The Internet is an interconnected collection of separate IPv4 and IPv6 networks, all communicating over a series of standardised protocols conceptualised in the OSI model. Traffic is routable between these separate networks.

Types of network

  • A LAN, or Local Area Network, refers to a single site.
  • WLAN refers to a Wireless LAN.
  • WAN, or Wide Area Network, typically refers to a network of LANs connected across the Internet via a VPN or via a private backbone.
  • PAN refers to a Personal Area Network, e.g. a mobile hotspot.

Types of communication

  • Unicast: direct node-to-node communication
  • BUM:
    • Broadcast: communication from one node to all peers within its Broadcast domains.
    • Unknown-unicast: communication from one node to another where the switch does not have the destination in its forwarding information base. The switch must mark the frame for flooding and send it to all forwarding ports within the VLAN. Known as unicast flooding.
    • Multicast: communication from one node to a subset of grouped nodes.


There are two commonly used transports on the Internet today:

  • TCP/IP provides reliable, ordered transmission of segments over sessions.
  • UDP offers lighter weight communication with lesser delivery guarantees.


Ports are used to expose multiple services from the same host address. They're grouped into defined ranges:

  • Source ports assigned to clients for sessions are in the ephemeral range (49,152–65,535)
  • Well-known ports between 0–1,023
  • Registered port numbers between 1,024–49,151

  1. 5-tuple
  2. Broadcast domains
  3. DNS
  4. Ethernet
  5. HTTP
  6. IPv4
  7. IPv6
  9. Kerberos
  10. LDAP
  11. Language Server Protocol
  12. OSI model
  13. Protocol Buffers
  14. Protocols
  15. SDN
  16. Services
  17. TCP
  18. Topologies
  19. UDP
  20. VLAN
  21. gRPC