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Chapter 8: Network Infrastructure
Warning! This is a private system. All use is monitored and recorded. Any
unauthorized use of this system may result in civil and/or criminal prosecution
to the fullest extent of the law.
Testing firewall rules
As part of your ethical hacking, you can test your firewall rules to make sure
they’re working as they’re supposed to.
Testing
A few tests can verify that your firewall actually does what it says it’s doing.
You can connect through the firewall on the ports that are open, but what
about the ports that can be open but shouldn’t be?
Netcat
Netcat (http://netcat.sourceforge.net) can test certain firewall rules
without having to test a production system directly. For example, you can
check whether the firewall allows port 23 (telnet) through. Follow these steps
to see whether a connection can be made through port 23:
1. Load Netcat on a client machine inside the network.
This sets up the outbound connection.
2. Load Netcat on a testing computer outside the firewall.
This allows you to test from the outside in.
3. Enter the Netcat listener command on the client (internal) machine
with the port number you’re testing.
For example, if you’re testing port 23, enter this command:
nc –l –p 23 cmd.exe
4. Enter the Netcat command to initiate an inbound session on the testing
(external) machine. You must include the following information:
• The IP address of the internal machine you’re testing
• The port number you’re testing
For example, if the IP address of the internal (client) machine is
10.11.12.2 and the port is 23, enter this command:
nc –v 10.11.12.2 23
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