When they are planning how to organize their IO , programs (and designers) normally assume thatrewriting (overwriting) an existing, already written file is the fastestsort of write operation possible and will not change the existing filelayout (for example, if it has been created to be sequential). Thisis because all of the data blocks have already been allocated and allof the metadata has been set up; if you write in block-aligned units,pretty much all the operating system has to do is shovel

Prompted by my old SpamByASN entry, I was recently asked how you woulddo IP to ASN lookups, and ideally ASN to IP lookups too. Since the fullanswer is complicated, I will do the simple and useful one first.

Assuming that nothing funny is going on, each IP address has exactlyone ASN that ultimately announces it. The easiest way to find out thismapping for a given IP address is to use the asn and aspath reverseDNS lookup zones that routeviews.org provides; these return TXT records with