Disabling Multicasting

Unanswered Question
Jul 28th, 2008

Hi all-

I don't have the ip pim multicast-routring statement enabled but I still see the multicasts registered by the outbound interface(Illustration below). How do I disable the interface from receiving multicasting on the router?

Output queue: 0/40 (size/max)

5 minute input rate 1000 bits/sec, 1 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

546817 packets input, 120079688 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 611662 multicast, 0 pause input

0 input packets with dribble condition detected

282204 packets output, 48309845 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 pause output

0 output buffer failures, 0 output buffers swapped out

Thanks in advance,


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Giuseppe Larosa Tue, 07/29/2008 - 07:55

Hello Sadik,

even without the ip multicast routing command and ip pim on the interface you can receive multicast packets on the interface.

Consider that if you are using a routing protocol on this LAN interface all hello packets of OSPF, EIGRP, and RIPv2 advertisements are sent with a L3 multicast destination mapped on a L2 multicast MAC address

So it could be right to receive those multicast IP packets/frames.

do a sh ip interface and verify if there are any multicast groups joined all SPF routers all DR SPF routers Ripv2 EIGRP

If you see any of this it is fine and acceptable.


In some scenarios enabling pim is a way to avoid to receive multicast frames in combination with RGMP on the LAN switch that connects this router to other ones.

Or in the LAN switch you should use IGMP snooping to optimize multicast forwarding on the VLAN (or the older CGMP but requires cooperation with a multicast enabled switch)

An easy solution could be an input ACL where you deny traffic with a multicast destination but I'm afraid packets would be still processed by the NIC if received.

The best is the previous one optimize multicast forwarding on the LAN switch

Hope to help



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