Multicast Notes - Part1

1- Multicast Address Range and Structure :

- (IANA) has assigned class D IP addresses to multicast applications. The first 4 bits of the first octet for a classD address are always 1110. IP multicast addresses range from 224.0.0.0 through 239.255.255.255

- IANA has assigned several ranges of multicast IP addresses for specific types of reasons. Those types are as follows:

■ Permanent multicast groups, in the range 224.0.0.0–224.0.1.255
(divided to local "unrouted" [224.0.0.1-224.0.0.255] like routing protocols multicast ips and "routed"
 [224.0.1.0-224.0.1.255] like 224.0.0.39-40 which are used by cisco Auto-RP.

■ Addresses used with Source-Specific Multicast (SSM), in the range 232.0.0.0–232.255.255.255
The purpose of these applications is to allow a host to select a source for the multicast
group. SSM makes multicast routing efficient, allows a host to select a better-quality source, and
helps network administrators minimize multicast denial-of-service (DoS) attacks.

■ GLOP addressing, in the range 233.0.0.0–233.255.255.255
It can be used by anyone who owns a registered autonomous system number (ASN) to create 256 global multicast addresses that can be owned and used by the entity.
By using a value of 233 for the first octet, and by using the ASN for the second and third octets, a
single autonomous system can create globally unique multicast addresses as defined in the GLOP
addressing RFC. For example, the autonomous system using registered ASN 5663 could covert
ASN 5663 to binary (0001011000011111). The first 8 bits, 00010110, equals 22 in decimalnotation, and the last 8 bits, 00011111, equals 31 in decimal notation. Mapping the first 8 bits to
the second octet and the last 8 bits to the third octet in the 233 range addresses, the entity who
owns the ASN 5663 is automatically allocated the address range 233.22.31.0 through
233.22.31.255.

■ Private multicast addresses, in the range 239.0.0.0–239.255.255.255
much like the IP unicast ranges defined in RFC 1918, namely 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

■ The rest of the multicast addresses are referred to as transient groups .