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Date: Thu, 21 Jun 2001 10:50:55 +0100
From: Mark Drayton <mark.drayton@4thwave.co.uk>
To: freebsd-questions@FreeBSD.ORG
Subject: Re: [OT] Domain names that are just numbers -- what's this??
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Patrick O'Reilly (patrick@mip.co.za) wrote:
> Andrei,
> 
> you said: --- Original Message ---
>   > Take the number and convert it to hex, then take each 2 hex digits
>   > and convert to decimal.
>   ... as seen in earlier mail from ravi --> [188.]63.107.146.186 ---
> 
> Please forgive my ignorance, but what's the [188.] doing before the
> rest of the IP???

The problem is that an IP address is a 32 bit unsigned int (4 bytes) but
808517866170 is a 40 bit int (5 bytes). The first byte is junk, and it
appears that the MS TCP/IP stack (and FreeBSD sometimes) drops it. This
is where the 188 comes from. I don't know if this is correct, or even if
there is a document defining what to do with IP addresses that are more
than 32 bits. Pointers?

Here's a perl program that will convert the 4 lowest bytes from a
decimal IP address to a dotted quad IP addresses:

----start----

#!/usr/bin/perl -w

use strict;
use Math::BigInt;

my $dec = Math::BigInt->new($ARGV[0]);

my $i = 0;
my @ip;

while ($i <= 3) {
	push @ip, ($dec >> ($i * 8)) & 255;
	$i++;
}

print join('.', reverse(@ip)) . "\n";

----end----

The output is a bit ugly (I can't find out how to change a Math::BigInt
object back to a scalar... suggestions appreciated):

[mark@tethys perl]$ perl ip.pl 808517866170
+63.+107.+146.+186

Cheers,

-- 

Mark Drayton

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