Users Guide

Table Of Contents

1560 IPv4 and IPv6 Multicast

recipient host. The IP routing protocols can route multicast traffic, but the IP

multicast protocols handle the multicast traffic more efficiently with better

use of network bandwidth.

Applications that often send multicast traffic include video or audio

conferencing, Whiteboard tools, stock distribution tickers, and IP-based

television (IP/TV).

What Is IP Multicast Traffic?

IP multicast traffic is traffic that is destined to a host group. Host groups are

identified by class D IP addresses, which range from 224.0.0.0 to

239.255.255.255. When a packet with a broadcast or multicast destination IP

address is received, the switch will forward a copy into each of the remaining

network segments in accordance with the IEEE MAC Bridge standard.

Eventually, the packet is made accessible to all nodes connected to the

network.

This approach works well for broadcast packets that are intended to be seen or

processed by all connected nodes. In the case of multicast packets, however,

this approach could lead to less efficient use of network bandwidth,

particularly when the packet is intended for only a small number of nodes.

Packets will be flooded into network segments where no node has any interest

in receiving the packet. The L3 multicast features on the switch help to

ensure that only the hosts in the multicast group receive the multicast traffic

for that group.

Multicast applications send one copy of a packet, and address it to a group of

receivers (Multicast Group Address) rather than to a single receiver (unicast

address). Multicast depends on the network to forward the packets to only

those networks and hosts that need to receive them.

Multicast Addressing

IPv4 multicast addresses in the range 224.0.0.X are reserved link local

addresses used for control plane traffic. Packets sent to these addresses are

always flooded to all ports. Do not use these addresses for multicast data

traffic. Because there is a 32:1 overlap in the IPv4 multicast address range, any

address in the range 224–239.0.0.x and 224–239.128.0.0 should never be used

for multicast data traffic.