Testing Port Availability

Networking/Security Forums -> Networking

Author: squiggie PostPosted: Wed Jul 05, 2006 8:28 pm    Post subject: Testing Port Availability
Good day everyone. I recently had a problem come up where I needed to test port availability and connection between a remote PC and a main PC. I could unc and transfer files from the remote to the main but I couldn't pull up pages on the main PC,which is hosting a web server, from the remote PC. I could however bring up pages from another PC inside the same subnet of the web server. This tells me that the web server is functioning but something is getting blocked by a router or firewall. I need to test the availability of port 80 and some other ports from the remote PC to the main.

Another tech told me that I could use telnet to test this since I couldn't really install an apps on the remote PC. My questions is, is this an accurate test for port availability? Does this simply tell telnet to try connecting on a specific port instead of using default port 23, and if so does all communication happen on that port specified? Also, would there be a way to test port availability on udp ports? Do any of you have any other suggestions for testing port availability without the ability to install any 3rd party apps? Thanks for all the help.

Author: apperraultLocation: Emeryville, CA PostPosted: Wed Jul 05, 2006 9:26 pm    Post subject:
for some programs this will work. i routinetly, if i am having connection problems, will try and telnet to the problem machine across the problem port.
telnet SERVENAME PORTNUMBER (telnet server 80) for example. That doesnt always work, but for somethings, and yes I think they are typically TCP protocols, they do work.

Other than that, I dont know of anything else that will tell you if a port is open. after i try to telnet, i usually end up greping through the Firewall or Router logs to find the source of the denial.


Author: ryansuttonLocation: San Francisco, California PostPosted: Wed Jul 05, 2006 10:16 pm    Post subject:
You could use a port scanner, google nmap.

Author: DaisetsuLocation: Arizona PostPosted: Thu Jul 06, 2006 2:17 am    Post subject:
nmap is probably your easiest way IF you can install software, which you said could be a problem.

If you have any way of remotely viewing your desktop (vnc, remote desktop, etc.) you could just do that then do GRC's shields up scan https://www.grc.com/x/ne.dll?bh0bkyd2

Author: ryansuttonLocation: San Francisco, California PostPosted: Thu Jul 06, 2006 4:01 pm    Post subject:
Nmap only needs to be installed on the source PC, not the remote PC.

Author: squiggie PostPosted: Thu Jul 06, 2006 5:36 pm    Post subject:
I didn't really think if shields up. The only problem with that is it scans 1 computer. I could scan the remotw computer and then the local one but I was looking for more of a straight through test solution. Good idea though.

I'll look into nmap. I haven't really played with that at all.

Thanks for the suggestions! Keep them coming if anyone can think of others.

Author: DaisetsuLocation: Arizona PostPosted: Thu Jul 06, 2006 11:21 pm    Post subject:
Whops, I must have read that wrong. I thought he said he couldn't install on the remote computer.

Author: windowsaliasgar PostPosted: Thu Nov 29, 2012 2:14 pm    Post subject:
Try to establish remote connection between main PC and remote PC using remote support services such as gosupportnow, logmeinrescue, GoToMyPC etc. and check whether remote connection gets successfully established or no. If yes, make sure that all the major ports on your firewall are opened up in order to test port availability.

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