HP VPN Firewall Appliances Appendix Protocol Reference

60
Multicast addresses
Network-layer multicast addresses (namely, multicast IP addresses) enable 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 8 Class D IP address blocks and description
Address block Descri
p
tion
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 Descri
p
tion
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.