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To instantly change your Network interface card’s (NIC) MAC Address or Physical Address on a freeBSD system the command to use is:
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ifconfig rl0 link f5:9a:f5:ed:b1:ab |
where rl0 is the NIC whose Physical address will be changed. This will change back to its original Physical Address when the system reboots.
To change the Physical Address of rl0 every time the system boots you need to open rc.conf (/etc/rc.conf) and add the following lines:
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ifconfig_rl0_alias0="link f5:9a:f5:ed:b1:ab" |
Good luck! 
