Re: [PATCH net-next v2 2/4] net: ipv6/addrconf: clamp preferred_lft to the minimum required

[Jiri Pirko <jiri@resnulli.us>]

Tue, Oct 24, 2023 at 11:23:08PM CEST, alexhenrie24@gmail.com wrote:
>If the preferred lifetime was less than the minimum required lifetime,
>ipv6_create_tempaddr would error out without creating any new address.
>On my machine and network, this error happened immediately with the
>preferred lifetime set to 1 second, after a few minutes with the
>preferred lifetime set to 4 seconds, and not at all with the preferred
>lifetime set to 5 seconds. During my investigation, I found a Stack
>Exchange post from another person who seems to have had the same
>problem: They stopped getting new addresses if they lowered the
>preferred lifetime below 3 seconds, and they didn't really know why.
>
>The preferred lifetime is a preference, not a hard requirement. The
>kernel does not strictly forbid new connections on a deprecated address,
>nor does it guarantee that the address will be disposed of the instant
>its total valid lifetime expires. So rather than disable IPv6 privacy
>extensions altogether if the minimum required lifetime swells above the
>preferred lifetime, it is more in keeping with the user's intent to
>increase the temporary address's lifetime to the minimum necessary for
>the current network conditions.
>
>With these fixes, setting the preferred lifetime to 3 or 4 seconds "just
>works" because the extra fraction of a second is practically
>unnoticeable. It's even possible to reduce the time before deprecation
>to 1 or 2 seconds by also disabling duplicate address detection (setting
>/proc/sys/net/ipv6/conf/*/dad_transmits to 0). I realize that that is a
>pretty niche use case, but I know at least one person who would gladly
>sacrifice performance and convenience to be sure that they are getting
>the maximum possible level of privacy.
>
>Link: https://serverfault.com/a/1031168/310447
>Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>

Again, Fixes tag and send to -net tree?