Get hostname, when IP address is known

[vi]

I have the following program

import java.net.*;
public class Inet1 {
public static void main(String[] a) throws Exception {
InetAddress i1 = InetAddress.getByName("www.sun.com");
System.out.println(i1.getHostAddress()); //209.249.116.195
InetAddress i2 = InetAddress.getByName("209.249.116.195");
System.out.println(i2.getHostName());
}
}

On the last println statement, I want the hostname to be printed i.e.
www.sun.com.
Given a hostname, I am able to get IP address. But, given an IP
address, I am not able to get the hostname.
Please suggest a solution.
Thanks.

 

[Oliver Wong]

I have the following program

import java.net.*;
public class Inet1 {
public static void main(String[] a) throws Exception {
InetAddress i1 = InetAddress.getByName("www.sun.com");
System.out.println(i1.getHostAddress()); //209.249.116.195
InetAddress i2 = InetAddress.getByName("209.249.116.195");
System.out.println(i2.getHostName());
}
}

On the last println statement, I want the hostname to be printed i.e.
www.sun.com.
Given a hostname, I am able to get IP address. But, given an IP
address, I am not able to get the hostname.
Please suggest a solution.
Thanks.

See RFC953: http://www.faqs.org/rfcs/rfc953.html

- Oliver

 

[Eric K Idema]

I have the following program

import java.net.*;
public class Inet1 {
public static void main(String[] a) throws Exception {
InetAddress i1 = InetAddress.getByName("www.sun.com");
System.out.println(i1.getHostAddress()); //209.249.116.195
InetAddress i2 = InetAddress.getByName("209.249.116.195");
System.out.println(i2.getHostName());
}
}

On the last println statement, I want the hostname to be printed i.e.
www.sun.com.
Given a hostname, I am able to get IP address. But, given an IP
address, I am not able to get the hostname.

There's nothing wrong with your code. It looks like Sun's nameserver
isn't configured properly for reverse lookups. Try a few more examples
and you'll find that some work and some don't. My experience is that
many companies don't get reverse dns right.

Eric

 

[Roedy Green]

Given a hostname, I am able to get IP address. But, given an IP
address, I am not able to get the hostname.

see http://mindprod.com/jgloss/ip.html for the whois source code.

It does not work unless you have a reverse DNS lookup. Some sites will
not support that. You can try out the code

java WhoIs mindprod.com
java WhoIs 24.85.32.136

Note that sometimes several domains share and IP and vice versa.

 

[Roedy Green]

It looks like Sun's nameserver
isn't configured properly for reverse lookups.

that is correct. You can go DNS->IP but not the reverse with Sun. Part
of the catch is reverse lookup can be used for spam harvesting, and
other annoying purposes.

 

[Roedy Green]

On the last println statement, I want the hostname to be printed i.e.
www.sun.com.

to get the info manually see http://mindprod.com/jgloss/whois.html

In those cases you are looking in private databases.