Open port 7 for echo in java

Question

I am trying to do simple ping operation using java code , i know that java does not support icmp so i just made a simple code that uses port 7 to send a request and wait for echo response

 Socket t = new Socket("127.0.0.1", 7);
    DataInputStream dis = new DataInputStream(t.getInputStream());
    PrintStream ps = new PrintStream(t.getOutputStream());
    ps.println("Hello");
    String str = dis.readUTF();
    if (str.equals("Hello"))
      System.out.println("Alive!");
    else
      System.out.println("Dead");
    t.close();

but this gives me

Exception in thread "main" java.net.ConnectException: Connection refused
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:579)
at java.net.Socket.connect(Socket.java:528)
at java.net.Socket.<init>(Socket.java:425)
at java.net.Socket.<init>(Socket.java:208)
at MobileCloud.Ping.main(Ping.java:11)

I read that i should change in the /etc/inetd.conf file but I have no such file .

You need to start the service that listens on port seven first. — Sibbo, Apr 08 '15 at 14:29
Not your question exactly, but see - [How to do a true Java ping from Windows?](http://stackoverflow.com/q/2448666/127035) — ewan.chalmers, Apr 08 '15 at 14:33

Steffen Ullrich · Answer 1 · 2015-04-08T15:11:35.547

1

Exception in thread "main" java.net.ConnectException: Connection refused

There is no server running on port 7 as you might verify with telnet 127.0.0.1 7. Thus the connection gets refused.

I read that i should change in the /etc/inetd.conf file but I have no such file

This depends on the system. You might need to install inetd. With your Ubuntu 14.04 this will be the inetutils-inetd package.

edited Apr 08 '15 at 15:11

answered Apr 08 '15 at 14:22

Steffen Ullrich

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ICMP uses port 7 so it should echo my message when i send a string with "hello" it should respond back. I just need to listen on port 7 – Karim Akhnoukh Apr 08 '15 at 15:08
ICMP does not use any ports at all. Ports are for TCP and UDP only. – Steffen Ullrich Apr 08 '15 at 15:09
I just need to study the RTT for some measurments so do you have alternative solution ? – Karim Akhnoukh Apr 08 '15 at 16:16
I think this is better asked as a new question, which should contain enough details about the environment where you need to measure the RTT and the restrictions you have. – Steffen Ullrich Apr 08 '15 at 16:29

Open port 7 for echo in java

1 Answers1