3com 8807 사용자 가이드
412
C
HAPTER
37: IP M
ULTICAST
O
VERVIEW
packet scales. Multicast packets use IP addresses of Class D as their destination
addresses, but Class D IP addresses cannot be contained in the source IP field of IP
packets.
addresses, but Class D IP addresses cannot be contained in the source IP field of IP
packets.
During unicast data transmission, a packet is transmitted "hop-by-hop" from the
source address to the destination address. However, in IP multicast environment, a
packet has more than one destination address, or a group of addresses. All the
information receivers are added to a group. Once a receiver joins the group, the
data for this group address starts flowing to this receiver. All members in the group
can receive the packets. This group is a multicast group.
source address to the destination address. However, in IP multicast environment, a
packet has more than one destination address, or a group of addresses. All the
information receivers are added to a group. Once a receiver joins the group, the
data for this group address starts flowing to this receiver. All members in the group
can receive the packets. This group is a multicast group.
Membership here is dynamic, and a host can join or leave the group at any time. A
multicast group can be permanent or temporary. Some multicast group addresses
are allocated by IANA, and the multicast group is called permanent multicast
group. The IP addresses of a permanent multicast group are unchangeable, but its
membership is changeable, and the number of members is arbitrary. It is quite
possible for a permanent group to not a single member. Those not reserved for
permanent multicast groups can be used by temporary multicast groups. Class D
multicast addresses range from 224.0.0.0 to 239.255.255.255. More information
is listed in Table 407 “Ranges and meanings of Class D addresses”.
multicast group can be permanent or temporary. Some multicast group addresses
are allocated by IANA, and the multicast group is called permanent multicast
group. The IP addresses of a permanent multicast group are unchangeable, but its
membership is changeable, and the number of members is arbitrary. It is quite
possible for a permanent group to not a single member. Those not reserved for
permanent multicast groups can be used by temporary multicast groups. Class D
multicast addresses range from 224.0.0.0 to 239.255.255.255. More information
is listed in Table 407 “Ranges and meanings of Class D addresses”.
Reserved multicast addresses that are commonly used are described in the
following table.
following table.
Table 407 Ranges and meanings of Class D addresses
Class D address range
Description
224.0.0.0~224.0.0.255
Reserved multicast addresses (addresses of permanent
groups). All but 224.0.0.0 can be allocated by routing
protocols.
groups). All but 224.0.0.0 can be allocated by routing
protocols.
224.0.1.0~238.255.255.255
Multicast addresses available for users (addresses of
temporary groups). They are valid in the entire network.
temporary groups). They are valid in the entire network.
239.0.0.0~239.255.255.255
Administratively scoped multicast addresses. They are valid
only in the specified local range.
only in the specified local range.
Table 408 Reserved multicast address list
Class D address range Description
224.0.0.0
Base Address (Reserved)
224.0.0.1
Addresses of all hosts
224.0.0.2
Addresses of all multicast routers
224.0.0.3
Unassigned
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
Mobile agents
224.0.0.12
DHCP server/Relay agent