IP Multicast Support

Multicast Support for Office Networks

The Windows 2000 router can provide full multicast capabilities for single router branch offices connected to a hub office with a multicast-enabled intranet. This configuration requires proper configuration of both the branch office and hub office router.

For the branch office router, all interfaces are added to the IGMP routing protocol and the interfaces for the branch office subnets are configured for IGMP router mode. The interface that connects to the hub office router is configured for IGMP proxy mode. The interface that connects to the hub office router can be a LAN interface (such as when using a T-Carrier or Frame Relay connection) or a demand-dial interface (such as when using dial-up analog phone lines, ISDN, or a router-to-router VPN connection). A demand-dial interface can be either on-demand or persistent. For more information about demand-dial interfaces and configuration, see "Demand-Dial Routing" in this book.

For the hub office router, all interfaces are added to the IGMP routing protocol and the interface connected to the branch office is configured for IGMP router mode. The interface that connects to the branch office router can be a LAN interface (such as when using a T-Carrier or Frame Relay connection) or a demand-dial interface (such as when using dial-up analog phone lines, ISDN, or a router-to-router VPN connection). The interface that connects the multicast core router subnet is configured for IGMP proxy mode.

IGMP Group Membership Report messages for group members are copied across the branch office link to the multicast core router subnet. Multicast traffic from branch office hosts is flooded from the branch office subnet across the branch office link to the multicast core router subnet.

In this configuration, multicast traffic sent between two hosts on the branch office intranet is copied to the branch office link, resulting in inefficient use of the bandwidth of the link to the hub office. To prevent intra-branch office multicast traffic from being copied to the branch office link, configure the applications or the ranges of multicast addresses on your MADCAP servers on the intranet to use IP multicast addresses from the administratively scoped range of 239.0.0.0 to 239.254.255.255, and configure the appropriate scope-based boundaries on the interface to the hub office.

The multicast support for branch office networks configuration is shown in Figure 4.11.

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Figure 4.11 Multicast Support for Branch Office Networks