Re: [PATCH v2 net] ipv6: addrconf: fix Juniper SSL VPN client regression

From: Bjørn Mork <bjorn@mork.no>
Date: Mon, 11 Jul 2016 16:43:50 +0200

The Juniper SSL VPN client use a "tun" interface and seems to
be picky about visible changes.to it. Commit cc9da6cc4f56
("ipv6: addrconf: use stable address generator for ARPHRD_NONE")
made such interfaces get an auto-generated IPv6 link local address
by default, similar to most other interface types. This made the
Juniper SSL VPN client fail for unknown reasons.

Fixing this regression by adding a new private netdevice flag
which disables automatic IPv6 link local address generation, and
making the flag default for "tun" devices.

Setting an explicit addrgenmode will disable the flag, so userspace
can choose to enable automatic LL generation by selecting a suitable
addrgenmode.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=121131
Fixes: cc9da6cc4f56 ("ipv6: addrconf: use stable address generator for ARPHRD_NONE")
Reported-by: Valdis Kletnieks <redacted>
Reported-by: Jonas Lippuner <redacted>
Suggested-by: Hannes Frederic Sowa <redacted>
Cc: 吉藤英明 <redacted>
Signed-off-by: Bjørn Mork <bjorn@mork.no>

What really irks me is that we "fixing" something without knowing what
actually is the problem.

Someone needs to figure out exactly what is making the Juniper thing
unhappy.  It really shouldn't care if a link local address is assigned
to the tun device, this is fundamental ipv6 stuff.