Information Technology Reference
In-Depth Information
Ta b l e 1 1-1 0
Multicast Addresses
Multicast Address
Description
224.0.0.0/24
Local network control block
224.0.0.1
All hosts or all systems on this subnet
224.0.0.2
All multicast routers
224.0.0.4
Distance-Vector Multicast Routing Protocol (DVMRP)
routers
224.0.0.5
All OSPF routers
224.0.0.6
All OSPF DR routers
224.0.0.9
RIPv2 routers
224.0.0.10
EIGRP routers
224.0.0.13
All PIM routers
224.0.1.0/24
Internetwork control block
224.0.1.39
Rendezvous point (RP) announce
224.0.1.40
RP discovery
224.0.2.0 to 224.0.255.0
Ad hoc block
239.000.000.000 to 239.255.255.255
Administratively scoped
239.192.000.000 to 239.251.255.255
Organization-local scope
239.252.000.000 to 239.254.255.255
Site-local scope
Layer 3-to-Layer 2 Mapping
Multicast-aware Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI) net-
work interface cards use the reserved IEEE 802 address 0100.5e00 for multicast addresses
at the MAC layer. This includes Fast Ethernet and Gigabit Ethernet. Notice that for the ad-
dress, the high-order byte 0x01 has the low-order bit set to 1. This bit is the
Individual/Group (I/G) bit. It signifies whether the address is an individual address (0) or a
group address (1). Hence, for multicast addresses, this bit is set to 1.
Ethernet interfaces map the lower 23 bits of the IP multicast address to the lower 23 bits
of the MAC address 0100.5e00.0000. As an example, the IP multicast address 224.0.0.2 is
mapped to the MAC layer as 0100.5e00.0002. Figure 11-24 shows another example look-
ing at the bits of multicast IP 239.192.44.56. The IP address in hexadecimal is
EF:C0:2C:38. The lower 23 bits get mapped into the lower 23 bits of the base multicast
MAC to produce the multicast MAC address 01:00:5E:40:2C:38.
