btw, the compare function is suppose to return -1, 0, +1, not just 0 and 1, so I expect your sort has some amount of randomness to it.

Maybe you want something like:

sub intermix { 
   my $a_prime = join('.', reverse(split(/\./, $a)));
   my $b_prime = join('.', reverse(split(/\./, $b)));
   $a_prime cmp $b_prime
}

my @list = ('10.1.1.1', '10.1.1.2', '10.2.2.1', '10.2.2.2');
@list = sort intermix @list;

use Data::Dumper;
print Dumper(@list);

__END__
output
======
$VAR1 = '10.1.1.1';
$VAR2 = '10.2.2.1';
$VAR3 = '10.1.1.2';
$VAR4 = '10.2.2.2';
[download]

Almost the same, but more efficient:

sub intermix { 
   my $a_prime = reverse($a);
   my $b_prime = reverse($b);
   $a_prime cmp $b_prime
}

my @list = ('10.1.1.1', '10.1.1.2', '10.2.2.1', '10.2.2.2');
@list = sort intermix @list;

use Data::Dumper;
print Dumper(@list);

__END__
output
======
$VAR1 = '10.1.1.1';
$VAR2 = '10.2.2.1';
$VAR3 = '10.1.1.2';
$VAR4 = '10.2.2.2';
[download]

This is the same thing as the last, but probably more efficient, especially for longer lists:

my @list = ('10.1.1.1', '10.1.1.2', '10.2.2.1', '10.2.2.2');
@list = map { $_->[0] } 
        sort { $a->[1] cmp $b->[1] }
        map { [ $_, ''.reverse($_) ] } 
        @list;

use Data::Dumper;
print Dumper(@list);

__END__
output
======
$VAR1 = '10.1.1.1';
$VAR2 = '10.2.2.1';
$VAR3 = '10.1.1.2';
$VAR4 = '10.2.2.2';
[download]

Note: Given addresses of the form 'a.b.c.d', the above snippets only work well if there is there is a common 'd' of for every 'a.b.c' in the list.