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

 ' i

On Sat, Jun 15, 2019 at 10:59 AM Alexandre Petrescu
<alexandre.petrescu@gmail.com> wrote:
>
>
>
> Le 06/06/2019 à 22:17, Warren Kumari a écrit :
> > On Thu, Jun 6, 2019 at 2:46 PM Sander Steffann <sander@steffann.nl> wrote:
> >>
> >> Hi Alexandre,
> >>
> >>> I maintain that 1111 1110 10 equals 0x3fa, because that's what my Windows Calculator says: I type 1111 1110 10 and it converts to 0x3fa.
> >>>
> >>> On another hand, I am rhetorically asked how can 1111 1110 10 be 0x3fa?
> >>>
> >>> (the 1111 1110 10 are the 10 leading bits of the IPv6 link local addresses, which is familiarly known to start with an fe80).
> >>>
> >>> On my side, this is a difficulty to understand this 0xfe80, especially since 1111 1110 10 is so printed in Figure in RFC4291.
> >>
> >> It's a prefix of an IPv6 address. IPv6 addresses are 128 bits long. Expand to 128 bits and try again :)
> >>
> >> 1111 1110 1000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 equals 0xfe800000000000000000000000000000. Not sure if Windows Calculator can handle that though…
> >
> > Windows calc probably can't, but:
> > $ echo 'print hex(0b1111111010 << (128-10))'  | python
> >
> > or https://repl.it/repls/AwareDecentGeeklog if you don't have Python
> > (because windows :-p)
>
> For sake of completeness, google puts '1111111010 in hex' as 0x423A3562.

Your point?
One billion, one hundred and eleven million, one hundred and eleven
thousand and ten is, in fact, 0x423A3562
In exactly the same way, if you enter '1+1' it gives you 2, and not 0b10.

Perhaps you actually meant "0b1111111010  to hex", which it correctly
converts to 0x3FA.

A number of people have (in my opinion very politely) suggested that
you spend some time reading up on subnetting. I'd second this
recommendation, and suggest "Internet Routing Architectures" by Sam
Halabi (http://www.ciscopress.com/store/internet-routing-architectures-9781578702336
) - while it was written in 2000, and is focused on IPv4, the concept
is *exactly* the same.

I suspect that, at this point, I'm simply being trolled --
unfortunately though, as the Operations AD I often have to counter the
accusation that the IETF is detached from operations and doesn't
understand how protocols we design are used -- this thread fully plays
into that.

W

>
> qwant does not convert it.
>
> Alex
>
> >
> > W
> >>
> >> Cheers,
> >> Sander
> >>
> >> --------------------------------------------------------------------
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> >> ipv6@ietf.org
> >> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6
> >> --------------------------------------------------------------------
> >
> >
> >

-- 
I don't think the execution is relevant when it was obviously a bad
idea in the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair
of pants.
   ---maf