linux-kernel - Re: [PATCH net-next] ipv6: don't generate link-local addr in random or privacy mode

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Date:   Wed, 17 Nov 2021 01:50:54 -0800
From:   Maciej Żenczykowski <maze@...gle.com>
To:     Lorenzo Colitti <lorenzo@...gle.com>
Cc:     Rocco Yue <rocco.yue@...iatek.com>, dsahern@...il.com,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, rocco.yue@...il.com,
        chao.song@...iatek.com, yanjie.jiang@...iatek.com,
        kuohong.wang@...iatek.com, Zhuoliang.Zhang@...iatek.com,
        markzzzsmith@...il.com
Subject: Re: [PATCH net-next] ipv6: don't generate link-local addr in random
 or privacy mode

> Can't 4 be the same as 3? The same netlink message can configure both
> the addr_gen_mode and the token, no?
>
> It seems to me that the following should work, and would be much simpler.
>
> 1. Bring the interface down. All addresses are deleted.
> 2. Send a netlink request to set addr_gen_mode RANDOM_LL_TOKEN or
> PRIVACY_LL_TOKEN and set the token.
> 3. Bring the interface up. Autoconf runs. The link-local address is
> generated from the token. An RS is sent. When the RA is received, the
> global address is generated using RFC 7217 or randomly.

Could you simply manually add an ipv6 link local address to the
interface while it is down (ip -6 addr add fe80::..../64 dev X), then
bring the interface up (ip link set dev X up)...
All that would need to happen is the automatic link local generation
would need to be suppressed if there's already a link local ip
configured - which sounds like a good idea anyway, since why have two?
(btw. even a manually added link local ip will get deleted when the
interface gets brought back down)