Multicast is an advanced transmission application that transits information packages from one point to multiple points by sending package once only. Unlike Unicast and Broadcast, when sending information package to multiple Mac addresses under one IP, Multicast will identify those Mac addresses registered to receive a specific info package and send that info to them only instead of to every Mac addresses under IP. In this way, Multicast reduces the heavy volume of traffic and loadings and transits information to specific group members.

It is a most advanced and beneficial feature to on-line paid video-watching program. On-line video providers want to deliver videos to customers who have paid to watch and to avoid videos are flowed to those who do not pay. By using Multicast application, providers could classify their users into several groups according to the videos selected and videos will be delivered to that specific group only.

ES3528MV2 is a L2 Fast Ethernet Standalone Switch and supports Multicast storm control application. Administrators could use the following steps to configure, monitor and check Multicast function:

How to check if IGMP Snooping function properly?

To use following commands to enable IP IGMP Snooping function:

SW_1#config
SW_1(config)#ip igmp snooping

IGMP snooping functions once a Multicast Router is connected to SW1.

As shown in the figure above, Port 28 of SW1 is connected to Multicast Router and it would be the mrouter port after IGMP general query is received. The Router Port Expire Time is 300 seconds by default.

SW_1#show ip igmp snooping mrouter
 VLAN M'cast Router Ports Type    Expire
 ---- ------------------- ------- --------
 1    Eth 1/28            Dynamic 0:4:39

Use "show IP IGMP snooping group" to check if whether multicast group 224.1.1.1 is learned by mrouter port. If the multicast group is learned, multicast traffic destined to 224.1.1.1 will not be flooded to other ports.

SW_1#sh ip igmp snooping group
Bridge Multicast Forwarding Entry Count:1
Flag: R - Router port, M - Group member port
      H - Host counts (number of hosts join the group on this port).
      P - Port counts (number of ports join the group).
 Up time: Group elapsed time (d:h:m:s).
 Expire : Group remaining time (m:s).

VLAN Group           Port        Up time     Expire Count
---- --------------- ----------- ----------- ------ --------
   1 224.1.1.1                               01:49      1(P)
                     Eth 1/28(R)

Once multicast group 224.1.1.1 is played by PC1 VLC client, IGMP membership report will be sent to SW1 by PC1 automatically.

SW1 will snoop the package and register port 1 as 224.1.1.1 multicast group member port, and Multicast traffic for 224.1.1 group will be forwarded to PC1 consequently.

SW_1#sh ip igmp snooping group
Bridge Multicast Forwarding Entry Count:1
Flag: R - Router port, M - Group member port
      H - Host counts (number of hosts join the group on this port).
      P - Port counts (number of ports join the group).
 Up time: Group elapsed time (d:h:m:s).
 Expire : Group remaining time (m:s).

VLAN Group           Port        Up time     Expire Count
---- --------------- ----------- ----------- ------ --------
   1 224.1.1.1                   00:00:00:03            2(P)
                     Eth 1/ 1(M) 00:00:00:03 04:17      1(H)
                     Eth 1/28(R)

After SW1 sends IGMP membership Report, PC1 starts to receive UDP multicast traffic (Shown as the figure below).

Multicast router sends out Generic Query to solicit the receiver to send report periodically and in this way, the mrouter port and multicast group registration entries will be updated constantly.