I know that the implementation of looking up subdomains is trivial. But now you just check the whois entry and that's it. If you want to check subdomains, where do you want to look? If the ISP was so kind to give a hint in the domain name, you are lucky, but this is very rare. Otherwise you have to traceroute almost every peer you see. There is no other way to tell where a peer is located. And if you look at the common names of peers it is more often the case that the type of connection is the subdomain. adsl.alicedsl.de adsl.euphonynet.be cable.infonet.ee Also many peer names make no sense at all, they are just the encoded IP or a node number. If you think, i misunderstand you, please give an example how it should work.