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Port security Violation, unknown MAC Address


I have a question regarding a MAC address that popped up twice on two different switches on our network; the MAC address is 7e77.3777.5776. We have setup port security on all our switches, allowing only two MAC Addresses per port. One for an IP phone and the other for machine.

When the violation occurred on two different occasions, I checked the last MAC Addressed that tried to access those ports and it turned out to be the same MAC address of 7e77.3777.5776. This MAC address can't be traced, I know the two people who are connected to those ports didn't try to connect any other machine to their port.

Would I be right to say that someone is using a spoofed MAC address? I believe it's not a physical connection. Someone else on this forum posted the very same question in 2011, and what's bizarre that he had the same problem with the very same MAC address.

Here's the link to his question posted on this forum:

His question wasn't answered, is this a known bug with Catalyst switches? The switches we have are 3560G and SW version on them is 15.2(SE5). Please help, 'cause it'd driving me crazy. Thank you

4 Replies 4



paul driver
VIP Expert VIP Expert
VIP Expert



For the time being you can prohibit any use of this mac address using a filer

mac address-table static 7e77.3777.5776 vlan xx drop




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Kind Regards

Paul, that is a good suggestion but would I be able to catch it again popping up as port security violation? 'cause if I can't then I would do it later. As I would like to know from where did MAC Address originated from? Could it be traced? Should I dare and think that we could be victim of ARP Poisioning? Is MAC Address Spoofing possible with Port Security enabled on all switches?

Any suggestion would be good. Thank you for responses



I do also happened the same with a network point and place the mac as drop and so far has not been blocked port:

WS-C2960X-48FPD-L  15.0(2)EX5            C2960X-UNIVERSALK9-M

mac address-table static 7e77.3777.5776 vlan xx drop

mac address-table static 7e77.377a.57d6 vlan xx drop



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