What does Nmap's -sO option accomplish during a penetration test?

Nmap's -sO option is specifically designed to scan for IP protocols that are in use on a target host. When this option is employed, Nmap sends packets with various protocol numbers in the IP header and then observes the responses. This allows penetration testers to identify which protocols are implemented and available on the target system, such as ICMP, UDP, and others, which can provide insights into the network's configuration and security posture.

Understanding the IP protocols in use can help in uncovering potential weaknesses or unauthorized services running on a system, as some protocols may be less commonly used or may not be secured adequately. This information can be valuable when planning further attacks or assessing the overall security of the network infrastructure.