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

Sander Steffann <sander@steffann.nl> Thu, 06 June 2019 18:46 UTC

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From: Sander Steffann <sander@steffann.nl>
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Subject: Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa?
Date: Thu, 06 Jun 2019 20:46:28 +0200
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Cc: IPv6 <ipv6@ietf.org>
To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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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…

Cheers,
Sander

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