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

[Mark Smith]

Hi Lorenzo,

On Mon, 13 Sept 2021 at 19:38, Lorenzo Colitti <lorenzo at google.com> wrote:
>
> On Mon, Sep 13, 2021 at 12:47 AM Mark Smith <markzzzsmith at gmail.com> wrote:
> > This is all going in the wrong direction. Link-local addresses are not
> > optional on an interface, all IPv6 enabled interfaces are required to
> > have one:
>
> The original patch did indeed disable the generation of the link-local
> address, but that patch was rejected. It sounds like the right
> approach here is to provide two new addressing modes:
>
> IN6_ADDR_GEN_MODE_RANDOM_LL_TOKEN
> IN6_ADDR_GEN_MODE_STABLE_PRIVACY_LL_TOKEN
>
> which would form the link-local address from the token passed in via
> IFLA_INET6_TOKEN, but would form non-link-local addresses (e.g.,
> global addresses) via the specified means (either random or stable
> privacy). I haven't looked at how to do that yet though.

I think there is a broader issue here.

If RFC7217 is used to generate the Link-Local address, then the
likelihood of the Link-Local address being a duplicate with the GGSN
is very low, because RFC7217 uses a function such as SHA-1 or SHA-256.
RFC7217 also performs DAD just in case, and triggers RFC7217 again if
a duplicate does occur.

RFC8064 recommends RFC7217 for all stable IPv6 addresses by default
now, which includes Link-Local addresses.

Following RFC8064 by Implementing RFC7217 for all stable IPv6
addresses the Linux kernel generates would solve both the 3GPP's
duplicate Link-Local address concern, and also make the Linux kernel
compliant with the latest SLAAC recommendation for default IIDs and
stable IPv6 addresses.

Regards,
Mark.