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I need a simple utility that allow me to check if a PC, attached to a local network, is able to reach a specified address:port using specified protocol like TCP or UDP

Machine's OS I will use to do the check is Windows XP.

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You should check our psexec from Microsoft Sysinternals. It will allow you to run a process on a given computer using given credentials. –  music2myear Oct 31 at 16:18

3 Answers 3

up vote 7 down vote accepted

Use simply telnet:

telnet hostname port

If you get a connection, something replies on that port.

If you get an error message, no program is listening on that port, or the hostname is invalid:

Connecting To hostname...Could not open connection to the 
host, on port <port>: Connect failed
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+1, telnet or the allmighty netcat (nc), but you have to grab that from "somewhere", so telnet is just fine. –  akira Apr 8 '10 at 12:01
    
@snark which protocol is used to do this test? TCP, UDP or other? –  Drake Apr 8 '10 at 12:28
    
TCP is used, as telnet establishes a connection. UDP is connectionless so you cannot tell if someone is listening or not. –  Snark Apr 8 '10 at 13:08
    
thanks. So there is no way to use a tool to check if UDP is allowed in output on a certain port? Only using the desired application and see it is working? –  Drake Apr 8 '10 at 15:40

nmap should be able to handle this.

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You can use iperf to check if UDP ports are reachable or not.

Example: Testing if port 5093 UDP is open on remote server 10.0.0.1

C:\>iperf -u -p 5093 -c 10.0.0.1
------------------------------------------------------------
Client connecting to 10.0.0.1, UDP port 5093
Sending 1470 byte datagrams
UDP buffer size: 8.00 KByte (default)
------------------------------------------------------------
[320] local 10.16.61.182 port 54574 connected with 10.0.0.1 port 5093
[ ID] Interval       Transfer     Bandwidth
[320]  0.0-10.0 sec  1.25 MBytes  1.05 Mbits/sec
[320] **Sent 893 datagrams**

As you can see the client successfully transferred 893 datagrams meaning the port is open indeed. In case the firewall was blocking the port, you should read a message like this:

Read failed: Connection reset by peer
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