Problem with IPv6 privacy addresses in 7.0

Problem with IPv6 privacy addresses in 7.0

[Chris Adams]

My normal use of my desktop system (Fedora 43) is to suspend at night
and wake in the morning, and then immediately SSH to my remote server,
where I stay logged in.  I use NetworkManager and have ipv6.ip6-privacy
set to prefer-temp-addr, and SSH configured to use SSH keepalives.

When I upgraded to kernel 7.0, I started having an issue with this - my
SSH session gets dropped, usually several times, in the first hour or
so, then I usually don't have any problem the rest of the day.  If I run
an IPv4 session at the same time, that seems to be fine, so I don't
think it's a network issue (I know that dual-stack doesn't always take
the same path).

What seems to be happening is that privacy addresses are removed while
the SSH session is still using them, before the timeout even.  I wrote a
script to watch public v6 addresses being added and removed, and this is
what I've seen so far today (the number at the end is the valid_lft
seconds), with the public prefix masked:

2026-05-21 07:39:17 removed xx::f4f/128 4673
2026-05-21 07:39:20 added xx::f4f/128 5400
2026-05-21 07:41:20 removed xx:3e8c:f8ff:fe60:1d5a/64 4922
2026-05-21 07:41:20 removed xx:7cb1:c518:1be0:d81d/64 4922
2026-05-21 07:41:23 added xx:3e8c:f8ff:fe60:1d5a/64 5398
2026-05-21 07:41:23 added xx:596a:f6f5:67b2:1d8f/64 5398
2026-05-21 08:14:43 added xx:fac3:61f6:ad18:d712/64 4987
2026-05-21 08:14:43 removed xx:596a:f6f5:67b2:1d8f/64 4991
2026-05-21 08:30:26 added xx:84b4:244e:bb14:94fd/64 5398
2026-05-21 08:30:26 removed xx:fac3:61f6:ad18:d712/64 5120

I woke the system at 07:39:08 and SSHed at 07:39:39, which used the d81d
source address.  That dropped in 2 minutes and I reconnected, which used
the 1d8f address.  That dropped at 08:14:43, I didn't notice right away,
I reconnected at 08:31:28 which used the 94fd address.

-- 
Chris Adams <linux@cmadams.net>