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IGMP Snooping on 2950 and still flooding multicast


I'm configuring IGMP Snooping on Cisco Catalyst 2950 Version 12.1(12c)EA1 Enhanced Image.

IGMP snooping seems correctly configured :

sw#sho ip igmp snooping vlan 1

vlan 1


IGMP snooping is globally enabled

IGMP snooping is enabled on this Vlan

IGMP snooping immediate-leave is disabled on this Vlan

IGMP snooping mrouter learn mode is pim-dvmrp on this Vlan

IGMP snooping is running in IGMP_ONLY mode on this Vlan

But I still receive a lot of multicast without having joined any IGMP groups (on my fa0/8 interface) :

sw#sho int fa0/8 counters

Port InOctets InUcastPkts InMcastPkts InBcastPkts

Fa0/8 3387781 41569 48 50

Port OutOctets OutUcastPkts OutMcastPkts OutBcastPkts

Fa0/8 75207017 42402 60322 1962

sw#sho mac-address-table multicast

Vlan Mac Address Type Ports

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

1 0100.5e00.0001 IGMP Gi0/2

1 0100.5e00.0002 IGMP Gi0/2

1 0100.5e00.000a IGMP Gi0/2

1 0100.5e00.00fa IGMP Gi0/2

1 0100.5e7f.fffa IGMP Fa0/8, Gi0/2

5 0100.5e00.0001 IGMP Gi0/2

5 0100.5e00.000a IGMP Gi0/2

20 0100.5e00.0002 IGMP Gi0/2

20 0100.5e00.000a IGMP Gi0/2

The verbose multicast group (proprietary application) is aka 0100.5e00.0001 on VLAN 1. As I used a sniffer, I know that I'm still receiving multicast packets for

Any help would be appreciated.

Please reply to my email address as well (



Community Member

Re: IGMP Snooping on 2950 and still flooding multicast

What you probably see are multicasts in the range 0100.5e00.00xx. The Cisco switches do not apply IGMP snooping on these addresses. Why?

224.0.0.x is dedicated to link-local multicasting (by IANA). These addresses map to the MAC addresses mentioned above. Quite a few applications use these addresses (just think of the routing protocols).

If you restriced forwarding to those who registered through IGMP (and therefore create a multicast CAM entry), these applications wouldn't work no longer.

Keep that in mind, when you choose multicast groups for your multicast applications.


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