Re: [PATCH] net: ipv6: don't generate link-local address in any addr_gen_mode

From: Rocco Yue
Date: Tue Jul 06 2021 - 08:52:30 EST

On Mon, 2021-07-05 at 10:35 -0600, David Ahern wrote:
> On 7/1/21 2:51 AM, Rocco Yue wrote:
>> On Wed, 2021-06-30 at 22:41 -0600, David Ahern wrote:
>> 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
>> 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
> the ones used for RAs, so add something like:
> to in6_addr_gen_mode.

Hi David,

Thanks for your reply.

According to your suggestion, I checked the ipv6 code again. In my
opinion, adding another addr_gen_mode may not be suitable.

In the user space, the process enable the ipv6 stable privacy mode by
setting the "/proc/sys/net/ipv6/conf/<iface>/stable_secret".

In the kernel, the addr_gen_mode of a networking device is switched to
IN6_ADDR_GEN_MODE_STABLE_PRIVACY by judging the bool value of

So, although adding an additional IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
user space process has some trouble to let kernel switch the iface's

This is not as flexible as adding a separate sysctl.

After adding "proc/sys/net/ipv6/<iface>/disable_gen_linklocal_addr",
so that kernel can keep the original code logic of the stable_secret
proc file, and expand when the subsequent kernel adds a new add_gen_mode
more flexibility and applicability.

And we only need to care about the networking device that do not
generate an ipv6 link-local address, and not the addr_gen_mode that
this device is using.

Maybe adding a separate sysctl is a better choice.
Looking forward to your professional reply again.