Switching

i have 2 queries
1...what for this protocol is, and how it works with juniper devices,,,if someone can explain shortly...or refer some relevant document...
2...On Ex series switches, if i m using Junos 9.2, or 10.4 versions, by defualt, igmp snooping is part of configurations, however if i try to see igmp statistics on command line, response i get it says igmp not running.
however if i have 11.4 version , in that case, default configuration is same and includes igmp snooping,,however if i want to see igmp statistics,,it showsw some statiscs field and does not say that igmp is not running here,, so does it mean there is some differnece with igmp support in junos versions???
secondly,,in junos 9.x, 10.x,, if igmp is not running,, what igmp snooping is good for????
plz guide

Hi Nasir,

IGMP and IGMP-Snooping are both different features:

IGMP will only work if you have it configured on an L3 interface (eg: vlan.x on an EX).  It is used by the switch to identify if any multicast receivers still exist in a VLAN and whether to continue forwarding multicast traffic to them.  If you don't have any L3 interfaces configured, then the "show igmp statistics" command will show nothing.

IGMP-Snooping is used by the switch to limit the flooding of multicast across an L2 segment.  Eg: if you have 20 active ports configured in a single VLAN, and a multicast stream is sent to a host in that VLAN, without IGMP-Snooping turned on, the switch would flood the stream out all 20 ports.  With IGMP-Snooping turned on, the switch intercepts multicast messages to determine which hosts are actually interested and builds a table of "interested" interfaces which it then forwards to.  You can look at this using "show igmp-snooping statistics"