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

Alexandre Petrescu <alexandre.petrescu@gmail.com> Tue, 29 October 2019 18:32 UTC

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From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
To: "Rajiv Asati (rajiva)" <rajiva@cisco.com>, Ted Lemon <mellon@fugue.com>
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Date: Tue, 29 Oct 2019 19:32:09 +0100
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Subject: Re: [v6ops] out-of-focus: why DHCPv6 breaks Android computers?
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Le 29/10/2019 à 13:38, Rajiv Asati (rajiva) a écrit :
> 
> Indeed. CPE router should allow keeping both M and A flags, to allow 
> simultaneous usage of DHCPv6 and SLAAC by the hosts.

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.

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 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).

(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).

Alex

> 
> About time to update RFC7084 - 
> https://tools.ietf.org/html/rfc7084#section-4.3
> 
> 
> 
> Cheers, Rajiv
> 
> 
>> On Oct 29, 2019, at 7:22 AM, Ted Lemon <mellon@fugue.com>; wrote:
>> 
>>  On Oct 29, 2019, at 6:37 AM, Alexandre Petrescu 
>> <alexandre.petrescu@gmail.com 
>> <mailto:alexandre.petrescu@gmail.com>> 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.
>> 
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