Port triggering is a technique that allows inbound traffic to access certain ports on a device only after an outbound traffic request has been made from those ports. It can enhance the security and performance of a device by opening ports only when needed and closing them when not in use. The output from the network enumeration activities shows that port 21 (FTP) and port 22 (SSH) are open only after port 80 (HTTP) has been accessed, which indicates that port triggering is most likely being used. A web application firewall, an intrusion prevention system, port isolation, or port address translation are other techniques that can affect network traffic, but they do not match the description of the output from the network enumeration activities. Reference: https://www.techopedia.com/definition/3846/port-triggering