push apps failing in Android until you disable IPv6

[Erik Kline]

All true.

I forgot to say that we've seen (years ago) routers than announced
2001:db8::/something, and if this were doing such a thing that could
lead to this situation.

On 9 May 2016 at 18:17, Tore Anderson <tore at fud.no> wrote:
> * Erik Kline <ek at google.com>
>
>> If this router were to send out an RA advertising itself as a default
>> router in this configuration that would probably cause the symptoms
>> you're seeing.  That's why I asked for a sample of any RAs seen on
>> such a network.  (Such a configuration would of course be broken,
>> effectively requiring Happy Eyeballs to function at all.)
>
> Assuming the source address selection is implemented in a sane way,
> just having a an IPv6 default router doesn't on its own explain the
> symptoms described. IPv4 should be preferred due to the Android device's
> link-local address not having the same scope as the IPv6 address of the
> web site or whatever. See RFC6724 sections 5 and 6, rule 2.
>
> The RA would have to additionally contain a PIO with global scope, as I
> understand it. Then you'd certainly get in trouble (disregarding Happy
> Eyeballs). Even a ULA PIO could be problematic if Android's source
> address selection algorithm isn't updated to RFC6724 defaults. RFC3484
> predates ULAs, so it treats them the same as other globally scoped
> addresses.
>
> Tore