How to test UDP Connectivity
Sometimes we need to check the UDP Connectivity? Â There are few free tools available in the net to test the UDP Connectivity but here we are going to describe about a utility called nmap, by which we will test the UDP Connectivity.
How would you be able to test and probe a port that listens for UDP connections? Or  how would you test a listening UDP port?
How to test a listening UDP port
If you have managed to create a daemonized service that opens port for UDP connections, here’s how to test that listening UDP port for UDP connections. Read on.
To test a listening UDP port, simply use nmap.
# nmap -p [port] -sU -P0 [host name | ip address]
# nmap -p 123 -sU -P0 example.com
# nmap -p 123 -sU -P0 123.123.123.123
From the command shown above, I am assuming that the host example.com is currently serving NTP service on UDP port 123.
Sample opened UDP port output:
~~~~~~~~~~~~~~~~~~~
Starting Nmap 4.52 ( http://insecure.org ) at 2008-04-29 10:56 WAT
Interesting ports on host.example.com (123.123.123.123):
PORT STATE SERVICE
123/udp open|filtered ntp
MAC Address: 00:02:A5:EC:00:8C (Compaq Computer)
Nmap done: 1 IP address (1 host up) scanned in 1.043 seconds
~~~~~~~~~~~~~~~~~~~
Not only you get to test and scan the UDP port, you also get the host’s current MAC address.
If you have a closed UDP port, you should be seeing similar lines as shown
~~~~~~~~~~~~~~~~~~~
Interesting ports on localhost (127.0.0.1):
PORT STATE SERVICE
123/udp closed ntp
~~~~~~~~~~~~~~~~~~~
hi
This does not work.
You can do it with a non-existent port on a remote host and it still comes back as filtered.
The only way to truly test if a UDP port is being filtered or blocked is if you have a server-side component on the “other side” of the device blocking you whereby you can try to send data back and forth to the server on a given UDP port.
Microsoft has PortQry, but it’s more for techies. For a web based solution you can use firebind.com. It’s a server on the Internet with a corresponding Java client that allows a user to send UDP or TCP packets from their machine to the Firebind server over any of the 65535 UDP or TCP ports. If the data packets can be sent back and forth to the server successfully over the given UDP or TCP port, then the port isn’t being blocked.
Perfect !!
It’s works
I’m looking for a tool like “firebind” that is non web based but that I can install on a Trixbox/Centos server that has no GUI but only text mode interface.
In fact I’d like to test outbound connection from this server machine to Internet from command promt.
Any idea?
Thanks in advance.
I’m surprised nobody here has mentioned netcat.
netcat (nmap has a rewrite called ncat) has a udp option (-u).
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