Re: Objection to draft-ietf-6man-rfc4291bis-07.txt

james woodyatt <jhw@google.com> Fri, 24 February 2017 00:06 UTC

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From: james woodyatt <jhw@google.com>
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Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
Date: Thu, 23 Feb 2017 16:05:57 -0800
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To: Nick Hilliard <nick@foobar.org>
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On Feb 23, 2017, at 15:38, Nick Hilliard <nick@foobar.org>; wrote:
> james woodyatt wrote:
>> Hmm, since RFC 6164 is a Standards Track document, it’s already
>> covered as a legitimate exception under the text I already proposed,
>> which seemed mostly well received, except by people who seem to think
>> it’s not enough to recognize standard IETF exceptions to the /64
>> subnet prefix requirement.
> 
> What's your advice to vendors then?  To disable all interface netmasks
> except /64 and /127?  Or to operators?

I am aware of at least one major vendor, whose devices in the field number well into the billions, devices that simply do not accept any subnet prefix other than /64. Seems to work fine for them because none of their devices are intended to be deployed in any of the standard scenarios where prefixes other than /64 are recommended by IETF.

My advice to vendors is pretty simple.

	1. Always support /64 subnets in general usage scenarios.
	2. Assume misconfiguration in general usage scenarios where subnets are not /64.
	3. Support /127 subnets if your device will be deployed under RFC 6164.
	4. Support any other standards as necessary, where limitations caused by non-/64 subnet prefixes are acceptable.

The text I proposed would allow vendors of host operating system the necessary cover to follow that advice. Dropping the requirement would mean my advice would have to change.

	1. Always prefer /64 subnets where available.
	2. Accept limitations entailed by necessity of accepting non-/64 subnets.
	3. Drop all features that depend on always receiving a /64 subnet.

Some of those features are pretty important to me, so that’s why I’m engaged in this debate.

> Are you really suggesting that "thou shalt use only prescribed netmasks on your interfaces" is a viable proposition? […]

In general usage scenarios? Yes. I am. I have a device in my pocket that does exactly that. Everyone in my family does. Those devices would not work very well if the /64 subnet requirement were dropped and operators felt free to ignore it, and adapting them to function on subnets with longer prefixes would entail making those devices less functional.


--james woodyatt <jhw@google.com <mailto:jhw@google.com>>