Sometimes we need to check the UDP Connectivity?  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
# nmap -p 123 -sU -P0

From the command shown above, I am assuming that the host is currently serving NTP service on UDP port 123.

Sample opened UDP port output:
Starting Nmap 4.52 ( ) at 2008-04-29 10:56 WAT
Interesting ports on (
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 (
123/udp closed ntp

Post By Gishore J Kallarackal (2,121 Posts)

Gishore J Kallarackal is the founder of techgurulive. The purpose of this site is to share information about free resources that techies can use for reference. You can follow me on the social web, subscribe to the RSS Feed or sign up for the email newsletter for your daily dose of tech tips & tutorials. You can content me via @twitter or e-mail.

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