code: @Override
      public int compareTo(IPv6AddressRange that)
      {
          if (!this.first.equals(that.first))
              return this.first.compareTo(that.first);
          else
              return this.last.compareTo(that.last);
      }
docs: The natural order of {@link com.googlecode.ipv6.IPv6AddressRange}s orders them on increasing first addresses, and on increasing last
  address if the first address would be equal.
  <p>
  Note that the natural order does thus not compare sizes of ranges.
  
  @param that range to compare with
  @return negative, zero or positive depending on whether this is smaller, equal or greater than that