Re: Problem with IPv6 privacy addresses in 7.0

On Wed, 27 May 2026 23:59:47 +0200 Fernando Fernandez Mancera wrote:

On 5/27/26 11:51 PM, Chris Adams wrote:

quoted

Once upon a time, Jakub Kicinski [off-list ref] said:  

quoted

Sounds plausible, pretty sure we knew this commit was risky to begin
with, but we had no direct proof that it'd break real life users.

Revert is the right course of action here. Would you be willing/able
to send the revert with your problem description and a Fixes tag
pointing to the reverted commit?  

I did want to add a little more test note:

It's definitely an interaction with NetworkManager.  If I stop NM and
run my VM start/stop test, nothing unexpected happens after.  If NM is
running and I do my VM test, when the next router advertisement is
received, NM replaces the privacy addresses.
  

As someone that is experienced in NetworkManager, I can confirm it is 
related. NetworkManager is querying the IPv6 address and when the 
connection is configured with ipv6.ip6-privacy=2 (prefer-temp-addr), 
NetworkManager creates a route to make the system use the temporary 
address for outgoing connections by default.

If the order is messed up, the address picked will likely be too. One 
could argue that this is partially fault of NetworkManager and that it 
should check the timestamps or preferred times rather than order.. but 
well, the rule is "do not break userspace".

Right, plus the justification for the change wasn't very strong 
in the first place. My internal compass is still pointing towards
a revert.

I hope this clarifies things.