2 and servers running a member of the Windows Server 2003 family.

WarningWarning
You cannot use the Mutual Authentication Required transaction mode with computers that are in a clustered environment, or any computers that are negotiating transactions with such computers. In that context, you can use the Incoming Caller Authentication Required transaction mode instead. In a clustered environment, the computer account for the Distributed Transaction Coordinator service specifies the cluster node's host name instead of the transaction node's host name, which prevents the authentication request from succeeding when the Mutual Authentication Required transaction mode is enabled.

AllowOnlySecureRpcCalls = 1

FallbackToUnsecureRPCIfNecessary = 0

TurnOffRpcSecurity = 0

Incoming Caller Authentication Required

Requires the local DTC to communicate with a remote DTC using only encrypted messages and mutual authentication. This setting is recommended for servers running Windows Server 2003 that are operating in a cluster.

Only Windows Server 2003 and Windows XP SP2 support this feature, so you should only use this if you know that the DTC on the remote computer runs either the Windows Server 2003 or Windows XP SP2 operating system.

AllowOnlySecureRpcCalls = 0

FallbackToUnsecureRPCIfNecessary = 1

TurnOffRpcSecurity = 0

No Authentication Required

Provides system compatibility between previous versions of the Windows operating system. When enabled, communication on the network between DTCs can fall back to a non-authentication or non-encrypted communication if a secure communication channel cannot be established. This setting should be used if the DTC on the remote computer runs a Windows 2000 operating system or a Windows XP operating system earlier than SP2. This setting is also useful when the DTCs that are involved are located on computers that are in domains that do not have an established trust relationship or if the computers are part of a Windows workgroup.

AllowOnlySecureRpcCalls = 0

FallbackToUnsecureRPCIfNecessary = 0

TurnOffRpcSecurity = 1

Why is this change important? What threats does it help mitigate?

These changes are important in order to secure any communication coming into or going out from the computer. By default, after installing Windows Server 2003 Service Pack 1, the computer will not accept or issue any network traffic and therefore will be less vulnerable to network attacks.

Additionally, the online network protocol has been upgraded to support a more securely encrypted and mutually authenticated communication mode. This helps to ensure that attackers can not intercept or take over communications between DTCs.

What works differently?

After installing Windows Server 2003 Service Pack 1, all network communication coming out of or getting into DTC is disabled. For example, if a COM+ object attempts to update a SQL database on a remote computer using a DTC transaction, the transaction fails. Conversely, if your computer is hosting a SQL database that components from remote computers try to access using a DTC transaction, their transactions fail.

How do I fix these issues?

If your transactions fail because of network connectivity, you can use MSDTC security properties, as described previously in this document, select the Network DTC Access check box, and then select the Allow Inbound and Allow Outbound check boxes, as appropriate.

If you want to change these setting programmatically as part of your Windows Server 2003 Service Pack 1 deployment, you can directly change the registry values that correspond to your desired setting as described in the table in “Securing all network communication by default,” earlier in this document. After you have changed the registry settings, you must restart the MSDTC service.

If you are using Windows Firewall to protect the computers in your organization, you must add MSDTC into the exception list in the Windows Firewall settings. To do so, use the following steps:

  1. In Control Panel, open Windows Firewall.

  2. Click the Exceptions tab, and then click Add Program.

  3. Click Browse, and then add c:\windows\system32\msdtc.exe.

  4. In Programs and Services, select the Msdtc.exe check box, and then click OK.

What settings are added or changed in Windows Server 2003 Service Pack 1?

 

Setting name Location Previous default value Default value Possible values

NetworkDtcAccess

HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \MSDTC \Security

1

0

0,1

NetwordDtcAccessTransactions

HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \MSDTC \Security

1

0

0,1

NetworkDtcAccessInbound

HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \MSDTC \Security

n/a

0

0,1

NetworkDtcAccessOutbound

HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \MSDTC \Security

n/a

0

0,1

AllowOnlySecureRpcCalls

HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \MSDTC

n/a

1

0,1

FallbackToUnsecureRPCIfNecessary

HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \MSDTC

n/a

0

0,1

TurnOffRpcSecurity

HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \MSDTC

n/a

0

0,1

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