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RE: Running code (Was: I-D Action: draft-ietf-6man-ipv6only-flag-03.txt)

"Manfredi (US), Albert E" <albert.e.manfredi@boeing.com> Fri, 26 October 2018 18:31 UTC

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From: "Manfredi (US), Albert E" <albert.e.manfredi@boeing.com>
To: Simon Hobson <linux@thehobsons.co.uk>, 6man WG <ipv6@ietf.org>
Subject: RE: Running code (Was: I-D Action: draft-ietf-6man-ipv6only-flag-03.txt)
Thread-Topic: Running code (Was: I-D Action: draft-ietf-6man-ipv6only-flag-03.txt)
Thread-Index: AQHUbJuG2Zjjso5+/km4+87SaUMNqaUwfHjwgAE2LoCAACLHMA==
Date: Fri, 26 Oct 2018 18:31:21 +0000
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References: <CAFU7BASO_ByzbanhLKnWV280O_fASd-8W+ujpj3sN6d2-whw2w@mail.gmail.com> <CACWOCC-u7aAPwAOcixYvt2On=-o_8X25GhqdXTfA+tWRC1o2XA@mail.gmail.com> <3beca72e-19c5-10af-02e5-c21a90d77100@gmail.com> <20181019.223739.271916573.sthaug@nethelp.no> <4f58643c-272e-507e-3282-c87befd42395@gmail.com> <0927741c-4e8e-fcf7-ddd6-3ba500ba4c3d@si6networks.com> <7B48A11D-31DE-443C-B73A-14642EA0A397@jisc.ac.uk> <7526af75-4359-6fc6-e39b-eb94024a04de@si6networks.com> <E1BB1232-C1A2-496A-8157-0682D91EED42@steffann.nl> <5E75F3CA-F1D2-4F4F-9CF7-EEEE59634C1E@gmail.com> <C46C990E-0A4F-4731-8CB1-FD204858935E@consulintel.es> <9B53019C-3506-4C9E-AFCF-D6125FA1A65B@gmail.com> <1157b739-3a66-8d45-e3e1-e5f904dfb9bc@asgard.org> <a00607f9-7ced-f889-b5cb-c2fe16367d73@si6networks.com> <66759b73-0a22-e1a9-49db-21154e8e1267@gmail.com> <37ba23b3-df19-9c2a-bdbe-ba7a99d72d05@si6networks.com> <0d6008a4-337b-2ccb-2d9f-837f786eca65@gmail.com> <bfa4397a-aa7a-1184-4147-4cbfbfd13603@si6networks.com> <8C587906-F0EE-4A61-9046-2BF AC52588C0@isc.org> <E8DE18B5-94FC-411C-A310-E49A382E0079@thehobsons.co.uk> <e0fa8fad1b4249c9af79788323b0a922@boeing.com> <3A03A073-72E2-43A8-90A4-5C29DF445361@thehobsons.co.uk>
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-----Original Message-----
From: ipv6 <ipv6-bounces@ietf.org> On Behalf Of Simon Hobson

>> That's one possible hint. Another, perhaps better one, would for the host to see if it has any IPv4 default router available at all.
>
> A default (or any) router is not needed for IPv4 to be running and needed - so not really a good hint.

Actually, I think that is one of the two best hints. The other one is DNS. Of course, any network which is "IPv6-only" can always have IPv4 islands in it, e.g. for that isolated lab. Bring your own switch(es). That's also true with any flag. You're right, an IPv4 router is not essential, but if not there, if no IPv4 addresses show up from the DNS, then you would naturally try IPv6. If you had not tried IPv6 before all of this.

>> Are any ARP requests ever received from the network?
>
> Like, from all the other nodes trying to see if IPv4 should be used ?

Yeah, I'm with you on this one.

> The problem you have is that you are only considering the sort of network you seem to be familiar with. There are lots and lots of network topologies - some of which are isolated networks with no routers.

And these pose no problem at all. They would exist even if they were connected, and even if all of the IPv6 routers had that IPv6-only flag set. It will always be possible to create such IPv4 networks that have no DNS and no routing.

If I were to design a heuristic, at a time when IPv4 is actually being sunset, I would have the host always try IPv6 first. If it works, don’t even try IPv4. You try IPv4 only if IPv6 doesn’t work, or doesn’t work for a particular destination.

> There may (actually, almost certainly will) be devices on the network that won't be trying to turn off IPv4.

That's why it's best to use the network's equipment in the heuristic. Default routers and DNS being good bets, DHCP being a secondary choice, not so good. And, if you always try IPv6 first, and have success, you'll never even attempt to use IPv4.

>> So, put the onus on the equipment vendors, in case the netadmin wants to shut off IPv4, to determine how to proceed.
>
> That's the surest way to guarantee failure. Without a standard to work to, you will get zero or more different ways - and if more than zero, then guaranteed interoperability issues.

And yet, this is the way it works for many potential network malfunctions. What Windows does is not the same as what Linux might do.

Bert

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