Configure MSDTC for Distributed Transactions

Few days ago, inside a Software project, I had to enable and configure MSDTC (Distributed Transaction Coordinator) between 2 machines: a Web Server using NServiceBus to process messages in a transaction and a SQL Server.
I encountered some issues and I would like to detail the order of few configuration steps as well as testing methods that should be done/checked before MSDTC in fully functional.

 
Step 1: Network connectivity

Make sure both servers can ping each other by the machine name, cause MSDTC uses netBIOS to establish a connection.

Start a command prompt window and execute on both servers:

  • ping [SERVER_NAME1]
  • ping [SERVER_NAME2]

Step 2: Enable MSDTC on both servers.

There are pictures for Windows 2008 Server and Windows 2003 Server because MSDTC location is changed from one WIndows edition to another. The options to check are the same though.

  1. Open Component Services:
  2. Component Services

  3. Access DTC Properties
  4. Windows 2003 - MSDTC location

    Windows 2003 - MSDTC location

    Windows 2003 - MSDTC location

    Windows 2003 - MSDTC location

    Windows 2008 - MSDTC location

    Windows 2008 - MSDTC location

     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     

  5. Enable MSDTC according to below options selected.
    Check only the red check boxes and click Apply.
     
  6. Windows 2008 - MSDTC properties

     
     
     
     
     
     
     
     
     
     
     
     

    A warning message will be popped in to inform that the Distribution Transaction Coordinator Windows service will be started (or restarted).
    MSDTC restart

  7. Set the startup type of Distribution Transaction Coordinator Windows service to Automatic.

If you don’t have Firewalls that prohibit external access to machine’s ports than you can stop here with the MSDTC configuration.
MSDTC will function great with basic configuration (Step 1 & Step 2) done only when there is no Firewall involved in network external communication. What do you do when there is a Firewall afterwards? In most Network configurations it is mandatory for securing the external access. If you follow all the steps detailed below, you should be able to make the MSDTC work without problems. Take a look at next steps.

Step 3: Restrict MSRPC dynamic port allocation.
 
MSDTC service depends on RPC protocol which stands in front of every Windows process that uses RPC. When you deal with MSDTC, you also have to consider the RPC access points. When MSRPC protocol is left with its default setting, all depending services including MSDTC is free to use a dynamically allocated port in the port range 1024-65535. Basically, it means that each re-start of MSDTC will result in a different port number. Fortunately you can restrict this port range which means that, instead of creating a rule in Firewall that opens all the ports from 1024 – 65535 you only need to insert the range of ports restricted in RPC setting.

There is one thing to be considered though:
 
There can be up to 100 services that depend on RPC and will be affected by this change. Make it not too small… not to big. Doing a little reading on the internet I saw that 50 – 100 ports would be a minimum – maximum for RPC depending services to function, but again it depends on each machine and how many processes depend on RPC. If you want to find out which are these look at RPC service at Dependencies tab and count the active ones.

RPC_Service

Perform these steps on both machines in order to configure a different port range. The port range does not have to be the same on both machines.

  1. Open Component Services properties windows
  2. Component Services Properties

  3. Access Default Protocols tab and insert a new port range.
  4. Change Port Range

Next, in order to be able to start a Distributed Transaction through MSDTC service – both participating servers must be configured to trust each other by allowing access to the each other’s port used by MSDTC service.

Step 4: Add Firewall Inbound rules

on SERVER 1: to allow inbound requests to the port range configured.
on SERVER 2: to allow inbound requests to the port range configured.
This will enable the communication between SERVER 1 and SERVER 2 through MSDTC service.

SERVER 1 will be able to access MSDTC allocated port from SERVER 2 and SERVER 2 will be able to access MSDTC allocated port from SERVER1.

Step 5: Restart both machines

You need to restart both machines where the port range was changed in order for these modifications to take effect.

 
Step 4: Testing MSDTC connectivity
 
After you had done all of the above, you might want to test first if a Distributed Transaction can be initialized and committed. There are 2 important Microsoft troubleshooting tools that I used and worked for me: DTCping and DTCtester. I will not detail the testing steps because all of them are covered in this post at step 2 and step 4.

  1. This was very helpful.
    Thank you.

    DN

  2. Good to know about the MSRPC dynamic port allocation.
    Thanks

  3. Extremely helpful! Much more concise then technet

  4. Brian Robertson

    Very helpful

  5. Gerardo Méndez

    :mrgreen:

    Thank You!!!

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