Class
Description
D address range
224.0.0.18
Virtual Router Redundancy Protocol (VRRP)
224.0.0.19 to 224.0.0.255
Other protocols
Like h
n
aving reserved the private network segment 10.0.0.0/8 for unicast, IANA has also reserved the
etwork segment 239.0.0.0/8 for multicast. These are administratively scoped addresses. With the
you can define the range of multicast domains flexibly to isolate IP
addresses between different multicast domains, so that the same multicast address can be used in
administratively scoped addresses,
different multicast domains without causing collisions.
E
n a multicast packet is transported in an Ethernet network, a
destination address because the destination is a group with an
5e, while the
ss.
Figure 25-4
thernet multicast MAC address
When a unicast IP packet is transported in an Ethernet network, the destination MAC address is the
MAC address of the receiver. Whe
multicast MAC address is used as the
uncertain number of members.
As stipulated by IANA, the high-order 24 bits of a multicast MAC address are 0x0100
low-order 23 bits of a MAC address are the low-order 23 bits of the multicast IP addre
describes the mapping relationship:
Figure 25-4
Multicast address mapping
XXXX X
X
XXX XXXX
XXXX XXXX
XXXX XXXX
1110
XXXX
5 bits lost
32-bit IP address
0XXX XXXX
XXXX XXXX
XXXX XXXX
0000 0001
0000 0000
0101 1110
48-bit MAC address
25-bit MAC address prefix
…
…
23 bits
he high-order four bits of the IP multicast address are 1110, representing the multicast ID. Only 23 bits
of the remaining 28 bits are mapped to a MAC address. Thus, five bits of the multicast IP address are
lost. As a result, 32 IP multicast addresses are mapped to the same MAC address.
Multicast Protocols
mapped
T
25-8
