IPV6 addresses

Colin Watson cjwatson at ubuntu.com
Mon Jun 25 10:43:54 UTC 2018

On Mon, Jun 25, 2018 at 11:09:43AM +0100, Colin Law wrote:
> When I run ifconfig on an 18.04 machine which has been upgraded over
> several versions I see an IPV6 address generated from the MAC address
> of the form
> fe80::xxxx:xxff:fexx:xxxx
> which has been generated using the technique in
> http://www.sput.nl/internet/ipv6/ll-mac.html.
> On another machine with a fresh install, however, the fe80:: address
> does not have any obvious relationship to the MAC address and has not
> got ff:fe at the appropriate place. I deduce from this that there
> other allowed techniques for generating the address but I can't find
> any reference to them anywhere.  Can anyone elucidate?

That sounds like IPv6 privacy extensions (RFC 4941).  The addresses in
question will be generated randomly.  You can configure privacy
extensions in network-manager.

As I understand it there isn't much particular benefit in having privacy
extensions cover link-local addresses, except maybe simplifying the
address allocation code (but I'm guessing here).  On the other hand
link-local addresses are only rather rarely useful anyway, so ...

Colin Watson                                       [cjwatson at ubuntu.com]

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