The TCP segment header does not include a total length field but only a header length field, how can TCP carry variable length data? Can the Internet specify the maximum lifetime for an IP datagram in wall-clock time(say, 24 hours) to limit the impact of those packet that traverse over looped routes? Justify your answer. What is the right mechanism used by the Internet? Assume the solution that allow us to incrementally/gradually upgrade the Internet with Ipv6 over time to replace the current IPv4 + what is the extra transmission overhead the solution has to pay? + Does every Internet router only need to operate one protocol, i.e, either IPv4 OR IPv6 but not both. Briefly explain what the man-in-the-middle attack is, and how you can defend against man-in-the-middle attack