I know that's not the answer you are looking for. But basically it's learning, learning, learning and practicing.
Given that you have a strong understanding of networking technologies and TCP/IP (that's the foundation network security builds on), read books about general networking security. Look for online videos/courses for network security. If you are interested in certification, study for CompTIA Security+, then go on with Cisco CCNA Security. While studying you'll get the idea on how to answer your question or to ask a question that can be answered.
