As most of the ISP now following the MAC base network security, some time you may need to change your mac book/iMac’s ethernet cards MAC address. It’s now too simple on mac os x. just open a terminal and paste this command, and don’t forget to change this command with your correct mac address.
sudo ifconfig en0 ether aa:bb:cc:dd:ee:ff
That’s it. Now check the magic 
That’s really a helpful information. Thanks for sharing
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i tried sudo…but it doesn;t works because i have been asked for the password, which i do not know. because i bought second hand i mac.
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