[CALUG] More UDP foolishness

Kelly Price strredwolf at gmail.com
Thu Apr 13 23:12:58 CDT 2006

On 4/13/06, Jason C. Miller <jason.c.miller at gmail.com> wrote:
> 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.  ;)

So we're looking at a remotely connected PC.

We need to know where you are connected in relation to that PC, and if
your laptop has Linux on it.

* If it's on a local network (wire/wireless), nmap.
* If it's not, but the PC has an direct IP address and so do you, nmap.
* If ether end is firewalled or behind a NAT router, you're screwed!

>                                                                -j
> 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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> --
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Kelly "STrRedWolf" Price

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