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Webcast-Catalyst9k
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L2 unwanted multicast traffic

I do a show mac in a new Sup2 CatOS 7.6(1) on a 4506 I see some many

ports with Xmit-Multicast equaling about 50% of the traffice. How can I

track down the source. This is only a Layer 2 network, no routers. I am

getting some complaints about Mitel IP Phones cutting in/out that sounds

like lost packets (could be Mitel phone/dsp firmware, but I want my show

mac to be clean before I point to Mitel... Seperately I see show in-lost

and out-lost on almost all the ports, about 5% of traffic.

I plugged into a port and did a sniffer trace. I see multicast traffic with a source of Symbol (we use their wireless phones with Mitel) destination is 01-a0-f8-f0-f0-04. How can I filter multicast from a layer 2 perspective with 4500/6500 switches? There are no routers.

Xmit-Unicast Xmit-Multicast Xmit-Broadcast

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

1/1 2169314 135905 79417

1/2 0 0 0

2/1 0 0 0

2/2 0 0 0

2/3 764136 513832 890126

2/4 &n bsp; 0

0 0

2/5 765068 513831 890126

2/6 0 0 0

2/7 766945 513832 890126

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

3 REPLIES

Re: L2 unwanted multicast traffic

Hello Jason,

Filtering multicasts is something that you do not want to do. In general, they represent a very low volume of the total bandwidth that is available.

One may get a wrong impression about this when a sniffer is attached to a network port where no other host is active. In that case, you only observe bcast, multicast and unknown destination mac adresses. This may seem a large amount of traffic but it is in fact a very little one.

Regards,

Leo

New Member

Re: L2 unwanted multicast traffic

In general I agree, but in this case the multicast traffic across all ports equals about 50% of the unicast traffic, and can't be explained. 50% seems unusual. Why send a broadcast across trunks to hosts that don't need the traffic? Multicast makes switching useless in a layer2 environment. We are back at hubs and bridges..when your hosts are across L3 links multicast is great..

Re: L2 unwanted multicast traffic

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