System Center Configuration Manager 2007 : Network Design - Use of BITS

The Background Intelligent Transfer Service optimizes file transfers based on network conditions. This optimization includes the following:

• Automatically adjusting the rate of the transfer, based on available bandwidth

• Suspending and resuming transfers that are interrupted

• Providing rudimentary consistency checking

• Using group policy and the Configuration Manager console to provide options for tuning BITS-enabled transfers

Let’s now look in depth at the BITS feature set, its use by ConfigMgr, and configuring BITS background transfers.

Configuration Manager makes extensive use of BITS to efficiently use network bandwidth and deal with network connections that are unreliable or not always available. BITS supports downloads over both HTTP and HTTPS. SMS 2003 took advantage of BITS for downloading software from distribution points to clients. Use of BITS in Configuration Manager 2007 has increased and is integral for copying data to branch distribution points, which use BITS to download and cache software packages from other distribution points. BITS 2.0 or higher is a required ConfigMgr component. Here are the key features of all BITS versions:

• File transfers that occur quietly in the background, using only bandwidth that is not required by other applications

• The ability to suspend and resume transfers interrupted by transient network conditions

BITS Versions for Configuration Manager Clients

BITS has been a component of all Windows operating systems since Windows XP, and it is available for Windows 2000. Microsoft has released several versions of BITS, with added functionality in each revision. The versions supported by Configuration Manager 2007 include the following:

• BITS Version 2.0— Supported for backward compatibility with systems running Windows 2000 Service Pack (SP) 4. Windows 2000 clients with earlier versions of BITS are upgraded to version 2.0 during client installation.

• BITS Version 2.5— Installed on all clients which support that version during client installation unless the client already has version 2.5 or higher. BITS 2.5 or higher is included on all systems running Windows Server 2008, Windows Vista, and Windows XP Service Pack 3. Version 2.5 can also be installed on machines running Windows Server 2003 SP 1 or SP 2 or Windows XP SP 2.

• BITS Version 3.0— Available on the Windows Server 2008 and Windows Vista operating systems only.

BITS versions 2.0 and 2.5 are available as separate downloads. Because BITS upgrades require a reboot, you may want to consider deploying the required BITS versions in advance to all clients needing an upgrade, to avoid a required reboot during ConfigMgr client deployment.

One problem with earlier versions of BITS is that the system is only aware of the traffic passing through the NIC. Even if the network segment to which the machine is connected is quite congested, if there is little or no network activity on the local machine it would appear to BITS that most of the bandwidth supported by the card is available. Under these conditions BITS transmits data at a high rate, potentially causing additional network congestion problems. BITS 2.5 and higher versions get around this limitation by pulling usage statistics from the Internet Gateway Device (IGD). Certain conditions must be met in order to pull statistics from the IGD:

• Universal Plug and Play (UPnP) must be enabled.

• The device must support UPnP byte counters.

• UPnP traffic (TCP 2869 and UDP 1900) is not blocked by any firewall device or software.

• The device must respond to GetTotalBytesSent and GetTotalBytesReceived in a timely fashion.

• The file transfer must traverse the gateway.

Event ID 16393 Source: Microsoft-Windows-Bits-Client

Modifying BITS Functionality Through Group Policy

In most circumstances, BITS will intelligently manage the use of network bandwidth without additional configuration. If you find that BITS-enabled transfers are consuming more bandwidth than desired or if you want to provide extra protection for other business-critical network activity, group policy can limit the bandwidth BITS will consume. The setting is specified in Kbps, and its name varies depending on the version of Windows you are running.

• For Windows Server 2003 group policy, the setting is called “Maximum network bandwidth that BITS uses.”

• For Windows Server 2008 group policy, the setting is “Maximum network bandwidth for BITS background transfers.”

In both versions of Windows Server, this setting is found under Computer Configuration -> Administrative Templates -> Network -> Background Intelligent Transfer Service. The setting, shown in Figure 1 for Windows Server 2008 group policy, allows a limit for a specific time interval (such as working hours) and a different limit for outside that interval. All versions of BITS supported by ConfigMgr also have a timeout for inactive transfers (defaulting to 90 days) that is configurable through group policy.

BITS 3.0 introduces several new group policy options. These allow you to control settings such as the maximum active download time for BITS jobs, the number of jobs allowed per user and per machine, and the maximum number of files per job.

Group policy settings are only available in Active Directory domains. Although group policies are generally applied at the domain or Organizational Unit (OU) level, BITS-related policies are examples of a policy that you might consider implementing at the site level.

An AD site is generally a region of high network connectivity. By applying the BITS-related policies to the site, you can control the behavior of all systems in your AD forest based on network location, regardless of their domain or OU membership.

Modifying BITS Functionality Within Configuration Manager

You can also define the maximum network bandwidth for BITS background transfers using the ConfigMgr console. The settings are specified on the BITS tab of the Computer Client Agent property sheet, located under System Center Configuration Manager -> Site Database -> Site Management -> <Site Code> <Site Name> -> Site Settings -> Client Agents -> Computer Client Agent - > BITS tab on the Configuration Manager console. As shown in Figure 2, these settings are similar to the group policy settings, but in this case they are applied either to all clients in the ConfigMgr site or to branch distribution points only.

Comparative Advantages of Group Policy and ConfigMgr Settings for BITS

Unlike group policy settings, the settings on the Computer Client agent apply to clients that are in workgroups or untrusted domains. These are global settings for all clients in the site, however, while group policy allows you to control the behavior of BITS for clients in specific domains, OUs, individual computers, or AD sites. You can achieve even more granular control of group policy by WMI filtering and/or security group filtering. These filtering techniques selectively apply group policy objects (GPOs) to users or computers based on the results of WMI queries or security group membership. An excellent resource on group policy management is available online at the Windows Server 2003 Tech Center (http://technet2.microsoft.com/windowsserver/en/library/):

• The section on WMI filtering is found at http://technet.microsoft.com/en-us/library/cc779036.aspx.

• Security group filtering is discussed in http://technet.microsoft.com/en-us/library/cc781988.aspx.

Windows Server 2008 group policy has a wider range of BITS-related options for BITS version 3.0 than that available through the ConfigMgr settings. Through ConfigMgr, however, you are able to assign BITS settings specifically to branch distribution points. Because there are different options available through group policy and ConfigMgr settings, you may choose to use both to control BITS behavior.

Other BITS Features

On client systems with multiple physical or virtual interfaces, BITS uses the GetBestInterface function to select the interface with the best route to the server it needs to access. Once the file transfer is complete, BITS verifies that the file size is correct. However, BITS does not perform a more extensive file integrity check to detect corruption or tampering that may have occurred.

Enabling a Distribution Point for BITS

In order to enable a distribution point to use BITS, the distribution point must be running IIS 6.0 or higher with ASP.NET and WebDAV (Web-based Distributed Authoring and Versioning) enabled. You can enable these features in various ways, depending on the version of Windows Server you are running. After meeting these prerequisites, you can enable a distribution point for BITS through a check box on the distribution point properties page, as shown in Figure 3. Note that BITS-enabled distribution points will download files to clients and branch distribution points using BITS; however, programs that run from the distribution point will use the standard SMB protocol.