3com 3031 Instruccion De Instalación
590
C
HAPTER
45: IP M
ULTICAST
them to the neighboring multicast router. The neighboring multicast router will
remove the unicast IP header and continue the multicast transmission. This
protects the network architecture from great change.
remove the unicast IP header and continue the multicast transmission. This
protects the network architecture from great change.
The main advantages of multicast are as follows:
■
Enhanced efficiency: It reduces network traffic and relieves server and CPU
loads.
loads.
■
Optimized performance: it eliminates traffic redundancy.
■
Distributed application: It enables multipoint applications.
Multicast Addresses
IP Multicast Addresses
Class D IP addresses are used in the destination addresses of multicast packets,
ranging from 224.0.0.0 to 239.255.255.255. Class D addresses cannot appear in
the source IP address fields of IP packets.
ranging from 224.0.0.0 to 239.255.255.255. Class D addresses cannot appear in
the source IP address fields 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 group of addresses. All the
information receivers are added to a group. Once a receiver joins the group, the
data for this group of addresses start flowing to this receiver. All members in the
group can receive the packets. Membership is dynamic, a host can join or leave
the group at any time.
source address to the destination address. However, in IP multicast environment, a
packet has more than one destination address or group of addresses. All the
information receivers are added to a group. Once a receiver joins the group, the
data for this group of addresses start flowing to this receiver. All members in the
group can receive the packets. Membership is dynamic, a host can join or leave
the group at any time.
A multicast group can be permanent or temporary. The multicast addresses
officially allocated form the permanent multicast group, and the others form the
temporary one. The IP addresses of a permanent multicast group are unchangable,
but its membership is changeable, and the number of members is arbitrary. It is
quite possible for a permanent group to not have a single member.
officially allocated form the permanent multicast group, and the others form the
temporary one. The IP addresses of a permanent multicast group are unchangable,
but its membership is changeable, and the number of members is arbitrary. It is
quite possible for a permanent group to not have a single member.
For ranges and meanings of Class D addresses, see Table 686.
Reserved multicast addresses that are commonly used are described in the
following table.
following table.
Table 686 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
Multicast addresses for local management. They are valid
only in the specified local range.
only in the specified local range.
Table 687 Reserved multicast address list
Class D address
Description
224.0.0.0
Base Address (Reserved)
224.0.0.1
Addresses of all hosts