[CALUG] More UDP foolishness

Jason C. Miller jason.c.miller at gmail.com
Thu Apr 13 22:45:06 CDT 2006

Oh...almost forgot.  The UDP port in question doesn't reside on your 
local machine.  Therefore, 'netstat' and other tools like that don't 
apply.  ;)


Jason C. Miller wrote:

>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. 
>                                                       -j   
>Columbia, Maryland Linux User's Group (CALUG) mailing list
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My blog: http://millersplace.blogspot.com/ 

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