Incrementing an address 4.7 octillion times (4.7e21) in order to add 4.7e21 to it (and then repeat the exercise 256 times!) is a crazy way of doing things.

NetAddr::IP does allow you to add an arbitrary number (not just 1); but how you deal with additions of numbers greater than the native integer is not explained.

Overall, it just seems easier to use a package that knows how to deal with 128bit integers.

Try this:

#! perl -slw
use strict;
use Data::Dump qw[ pp ];
use Math::Int128 qw[ uint128 ];

sub IPv6toUint128 {
    my $n = uint128( 0 );
    my $ip = shift;
    my @bits = split ':', $ip, 8;
    my $missing = 9 - @bits;
    @bits = map { length() ? hex( '0x' . $_ ) : ( (0) x $missing ) } @
+bits;
    $#bits = 7;
    $n = $n * 65536 + $_ for @bits;
    return $n
}

sub Uint128toIPv6 {
    my $mask = uint128( 0xffff );
    my $n = shift;
    my @bits = map {
        my $bits = ( $n & $mask   ) >> ( $_ * 16 );
        $mask <<= 16;
        $bits;
    } 0 .. 7;
    @bits = map{ sprintf '%04x', $_  } reverse @bits;
    return join ':', @bits;
}

my $n = IPv6toUint128( '2001:db8::' );
# my $step = uint128( '4722366482869645213696' );
my $step = uint128( 1 ); $step <<= 72; # 128 - 56

print Uint128toIPv6( $n += $step ) for 1 .. 256;

__END__
C:\test>1148545
2001:0db8:0000:0100:0000:0000:0000:0000
2001:0db8:0000:0200:0000:0000:0000:0000
2001:0db8:0000:0300:0000:0000:0000:0000
2001:0db8:0000:0400:0000:0000:0000:0000
2001:0db8:0000:0500:0000:0000:0000:0000
...
2001:0db8:0000:fc00:0000:0000:0000:0000
2001:0db8:0000:fd00:0000:0000:0000:0000
2001:0db8:0000:fe00:0000:0000:0000:0000
2001:0db8:0000:ff00:0000:0000:0000:0000
2001:0db8:0001:0000:0000:0000:0000:0000
[download]

My conversion routines could stand a bit of cleaning up; but they suffice for the purposes of this post.

Of course, if you need the addresses in compact form (why would you; any software should also accept the long form), then you can input the strings produced above to NetAddr::IP and have it compact them for you.