stable_secret IPv6 address

file: /proc/sys/net/ipv6/conf/interface/stable_secret IPv6 address
variable: net.ipv6.conf.interface.stable_secret IPv6 address
Official reference

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.