On Fri, Feb 24, 2017 at 1:53 AM, Pierre Pfister <pierre.pfister@xxxxxxxx> wrote:
Hello David,Le 24 févr. 2017 à 08:15, David Farmer <farmer@xxxxxxx> a écrit :On Thu, Feb 23, 2017 at 9:13 PM, Fernando Gont <fgont@xxxxxxxxxxxxxxx> wrote:I'd remove a few sentences here, as in:
IPv6 unicast routing is based on prefixes of any valid length up to
128 [BCP198]. Subnet prefixes of /64 are RECOMMENDED for general
purpose use, subnet prefixes of /127 are RECOMMENDED for point-
to-point router links [RFC6164]. The rationale for the 64 bit
boundary in IPv6 addresses can be found in [RFC7421].The problem is you have stripped out all the implementation guidance and only left operational guidance. But maybe the the right idea is to separate the two, putting the operational guidance in Section 2.4 where we are talking about prefixes and the implementation guidance in section 2.4.1 where we are talking about IIDs.
2nd Paragraph of 2.4;
IPv6 unicast routing is based on prefixes of any valid length up to
and including 128 [BCP198]. However, subnet prefixes of 64 bits in
length are REQUIRED for use with Stateless Address Autoconfiguration
(SLAAC)[RFC4862] and are RECOMMENDED for all other general purpose
use. The rationale for the 64 bit boundary in IPv6 addresses can be
found in [RFC7421].Except RFC4862(SLAAC) does not say anywhere that 64 bits long IIDs are required.Only mention I find of 64 is given as an example for EUI-64 for ethernet links.
I believe most implementations of SLAAC require /64, but I could be wrong.
4th paragraph of 2.4.1
For all unicast addresses, except those that start with the binary
value 000, support for Interface IDs that are 64 bits long is
REQUIRED, support for other Interface IDs lengths is OPTIONAL. The
rationale for the 64 bit boundary in IPv6 addresses can be found in
[RFC7421].1) The ::/3 rule is blatantly ignored by all implementations that I know of.I don't see how something that has been ignored for years, and hasno implementation and deployment experience, could make its way to full standard.
I'm willing to let that go too, but it was there so I left it for now.
2) "support for other Interface IDs lengths is OPTIONAL" -> Wait. What !?This is not a compromise. You are just relaxing the requirement even more than it already is.This is not what is implemented, nor what is deployed.
Most routers let you specify any subnet length you want they default to /64 usually. Also, many host OSes when you manually config let you specify any subnet length too. By making it OPTIONAL, I'm saying it ok to do that, or not if the you don't want too.
- Pierre
This clearly say that implementations that only support 64 bit IID lengths are just fine, but also says implementations that allow IID lengths other than 64 bits are just fine too. I think the current and historic text actually implies implementations are not to allow other IID lengths, is that what we really intended to say? A lot of implementations seem to allow other IID lengths, are they wrong? I don't think so.This also gives strong operational guidance that 64 bit length subnet prefixes are expected in most situations. Reinforcing the 64 bit boundary, however without outlawing the use of other subnet prefix lengths when implemented and they could be useful. This is done without distracting from the 64 bit boundary, by not directly calling attention to RFC6164 or the other longer prefix lengths. Since BCP198 and RFC7421 both reference RFC6164 calling it out here doesn't seem necessary, and would unnecessarily weaken the focus on the 64 bit boundary that I'm trying to maintain.I don't see how this text would require changes in any code, nor does it imply other IID lengths are not allowed operationally, again which a lot of implementations seem to allow.
===============================================
David Farmer Email:farmer@xxxxxxx
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE Phone: 612-626-0815
Minneapolis, MN 55414-3029 Cell: 612-812-9952
===============================================
David Farmer Email:farmer@xxxxxxx
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE Phone: 612-626-0815
Minneapolis, MN 55414-3029 Cell: 612-812-9952
===============================================