Manual
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Москва, Новозаводская ул., 18, стр. 1 
254 
SwitchB(config)#ip igmp snooping 
SwitchB(config)#ip igmp snooping vlan 100 
SwitchB(config)#ip igmp snooping vlan 100 mrouter interface ethernet 1/0/1 
Multicast Configuration 
The same as scenario 1 
IGMP Snooping listening result: 
Similar to scenario 1 
Scenario 3: To run in cooperation with layer 3 multicast protocols. 
switch  which  is  used  in  Scenario  1  is  replaced  with  ROUTER  with  specific  configurations 
remains the same. And multicast and IGMP snooping configurations are the same with what it 
is in Scenario 1. To configure PIM-SM on ROUTER, and enable PIM-SM on vlan 100 (use the 
same PIM mode with the connected multicast router) 
Configurations are listed as below: 
switch#config 
switch(config)#ip pim multicast-routing  
switch(config)#interface vlan 100 
switch(config-if-vlan100)#ip pim sparse-mode  
IGMP snooping does not distribute entries when layer 3 multicast protocol is enabled. It only 
does the following tasks. 
Remove the layer 2 multicast entries. 
Provide query functions to the layer 3 with vlan, S, and G as the parameters. 
When layer 3 IGMP is disabled, re-enable distributing layer 2 multicast entries. 
By looking up the layer 3 IPMC entries, it can be found that ports can be indicated by the layer 
3 multicast entries. This ensures the IGMP snooping can work in cooperation with the layer 3 
multicast protocols. 
28.10.4 IGMP Snooping Troubleshooting 
On IGMP Snooping function configuration and usage, IGMP Snooping might not run properly 
because of physical connection or configuration mistakes. So the users should note that: 
Make sure correct physical connection 
Activate IGMP Snooping on whole configuration mode (use ip igmp snooping) 
Configure  IGMP Snooping  at VLAN  on  whole  configuration mode  (  use  ip  igmp  snooping 
vlan <vlan-id>)  
Make  sure  one  VLAN  is  configured  as  L2  common  checker  in  same  mask,  or  make  sure 










