TERMINAL SERVER LOAD BALANCING

Description: Terminal Server Load Balancing refers to either Session Directory and Microsoft Network Load Balancing used with Windows Server 2003 Terminal Servers, or Session Broker used with Windows Server 2008 Terminal Servers*. A Terminal Server Farm is often described as two or more Terminal Servers configured to use a Session Directory or Session Broker server and load balanced with either Microsoft NLB, DNS round-robin, or a third-party load balancer. 

* Microsoft Network Load Balancing can still be used for Windows Server 2008 Terminal Servers although it is not necessary

Scoping the Issue:  There are several common issues that we see with Terminal Server Load Balancing, and scoping the issue will depend on the symptoms that you are experiencing:

1. Windows Server 2008:  Event ID 1019, 1016, or 1001 with a source of TerminalServices-SessionBroker or TerminalServices-SessionBroker-Client logged in the system event log of the Session Broker server or the Terminal Server
   Windows Server 2003:  Event ID 1019, 1016, or 1001 logged in the system event log of the Session Directory server or the Terminal Server
2. Users are not being re-vectored to a disconnected session in the farm and instead receive a new session on a different server.
3. Users are not load balanced evenly across servers in the farm.

Data Gathering:  In all instances, collecting either MPS Reports with the General, Internet and Networking, Business Networks and Server Components diagnostics, or a Performance-oriented MSDT manifest must be done.  Additional data required may include the following:

• Details on your Terminal Server farm, including the operating system of the Terminal Servers, the load balancing method that is in use (NLB, Session Broker and DNS, Session Broker and NLB, or hardware based), the number of servers in your farm, and the client operating system and RDP client version.
• A copy of a Session Directory or Session Broker log taken while the problem was occurring
• A network trace taken with Network Monitor from the RDP client while reproducing the problem

Troubleshooting / Resolution:  Troubleshooting will depend on which problem you are experiencing:

Event ID 1019, 1016 or 1001

• This problem is normally caused by not configuring the Session Directory or Session Broker server correctly. The Session Directory/Broker server must have the computer account of each Terminal Server that will be in the farm added to the local Session Directory Computers group. Without this computer account, the Session Directory/Broker will not allow a Terminal Server to join the farm. Note that the group is still named Session Directory Computers even on Windows Server 2008.

Users are not being re-vectored to a disconnected session in the farm and instead receive a new session on a different server 

• Check to make sure that users are connecting via the farm name and not directly to each Terminal Server node
• Check to make sure the Terminal Servers have joined the Session Directory/Broker by looking for an event ID 1017 logged in the System event log of the Session Directory/Broker server
• Check to make sure the user is using the latest RDP client available for their operating system and that the RDP client supports Session Directory or Session Broker. Some thin clients do not have the support for this in their RDP client
• If using a hardware-based load balancer, confirm with the manufacturer that the device is configured correctly to support Microsoft Session Directory

Users are not load balanced evenly across servers in the farm

• Check to make sure that users are connecting via the farm name and not directly to each Terminal Server node
• Check to make sure the Terminal Servers have joined the Session Directory/Broker by looking for an Event ID 1017 logged in the System event log of the Session Directory/Broker server
• Check to make sure the user is using the latest RDP client available for their operating system and that the RDP client supports Session Directory or Session Broker. Some thin clients do not have the support for this in their RDP client
• If using a hardware-based load balancer, confirm with the manufacturer that the device is configured correctly to support Microsoft Session Directory
• If you are running Windows Server 2008 Session Broker, install the following hotfix on the Session Broker server:  Microsoft KB Article 955365: The Windows Server 2008 Terminal Services Session Broker Service incorrectly balances the load among terminal servers after it runs for a while

Additional Resources:

• Microsoft KB Article 327508: How to turn on the Terminal Services Session Directory Logging Service
• Microsoft KB Article 955365: The Windows Server 2008 Terminal Services Session Broker Service incorrectly balances the load among terminal servers after it runs for a while