[CALUG] More UDP foolishness

Jason C. Miller jason.c.miller at gmail.com
Thu Apr 13 22:43:19 CDT 2006

Heck....why not!  Here's my random question for the week...  :)

So, anyway, a lot of troubleshooting and investigation is required with 
the stuff that I work on.  For as long as I can remember, I've used 
'telnet' as the simplest way to determine whether or not a TCP port is 
bound to by an application on a machine.  It's simple, quick, easy, and 
comes stock on just about every OS imaginable.  It's a good way to 
verify that the 3-way-handshake works on a given port.


Can't say it's been quite that simple for the UDP side of the house.  
Since UDP is connectionless, the mechanisms for determining if a port is 
bound to is a tad different.  Instead of conveniently getting a 
(RST,ACK) TCP reply, UDP relies on the receipt of ICMP 'Destination 
Unreachable' messages to tell it that the port is not open.  Typically, 
I've relied on applications like nmap.  However, I don't really feel 
like installing it wherever I go.  I've also written simple progs to do 
it, but it's very inconvenient.

So, the question is....can anybody recommend a COMMON program that you 
would find on most operating systems that could be pointed at an 
arbitrary UDP port and would tell you the status of that port?  Seems 
like it'd be simple, but I can't seem to think of any at the moment. 


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