strict requirements for new assignments within this address space. The
239.0.0.0239.255.255.255 range is equivalent in purpose to the private
networks defined by RFC 1918.
warded by an IP router. Both ranges of addresses are used by applications
and network protocols. The first group, classified as local-link, is meant to
remain local to the subnet or broadcast domain on which the system resides.
The second group is a global address that can be routed and forwarded
across multiple IP routers.
there be a way to use multicast across routers instead of limiting it to the
physical segment where hosts were located. In regular unicast, MAC
addresses are layer 2 addresses, and in order for the local host to reach
remote hosts, layer 3 logical IP addresses are used to route data to the des-
tination. Once the packet reaches the remote subnet, the Address Resolution
Protocol (ARP) is used to find the MAC address of the host. By using an
existing ARP table, or via an ARP request, the MAC address that is associ-
ated to the layer 3 IP address is found and the packet is forwarded to the des-
tination host.
5e, is used for all Ethernet multicast addresses. This leaves another 24 bits
for use in creating the multicast MAC address. When the MAC address is
generated, the 25th bit (or high order bit) is set to 0 and then the last 23 bits
of the IP address are mapped in to the remaining 23 bits of the MAC address.
Figure 9.4 depicts how this looks.
239.255.255.255
domain
Scoped