Exam 312-50v13 topic 1 question 286 discussion

The correct answer is: **C. Linux OS** * **TTL (Time to Live)**: * A default **TTL of 64** is typically associated with **Linux/Unix-based systems**, including **Linux** and **macOS**. * Windows usually starts with TTL 128. * Solaris often uses TTL 255. * **TCP Window Size: 5840**: * The **default TCP window size of 5840** is **strongly associated with Linux systems**. * macOS typically uses a window size of 65535 or other values. * Windows often uses 8192 or 16384 as default window sizes. ### Conclusion: * **TTL 64 + Window Size 5840** = **Linux OS** fingerprint.

C) - Linux The common default TTL values are: • 64 – Linux/MAC OSX systems • 128 – Windows systems • 255 – Network devices like routers https://www.imperva.com/learn/performance/time-to-live-ttl/ A default TCP window size of 5840 bytes is historically associated with Linux-based operating systems (older kernels), specifically: • Linux 2.4.x and some early Linux 2.6.x kernels • Also seen in embedded Linux devices, such as routers or IoT gear based on older kernels Why 5840 Bytes? • The value 5840 bytes is intentionally chosen to fit within a 1460-byte MSS (Maximum Segment Size) without IP or TCP options. • This was a default TCP receive window that Linux used before dynamic window scaling became more common. • Modern Linux kernels typically negotiate higher window sizes using TCP window scaling (RFC 1323).

The TTL (Time to Live) and the TCP window size can be used to help identify the operating system of a target machine, as different OSes tend to set these values in specific ways. - TTL: 64: The TTL value of 64 is commonly associated with Linux or Mac OS. Both of these operating systems often use 64 as the default TTL value for outgoing packets. - Window Size: 5840: The TCP window size is another key indicator. A window size of 5840 is typical of Windows OS, as it generally uses values that are in this range. However, considering both the TTL and the window size together: - A TTL of 64 combined with a window size of 5840 strongly suggests Windows OS. In summary, based on the TTL value and window size, the target machine is most likely running Windows OS.