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

Jen Linkova <> Wed, 30 October 2019 02:57 UTC

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From: Jen Linkova <>
Date: Wed, 30 Oct 2019 13:56:57 +1100
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To: Alexandre Petrescu <>
Cc: "Rajiv Asati (rajiva)" <>, Ted Lemon <>, "" <>
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Subject: Re: [v6ops] out-of-focus: why DHCPv6 breaks Android computers?
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On Wed, Oct 30, 2019 at 5:32 AM Alexandre Petrescu
<> wrote:
> At high level, it makes sense to require to allow simultaneous DHCP and
> SLAAC usage on a same subnet; a private email suggests the same.
> With that, Android and Windows would live ok side-by-side on same subnet.

I'm still not sure I understand why you need DHCP for Windows...Unless
you got that Windows in an antique shop...;)
I have plenty of Windows machines in the network (in an IPv6-only one as well).

> Further, thinking about how to implement the req, one would wonder
> whether the prefix in PIO with A flag set in an RA with M set, would be
> the same as the prefix used by the DHCP Server to form and deliver
> addresses?

> (if yes, I think that is difficult to achieve: (1) difficult to put same
> prefix in the software implementing RA sending, and in the DHCP server
> connfig files

Could you elaborate on this one? How is "putting the prefix in the
software implementing RA sending" different from "configuring a prefix
on a router interface"?
It's like saying 'difficult to configure the same IPv4 or IPv6 prefix
on the router interface and on DHCP server'

>and (2) difficult to make sure the Server does not form an
> address for a Client, address that a Host has already formed in the same
> prefix).

That's could be done to the some degree of confidence - if the pool is
using the first addresses in the prefix (let's say, the highest 50
bits if the interface ID set to 0) then
it's rather unlikely that such interface ID would be generated by SLAAC.
However that's a good point, thanks for another item in my collection
of 'why I don't need DHCPv6' reasons ;))

> (because of that reason, I think that trying to implement that
> requirement would lead to designating a prefix for SLAAC and another
> prefix for DHCP; that may sound a little bit as a waste).

I'm sure operating such a network will

> >> On Oct 29, 2019, at 7:22 AM, Ted Lemon <> wrote:
> >>
> >>  On Oct 29, 2019, at 6:37 AM, Alexandre Petrescu
> >> <
> >> <>> wrote:
> >>> 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.
> >>
> >> That’s the problem.   It should turn on the managed bit but not
> >> turn off the autonomous bit.  The two can validly be on at the
> >> same time.
> >>
> >> Of course, since their meanings are deprecated, it’s not too
> >> surprising that implementations get this wrong.
> >>
> >> _______________________________________________ v6ops mailing list
> >>
> _______________________________________________
> v6ops mailing list

SY, Jen Linkova aka Furry