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

Alexandre Petrescu <alexandre.petrescu@gmail.com> Thu, 02 March 2017 08:24 UTC

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Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt
To: Brian E Carpenter <brian.e.carpenter@gmail.com>, =?UTF-8?Q?Dan_L=c3=bcdtke?= <mail@danrl.com>
References: <20170223134026.GI5069@gir.theapt.org> <58B014F6.2040400@foobar.org> <6DA95097-8730-4353-A0C9-3EB4719EA891@google.com> <CAN-Dau0s04c=RV0Y8AGaxBPFui41TWPTB+5o0K2Lj-iah0An1w@mail.gmail.com> <CAL9jLaYirty22iGiEjEaYq3_KA1FZhxBTOBWuFOXQ9C-WPd5xQ@mail.gmail.com> <CAN-Dau0n6oFm538XdJOcuO1yg92BCDD3mBu5YfBVm_+g-gtcKA@mail.gmail.com> <CAL9jLaYO=uYgVfSZ0SoSe0SujJ1xgwEKE8WLzo_keJHywgXTtg@mail.gmail.com> <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> <92160C59-79EC-4EB0-BFD5-69697A5E1306@danrl.com> <f1ce0d13-efee-4be0-290d-f81e9ca9e6f5@gmail.com> <4ee56eb1-81f1-54bc-99ff-86aaa816aae5@gmail.com>
From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Date: Thu, 2 Mar 2017 09:24:14 +0100
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Le 01/03/2017 à 22:20, Brian E Carpenter a écrit :
> On 02/03/2017 08:47, Alexandre Petrescu wrote:
>>
>>
>> Le 01/03/2017 à 12:23, Dan Lüdtke a écrit :
>>>
>>>> On 28 Feb 2017, at 13:04, Alexandre Petrescu
>>>> <alexandre.petrescu@gmail.com>; wrote:
>>>>
>>>> Finally, there is no advice of what bits to put between fe80::
>>>> and a 64bit the Interface ID - zeros or ones?  linux says it's
>>>> a fe80::/64 and IIRC BSD says it's a fe80::/10.  The routing
>>>> entries based on that can make for interop problems.
>>>
>>> I think there is advice. As I understand, /10 is reserved but
>>> only /64 is specified.
>>
>> Sorry, I dont understand that?
>>
>> What is the difference?  Why reserving X if only specifying Y?
>> What other concept is similar: is there some other number which is
>> reserved and only number+1 is specified?
>>
>> Why couldnt we just reserve without specifying?  Or specifying
>> without reserving?
>>
>> If we continue with reserving _and_ specifying we continue wasting
>> these 54bits there.
>>
>> What are these 54bits for?
>
> Nothing. They are reserved and must be zero. That's quite common in
> protocol design.

If so, then it's not a fe80::/10, but an fe80::/64, and we should
refrain from writing fe80::/10 anywhere.

Which brings back the question of why 64?

> Link-local is a special case, because it must be possible to create
> an address with absolutely no prior information.

I agree, an LL should be created w/o prior info coming out of the computer.

But, among other requirements, that address should have less privacy
issues too.  In an LL a longer IID (e.g. a 108bit IID) would have better
privacy characteristics than a 64bit IID - resist longer to brute force
attacks.

By the fe80::/10 definition it is allowed to set a 108bit IID in LL, but
by fe80::/64 definition it is not.

In other settings with less computers on a subnet (less privacy
concerns), or less interfaces on a computer (IoT), an IID of length 1
for a LL address would be sufficient, which would make an fe80::/127
relevant as well.  Why must they support fe80::/64 when they dont need
that much?

These questions are all the more important when knowing that many IP
stacks make these numerous fe80::/64 entries in the rt table, by default.

In IPv4 computers their rt table is a clean slate after boot... no need 
to clean.

Alex

>
> Brian
>
>>
>> Alex
>>
>>>
>>>
>>> RFC 4291 IP Version 6 Addressing Architecture 2.5.6.  Link-Local
>>> IPv6 Unicast Addresses
>>>
>>> Link-Local addresses are for use on a single link.  Link-Local
>>> addresses have the following format:
>>>
>>> |   10     | |  bits    |         54 bits         |          64
>>> bits           |
>>> +----------+-------------------------+----------------------------+
>>>
>>>
|1111111010|           0             |       interface ID         |
>>> +----------+-------------------------+----------------------------+
>>>
>>>
>>>
>>>
Cheers,
>>>
>>> Dan
>>>
>>
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>
>>
>