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

[Tom Herbert <[e-mail]>]

On Mon, Jun 10, 2019 at 6:58 AM Mudric, Dusan (Dusan) <[e-mail]> wrote:
>
> > On Friday, June 7, 2019 at 3:48 PM Tom Herbert
> > <[e-mail]> wrote
> > >
> > > >
> > > > Message: 3
> > > > Date: Fri, 7 Jun 2019 10:53:28 -0700
> > > > From: Fred Baker <[e-mail]>
> > > > To: Alexandre Petrescu <[e-mail]>
> > > > Cc: IPv6 <[e-mail]>
> > > > Subject: Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?
> > > > Message-ID: <[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.

FE8::/10 - FEB::/10, only three digits in IPv6 notation? So wouldn't
FE8::/10 == 0FE8::/10 == 0FE0::/10 == FE0::/10. I don't think that's
right.

Tom

>
> >
> > Tom
> >