Folks, After over 10 (yes, *ten*) years, we have finally addressed security/privacy issues in the generation of IPv6 stable addresses in most popular operating systems. The traditional scheme/algorithm to generate stable IPv6 addresses with SLAAC required that the underlying MAC address be employed to generate the Interface Identifier. That is, the underlying MAC address would be embedded in the lower bits of an IPv6 address. This scheme allowed for host-tracking (since MAC addresses are usually globally-unique), address scanning (since addresses will follow specific patterns) and a number of other issues. In 2011, I submitted an IETF Internet-Draft proposing a scheme for generating stable addresses with SLAAC, meant to replace the traditional scheme. The scheme could be summarized and simplified as: Interface_ID = Hash(Prefix, Secret). Thus, interface identifiers would be stable within the same subnet, but vary across subnets. [Replacing the traditional scheme with this new scheme was anything but easy -- if you're curious, please check the "IPv6 Addressing" section in <https://www.si6networks.com/2020/08/06/a-brief-history-of-recent-advances-in-ipv6-security-part-i/> ] Over time, popular operating systems and packages adopted the proposed algorithm: the Linux kernel, NetworkManager, OpenBSD's slaacd, MacOS, etc. Eventually, virtually every popular OS had adopted the scheme.... except Windows. Based on a recent note by Brian Carpenter, I ended up testing Windows 11, and I can confirm that it does implement RFC 7217 / RFC 8064! Therefore, e.g. if multiple prefixes are employed on a subnet, the stable addresses for each of such prefixes will employ a different Interface Identifier, thus avoiding the security/privacy issues discussed above -- this is really good news! Unfortunately, Windows still generates temporary addresses with the algorithm specified in RFC 4941, thus resulting in all temporary addresses for a given interface employing the same Interface Identifier (!). This problem has been addressed in RFC 8981... but it's implementation is not yet widespread, yet (it has been incorporated in e.g. the Linux kernel, though). I just hope it doesn't take Windows and others yet another 10+ years to implement RFC 8981, to finally address the remaining security/privacy issues in IPv6 address generation! [Original article with screenshots: https://www.linkedin.com/posts/fernandogont_after-over-10-yes-ten-years-we-h... ] Thanks! Regards, -- Fernando Gont SI6 Networks e-mail: fgont@si6networks.com PGP Fingerprint: F242 FF0E A804 AF81 EB10 2F07 7CA1 321D 663B B494