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Re: problem statement [was Re: New Version Notification for draft-hinden-ipv4flag-00.txt]

Brian E Carpenter <brian.e.carpenter@gmail.com> Wed, 22 November 2017 02:32 UTC

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Subject: Re: problem statement [was Re: New Version Notification for draft-hinden-ipv4flag-00.txt]
To: David Farmer <farmer@umn.edu>
Cc: Nick Hilliard <nick@foobar.org>, Lorenzo Colitti <lorenzo@google.com>, IETF IPv6 Mailing List <ipv6@ietf.org>
References: <151090059151.22321.3357672601322845792.idtracker@ietfa.amsl.com> <E838C63E-7612-4AA4-9375-854C184D699E@gmail.com> <CAFU7BAQKoWPcEFQZgU3k_d0gUL4en6d2pyNq1V4RMNZ6HrSG8w@mail.gmail.com> <649be36e-5006-7688-448f-bc2794d6a39c@gmail.com> <CAKD1Yr3WC+vwL_=0PeiJ_D85NqFVTCkb8c83x-ZtGhAbSELGMA@mail.gmail.com> <5A119443.2030108@foobar.org> <CAFU7BASwgLfkO-4kk9-vba_P+jmcFHD5+Hy_7b3cnNkOSv30wg@mail.gmail.com> <CAKD1Yr3pKk22Hkxy4_8YMZYiA4Wwp=6JzdRDKFGdTY1gf=ntfA@mail.gmail.com> <alpine.DEB.2.20.1711200848390.32099@uplift.swm.pp.se> <5A12FBE4.9030101@foobar.org> <alpine.DEB.2.20.1711210647151.32099@uplift.swm.pp.se> <5A144A78.6060108@foobar.org> <CAKD1Yr3oQvkSX7ARxfGQVg08=-PTKRFPg1wz_zUKSSAHmMbyMA@mail.gmail.com> <5A14A9A1.5020803@foobar.org> <ea9f56bb-2334-5a5a-9026-d45c74b41d4b@gmail.com> <CAN-Dau0TfDedocjOTkaoiHxDQNemCbTY9Q1in1wqHGoMdYdnHQ@mail.gmail.com>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Wed, 22 Nov 2017 15:32:27 +1300
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On 22/11/2017 13:42, David Farmer wrote:
> On Tue, Nov 21, 2017 at 6:15 PM, Brian E Carpenter <
> brian.e.carpenter@gmail.com> wrote:
> 
>> On 22/11/2017 11:33, Nick Hilliard wrote:
>>> Lorenzo Colitti wrote:
>>>> On Wed, Nov 22, 2017 at 12:47 AM, Nick Hilliard <nick@foobar.org>
>> wrote:
>>>>> There would also be a requirement
>>>>> for the network edge to be able to filter out RAs with this option,
>>>>
>>>> Why is it not sufficient to configure the routers that emit the RAs?
>>>
>>> because you're assuming congruity between ipv4 and ipv6 connectivity on
>>> a network, which is not codified in any ietf document that I'm aware of.
>>>  If there is a incongruity between management of the two protocols, then
>>> the l2 network must have a mechanism to stop an ipv6 gateway from
>>> attempting shutting down ipv4 services.
>>
>> This is a very interesting point. If every IPv6 router on a link believes
>> there is no IPv4 router/DHCP service, they would all send flag==1 in the
>> proposed solution. So the proposal only works if at least one IPv6 router
>> is colocated with an IPv4 router, and therefore knows to send flag==0.
>> Oops.
>>
> 
> This is a problem only if the flag is set automatically and their is no
> mechanism to override the automatic setting.  Most routers with an IPv6
> address configured on an interface by default will send an RA unless you
> configure them not to.  So, an IPv6 router without IPv4 configured on the
> interface should set this flag, unless configured otherwise.  In other
> words you need to be able to tell an IPv6 router there is IPv4 on the
> interface even if router is not providing it.
> 
> It is quite possible that the IPv6 topology is incongruous from the IPv4
> topology, however it is doubtful than the management is also incongruous.

Yes, but do you think we should push a mechanism that assumes correct
configuration by humans in order to work reliably? 
(Arguing against my own proposal, not for the first time ;-).

     Brian

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