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If I was to use the same mac address as another device on the same network (wifi), at different times (one after the other). Would the devices for the network experience any problems, glitches or failure, while or after using the same mac address? I would be cloning the mac address from one of the devices.

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  • ARP caching might be problematic, depending on how long that lasts and how closely the two different hosts reuse the same MAC. – thrig Aug 24 '15 at 21:23
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    The MAC address table on your switches might prove problematic as well, dependent upon whether or not the two devices are connected to the same switch port or to different switch ports. – joeqwerty Aug 24 '15 at 21:26
  • Entirely depends on the network and how it is configured, especially with regards to security. For instance, if there is any sort of policy based decisions based on the platform (newer BYOD type setup where laptop may be treated one way and your smart phone anohter), this may create all sorts issues and get one or both devices flagged. – YLearn Aug 25 '15 at 0:34
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As long as the two devices are not active at the same time, then it won't be a problem. How quickly the network realizes that the MAC address has moved from one device to the other depends on the specific implementation of the switches used in the network as well as on the traffic patterns.

In principle what you describe would look the same to the network as if you unplugged the device from one location in your network and plugged it in another location.

If you are using WiFi you need to be aware that many WiFi drivers don't support changing the MAC address like you describe. Most drivers for wired Ethernet do support it.

After the MAC address was moved from one device to the other, the device which just got the MAC address should send a single broadcast packet to the network in order to ensure that all switches on the network have updated their CAM table.

Neighbor caches on various devices on the network map from IP address to MAC address. This means that all packets to the IP addresses assigned to the network interface where you have been using the MAC address will now be send to the device which took over the MAC address.

You better ensure that the device which took over the MAC address is prepared to handle traffic to all IP addresses which the previous device mapped to the MAC address. If you are implementing a failover solution, then this behavior would be considered a useful feature. If you are not implementing a failover solution, then it is most likely a mistake to use the same MAC address on two devices.

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