We can use nc (netcat) to test the connection between two servers.
For example, to test whether TCP port 1048 can be used on the server (IP 10.0.3.48 as an example) side:
On the server:
$ nc -l 1048
On the client
$ nc 10.0.3.48 1048
If it can connect to the server, type something into it. If the server can also see it, the connection has no problem.
For testing UDP connection, we can simply add the '-u' option to nc:
$ nc -u -l 1048
$ nc -u 10.0.3.48 1048
To check the ports which have programs listening to:
$ netstat -putln
More using examples of nc in "TCP/IP connection testing with nc (netcat)": http://www.xinotes.org/notes/note/1080/