Asante Technologies 39240, 480 6.2 Managing IP Multicast Traffic

6.2 Managing IP Multicast Traffic

Multicast traffic is a means to transmit a multimedia stream from the Internet (a video conference, for example)

without requiring a TCP connection from every remote host that wants to receive the stream.

Traditional IP communication allows a host to send packets to one host (unicast transmission) or to all hosts

(broadcast transmission). IP multicast provides a third scheme, allowing a host to send packets to a group of hosts

(group transmission). A multicast address is chosen for the members of a multicast group . Senders use that address

as the destination address of a datagram to reach all hosts of the group. The stream is sent to the multicast address,

and from there, it is delivered to all interested parties o n the Internet. Any host, regardless of whether it is a member

of a group, can send to that group. However, only the members of the group receiv e the message.

The IntraCore IC39240.IC39480 supports the snooping of Internet Group Management Protocol (IGMP) messag es

that are used between hosts on a LAN and the switch(s)/routers on that LAN to track the multicast groups of which

hosts are members. The switch supports IGMP Version 2 that has suc h features as the IGMP query timeout and the

maximum query response time.

The Internet Group Managem ent Protocol (IGMP) manages the multicast groups on a LAN. IP hosts use IGMP to

report their group membership to directly connected multicast switches. Switches executing a multicast protocol

maintain forwarding tables to forward multicast datagram’s. Switches use the IGMP to learn whether members of a

group are present on their directly attached sub-nets. Hosts join multicast groups by sending IGMP report messages.

IGMP uses group addresses, which are Clas s D IP addresses. The high-order four bits of a Class D address are

1110. Therefore, host group addresses can be in the range 224.0.0.0 to 239.255.2 55.255.

The address 224.0.0.0 will no t be assigned to any group. T he address 224.0.0.1 is assigned to all systems on a sub-

net. The address 224.0.0.2 is assig ned to all switches on a sub-net.

Forwarding Unkn own Multicast Packets. Unknown multicast packets are those packets with destination IP

multicast addresses not learned b y the switch. By default, the switch forw ard s all su ch traffic.

Use the following commands to configure IGMP.

Enable the IGMP Snooping

To enable/disable IGMP, use the command below. Unknown multicast traffic will not be forwarded once igmp is

enabled.

Command Purpose

Set igmp {enable | disable} Enable/Disable IGMP

48 Asante IntraCore IC39240/480 User’s Manual