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

Jen Linkova <furry13@gmail.com> Wed, 30 October 2019 04:26 UTC

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From: Jen Linkova <furry13@gmail.com>
Date: Wed, 30 Oct 2019 15:26:15 +1100
Message-ID: <CAFU7BASR5ODRmu-FUK_BREzXEfphN=t2mvmrXt4iXGFP-28sNQ@mail.gmail.com>
To: "Rajiv Asati (rajiva)" <rajiva@cisco.com>
Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>, Ted Lemon <mellon@fugue.com>, "v6ops@ietf.org" <v6ops@ietf.org>
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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 2:35 PM Rajiv Asati (rajiva) <rajiva@cisco.com>; wrote:
> Yes, same prefix can be specified in DHCPv6 server and router RA PIO. If ever a conflict between the IPv6 addresses at a host, then the host could use DAD to resolve the conflict (and recycle the SLAAC derived address). Standard machinery.

Well, I guess the more tricky case is 'a host got an address from
DHCP, DAD is failing because another host already assigned the same IP
(manually or via SLAAC)'. What's next (besides sending DECLINE back to
the server)?
Split-brain condition in address assignments is hard. The more I read
this thread the less I see the point of having DHCPv6 (for address
assignment) when we have SLAAC.

Oh...I think I'm breaking the promise I made to myself ("never get
involved into SLAAC vs DHCP discussion ever') again...;))


> -----Original Message-----
> From: Alexandre Petrescu <alexandre.petrescu@gmail.com>;
> Date: Tuesday, October 29, 2019 at 2:32 PM
> To: Rajiv Asati <rajiva@cisco.com>;, Ted Lemon <mellon@fugue.com>;
> Cc: "v6ops@ietf.org"; <v6ops@ietf.org>;
> Subject: Re: [v6ops] out-of-focus: why DHCPv6 breaks Android computers?
>
>
>
>     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.
>     >>
>     >> _______________________________________________ v6ops mailing list
>     >>  v6ops@ietf.org https://www.ietf.org/mailman/listinfo/v6ops
>
>
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-- 
SY, Jen Linkova aka Furry