Ravindra BagaleCourses & study guides

Chapter 1: Networking Fundamentals

Common Mistakes I See Students Make

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  • Confusing IP and port. Opening port 80 in the security group does not give your server a public IP, and having a public IP does not open any port. You need both.
  • Opening every port to 0.0.0.0/0 "just to test". Then forgetting to close it. Databases like MySQL (3306) and MongoDB (27017) get attacked within hours.
  • Thinking 192.168.x.x or 10.x.x.x is reachable from the internet. Private IPs never route on the internet; that is the whole point of RFC 1918.
  • Forgetting that the auto-assigned public IP changes after stop/start. Students update their DNS or WordPress URL, stop the instance for the night, and the next day nothing works.
  • Using :: twice in an IPv6 address (e.g. 2001::1::5) — invalid, because the length becomes ambiguous.
  • Counting all addresses as usable. A /24 in AWS gives 251 usable IPs, not 256 or 254.