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IGMP Snooping / Empty Mac-Address Table


We've got two 4500-X as VSS configured and 3750-X as Access Switches. We want to use IPTV Multicast in this Network. The Core is configured as PIM Multicast Router in Sparse-Dense Mode and the Access Switches are snooping for IGMP Pakets. After connecting a Client asking for Multicast Stream ( the Mac Address Table on the Access Switch is empty:

#show mac address-table multicast

Vlan    Mac Address       Type        Ports

----    -----------       ----        -----

But it recognizes the Group the Client is asking for:

#show ip igmp snooping group

Vlan      Group                    Type        Version     Port List


150             igmp        v2          Gi1/0/3, Po2

The IGMP Snooping Settings on the Access Switch looks like this:

Global IGMP Snooping configuration:
IGMP snooping                : Enabled
IGMPv3 snooping (minimal)    : Enabled
Report suppression           : Enabled
TCN solicit query            : Disabled
TCN flood query count        : 2
Robustness variable          : 2
Last member query count      : 2
Last member query interval   : 1000

Vlan 150:
IGMP snooping                       : Enabled
CAPWAP enabled                      : Disabled
IGMPv2 immediate leave              : Enabled
Multicast router learning mode      : pim-dvmrp
CGMP interoperability mode          : IGMP_ONLY
Robustness variable                 : 2
Last member query count             : 2
Last member query interval          : 1000

Why is the Multicast Mac-Address table empty? Any Ideas?



Everyone's tags (5)
New Member

I have this same problem. Did

I have this same problem. Did you ever figure it out?

New Member

Hi Ralphy006Only the IGMP

Hi Ralphy006

Only the IGMP Querier / PIM Router is showing entries in the "show mac address-table multicast" table. The access switches only care about IGMP snooping groups which can be seen with "show ip igmp snooping groups".


New Member

Thanks Marc. That's

Thanks Marc. That's interesting.

On a somewhat related note.... do you know if the end-device automatically populates the destination mac-address for a multicast frame? I am aware there is always a correlating mac-address for every IP multicast address. But wasn't sure if there was still something similar to "ARP". Or if the end-device talking multicast just auto populates the destination mac.

Thanks in advance!

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