[Pkg-utopia-maintainers] Bug#996804: NetworkManager reverts to EUI-64 addresses after Bullseye upgrade

[Michael J. Redd]

Package: network-manager
Version: 1.30.0-2
tags: ipv6

I'm running a Debian system on a LAN segment configured to assign IPv6
addresses via SLAAC. After upgrading from Buster to Bullseye,
NetworkManager starts the system with an IPv6 stable-privacy address as
usual. However, after some time (possibly during address renewal), a
standard EUI-64 address with the "mngtmpaddr" flag is created in
addition and this address takes precedence (i.e. new connections
originate from this EUI-64 address).

The sysctl values for this are, I assume, default, as I have not
changed them:

$ sudo sysctl -a | grep use_tempaddr
net.ipv6.conf.all.use_tempaddr = 0
net.ipv6.conf.default.use_tempaddr = 0
net.ipv6.conf.eno1.use_tempaddr = 0
net.ipv6.conf.lo.use_tempaddr = -1

As is NetworkManager's config:

$ nmcli conn show "Ifupdown (eno1)" | grep addr-gen-mode
ipv6.addr-gen-mode:                     stable-privacy

Restarting the NetworkManager service and bringing the interface down,
then up, resets everything back to the expected stable-privacy
addresses.

In case it could be relevant, the Ethernet controller being used on
this system is an Intel I219-V. The latest point release kernel as of
this writing (5.10.0-9-amd64/5.10.70-1) is also being used.