[CALUG] More UDP foolishness

Eric K. Dickinson Eric.Dickinson at nih.gov
Fri Apr 14 06:20:59 CDT 2006

nc ?

Eric K. Dickinson
Building Engineer
8778548389 at page.metrocall.com

CNE, GNU/Linux Geek Windows 2000 MCSE, CISSP

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.
> However...
> 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   
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