Let's use Metasploit to perform firewall identification:

1. To use the Metasploit ACK scan module to perform firewall and filtering identification, you must first launch the MSF console from a Terminal in Kali Linux and then select the desired auxiliary module with the use command:

2. Once the module has been selected, the show options command can be used to identify and/or modify scan configurations. This command will display four column headers to include: Name, Current Setting, Required, and Description:
   • The Name column identifies the name of each configurable variable
   • The Current Setting column lists the existing configuration for any given variable
   • The Required column identifies whether a value is required for any given variable
   • The Description column describes the function of each variable
3. The value for any given variable can be changed using the set command and providing the new value as an argument:

4. In the example provided, the RHOSTS value was changed to the IP address of the remote system that we wish to scan. Additionally, the number of threads is changed to 25. The THREADS value defines the number of concurrent tasks that will be performed in the background. Determining thread values consists of finding a good balance that will noticeably improve the speed of the task without overly depleting system resources. For most systems, 25 threads is a fast and reasonably safe number of concurrent processes.
5. After updating the necessary variables, the configurations can be verified using the show options command again. Once the desired configurations have been verified, the scan can be launched:

Results have been truncated for space. The following is the conclusion of our scan:

In this instance, the only output provided is the metadata about the scan to indicate the number of systems scanned and that the module execution has completed. This lack of output is due to the fact that the responses associated with the SYN and ACK injections were exactly the same from port to port because the Metasploitable2 system that was being scanned is not behind any firewall.