Need to check connectivity between PCs on specific port...

[FoolishTech]

Is there any software, not a port scanner, but a port TESTER, where I can use to test communication between two PCs on a specific port?!?

I have a client with a software vendor who just cannot get their software to work for my client, and the client is starting to get ill with my company over the issue. The software resides on five workstations and a "server" (another workstation) all in a workgroup configuration, no domain.

The 3rd party client software seems to stall when it tries to connect to the server component, so their crappy software just sits there eating up 50% cpu appearing to do nothing but display a splash screen, and leading the software company to believe that something between the client workstation and the server is blocking it's particular UDP port. So they are throwing the ball into our court, saying there is an issue with the network we need to fix.

That may be, our client is a convention center and regularly has customers splicing into their network and messing with stuff. Last time I was physically out there a customer had plugged in their own switch in one of the closets, and had removed a patch cable from one of the main switches to plug it up, leaving several other rooms without network connectivity! Oh yeah. There is a domain and several independent workgroup setups there, several wiring closets, two server rooms, etc. It's a big place with lots of patchwork due to having different IT companies over the years. As much as that's a bad situation, they don't want to pay us to fix it. Also, we like to work remotely due to distance, so we're not going out there for some simple issue with this 3rd party software vendor when everything else on the network is working properly.

I would run a port scanner from the workstation targeted at the server to see if the port appeared open, but it doesn't -- UDP doesn't always respond well to port scanners I've discovered after reading several articles, plus who knows how the server component listening on that UDP port reacts to the scanner...

Everything else works between the two workstation and server, ping, file and printer sharing, etc. Naturally I've had the company try it's software with firewalls/anti-virus disabled. I've even formatted/reloaded Windows on both one workstation and the "server" after the software company initially blamed it on a virus.

So in short, I'm looking for a port TESTER of sorts, that I can use to test communication between two PCs on a specific port?!? Is there another way, or something more simple than I am thinking of? I'm by no means a network guru and have been assigned this issue by others who possibly are, but think their time is too valuable to mess with this issue. Any tips for me?

Thanks!

[Elemdee]

I'm wondering if Wireshark would do what you're looking for...take a look at this...steps 4 and 5. Rather confusing looking if you've not used it before (as I haven't, lol) but it's used a lot in Networking captures, etc.

http://wiki.wireshark.org/CaptureSetup

download at www.wireshark.org

[onetech4all]

How about the command netstat -an to check for the open port that needs to be opened? You can use, I think, it's called fport to see what service is running on what port or the port that you need the software to run on.
Could you have software/OS compatibility issues and that's why all you get is just a splash screen?
If you need just a port scanner, that you can run against a machine on the network, use ipscan from angryziber.com.

[Rodrick]

Telnet?

(filler text)

[Martyn]

Netstat will tell you what ports are being used. It could be the port is already in use by another program, it happened to me once. You could see if you can change the port it uses a lot of programs allow this. What port number is it working on? The machine you are trying to connect to should be 'listening' on that port

[TechguyUK]

Originally Posted by Rodrick

Telnet?

+1 Telnet.

Setup a server on one machine, listening on whichever port you want and then use 'telnet xxx.xxx.xxx.xxx yy' where x is the IP address of the server and y is the port

[snifferpro]

My vote would be for Wireshark.

In basic use, you can just start a standard capture and capture all packets on
the network.

I would start Wireshark, start a capture (without filter), and have the workstation
attempt to contact the server. Let the capture run for 5 minutes then stop it. Shouldn't need
more than that.

Find the IP address of the workstation, and filter for that ip address in your capture
file.

You should see the request go out to the server and the response from the server.
If you get no response, then the problem would most likely exist on the server
and not on the network.

You can also filter on the servers ip address looking for requests from the client ip
address and the servers response. Again, if the server doesn't respond then the issue
is on the server. If there is a response from the server, then you have to look at
where that response is going.

This is where Wireshark or any packet sniffer shines.

[Martyn]

Yes if you understand packet/frame tracing Wireshark is definitely the way to go. Used it, and it's previous name Ethereal, many times over the years.