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Open and Closed ports on a system.

Posted on 2007-11-18
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Last Modified: 2012-06-22
Hi experts,
How can i find out open and closed ports on a particular system, i know there is a command called netstat but the output it produces does not list all open ports and closed ports.
Is there a utility to find out all open and closed ports.
Thanks in advance.
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Question by:KASPBoodai
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eulac earned 300 total points
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you can use the option -a, to view all connections and listening ports.

command:
     netstat -a
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by:KASPBoodai
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 TCP   pc:2735   xyz:epmap  TIME_WAIT
 
  TCP    pc:5101   172.30.22.104:4562     ESTABLISHED

  TCP    pc:7374   pc:0  LISTENING

  UDP    pc:snmp   *:*
  UDP    pc:snmptrap  *:*
 
Can you explain the above output.
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by:eulac
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explain:
        TCP   pc:2735   xyz:epmap  TIME_WAIT

        TCP   - the protocol that your PC use to access
        pc      - your computer name
        2735  - the port number you are using to access
        xyz    - the computer name you are accessing
        epmap  - the port you are accessing, there is a corresponding port number for epmap.
        TIME_WAIT - connection is already disconnected.

same explanation for other lines.
         ESTABLISHED - means your connection is ok.
         LISTENING - meaning your port is open for access by other computers.
         snmp   - there's a corresponding port number for this.

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by:rulirahmadi
rulirahmadi earned 200 total points
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Windows Defender maybe?
http://www.microsoft.com/athome/security/spyware/software/default.mspx

Go to Tools > Software Explorer > Network Connected Programs.
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by:KASPBoodai
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Thanks eulac but i wanted to know what *:* stands for, the output is derived from my system and i was confused to see *.* therefore will appreciate if u can explain this.
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by:KASPBoodai
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rulirahmadi will this software list all open and closed ports i know one software port invador but am not able to locate the software on the internet.
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by:eulac
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*.* means your own PC.
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by:KASPBoodai
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but then this command does not show any closed or blocked ports???
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by:eulac
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closed or blocked are those who are not listed in netstat -a.

you can view all port range @:
         http://docs.hp.com/en/5990-7252/ch01s01.html
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by:KASPBoodai
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thanks for the information eulac, let me know if u know any such software which gives u a gui output and is more informative.
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by:rulirahmadi
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>> will this software list all open and closed ports
AFAIK yes. FYI, Windows Defender is a free software.
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by:eulac
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you may use Advanced Port Scanner which is free.

http://www.famatech.com/products/utilities/portscanner.php
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by:KASPBoodai
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ok one last question i installed the software and have ran a port test on my pc, it displayed open ports and closed ports, does the closed port mean blocked portsd or it simply means its not in use at the moment but open for future access.
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by:eulac
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closed means, not in use.

you can use your firewall to check you blocked ports.
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by:KASPBoodai
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Well thanks a lot enjoy the points.
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by:eulac
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thanks too...
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by:rulirahmadi
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Me too, thanks too :)
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