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Level 1
Level 1


we have Cisco Nexus 5K used as plane L2 switch. 1 multicast feed server & 4 receiver machines are connected to same switch port.

by default igmp snooping is enabled. observed receivers were unable to receive multicast feeds. but when i disabled igmp snooping globally receiver were able to receive multicast.

Q1. what can be causes so that after enabling igmp snooping receiver stops to receive traffic.

Q2. on layer 3, pim is enabled, i know command to check whether multicast is forwarded to receiver or not but on layer 2 switch how to check it.

also can you suggest me some nice simple document about working of multicast on L2 & L3 switches separately.

i have very basic knowledge of multicast, can you please tell me how to verify whether multicast traffic is received on feed server port on L2 switch... and whether multicast is forwarded to receiver or not.


4 Replies 4


do you have an IGMP snooping querier configured on the Nexus ? What do you mean by '1 multicast feed server & 4 receiver machines are connected to the same switch port ? Is there a hub connected to one switch port ?

And how is your Layer 3 device connected to the Nexus ?

Best would be to post the configs of both devices...


Only one switch is there; 1 multicast feed sender server & 4 receiver machine clients are connected to same switch on different different port..(no hub nothing)... by default all ports are in vlan1; nothing extra is configured; all is default;

so nothing to post about config; if disable igmp snooping receiver start to receive multicast & if enable it receiver stop to receive multicast. 


try and enable the 'ip igmp snooping querier' command on your VLAN interface.

vlan configuration XXX (XXX is your VLAN number)
ip igmp snooping querier x.x.x.x (x.x.x.x is any free IP address in that VLAN)


igmp snooping is active by default in all vlans if you disable globally it's disabled on individual enabled vlans even if they are interface enabled!

You also say you've enabled pim but state the mc traffic is all l2 so this isn't required

Can you confirm if the mc source is on the same vlan as the receivers 

Can you post

show igmp snooping 



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