This IPv6 address will be used as a secret to generate IPv6 addresses for link-local addresses and autoconfigured ones. All addresses generated after setting this secret will be stable privacy ones by default. This can be changed via the addrgenmode ip-link. conf/default/stable_secret is used as the secret for the namespace, the interface specific ones can overwrite that. Writes to conf/all/stable_secret are refused.
It is recommended to generate this secret during installation of a system and keep it stable after that.
By default the stable secret is unset.
Nb: per interface setting (where “interface” is the name of your network interface); “all” is a special interface: changes the settings for all interfaces.source