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I have connected three servers to Cisco Nexus 7000 switch. Server1 send multicast packets, server2 subscribes to multicast packets and server3 is for the tests. No matter if I subscribe to multicast from server2 or not all interfaces are flooded by multicast packets even I have had IGMP snooping enabled.

What is going on here???

This is my configuration:

switch(config-vlan)# show ip igmp snooping
Global IGMP Snooping Information:
IGMP Snooping enabled
Optimised Multicast Flood (OMF) enabled
IGMPv1/v2 Report Suppression enabled
IGMPv3 Report Suppression disabled
Link Local Groups Suppression enabled
VPC Multicast optimization disabled
Group timeout configured: never

IGMP Snooping information for vlan 1
IGMP snooping enabled
Lookup mode: IP
Optimised Multicast Flood (OMF) enabled
IGMP querier none
Switch-querier disabled
IGMPv3 Explicit tracking enabled
IGMPv2 Fast leave disabled
IGMPv1/v2 Report suppression enabled
IGMPv3 Report suppression disabled
Link Local Groups suppression enabled
Router port detection using PIM Hellos, IGMP Queries
Number of router-ports: 0
Number of groups: 1
VLAN vPC function disabled
Active ports:
  Eth1/3      Eth1/5      Eth1/7

IGMP Snooping information for vlan 4045
IGMP snooping enabled
Lookup mode: IP
Optimised Multicast Flood (OMF) enabled
IGMP querier none
Switch-querier disabled
IGMPv3 Explicit tracking enabled
IGMPv2 Fast leave disabled
IGMPv1/v2 Report suppression enabled
IGMPv3 Report suppression disabled
Link Local Groups suppression enabled
Router port detection using PIM Hellos, IGMP Queries
Number of router-ports: 0
Number of groups: 0
VLAN vPC function disabled
Active ports:

switch(config-vlan)#
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That was easy and embarrassing - we have been sending packets to multicast 225.0.0.1 and 239.0.0.1-16 which are multicast range without IGMP Snooping filtering, according to:

1) IETF specification: https://tools.ietf.org/html/draft-ietf-mboned-ipv4-mcast-unusable-01

2) Cisco documentation (page 7-9): http://www.cisco.com/c/dam/en/us/support/docs/ip/ip-multicast/ipmlt_wp.pdf

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