UNIX for Dummies Questions & Answers

Hi gurus of unix!!!!, I have a little question. I nedd your helps
The scenarios is the following
I have tree equipment that are installed in different places. I use a carrier to interconnect the equipment.
Some Port's (TCP) need to be open for an application that must be function correctly.
For example:
Place 1: have the following IP 10.20.30.1
Place 2: have the following IP 20.30.40.1
Place 3: have the following IP 30.40.50.1

The application need the following port(TCP), for example 1020, 21, 53, 8080

I talk to the Network Administratos of the Carrier and he tell me that these port (TCP) are open in your firewall/router.
The question is How I verify that this port are open?,
Suppose that the application is properly installed
Help me please.
Regard
Andres

Generally you can telnet to the port to see if it's open. If you get "Connection refused" that means 1) you can't get to that port/ip or 2) there's nothing listening on that port. If you are able to connect and have to break out of the telnet session you were successful.

To telnet to a specific port use:

telnet <ip> <port>

so:

telnet 10.20.30.1 1020
telnet 10.20.30.1 21
...

Very simple:

Code:

nmap -sS -vvv -p 1020,21,53,8080 10.20.30.1 20.30.40.1 <...>

Very, very simple, though hard to properly automate:

Code:

telnet 10.20.30.1 21
telnet 10.20.30.1 1020
...

Slightly more complex, but ideal for automation:

Code:

netcat -z -w 3 10.20.30.1 21 && echo "Open" || echo "Closed"

Thanks!!!!!!
mglenney, pludi
Excellent tips!!!!!!!