The IPV6 protocol has a feature called "Extended Unique Identifier" or EUI-64 witch in short uses the MAC address of the network card when choosing an IPV6 Adress.

Proof: http://www.youtube.com/watch?v=30CnqRK0GHE&NR=1 at 7:36 video time.

If you want to be anonymous on the internet (so that nobody can find you when you download something, etc.) you need this EUI-64 to be bipassed in order for the MAC address not to be discovered by harmful third parties on the internet and for privacy.

How do you avoid EUI-64 MAC address usage in IPV6 selection in Ubuntu? Also for DHCP IPV6?


Omitting the MAC address improves your privacy, but it doesn't "make you anonymous". Every (IPv4 or IPv6) network still has a unique prefix, otherwise you wouldn't be able to receive any packets.

In any case, this site shows how to enable the randomized suffix: http://otrs.menandmice.com/otrs/public.pl?Action=PublicFAQ&ItemID=91

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  • Just to "round out" this question, would using a spoofed MAC (ifconfig hw ether on NICs that support it for example) along with the rfc4941 extensions enabled further improve privacy or does the IPv6 stack still create the address using the actual NIC's MAC instead of the spoofed one? – bumbling fool Feb 10 '11 at 4:14
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    @bumbling fool It wouldn't increase privacy. Computers outside your LAN never see your MAC (unless it is part of your IP address). MAC addresses are like a computer's name. If you are in a room and someone says your name, it gets your attention and you listen. Computers on a LAN listen for packets with their name and usually ignore the rest. As soon as your traffic is routed (like a person standing in a doorway and passing on a message) your MAC is replaced by the router's MAC and your IP address is used to tell where the traffic should go. MAC spoofing is for being "anonymous" on a LAN only. – Azendale Jul 8 '11 at 4:34
  • Your answer is missing the answer. (i.e. a link-only) – Antti Haapala Feb 18 '17 at 17:16


gksudo gedit /etc/sysctl.conf

Add the following line to the end of the file:


(use the following instead if you want this for all interfaces and are willing to restart)


Save the file and close Gedit.
Run sudo sysctl -p (or if you did the optional part restart).

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