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DELL S50V User Manual

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Internet Group Management Protocol
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IGMP Snooping
Multicast packets are addressed with multicast MAC addresses, which represent a group of devices, rather 
than one unique device. Switches forward multicast frames out of all ports in a VLAN by default, even 
though there may be only some interested hosts, which is a waste of bandwidth. IGMP Snooping enables 
switches to use information in IGMP packets to generate a forwarding table that associates ports with 
multicast groups so that when they receive multicast frames, they can forward them only to interested 
receivers.
IGMP Snooping Implementation Information
•
IGMP Snooping on FTOS uses IP multicast addresses not MAC addresses.
•
IGMP Snooping is not supported on stacked VLANs.
•
IGMP Snooping is supported on all S-Series stack members.
•
IGMP Snooping reacts to STP and MSTP topology changes by sending a general query on the 
interface that transitions to the forwarding state.
Configuring IGMP Snooping
Configuring IGMP Snooping is a one-step process. That is, enable it on a switch using the command 
ip 
igmp snooping enable 
from CONFIGURATION mode. View the configuration using the command 
show 
running-config 
a VLAN using the command 
no ip igmp snooping
 from INTERFACE VLAN mode.
Figure 19-9.  Enabling IGMP Snooping
Related Configuration Tasks
•
•
•
•
Enabling IGMP Immediate-leave
Configure the switch to remove a group-port association upon receiving an IGMP Leave message using the 
command 
ip igmp fast-leave
 from INTERFACE VLAN mode. View the configuration using the command 
show config
 from INTERFACE VLAN mode, as shown in 
FTOS(conf)#ip igmp snooping enable
FTOS(conf)#do show running-config igmp
ip igmp snooping enable
FTOS(conf)#