Poor man's firewall test

on the Destination host:

nc -l myhost.acme.com 3872

and make sure you are actually listening:

netstat -an | grep 3872
tcp        0      0 10.33.80.121:3872           0.0.0.0:*                   LISTEN

On the Source host:

echo ciao | nc myhost.acme.com 3872

and the "ciao" should appear on Destination and the nc should exit.

If you don't have nc installed, there are alternatives to nc:

wlst or python:

import socket
HOST = 'myhost.acme.com'
PORT = 3872
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

s.connect((HOST, PORT)) 

s.send('Hello, world')
data = s.recv(1024)
s.close()

(see http://docs.python.org/release/2.5.2/lib/socket-example.html)

or simply  run

telnet myhost.acme.com 3872

To receive data, run Java or python:

from java.net import ServerSocket

ss = ServerSocket(3872)

ss.accept()

(see http://docs.oracle.com/javase/6/docs/api/java/net/ServerSocket.html )

The great advantage of nc is that you can bind to any IP on the source host:

nc -s "your_ip_here"

To check if nc could actually connect, do:
echo ciao | nc....
echo $?

1 means "unable to connect", 0 means "connected"

echo a | nc -s "10.26.20.116" -w 1 10.51.87.24 1722 ; echo $?

A script to check firewall could very well be:

#!/bin/sh
#This script is to check that a firewall rule is operational
#Author name : Pierluigi Vernetto


function checkFirewall {
 sourceIPsArray=$(echo $sourceIPs | tr "," "\n")
 destinationIPsArray=$(echo $destinationIPs | tr "," "\n")
 for sourceIP in $sourceIPsArray 
 do
        for destinationIP in $destinationIPsArray
        do
            echo a | nc -s "$sourceIP" -w 2 $destinationIP $port
            if [[ $? -eq 0 ]] 
             then echo $sourceIP $destinationIP $port success
             else echo $sourceIP $destinationIP $port failure
            fi   
        done
    done
}

sourceIPs=10.56.218.91,10.56.218.93,10.56.218.90,10.56.218.94,10.56.218.92
destinationIPs=10.56.128.10,10.56.128.8,10.56.128.9
port=1522

checkFirewall