check / Scan a port

Arera · Joined: 23 Sep 2007 Posts: 386 Location: Wuppertal, Germany

Hi,
I'm using the WIZ820IO to send messages to a couple of destinations, via UDP and as TCP client.

By socketconnecting to the TCP server, I can find out if the server accepts the message by checking the result of socketconnect.

But what about UDP?
I can ping the destination IP, but that still does not say if the port is open.
Is there way to determin, if destination-port is open?

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

UDP is a connectionless protocol. So you never know if your data arrives. Only if you get an answer. But then you are making some kind of protocol.
UDP is good for raw data since it has less overhead. But for own development i would advise to use TCP.

MAK3 · Joined: 24 Sep 2010 Posts: 449 Location: Germany

Hi Arera,

I have written some Getting started here:
http://wiki.mcselec.com/MCS_Wiki_Main_entry

Maybe you can add your findings.

MAK3

Arera · Joined: 23 Sep 2007 Posts: 386 Location: Wuppertal, Germany

I m bound to udp, because it is standard for professional syslogging software.
I am not a network expert, but there are programs available to check open ports on a pc (portscanners). My idea is to build a portscanner to find out, if the desination port is open.
At this point my knowledge ends, so I hoped to find some ideas here!
Ben, evert and many others seem to know quite everything. Go ahrad, think!!!
Very Happy

MAK3 · Joined: 24 Sep 2010 Posts: 449 Location: Germany

Hi,

albertsm · Joined: 09 Apr 2004 Posts: 5916 Location: Holland

Thanks for your tutorials MAK3, i recently got a wiz820 Smile

. So it is good to have this info clearly presented.

About UDP : ping is essentially a protocol too : you send some data and when it is received by the host, it will send some data back.
But most servers have ports blocked or a stealth mode where they simply do not answer.
So my point is still that you can not know if a server is active, listening or whatever unless there is some protocol that uses UDP.
You should check the protocol for your equipment.

six1 · Joined: 27 Feb 2009 Posts: 553

not possible to scan Ports on UDP if you don't know exactly, what the Server does! (if you know details from how the server works, there is a little chance!)

http://de.wikipedia.org/wiki/Portscanner

UDP Scan
Ein direkter Scan von UDP Ports ist nicht möglich, da das Protokoll verbindungslos arbeitet.