Re: [v6ops] out-of-focus: why DHCPv6 breaks Android computers?

Alexandre Petrescu <alexandre.petrescu@gmail.com> Tue, 29 October 2019 10:37 UTC

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To: Jen Linkova <furry13@gmail.com>
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From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Subject: Re: [v6ops] out-of-focus: why DHCPv6 breaks Android computers?
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Le 29/10/2019 à 01:18, Jen Linkova a écrit :
> On Mon, Oct 28, 2019 at 8:47 PM Alexandre Petrescu 
> <alexandre.petrescu@gmail.com>; wrote:
>> Why the presence of a DHCPv6 server breaks Android computers?
>> 
>> On my CPE at home, of ISP Free, I noticed recently this message: 
>> 'Watch out: if you activate the DHCPv6 server, certain Android 
>> computers are at risk of loosing their IPv6 connection'.
>> 
>> Why and how the presence of a DHCPv6 server on the CPE breaks 
>> Android computers?
> 
> The presence of DHCPv6 should not break Android devices (have not 
> seen it before).

I may have not used the right word 'break'; a more conforming
translation is 'loose their IPv6 connection'.

While trying, that is what seem to happen: when turning on DHCPv6 server
on the CPE the Android stops browsing ipv6.google.com. (it could browse
when it was off).

Remark, under same conditions, my Windows PC resists well this flipping
of the DHCPv6 Server on CPE - it continues browsing ipv6.google.com
after the flipping.

> Try it and see what happens?

Thanks, I did learn a few things while trying.

> The only theory I have is that by 'activating DHCPv6'  your CPE 
> actually means 'disabling SLAAC'. Then yes, it would break things.

Well no.  After  activating DHCPv6 on CPE the CPE sent three RAs
changing the Lifetime and flipping the M(anaged) and A(utonomous) flags.

Packet dumps available upon request.

>> I would like to try this DHCPv6 server to connect my Windows 2-in-1
>> computer to work at home,
> 
> Get the Creator update ;) Then it would work with RDNSS ;)

Well, I have Windows 10 latest version (not Creator), but it seems to
work ok.

The RDNSS option is present already in the RAs sent by the CPE.  But I
do not understand why would one suggest the use of RDNSS could solve
this problem.

Alex

>