Reading sysctl docs, I found the following:

use_tempaddr - INTEGER
    Preference for Privacy Extensions (RFC3041).
      <= 0 : disable Privacy Extensions
      == 1 : enable Privacy Extensions, but prefer public
             addresses over temporary addresses.
      >  1 : enable Privacy Extensions and prefer temporary
             addresses over public addresses.
    Default:  0 (for most devices)
         -1 (for point-to-point devices and loopback devices)

So, when I set the use_tempaddr parameter to 0 , the Privacy Extensions are disabled, which means no temp addresses are used. When set to 2 , the Privacy Extension are enabled, and hence temp addresses are used. But when I set use_tempaddr to 1 the Privacy Extension are enabled but the temp addresses aren't used... So what's the purpose of having the three options, when only two of them make sense? What's the use case for use_tempaddr set to 1 ?

  • you'll probably get some answers with rationalizations for that -- but the long and short of it is that it makes no sense, just like having ipv6 addresses generated from the MAC in the 1st place or keeping the MAC-generated address around ("preferred" or not) when using privacy extensions. You should look into using rfc7217 instead. – Uncle Billy Feb 10 at 8:06
  • from a strictly technical point of view, notice that an application can bind an outgoing socket to any address set on an interface -- the "preferred" option only tells the kernel which local address to use when the app doesn't bind the socket explicitly. – Uncle Billy Feb 10 at 8:11
  • Having the original IPv6 addr makes sense -- ppl from the net can connect to you and they always can connect using the same addr, so you don't have to give it to them each time when you're using Privacy Extensions. – Mikhail Morfikov Feb 10 at 8:17
  • there are such things like dynamic dns ;-) – Uncle Billy Feb 10 at 8:18
  • Why to use it when it works OOTB? – Mikhail Morfikov Feb 10 at 8:28

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