Configuring IP Multicast Scopes

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Multicast addressing supports dynamic membership, under which individual computers can join or leave a multicast group at any time. Group membership is not limited by size, and computers are not restricted to membership in any single group.

On all IP networks, each computer must first be configured with its own unicast IP address. After assigning this unicast address, you can configure the computer to support a multicast address. A multicast group of computers shares the same multicast IP address. IPv4 multicast addresses range, in dotted decimal notation, from 224.0.0.0 through 239.255.255.255 (224.0.0.0/4). Such a multicast group also uses a MAC-layer multicast address, which allows all devices to filter unsolicited multicast traffic at the link layer. Ethernet addresses reserved for multicasting range from 01-00-5E-00-00-00 through 01-00-5E-7F-FF-FF.

Typically, you specify IP address ranges for multicast scopes on your MADCAP server in the following ways:

  • Administrative scoping is designed for multicast IP addresses used privately on your intranet. You use the 239.192.0.0 range of the multicast (Class D) address space with a subnet mask of 255.252.0.0. This is known as the IPv4 Organization Local Scope. It provides 262,144 group addresses (218) for use in all subnets on your network. For more information about administrative scoping, see RFC 2365, "Administratively Scoped IP Multicast."

  • Global scoping is designed for multicast IP addresses used on the Internet. You use the 233.0.0.0 range of the multicast address space. Global addresses are allocated in the following way:

    • IANA (or another network registry) allocates and reserves the first 8 bits of the range (the "233" portion).

    • The next 16 bits are based on your Autonomous System (AS) number. For information about obtaining your existing AS number or acquiring a new one, see "Using multicast scopes" in Help and Support Center for Windows Server 2003.

    • The last 8 bits provide the IP address range from which to configure any multicast scopes for group addresses that you want to use publicly on the Internet. Use a subnet mask of 255.255.255.0.

    For more information about global scoping, see RFC 3180, "GLOP Addressing in 233/8." For more information about AS numbering, see RFC 1930, "Guidelines for Creation, Selection, and Registration of an Autonomous System (AS)."