F3726, F3211, F3174, R5135, R3816-HP Firewalls and UTM Devices Appendix Protocol Reference-6PW100

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 assigned the Class D address space (224.0.0.0 to 239.255.255.255) for IPv4

multicast.

Table 8 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. Other IP addresses can be used by routing protocols and

for topology searching, protocol maintenance, and so on. Table 9

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.

224.0.1.0 to 238.255.255.255

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.

239.0.0.0 to 239.255.255.255

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.

"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. For more information, see RFC 2770.

Table 9 Some reserved multicast addresses

Address Description

224.0.0.1 All systems on this subnet, including hosts and routers.

224.0.0.2 All multicast routers on this subnet.

224.0.0.3 Unassigned.

224.0.0.4 DVMRP routers.

224.0.0.5 OSPF routers.

224.0.0.6 OSPF designated routers and backup designated routers.

224.0.0.7 ST routers.

224.0.0.8 ST hosts.

224.0.0.9 RIPv2 routers.

224.0.0.11 Mobile agents.