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I have 2 PCs at home connected to a router. I am trying to establish a TCP connection from PC2 to PC1. I have installed TCP Test Tool 3.0 on both and have set PC1 to listen on port 54100. On PC2 I have tried to establish a connection to PC1 (192.168.237.101) on port 54100. This port is unblocked in windows firewall on both PC1 & PC2.

PC1, using TCP Test Tool, shows nothing when I try and connect from PC2. So I installed WireShark on PC1. With WireShark I can see the TCP connection packet arrive at PC1. But for some reason the TCP Test Tool isn't seeing it (or is ignoring it for some reason).

What could be the issue?

[Edit] Further info:

PC1 Win8 - Firewall off, tried both fixed connection and wireless connection

PC2 WinXP - Firewall off, wireless connection

I can connect from PC1 to PC2 using TCP (and via telnet) I cannot connect from PC2 to PC1. Using netstat I can see a TCP listener on the correct port.

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    upvoted to 0 because I can't see why this question deserves a -1, it's well written and provides adequate information to begin troubleshooting.
    – YetiFiasco
    Commented Sep 24, 2014 at 9:29

3 Answers 3

Reset to default
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Ensure that both Windows firewalls are disabled. Ensure your TCP Test Tool software is running on PC2 and try to telnet from PC1 to PC2. If the tool is listening correctly you should get some feedback in your telnet window. If you don't see anything it may be that the tool isn't listening on the correct port. You can then use a netstat command on PC2 to check to see the ports that are open. Nick R.

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  • Thanks for that, see the additional info I have added. Works in one direction (the wrong one for my purposes). Any further suggestions for that to look at?
    – Dale K
    Commented Sep 24, 2014 at 9:24
  • You probably didn't mean it this way, the it was the "both windows firewalls" being both the F$%^&ing Public & Private profiles on Win8. When I first turned it off, I don't know where I was, but there was a single off box, but it was actually the wrong profile. Once I turned both profiles off it worked a treat. And while I had created exception rules, they also were for the wrong profiles. Bloody thing... thanks again.
    – Dale K
    Commented Sep 24, 2014 at 10:23
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So, wireshark says the packet arrives? No firewalls?

As a next step, just to exclude it, I'd recommend connecting a simple client-server setup using sockets, written in your preferred language. Admittedly I don't have one around... The client can actually be telnet, the server ideally displays what you write. Good luck.

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  • Hey Ben :) "TCP Test Tool" is pretty much exactly that - a simple client server setup using sockets. It was the firewall - see my comment above. Phew... thats a few hours of my life I will never get back.
    – Dale K
    Commented Sep 24, 2014 at 10:26
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Sometimes I really hate Windows Networking....

First have a look at this post and check my trouble shooting steps:

Complex Home Networking Setup Advice

Now some really extra stupid windows steps....

You have a 2 pc Lan, both connected to the same modem/router by Wi-Fi or Ethernet All TCP/IP settings on both machines are setup to the DEFAULT settings (all on auto)

PC1 has 8 gig of ram, windows 7 and is super fast PC2 has 2 gig of ram, windows 7 and is a bit slower

But PC1 can't share files with PC2 and vice versa, why not?

To make life easer in windows networking, over the years they added stuff that actually makes thing a bit harder.

1) The Home/Work/Public network choice

In order to increase security and make your computer hidden (therefore more safe because it's hiding) they came out with this setting. The more hidden your system is, the harder it is to get networking to work. In a home environment, choose Home Network for the type, this should make your computer completely visible to the other computers in your lan.

2) The workgroup

Both machines need to have the same workgroup name, the default: workgroup is ok if it's the same on both.

3) The Browse Master

One machine needs to be the Browse Master, this usually the fastest machine or the machine with the highest version of windows. The BM acts as a mini DHCP server just for your little LAN, and windows computers can and do fight sometimes for this role.

see this link about another's person issue with the BM:

http://scottiestech.info/2009/02/14/how-to-determine-the-master-browser-in-a-windows-workgroup/

and from Microsoft:

http://support.microsoft.com/kb/188305

4) The home group

Next you have to setup a homegroup, one machine must create it and password protect it therefore any other machine in the lan with the password can join the homegroup and share files

I know this makes it more complicated, but not really, if PC1 created the homegroup (with the default workgroup name) with the PW 123XXX. If I buy a brand new computer PC3 and I know the PW (123XXX) then I just have to connect the new pc to the router and join the homegroup, once the PW is accepted, I can start sharing files.

EASY??? no, but once it's all set up YES VERY EASY TO CONNECT

BUT REMEMBER: WINDOWS COMPUTERS DO NOT ALWAYS WORK THE WAY THEY ARE SUPPOSED TO EVEN IF YOU DO EVERYTHING RIGHT, SOMETIMES THE ONLY SOLUTION IS TO GO TO MAC OR LINUX

ALSO, if you need help with any of these steps, just ask

Larry Hyman

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  • I appreciate your efforts however as best I can tell none of those settings affect a raw TCP connection which is what I am interested in.
    – Dale K
    Commented Sep 24, 2014 at 1:09
  • I know it's crazy, but do me a favor, try putting in all the settings, also make sure you do not disable TCPIP6 in windows 7, in fact leave all the DEFAULT stuff as default. Then try your packet trace again. I know it's crazy but sometimes if the homegroup is not set up, then windows will just reject all incoming connections. Also, MAKE SURE THE WINDOWS FIREWALL IS OFF WHILE YOU ARE TESTING.. If all else fails (like it has happened to me so many times) It might be a problem with windows (on some machine) that may require a format and reinstall, why I don't know, so we waist five more hours...
    – Larry Hyman
    Commented Sep 24, 2014 at 1:17
  • Sorry dude, but as suspected your answer was not relevant to a simple low level TCP connection.
    – Dale K
    Commented Sep 24, 2014 at 10:26

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