Question

I am trying to use this c socket class, but it only works when I use it on my own computer.

Desktop only

Server is started like this: cSocketServer -p:2030 -i:192.168.178.22

Client connects: cSocketclient -p:2030 -s:192.168.178.22

Works fine.

Desktop server, laptop client

Server: cSocketServer -p:2030 -i:192.168.178.22

Client: cSocketclient -p:2030 -s:192.168.178.22

Exact same as above, but this fires the connect failed: 10060 error. Which essentially means it timed out.

Desktop only (external address)

Server: cSocketServer -p:2030 -i:192.168.178.22

Client: cSocketclient -p:2030 -s:xx.xx.xx.xx

Where xx.xx.xx.xx is my external ip address.

Same error: connect failed: 10060. Port 2030 is definitely open and accessible, because I tested it with a few unrelated applications that allow their users to choose their own ports (like utorrent). While those run, whatismyip.org states port 2030 is open. But when I run my application it sais it Timed-out. Those applications do not have any special privileges in the firewall.

But even if I did mess up some firewall/router settings (which I’m fairly sure I didn’t) that wouldn’t explain why I can’t connect to the server from within my local network. Other services (such as file sharing) work fine so there is definitely a connection between the 2 computers.

Both client and server run on windows 7 64-bit.

Also; for some reason, each client that connects gets their own inbound port assigned or something? Is that normal? When clients connect the server states;

Accepted client: 192.168.178.22:55156
Accepted client: 192.168.178.22:55164
Accepted client: 192.168.178.22:55176

What’s that all about?

Answer 1

If two TCP connections have the same source IP, destination IP, source port, and destination port, there would be no way to tell them apart. To ensure they differ somewhere, clients typically assign a unique source port to every outbound connection they make.

As for the errors, you really need to do some troubleshooting. Do the listening sockets show up in a ‘netstat’? Do you get the same problem with the firewalls turned off? Are the server and client on the same LAN (for the internal address case)? Is port forwarding enabled and working in the router (for the external address case)?

My bet is that the external address case won’t work because you haven’t configured the port to be forwarded by your router or your router doesn’t support hairpin (local access to external IP). Other programs may work because they support UPnP or don’t rely on hairpin (all access to external IPs come from outside your LAN).

I have no immediate explanation for why your desktop-to-laptop won’t work inside your LAN. Are you sure both computers are in the same LAN? Can they ping each other?