How to discover if a specific address/port is reachable?

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.

1

3 Answers

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

4

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

nmap should be able to handle this.

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