IGMP throttling normally is used by service providers to control the quantities of channels that could be subscribed by users at one time. By doing this, service providers prevent users from attaching to too many hosts without be charged and from wasting the bandwidth.

Step 1. Enter interface 27 and configure igmp max-groups to 2. After two multicast groups learned this port, other join packets will be discarded by port 27. Configuration status is as follow:

SW_1(config)#interface e 1/27
SW_1(config-if)#ip igmp max-groups 2
SW_1(config-if)#ip igmp max-groups action deny

Step 2. Check the configuration

SW_1#sh ip igmp throttle interface e 1/27
Eth  1/27 Information
                   Status : TRUE
                   Action : Deny
     Max Multicast Groups : 2
 Current Multicast Groups : 2

From the multicast registration table shown below, it is clear that only 224.1.1.2 and 224.1.1.3 are learned by PC2, and therefore PC2 plays video streams transmitted from these two groups only.

SW_1#sh ip igmp snooping group
Bridge Multicast Forwarding Entry Count:7
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
---- --------------- ----------- ----------- ------ --------
   1 224.0.1.75                  00:00:52:00            2(P)
                     Eth 1/25(M) 00:00:52:00 03:21      1(H)
                     Eth 1/28(R)
   1 224.1.1.1                               02:57      1(P)
                     Eth 1/28(R)
   1 224.1.1.2                   00:00:43:13            2(P)
                     Eth 1/27(M) 00:00:43:13 03:19      1(H)
                     Eth 1/28(R)
   1 224.1.1.3                   00:00:42:53            2(P)
                     Eth 1/27(M) 00:00:42:53 03:21      1(H)
                     Eth 1/28(R)
   1 224.1.1.4                               01:11      1(P)
                     Eth 1/28(R)
   1 239.255.255.250             00:00:51:55            2(P)
                     Eth 1/ 1(M) 00:00:38:27 03:16      1(H)
                     Eth 1/28(R)
   1 239.255.255.254             00:00:51:57            2(P)
                     Eth 1/25(M) 00:00:51:57 03:17      1(H)
                     Eth 1/28(R)

When IGMP throttling is enabled, the ip igmp max-groups action is "deny." There is another action "replace:"

SW_1(config)#int e 1/27
SW_1(config-if)#ip igmp max-groups action replace

SW_1#sh ip igmp snooping group
Bridge Multicast Forwarding Entry Count:7
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
---- --------------- ----------- ----------- ------ --------
   1 224.0.1.75                  00:00:55:02            2(P)
                     Eth 1/25(M) 00:00:55:02 02:18      1(H)
                     Eth 1/28(R)
   1 224.1.1.1                   00:00:00:34            2(P)
                     Eth 1/27(M) 00:00:00:34 03:47      1(H)
                     Eth 1/28(R)
   1 224.1.1.2                               02:25      1(P)
                     Eth 1/28(R)
   1 224.1.1.3                   00:00:45:55            2(P)
                     Eth 1/27(M) 00:00:45:55 02:23      1(H)
                     Eth 1/28(R)
   1 224.1.1.4                               01:08      1(P)
                     Eth 1/28(R)
   1 239.255.255.250             00:00:54:58            2(P)
                     Eth 1/ 1(M) 00:00:41:29 02:21      1(H)
                     Eth 1/28(R)
   1 239.255.255.254             00:00:54:59            2(P)
                     Eth 1/25(M) 00:00:54:59 02:19      1(H)
                     Eth 1/28(R)

If the action is "Replace", the latest report will replace the previous one.