3com 3031 Instruccion De Instalación

IP Multicast Protocols

591

Ethernet Multicast MAC

Addresses

When unicast IP packet is transmitted on the Ethernet, the destination MAC
address is the MAC address of the receiver. However, for a multicast packet, the
destination is no longer a specific receiver but a group with unspecific members.
Therefore, the multicast MAC address should be used. A multicast MAC address
corresponds with a group of multicast IP addresses. As Internet Assigned Number
Authority (IANA) provisions the high 24 bits of a multicast MAC address are
0x01005e and the low 23 bits of a MAC address is the low 23 bits of a multicast IP
address.

Figure 144 Mapping between a multicast IP address and an Ethernet MAC address

Because only 23 bits of the last 28 bits of an IP multicast address are mapped to
the MAC address, a single MAC address represents 32 IP multicast addresses.

IP Multicast Protocols

Multicast involves multicast group management protocols and multicast routing
protocol. Internet Group Management Protocol (IGMP), the basic signaling
protocol for IP multicast, is the currently adopted multicast group management

224.0.0.2

Addresses of all multicast routers

224.0.0.3

Not for allocation

224.0.0.4

DVMRP routers

224.0.0.5

OSPF routers

224.0.0.6

OSPF DR

224.0.0.7

ST routers

224.0.0.8

ST hosts

224.0.0.9

RIP-2 routers

224.0.0.10

IGRP routers

224.0.0.11

Active agents

224.0.0.12

DHCP server/Relay agent

224.0.0.13

All PIM routers

224.0.0.14

RSVP encapsulation

224.0.0.15

All CBT routers

224.0.0.16

Specified SBM

224.0.0.17

All SBMS

224.0.0.18

VRRP

...

Table 687 Reserved multicast address list

Class D address

Description

1110XXXX

32-bit IP address

48-bit MAC address

5 bits unmapped

Last 23 bits to be directly mapped

XXXXXXXX