无法与服务器正在侦听的端口通信

Question

I have an application which listens to port(8087). There is a client process which give request to this server and server will send response message back. After some requests and response, my client process is not able to connect to that port.

I could see a port listening when i used netstat tool. Also my process is running.

# netstat -a | grep 8087
tcp        0      0 0.0.0.0:8087            0.0.0.0:*               LISTEN

But i am not able to connect to that port from a client. What could be the reason for this?

Answer 1

Try the following steps

1. On the server machines run the command "iptables -nL" to see which policies are set. If firewall rules are set, delete the rules and try connecting again.

2. Run following tcpdump command on the server machine

   tcdump -nnvX -s0 -iem1 host client_machine_ip and port 8087

   and following tcpdump command on the client machine

   tcdump -nnvX -s0 -iem1 host server_machine_ip and port 8087

   This will tell you if client machine is sending packet out and server machine is receiving it.

3. Run the command "netstat -ans" on server machine and under the IP and TCP labels, see if any packets are getting dropped.

4. Check in /var/log/messages on server machine if any errors are getting reported.

Hope this helps.