H3C S7500E Series Ethernet Switches Operation Manual
Operation Manual – Multicast
H3C S7500E Series Ethernet Switches Chapter 1 Multicast Overview
1-7
hosts, and the TCP/IP stack must support reception and transmission of multicast
data.
1.3.1 Multicast Addresses
To allow communication between multicast sources and multicast group members,
network-layer multicast addresses, namely, multicast IP addresses must be provided.
In addition, a technique must be available to map multicast IP addresses to link-layer
multicast MAC addresses.
I. IPv4 multicast addresses
Internet Assigned Numbers Authority (IANA) assigned the Class D address space
(224.0.0.0 to 239.255.255.255) for IPv4 multicast. The specific address blocks and
usages are shown in
Table 1-2.
Table 1-2 Class D IP address blocks and description
Address block Description
224.0.0.0 to 224.0.0.255
Reserved permanent group addresses. The IP address
224.0.0.0 is reserved, and other IP addresses can be
used by routing protocols and for topology searching,
protocol maintenance, and so on. Commonly used
permanent group addresses are listed in
Table 1-3. A
packet destined for an address in this block will not be
forwarded beyond the local subnet regardless of the
Time to Live (TTL) value in the IP header.
224.0.1.0 to
238.255.255.255
Globally scoped group addresses. This block includes
two types of designated group addresses:
z 232.0.0.0/8: SSM group addresses, and
z 233.0.0.0/8: Glop group addresses; for details, see
RFC 2770.
239.0.0.0 to
239.255.255.255
Administratively scoped multicast addresses. These
addresses are considered to be locally rather than
globally unique, and can be reused in domains
administered by different organizations without causing
conflicts. For details, refer to RFC 2365.
Note:
z The membership of a group is dynamic. Hosts can join or leave multicast groups at
any time.
z “Glop” is a mechanism for assigning multicast addresses between different
autonomous systems (ASs). By filling an AS number into the middle two bytes of
233.0.0.0, you get 255 multicast addresses for that AS.