Re: [v6ops] Stateful SLAAC (draft-ietf-v6ops-unique-ipv6-prefix-per-host)

Fred Baker <fredbaker.ietf@gmail.com> Tue, 14 November 2017 00:43 UTC

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From: Fred Baker <fredbaker.ietf@gmail.com>
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Subject: Re: [v6ops] Stateful SLAAC (draft-ietf-v6ops-unique-ipv6-prefix-per-host)
Date: Tue, 14 Nov 2017 08:43:03 +0800
In-Reply-To: <5A0999A4.3040807@foobar.org>
Cc: Fernando Gont <fgont@si6networks.com>, "v6ops@ietf.org WG" <v6ops@ietf.org>, "6man@ietf.org" <6man@ietf.org>
To: Nick Hilliard <nick@foobar.org>, Lorenzo Colitti <lorenzo@google.com>
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Chair hat off.

> On Nov 13, 2017, at 9:09 PM, Nick Hilliard <nick@foobar.org>; wrote:
> 
>>> From a operational point of view, one would wonder why pursue this path
>>    as opposed to e.g. do DHCPv6
>> 
>> As for DHCPv6 specifically, one reason is that DHCPv6-only networks are
>> not recommended by the IETF. RFC 7934.
> 
> reminder: there is no WG consensus that this is what RFC 7934 means.

I just went back to read it. Having an argument with the author of a document about what it means is an interesting tactic.

There are 26 references to DHCP(v6) in the document. The vast majority of them are factual - "it does this, and there are networks that use it".

The two references I found that are negative statements about DHCP are about IA_NA. Section 8, second and third paragraphs, reads

   Due to the drawbacks imposed by requiring explicit requests for
   address space (see Section 4), it is RECOMMENDED that the network
   give the host the ability to use new addresses without requiring
   explicit requests.  This can be achieved either by allowing the host
   to form new addresses autonomously (e.g., via SLAAC) or by providing
   the host with a dedicated /64 prefix.  The prefix MAY be provided
   using DHCPv6 PD, SLAAC with per-device VLANs, or any other means.

   Using stateful address assignment (DHCPv6 IA_NA or IA_TA) to provide
   multiple addresses when the host connects (e.g., the approximately 30
   addresses that can fit into a single packet) would accommodate
   current clients, but it sets a limit on the number of addresses
   available to hosts when they attach and therefore limits the
   development of future applications.

I think it is absolutely fair to say that the RFC doesn't recommend (recommends against) the mechanism that IA_NA uses. That said, the laptop I'm typing on (a Mac) generally keeps 2-3 addresses per interface and has several interfaces. 30 is a viable number for it. I can also report that I have worked in an environment that only uses DHCPv6, and it worked just fine for any purpose I put it to.