Multicast is an operating system deployment feature in Microsoft System Center Configuration Manager 2007 R2 that conserves network bandwidth by simultaneously sending data to multiple clients rather than sending a copy of the data to each client over a separate connection. Multicast allows multiple computers to download an operating system image package as it is sent by the distribution point rather than each client being sent the package independently. This can conserve network bandwidth in environments where multiple clients are likely to be downloading the same operating system image at the same time.

The information in this topic applies only to Configuration Manager 2007 R2 and Configuration Manager 2007 R3.

Multicast Network Configurations

Multicast requires configuration of the multicast IP addresses, ports, and network configurations for multicast communication. In addition, the distribution point that has multicast enabled must have Allow clients to transfer content from this distribution point using BITS, HTTP, and HTTPS (required for device clients and Internet-based clients) enabled.

Multicast Account

The multicast account specifies the Windows user account to be used when making Configuration Manager 2007 database connections for the multicast configuration. The default setting uses the computer account for the distribution point. A different user account can be specified.

Best practice is to use the minimum necessary permissions for performing a specific task.

IP Addresses and UDP Ports

The multicast service point must be configured to specify the multicast IP addresses and user datagram protocol (UDP) port range used by multicast sessions, 63000–64000. These IP addresses and ports must be accessible by computers requesting operating system images so the routers in between must be configured to allow multicast traffic. The IP addresses must be within the range of multicast IP addresses between– The settings for multicast might require configuration of firewalls and routers to ensure that multicast traffic is not blocked.

By default, the IP address will be obtained from a DHCP server that is enabled to distribute multicast addresses. Depending on the network environment, the administrator can instead specify a range of IP addresses.

Multicast Schedule

By default, multicast is performed using an unscheduled multicast called autocast. Autocast allows clients to begin downloading immediately. If an autocast is already in progress, the client joins the multicast and downloads the package and then downloads any portion of the package it missed because it joined late. If no session is in progress when a client requests an image, the multicast session begins immediately.

Alternatively, the administrator can configure multicast to distribute images when specific scheduling conditions are met. A scheduled multicast requires clients to wait until the Session start delay in minutes has passed or until the Minimum number of clients is reached before the multicast session begins. After a multicast session begins, new clients must wait for the next session.

Deploying operating system packages via autocast might require more bandwidth, but it does not require that clients wait to begin the download.

Network Profile

Specifies the profile of the network used for multicast. Each profile contains settings to optimize performance for the specified speed, such as the maximum transport window size, the transport cache size, and the block size.

Network Considerations for Multicast

Enabling multicast allows Configuration Manager 2007 clients to share a multicast of an operating system image sent by a distribution point. During an operating system deployment task sequence, the client requests an operating system image from a distribution point.

The distribution point assignment for a multicast deployment is made like a normal assignment, including the determination as to whether the distribution point is local or remote based on whether it is within a fast network boundary. The client is then assigned to a distribution point based on a list that favors local multicast-enabled distribution points, if available. If a client cannot receive a local multicast distribution other non-multicast local distribution points and remote distribution points are tried. Operating system images are never distributed from a remote distribution point using multicast. Branch distribution points cannot use multicast for operating system deployment. For more information about how package source files are located, see Configuration Manager and Content Location (Package Source Files).

Best practice recommends that the same distribution point is not used both for multicast and for unicast distributions in network environments that are likely to have high volumes of operating system deployment. For this reason, operating system deployment driver packages and non-multicast operating system images should be located on distribution points other than the multicast-enabled distribution point.

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