Wednesday, January 12, 2011

Check remote UDP connectivity from Linux

Hi there,
You all know how to check TCP port connectivity from a Linux or UNIX machine to a remote machine using telnet as per th example below
$ telnet 25

but we can't adopt TELNET to check UDP connectivity.

Linux and most of the UNIXes come with a network layer utility called nc (abbreviation for netcat) which is very useful to check UDP connectivity and to explore a lot with both TCP and UDP.

An example is shown below

# nc -v -u -z -w 3 123
Connection to 123 port [udp/ntp] succeeded!


shijusmart said...

Nice one !!!

Anonymous said...


It doasn't work under ubuntu!!

On a console I did:
root@gateway:~# nc -vv -u -l -p 123
listening on [any] 123 ...

On the other
root@xmg-pc:/tmp# nc -vv -z -u -w 3 localhost 123

As you see nothing happen!!

Psycho Tux said...
This comment has been removed by the author.
Psycho Tux said...

I do not understand -vv and -w.. The -w has nothing to along with -l option. Can you try without these options... And what is that localhost means. Are you trying locally on client machine xmg-pc? Try with gateway...