Multicast Addresses - HP MSR ASM Configuration Manual

Multicast addresses

Network-layer multicast addresses (namely, multicast IP addresses) enables communication between
multicast sources and multicast group members. In addition, a technique must be available to map
multicast IP addresses to link-layer multicast MAC addresses.
The membership of a group is dynamic. Hosts can join or leave multicast groups at any time.
IP multicast addresses
IPv4 multicast addresses:
•
The IANA assigns the Class D address space (224.0.0.0 to 239.255.255.255) for IPv4 multicast.
Table 2 Class D IP address blocks and description
Address block
224.0.0.0 to 224.0.0.255
224.0.1.0 to 238.255.255.255
239.0.0.0 to 239.255.255.255
"Glop" is a mechanism for assigning multicast addresses between different ASs. By filling an AS
number into the middle two bytes of 233.0.0.0, you get 255 multicast addresses for that AS. For
more information, see RFC 2770.
Table 3 Some reserved multicast addresses
Address
224.0.0.1
224.0.0.2
224.0.0.3
224.0.0.4
224.0.0.5
224.0.0.6
224.0.0.7
224.0.0.8
224.0.0.9
224.0.0.11
Description
All systems on this subnet, including hosts and routers.
All multicast routers on this subnet.
Unassigned.
DVMRP routers.
OSPF routers.
OSPF designated routers and backup designated routers.
ST routers.
ST hosts.
RIPv2 routers.
Mobile agents.
Description
Reserved permanent group addresses. The IP address 224.0.0.0 is
reserved. Other IP addresses can be used by routing protocols and
for topology searching, protocol maintenance, and so on.
lists common permanent group addresses. A packet destined for an
address in this block will not be forwarded beyond the local subnet
regardless of the TTL value in the IP header.
Globally scoped group addresses. This block includes the following
types of designated group addresses:
•
232.0.0.0/8—SSM group addresses.
•
233.0.0.0/8—Glop group addresses.
Administratively scoped multicast addresses. These addresses are
considered locally unique rather than globally unique, and can be
reused in domains administered by different organizations without
causing conflicts. For more information, see RFC 2365.
6
Table 3