Duplicate mac address on cisco switch

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What Happens when there are duplicate MAC Addresses. How many MAC Addresses can a Switch learn?

Did you mean:. All community This category This board. Ranil Herath. MAC Address duplicates.

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Hi All, We have a 5-member Cisco x switch stack. Wonder if anyone could shed some light on this. Very much appreciate your help. Thanks in advance. Ranil Solved! Labels: Other Switching. I have this problem too. Accepted Solutions. Mark Malone. VIP Mentor. It's not meant to prevent unauthorized devices to be connected to a RJ45 socket aka Ethernet port. Normally you configure the RJ 45 sockets in your office that are terminated on a Patch Panel and connected to the switch to allow a certain amount of MAC the given port can learn before taking any action protect, restrict, shutdown.

In doing so you're preventing from a possible MAC overflow attack's that can be executed against your switch. Again it's my personal opinion the question doesn't make much sense. If you can prove there's a real life reason why you would even care of configuring it that way, let me know.


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  6. You probably will want to look into port-security sticky dynamically learns the MAC then configure aging to age out old MAC Addresses on each interface. You wont be able to have port security configured and at the same time allow a MAC to move from interface to interface without problems.

    Re: duplicate mac address switchport

    As stated above, it defeats the purpose of port-security. When you set your aging parameters you have several options, you can have it based on time, or type, or statically set:.

    Like Ron says in his response, you will want to have port-security to dynamically learn sticky the MAC addresses, possible set a max amount to learn on each interface, and configure the aging parameters to what best suits you. If traffic with a secure MAC address that is configured or learned on one secure port attempts to access another secure port in the same VLAN, applies the configured violation mode. The MAC address table of the switch will only allow a single MAC address on a single port so that it knows, in a deterministic manner, to which port it should send traffic with that destination address.

    MAC address spoofing is an attack which will cause disruption by bouncing the MAC address table among two or more ports. Port security can be used without specifying exact MAC addresses. A port can dynamically learn a MAC address, and keep it on that port for a specified time period.

    Cisco has documents which explain port security in detail, e. Chapter: Port Security :. You can use port security with dynamically learned and static MAC addresses to restrict a port's ingress traffic by limiting the MAC addresses that are allowed to send traffic into the port.

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    List all learned mac addresses on interface/port | Ubiquiti Community

    When you assign secure MAC addresses to a secure port, the port does not forward ingress traffic that has source addresses outside the group of defined addresses. Commented: The order Look at the conf for the MAC that it has assigned. If not then look for a duplicate MAC address are you moving this device from one location to another?

    If these are VM servers which sounds like they might be if they are triggering your err-disable state on the switch port. The sticky commands means the switch-port will learn what MAC address is connected to that port and will write it into its running configuration.

    Its a way to have the switch automatically add the MAC address of the device connected without specifying it manually. The default action of port-security is set to disable you can set this to restrict as well. Author Commented: I'll have to double check. That makes sense, and is something I'll check on. Is there ever a need to clear ARP or anything else?

    Learn More! Good info Smitty, but these were stand-alone servers. I'm thinking the MAC address specified on another switchport is the problem.