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Subject: Re: [PATCH] net: ipv6: don't generate link-local address in any
 addr_gen_mode
To:     Rocco Yue <rocco.yue@mediatek.com>
Cc:     "David S . Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com,
        rocco.yue@gmail.com, chao.song@mediatek.com,
        kuohong.wang@mediatek.com, zhuoliang.zhang@mediatek.com
References: <46a9dbf2-9748-330a-963e-57e615a15440@gmail.com>
 <20210701085117.19018-1-rocco.yue@mediatek.com>
From:   David Ahern <dsahern@gmail.com>
Message-ID: <62c9f5b7-84bd-d809-4e33-39fed7a9d780@gmail.com>
Date:   Mon, 5 Jul 2021 10:35:00 -0600
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On 7/1/21 2:51 AM, Rocco Yue wrote:
> On Wed, 2021-06-30 at 22:41 -0600, David Ahern wrote:
>> On 6/30/21 9:39 PM, Rocco Yue wrote:
>>>
>>> Hi David,
>>>
>>> Thanks for your review.
>>>
>>> This patch is different with IN6_ADDR_GEN_MODE_NONE.
>>>
>>> When the addr_gen_mode == IN6_ADDR_GEN_MODE_NONE, the Linux kernel
>>> doesn't automatically generate the ipv6 link-local address.
>>>
>>
>> ...
>>
>>>
>>> After this patch, when the "disable_gen_linklocal_addr" value of a device
>>> is 1, no matter in which addr_gen_mode, the Linux kernel will not automatically
>>> generate an ipv6 link-local for this device.
>>>
>>
>> those 2 sentences are saying the same thing to me.
>>
>> for your use case, why is setting addr_gen_mode == 1 for the device not
>> sufficient?
>>
> 
> For mobile operators that don't need to support RFC7217, setting
> addr_gen_mode == 1 is sufficient;
> 
> But for some other mobile operators that need to support RFC7217, such as AT&T,
> the mobile device's addr_gen_mode will be switched to the
> IN6_ADDR_GEN_MODE_STABLE_PRIVACY, instead of using IN6_ADDR_GEN_MODE_NONE.
> The purpose is: in the IN6_ADDR_GEN_MODE_STABLE_PRIVACY mode, kernel can
> gererate a stable privacy global ipv6 address after receiveing RA, and
> network processes can use this global address to communicate with the
> outside network.
> 
> Of course, mobile operators that need to support RFC7217 should also meet
> the requirement of 3GPP TS 29.061, that is, MT should use IID assigned by
> the GGSN to build its ipv6 link-local address and use this address to send RS.
> We don't want the kernel to automatically generate an ipv6 link-local address
> when addr_gen_mode == 2. Otherwise, using the stable privacy ipv6 link-local
> address automatically generated by the kernel to send RS message, GGSN will
> not be able to respond to the RS and reply a RA message.
> 
> Therefore, after this patch, kernel will not generate ipv6 link-local address
> for the corresponding device when addr_gen_mode == 1 or addr_gen_mode == 2.
> 

I think another addr_gen_mode is better than a separate sysctl. It looks
like IN6_ADDR_GEN_MODE_STABLE_PRIVACY and IN6_ADDR_GEN_MODE_RANDOM are
the ones used for RAs, so add something like:

IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
IN6_ADDR_GEN_MODE_RANDOM_NO_LLA,

to in6_addr_gen_mode.