devutils/ATFQ/book ATFQ git

Part I · How it works

6. How networks work

  1. 6.1Network layers: OSI and TCP/IPA network is built in layers, each using the one below: link (Ethernet, Wi-Fi), network (IP), transport (TCP, UDP), application (HTTP, DNS, SSH).
  2. 6.2What happens when you open a websiteDNS: the name becomes an IP address (19.2).
  3. 6.3IP addresses, subnets and NATAn IPv4 address is 32 bits, written 192.168.1.23. /24 means the first 24 bits name the network and the rest the machine.
  4. 6.4TCP, UDP and connectionsTCP gives a reliable, ordered stream: it numbers the bytes, waits for acknowledgements and sends again what was lost.
  5. 6.5Ethernet, MAC addresses and ARPOn a local network, frames travel from MAC address to MAC address: 48-bit hardware addresses such as f4:92:bf:0e:21:7a.