can’t telnet a port even the port is open

I saw a similar question but it does not answer mine. so I have a program running on a server machine with port, 1234, say, I want to telnet from another machine, the port 1234 is open for listening on server machine, when I use “telnet 1234″ from my client machine, I got “trying …” then it never finishs trying.

the other similar post says: I need to configure client host? how? my two machines are all running ubuntu linux.