Basic concepts

  • All traffic on the internet is split-up into messages called packets

  • packet is a short message sent from one computer to another.

  • ping is simpler than HTTP, but HTTP is not based on ping

  • In everyday softwares the HTTP layers is implemented by programs such as browsers and servers

  • Lower layers such as TCP is implemented in the Operating System.

  • nc command is a thin wrapper over TCP

Layer Protols Concepts
Application HTTP, SSH URLs, password
Transport TCP, UDP port numbers, sessions
Internet IP IP Address, routes
Hardware wifi, ethernet, DSL signal strength, access points

  • Each Top layer depends on the layer below it, however each layer functions independently and do not need worry about the layers below it

  • ports distinguishes different applications/programs running on the same server. nc command is used to listen on to that port.

  • The port range that a normal (non-root) user can listen on is 1024 through 65535.

  • But if you use root access (including sudo) then you can listen on ports down to 1.