IPV6 addresses

Colin Law clanlaw at gmail.com
Mon Jun 25 12:34:01 UTC 2018


On 25 June 2018 at 11:43, Colin Watson <cjwatson at ubuntu.com> wrote:
> 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.

I don't think that is it, as far as I can see that is about how to
generate temporary addresses.  I think the fe80 address is a fixed
address automatically generated that can be used for local comms.

Colin



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