128 is the TTL value that Henry obtained, which indicates that the target OS is Windows. TTL (Time to Live) is a field in the IP (Internet Protocol) header that specifies how long a packet can remain in a network before it is discarded or dropped. TTL is usually expressed in seconds or hops (the number of routers or gateways that a packet passes through). TTL is used to prevent packets from looping endlessly in a network or consuming network resources . Different operating systems have different default TTL values for their packets. By observing the TTL value of a packet from a target system or network, one can infer the operating system of the target . Some common TTL values and their corresponding operating systems are:
* 64: Linux, Unix, Android
* 128: Windows
* 255: Cisco IOS
* 60: Mac OS
In the scenario, Henry used Nmap tool to discover the OS of the target system. Nmap (Network Mapper) is a tool that can perform various network scanning and enumerationtasks, such as port scanning, OS detection, service identification, etc . Nmap can use various techniques to detect the OS of a target system, such as TCP/IP fingerprinting, which involves analyzing various TCP/IP characteristics of packets from the target system, such as TTL value. In the scenario, Henry obtained a TTL value of 128 , which indicates that the target OS is Windows.