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

otroan@employees.org Tue, 28 March 2017 13:53 UTC

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Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
Date: Tue, 28 Mar 2017 08:53:18 -0500
In-Reply-To: <1b6154d2-14a7-0d85-7a81-18a5367c0330@gmail.com>
Cc: 6man WG <ipv6@ietf.org>
To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
References: <20170223134026.GI5069@gir.theapt.org> <CAN-Dau1vJV5O_Ythp6THkAu4-YZXV82Upny1V+ybbjCVZQQX=A@mail.gmail.com> <27cce319-18ac-5c0e-3497-af92344f0062@gmail.com> <de4988be-6031-08d9-84ce-21c3fa4f9bc9@gmail.com> <98401ef7-cf41-b4a0-4d11-a7d840181bd0@gmail.com> <1047f5fc-ae40-be52-6bab-27f31fe5e045@gmail.com> <9a94feac-8d59-b153-d41c-04fc371e4db4@gmail.com> <CAO42Z2z7v4gDk91b6Of-1sczV88m3B9kzn0MeJU_VBJ416k6Ww@mail.gmail.com> <ae35b45a-0398-840f-fc0d-1f64dd2fcc58@gmail.com> <CAJE_bqdZezDRti5LqCKnmU9QkwwhdejP22gXwk3wLKiS0mhx+Q@mail.gmail.com> <dfc8570d-fff0-39fe-a53f-db2c81c0ec8f@gmail.com> <CAJE_bqdHv0vw_kFFBZ2NE98t0nhkCR5rz8f=UOpwmvqtVjNqhg@mail.gmail.com> <d7c50847-47b4-48a7-d2c4-7b207898c84b@gmail.com> <CAJE_bqdzZ6VBCN_+FvX6Np=21PuuPCFX3mOuZ6MVQd=zj7aE5A@mail.gmail.com> <CAJE_bqfD_wkSgR1XBWSFXeVxZ+Qx+ai2qKoND89NW__m6yG2YQ@mail.gmail.com> <fd f728eb-90f5-facd-3cbe-5f3ba8cac0d1@gmail.com> <E162D74A-7A40-4266-921B-DA55998563BD@thehobsons.co.uk> <1b6154d2-14a7-0d85-7a81-18a5367c0330@gmail.com>
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Alexandre,

I think we have spent enough time on this subject now.
If you want to discuss this further I suggest you do that off-line.

Best regards,
Ole

> On 28 Mar 2017, at 07:46, Alexandre Petrescu <alexandre.petrescu@gmail.com>; wrote:
> 
> 
> 
> Le 28/03/2017 à 02:02, Simon Hobson a écrit :
>> Alexandre Petrescu <alexandre.petrescu@gmail.com>; wrote:
>> 
>>> Actually one can wonder why RFC writers decided to write fe80::/10
>>> when they could have written fe81::/10 equaly well.  Or even
>>> fe90::/10 or febf::/10.  All these designate the same 10bits - the
>>> mask 1111 1110 10.
>> 
>> I thought this was answered a good few messages ago.
> 
> I did not see?
> 
>> It is customary to always write the "lowest value that fits"
> 
> I did not know it was customary?  Maybe it should be documented.
> 
> As opposed to IPv4 decimal notation, in IPv6 hexa it's very difficult to
> compare visually two IPv6 addresses, and tell which is lower value.
> 
>> - ie the one where all the non-prefix bits are zero. So fe80::/10
>> fits - all the bits after the first 10 are zero fe81::/10 does not
>> fit - when you mask off the non-prefix bits you get a different
>> value
> 
> Well, makes sense.
> 
> But from this to say that LL addresses are _only_ those that start with
> fe80 there is a long way.
> 
>> So while in terms of maths, after doing the masking you get the same
>> result, by not applying the "all host bits are zero" rule - you have
>> introduced confusion for humans.
> 
> Ok.
> 
> But humans introduce further confusion when mandating these host bits to
> be 0.
> 
> These bits are not necessarily 0 - they can be whatever.
> 
> That is a need to say 'whatever' - not necessarily '0'.
> 
>> As pointed out, 172.17.0.0/12 might make as much sense as
>> 172.16.0.0/12 IFF you ignore this feature. Applying the mask to
>> 172.17.0.0/12 gives you non-zero host bits -
> 
> A-ha!  I did not know that.
> 
>> hence why we don't use that. It's all to do with consistency and
>> avoidance of confusion. And we need as much of that as we can - I
>> know plenty of supposedly network capable people who cannot
>> understand the concept of 172.16.1.0/23 being a valid IP address !
> 
> But there should be a way to say that 172.16.0.0/12 is just one valid example, not the only one.
> 
> That 172.17.0.0/12 is also a private address.
> 
> Just like when one types 'ls abc*' vs typing 'ls abcd'.
> 
> That is the need.
> 
>> But to be frank, I still can't see what the proposal is about - just
>> what use case does it solve ?
> 
> Well, the discussion is issued from the following observations:
> - rfc4291bis calls it fe80::/10 with a 64bit IID, whereas rfc2464bis
>  calls it fe80::/64 - which is right?
> - BSD code recognizes an LL address by its 10 first bits only (not by
>  64): it drops an ND message if not convinced.  That is reason enough
>  to visit the problem closely.
> - much f2f conversation calls ULA an "fd00" and an LL an "fe80".  This
>  goes very far when assigning addresses on interfaces.  Few if any
>  assign an "fe81" or an "fc00", although both are correct LL and ULA
>  respectively.
> 
> And I think it is so because of the textual representation of IPv6
> addresses.
> 
> Alex
> 
>> 
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