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New Member

Span/Monitor on 3750 Missing IGMP Packets


I have been monitoring a client attached to a port on a 3750 using Span monitor. The client is recieving multicast stream from a server. IGMP is used to control this stream between the client and the router and the switch is doing IGMP snooping. The client is the only client there are no others on the switch. I am trying to monitor the IGMP between the router and client by using span/monitor of the client port, but when I do this I see IGMP Packets from the router but none from the clien although I know the client is sending them because I also have ethereal running on the client. Can anyone shed any light on this why span/monitor does not see the igmp packets from the client?

m/cast client----3750----router-----m/cast server


Re: Span/Monitor on 3750 Missing IGMP Packets

is your multicast server on a different subnet/vlan as the sourcePort you are using for SPAN?

if so, this traffic will not be monitored by SPAN.

only traffic that enters/leaves sourcePorts or sourceVLANs can be monitored. if monitoring incoming traffic, any traffic that gets routed from another vlan to the sourceVLAN will not be monitored.

see this link for more info:

New Member

Re: Span/Monitor on 3750 Missing IGMP Packets

Hi, yes my m/cast server is on the far side of a mpls network, but really it is not these packets i want to see rather i want to see igmp join and leave conversation between m/cast client and router, this i am not picking up.