software not working because of port block?

I have a proprietary software on two different internal networks. on one the client-side software can access the server, and the second network, they can't.

I have no real clue which ports are needed,

1. What's the best way to find out? will telnet x.x.x.x port# work?

2. Does one side (server) have to be listening on a port to be able to detect that it is open? If it doesn't listen, than requests end up no where. right?

3. For Window share ports (nmbd,smbd), is it possible to check with the telnet method? What's a good way to check these?


Thanks for any information regarding any of the above,


PS: both networks are able to ping the server IP where the server-side portion is located.



Dan

re: software not working because of port block?

My recommendation would be to put a software package sniffer on both and attempt to connect. You can then filter by 'outgoing.' Depending on what OS these are on, there are different ways to do that.

You'll see the initial handshake from one box's IP to another, and from there open that first port. Then repeat the whole thing, and you'll see what the other box responds on.

If these are Windows, you can use Wireshark; Linux - tcpdump.

To test to see if the port is open you can run the telnet test, but you will first need to ensure the other server is listening on that port, probably with the nestat command.

re: software not working because of port block?

Thanks, found the ports. IT Dept is blocking them. It's their problem now.

re: software not working because of port block?

netstat is a useful tool to find out this sort of information too, and it is part of Windows and Linux so doesn't need installing on either system, although as is often the case where Windows has copied a *nix tool the *nix one has more features.

However it lists all open sockets and if the are listening or connected allong with port numbers and IP addresses and can also resolve which program opened them.