sloowwwww Reverse DNS lookup

[Tim McGuire]

Here is my simple code:

   
try{
	      address = InetAddress.getByName(ip).getHostName();
		} catch(UnknownHostException uhe){
			uhe.printStackTrace();
		}
		System.out.println("address :" + address);
 

I understand that there is no guarantee that this will return a proper host name. For some ip addresses, this takes a ridiculously long time to return, often with just the same ip address I put in. Other ip addresses are faster. Meanwhile, netstat from the command line returns all IP addresses instantly.

So I have three questions:
1) InetAddress API says that it uses a "System Configured lookup setting" to resolve the ip address to a host name. what settting would this be?
2) Why do some ip addresses take longer than others?
3) How does netstat get this same information so much faster?

I am loking through the SIGAR code for their netstat implementation and it just uses something similar to what I put above.