I’m having a problem with multicast causing flapping between a trunk port and an access port.
Switch A is the core (a 4507)
Switch B (a 3850) is trunked to the core with multiple vlans. When I connect a sender and a receiver to switch B, after a little bit, and seemingly at random, I will get a message on the console of switch B saying some mac address on vlan 50 is flapping between the port configured as the trunk and the multicast sender.
On the 4507, vlan 50 has an ip address and is set to pim dense mode
On the 3850, there is also an ip address but no pim
Both switches have the same vlans on the trunk.
There is no physical loop and I can’t figure out what is causing the flapping.
Just wanted to followup and say that while trying to investigate this, the problem sems to have gone away as mysteriously as it started. I'm thinking there was broken switch or some other device plugged in at a users desk that was causing the problem.
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