Multicast Support

Media services are becoming common on the Internet and on private networks. Windows 2000 TCP/IP supports the forwarding of multicast traffic, and Windows 2000 Routing and Remote Access service supports the Internet Group Management Protocol (IGMP) as a router. IGMP is used by hosts to join a multicast group. The Routing and Remote Access Service IGMP–enabled interfaces can operate in one of two modes:

• IGMP proxy mode interfaces forward IGMP reports and multicast traffic from other interfaces that are running in IGMP router mode.
• IGMP router mode interfaces listen for IGMP traffic from hosts and update the TCP/IP multicast forwarding table as appropriate, as well as sending IGMP queries.

The IGMP proxy that is provided with Windows 2000 Server is designed to pass IGMP Membership Report packets from a single network intranet to a multicast-capable portion of the Internet.

You can position the IGMP proxy router in the DMZ of the corporate infrastructure to provide internal network hosts with video and audio traffic from the Internet. Ensure that the IGMP router is on a high-bandwidth network with fast switches to minimize bottlenecking. The VPN server that is in the DMZ can also be used as an IGMP router, but only in smaller network structures where the server will not be overloaded with remote access and multicast traffic.

When you configure the IGMP interfaces, the interface that is in proxy mode faces the multicast-enabled Internet and the interface that is in router mode faces the internal network. An example is shown in Figure 7.6.

Enlarge figure

Figure 7.6 IGMP Interface in Proxy Mode

Note

The example in Figure 7.6 will work only if the hardware router connecting the Windows 2000 IGMP router to the Internet is multicast capable, and if the ISP is on the multicast backbone.

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