Core issue
Packets with a multicast MAC address as the source MAC cause the %SYS-4-P2_WARN: 1/Invalid traffic from multicast source addressmessage to be logged on a Catalyst switch.
Resolution
The following is an example of the syslog output when this error occurs:
%SYS-4-P2_WARN: 1/Invalid traffic from multicast source address 81:00:01:00:00:00 on port 2/1
The Invalid traffic from multicast source address syslog message is generated when the switch receives packets with a multicast MAC address as the source MAC.
Using a broadcast or multicast MAC address as the source MAC for a frame is not standards-compliant behavior. However, the switch still forwards traffic sourced from a multicast MAC address.
The syslog message indicates the multicast MAC address in the source MAC field of the frame, and the port on which the traffic was received.
The workaround is to identify the end station that is generating frames with a multicast source MAC address. Typically, such frames are transmitted from a traffic generator (for example, SmartBits) or third party devices that share a multicast MAC address, such as a load balancing firewall or server product.
Use a sniffer to identify the device generating the frames with multicast MAC addresses as source MAC addresses. This must be done at the time the messages are being logged. Start the trace at the port indicated in the error message.
Error message
%SYS-4-P2_WARN: 1/Invalid traffic from multicast source address
