UnknownHostException for server through java client code

Question

I am not able to connect to an remote known server through Java code; java.net.NoRouteToHostException: No route to host exception occurs when connection is tried.

But strangely, I am able to connect to same server through ssh.

Details: Simple Java client when tries to establish connection with Java standalone server, while conneting the exception occurs at following statement:

Socket socket = new Socket(ServerIP ServerPort);

The port needed is open on server so that externally request can come in.

Again the following is returns false

InetAddress.getByName(SERVER_IP).isReachable(1000)

The Server is running on Fedora, Java 5.

FYI: Java cannot resolve DNS address from AIX: UnknownHostException is almost same to my question, but somehow this is neither AIX nor dns related; moreover I feel the issue to be more of Network or firewall issue.

Please guide me.

score 1 · Answer 1 · answered Sep 07 '09 at 12:23

1

This is the error you'd expect from a host being firewalled. Can you telnet to the same port on that IP?

answered Sep 07 '09 at 12:23

Cian

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you guessed it right, I cannot telnet, although the netstat show me that the port is open for listening. netstat -pan | grep 5014 tcp 0 0 :::5014 :::* LISTEN 6212/java – nilesh Sep 08 '09 at 06:00
netstat will only tell you whether the port is listening, not if it's firewalled. It's entirely possible there's something in between blocking traffic, or a iptables/pf/ipfilter on the host, none of which would show up in netstat. – Cian Sep 08 '09 at 08:11
Recently I checked, I am able to telnet certain ports (the port on which mysql-cluster is running) ; but not any other such as 5000 mentioned earlier. I even tried to use some other ports but to no use. – nilesh Sep 08 '09 at 16:05
Sounds like a firewall issue. E_CONTACT_NETWORK_ADMIN – Cian Sep 08 '09 at 16:50

score 0 · Answer 2 · answered Sep 07 '09 at 15:57

The Socket constructor should only attempt to resolve if the hostName is null, and then it tries to resolve the local host. Is your /etc/hosts file set up properly?
What does the following code return? (Please use the host name, not the ip ).
```
System.out.println(InetAddress.getByName(hostName));
```

UnknownHostException for server through java client code

2 Answers2