• DNS Main architecture
  • DNS Requests
  • DNS Zone file records
  • DNS Security
  • Useful commands / tool

DNS Main architecture

This post is a personal “pot-pourri” of some researches I have made on main memory (RAM) and OS initialization steps …


  • CPU real mode
  • CPU protected mode
  • Paging
  • Kernel memory management
  • Process memory management
  • ELF extension
  • Linux booting steps (for main memory)

CPU real mode

Most CPUs (Intel) start in “real mode”.
This mode…

This blog post follows the previous one on the Central Processing Unit (CPU).

“CPU, cores, tasks, hyperthreading, multithreading, user threads, multi-cores”
A lot of vocabulary exists when it comes to parallelism in CPUs / OS.
Moreover, we don’t know exactly what is responsible for what:
Hardware ? CPU ? Assembly ? OS…


  • What is a CPU ?
  • CPU main components
  • CPU interrupts
  • AMD, Intel, ARM

What is a CPU ?

The Central Processing Unit (CPU) is the brain / heart of a computer as it executes instructions.
Instructions are coded in a language called “assembly” which is the only one spoken by the CPU.
Each CPU manufacturer has its…

‘VPN’ has become a catch-all term nowadays.
What does VPN mean ?
→ A software used to insure privacy on the internet ?
→ A way to connect 2 distant private networks together ?
→ An encryption mechanism ?
→ A tunneling protocol ?
→ A type of router / firewall ?
→ A layer 2…

This blog post aims to create a big picture of cryptography in the IT world.


  • Vocabulary
  • Symmetric Ciphers
  • Asymmetric ciphers
  • Diffie-Hellman key exchange
  • Hash
  • HMAC — Keyed-hash message authentication code
  • Digital Signature
  • Certificates


In the last blog post, we studied the Internet Protocol and how computers can transmit packets between them.

Now let’s understand two most commonly used upper-layer protocols: UDP and TCP.


  • UDP
  • TCP
  • Socket abstraction

UDP (User Datagram Protocol)

UDP is very close to the lower protocol (IP) as it doesn’t add much features /…

This blog post aims to create a big picture of the Internet protocol (IP) and the internetwork infrastructure allowing the transmission of IP packets.


  • Main IP transmission principle
  • IP packet anatomy
  • Routers
  • How are IP addresses attributed to LIRs (Local Internet Registries)?
  • Routing inside a LIR?
  • Routing between LIRs: BGP…

Studying network programming, I understood how to use Linux sockets in order to communicate with other systems/computers. I also studied a lot of higher level technologies built on top of sockets such as http, ssh, ftp.

I wrote this blog post while improving my understanding of Linux kernel networking features…

Images are at the source of nearly every media. Therefore, I think it is interesting to get a glimpse of how images are stored on a computer. I have decided to get a tour of the most famous image format : jpg (or “jpeg”, as you may prefer).


  1. The basics

Grégoire Monet

I write my own computer science “cheatsheets” and “big pictures” as posts here. I mainly do it for myself but it may benefit others

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