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Marc Aemmer
Beginner

IGMP Snooping / Empty Mac-Address Table

Hi,

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 (239.15.14.16) 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       239.15.14.16             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?

Thanks,

Marc

3 REPLIES 3
Ralphy006
Beginner

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

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".

regards,
Marc

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!