osi-model

Again and again I read somethings about the osi-model without knowing it. This cause that I can not understand the things correctly. So I will describe the osi-model hoping to remember it and the different layers:

The user:
– layer 8: the user (this layer is more or less a joke and does not exists)

The application:
– layer 7: application layer (http, ftp, …)
– layer 6: communication layer or presentation layer (http, ftp, …)
– layer 5: session layer (http, ftp, …)

The transport:
– layer 4: transport layer (TCP/UDP, …)
– layer 3: network layer (IP, …)
– layer 2: data link layer (MAC, …)
– layer 1: physical layer (ethernet, …)

Layer 1 to 4 will manage the transport of all packages. Layer 5 to 7 provide the application-data-flow. Layer 8, which does not exists is the user. If it is a layer-8-problem than the it is the faul of the user.

most important ports #tcp/udp

Today I want to describe the most important ports that a developer probably should know about. So check this out:

  • 20: ftp-data (file transfer; default data)
  • 21: ftp (file transfer; control)
  • 22: secure shell
  • 23: telnet
  • 25: simple mail transfer
  • 53: domain name system (DNS)
  • 67: boostrap protocol server (dhcp server)
  • 68: boostrap protocol client
  • 69: tpft (trivial file transfer protocol)
  • 80: http
  • 110: post office protocol – version 3 (pop 3)
  • 119: network news transfer protocol
  • 123: network time protocol
  • 137/138/139: NetBIOS
  • 143: internet message access protocol (imap)
  • 161/162: simple network managment
  • 443: https
  • 445: Microsoft DS
  • 465: smpts (smtp secure)
  • 500: ip-security vpn
  • 587: simple mail transfer submission (smtp)
  • 993: impas (imap4 over tls/ssl)
  • 995: pop3 over tls/ssl
  • 989/990: ftp over tls/ssl
  • 3389: remote desktop