my @sorted_keys = map  {$_->[0]}
                  sort {$a->[1] <=> $b->[1]
                     || $a->[2] <=> $b->[2]
                     || $a->[3] <=> $b->[3]
                     || $a->[4] <=> $b->[4]}
                  map  { [ $_, split /\./ ] }
                  keys %ip;
foreach (@sorted_keys) {
  # do something
}