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I want to run a service which require to connect with some source using port 20000 but it is not connecting. I want to test my this port is blocked or open.

Root
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  • This question is perhaps a bit short on words, but try using `netstat -an` or `netstat -lnptu` to figure out whether port 20000 is in LISTENING or perhaps ESTABLISHED state. I assume you are talking about a TCP connection here - if UDP your problem is something else. Add more details - then maybe better answers (and even a positive score) will come :-) – MrMajestyk Feb 03 '15 at 13:19

2 Answers2

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Useful utilities :

  • 1.Telnet

  • 2.nc

  • 3.nmap

Scenario: For checking remote system tcp 80 port status

Usage :

telnet myserver.com 80 
nc -v myserver.com 80
nmap myserver.com 80

Response Analysis :

if you get a time out or deny : the port is not open

suppose if you get "Connection refused" : then port is open but process is not listerning

If you get a connection successful : Port is open and process is listen

Solution:

start/restart the listening process (if connection refused)

Ask network team to monitor the connection we can confirm whether it is blocked from intermediate network firewall or from server firewall/iptables

Note :

  • Suppose firewall configured to Reject packets instead of Drop then u will get "connection refused" error , so here in this case we can't ensure wheteher process is listern or not.

For checking udp port (like ntp) you can use below nc option

nc -uzv yourserver.com 123

midhun k
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You can try NMAP to scan ports that are "open" on you local machine like:

nmap -sS -O -p20000 127.0.0.1

Or to a netstat to check what port is used by a service.

Like so:

netstat -lnptu

Andrius
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