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

[Alexandre Petrescu <[e-mail]>]

Le 10/06/2019 à 18:46, Yucel Guven a écrit :
> No need to define as a range.
> When you specify the prefix-length, it already defines a range.
> e.g. FE80::/10 (absolutely not  FE8::/10)  has the range of
> fe80:0000:0000:0000::/10 - febf:ffff:ffff:ffff::/10

YEs, but if you only use the /10 to define a range, you introduce 
ambiguity in notation.

People think that FE80 is the only hextet that can designate a 
link-local address.  That is wrong.  FE81 also is a hextet that 
designates a link-local address.  There are more.

That is a notation problem.

Alex

> 
> Reg.'s
> Yucel
> 
> On Mon, Jun 10, 2019 at 3:58 PM Mudric, Dusan (Dusan) <[e-mail] 
> <mailto:[e-mail]>> wrote:
> 
>      > On Friday, June 7, 2019 at 3:48 PM Tom Herbert
>      > <[e-mail] <mailto:[e-mail]>> wrote
>      > >
>      > > >
>      > > > Message: 3
>      > > > Date: Fri, 7 Jun 2019 10:53:28 -0700
>      > > > From: Fred Baker <[e-mail]
>     <mailto:[e-mail]>>
>      > > > To: Alexandre Petrescu <[e-mail]
>     <mailto:[e-mail]>>
>      > > > Cc: IPv6 <[e-mail] <mailto:[e-mail]>>
>      > > > Subject: Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?
>      > > > Message-ID: <[e-mail]
>     <mailto:[e-mail]>>
>      > > > 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.
>     [Dusan] In this example fe80::ac2f:ea58:94a:438/64 is LL address
>     with 0xfe80 0x0000 0x0000 0x0000 prefix. Based on LL prefix
>     definition, this LL address can have a value of
>     feab::ac2f:ea58:94a:438/64 and still have the binary 10 bit prefix
>     1111111010
> 
>     May be LL address can be defined in hex notation as a range FE8::/10
>     - FEB::/10? This range always has the same well know LL identifier,
>     the binary 10 bit prefix 1111111010.
> 
>      >
>      > Tom
>      >
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