ACK scans

Another interesting method of scanning is enabling the ACK flag within a packet. This technique is used to determine any form of filtering that may be performed by a network security device, such as a firewall.

While we haven't talked about firewalls yet, we are going to a little later. However, for right now, we will say that firewalls perform filtering of traffic from one network to another (for example, the internet to your local intranet

During a penetration test, we may be on the external network of the organization, such as the internet. Most organizations deploy a firewall at their perimeter, between the internet and their local area network (LAN) to help prevent any threats from entering or leaving their network. We can use an ACK scan to help us determine whether our target organization has a firewall in place. To execute an ACK scan, select ACK from the list in the nmap window in the NetHunter app and enter the target IP address:

ACK scan selection from dropdown