multicast address is used to send a packet from a single source to multiple network interfaces.
all IPv6 routers must support multicast
parts of a multicast address:
first 8 bits: indicate the address is within multicast scope (1111 1111 or ff)
next 4 bits: used to flag types of multicast if necessary
otherwise set to 0
next 4 bits: determine the scope
E.g., 1 is node-local (to all interfaces on the same node), 2 is link local
final 112 bits define multicast groups within that scope
Multicast Listener Discovery (MLD) protocol allows nodes to join a multicast group and discover whether members of a group are present on a local subnet
broadcast addresses are not implemented in IPv6
hosts use an appropriate multicast address instead
allow an interface to transmit to all interfaces or routers on the same node or local link
IPv4 address resolution to hardware interfaces uses ARP
ARP is inefficient because of broadcasts and requires every node to process its messages