Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?

Le 07/06/2019 à 21:47, Tom Herbert a écrit :
> On Fri, Jun 7, 2019 at 12:30 PM Mudric, Dusan (Dusan) <dmudric@avaya.com> wrote:
>>
>>>
>>> Message: 3
>>> Date: Fri, 7 Jun 2019 10:53:28 -0700
>>> From: Fred Baker <fredbaker.ietf@gmail.com>
>>> To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
>>> Cc: IPv6 <ipv6@ietf.org>
>>> Subject: Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?
>>> Message-ID: <A722E202-7671-4111-BA92-8A67B3D3B924@gmail.com>
>>> Content-Type: text/plain; charset="us-ascii"
>>>
>>>
>>>
>>> If I have prefix fe80::/10, as described in RFC 4291, the next bit is bit 11. Doing
>>> the same subdivision of the prefix is fe80::/11 and fea0::/11.
>> [Dusan] The hexadecimal definition for LL address is not syntactically correct. The binary 10 bit prefix 1111111010 cannot be presented as hexadecimal FE80::/10. It is rather a range FE80::/10 - FEBF::/10. In this notation, FE80::/10 = FEBF::/10,  because the first 10 bits are equal and other 6 should be ignored. 111 1111010 can be defined as FE80::/10 only if every time it is also mentioned that the trailing 6 bits are all zero.
> 
> By that logic, we'd have to mention that the trailing 118 bits are
> zero.  E.g. FE80::/10 == FEBD:F676:BBBB:C654:FEBD:F676:BBBB:C654/10
> also. It's obviously convenient canonical notication to express all
> the trailing bits as zeroes for a prefix, but not required. For
> instance, ifconfig shows my host address as fe80::ac2f:ea58:94a:438/64
> which in one string indicates both a fully qualified address and it's
> prefix bits.

Your system (sorry, not anything against your or your system) telling 
fe80::ac2f:ea58:94a:438/64 is relatively against IANA telling a 
link-local prefix is fe80::/10.

IANA telling the link local address is fe80::/10 is just one 
illustration.  It could have said the link-local prefix is fe81::/10 
too.  It is equally right.

RFC4291 saying 54bits are reset is against IANA saying fe80::/10 which 
lets the 54bits be anything.

Alex

> 
> Tom
> 
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