Comment by ectospheno

I suppose I could have said how.

Windows in powershell:

  SetNetIPv6Protocol -UseTemporaryAddresses Disabled
  SetNetIPv6Protocol -RandomizeIdentifiers Disabled

Linux:

  sysctl net.ipv6.conf.all.use_tempaddr=0

or in NetworkManager config file:

  ip6-privacy=0

OpenBSD:

  ifconfig em0 inet6 -temporary