Internet & Networking Basics
Every telecom and IT professional needs a solid understanding of how networks actually work — from how data is broken into packets, to how those packets find their way across continents. This guide covers the foundational models, protocols, and concepts that underpin the internet and every enterprise network on Earth.
The OSI Model — Seven Layers
The OSI (Open Systems Interconnection) model, published by ISO in 1984, defines a seven-layer framework for understanding how data travels from one device to another. Each layer handles a specific responsibility and communicates only with the layers directly above and below it:
The layer closest to the end user. Application protocols define how software applications format and exchange data. HTTP is the protocol of the web; SMTP carries email; DNS resolves hostnames to IP addresses.
Provides end-to-end communication between applications. TCP guarantees delivery and ordering via acknowledgements and retransmission. UDP is connectionless — faster but with no reliability guarantee, used for real-time media and DNS queries.
Handles logical addressing (IP addresses) and routing — choosing the path a packet takes across multiple networks. Routers operate at Layer 3, reading the destination IP address and forwarding packets toward their destination.
Handles communication between directly connected devices on the same network segment. Uses MAC (Media Access Control) addresses to identify devices. Switches operate at Layer 2, forwarding frames based on MAC address tables learned from network traffic.
Layer 1 (Physical) — raw bits over cable, fibre, or radio waves; defines voltages, frequencies, and connector types. Layer 5 (Session) — manages sessions between applications (TLS handshake setup, dialog control). Layer 6 (Presentation) — data formatting, encryption, and compression (TLS encryption, JPEG encoding). In practice, Layers 5 and 6 are rarely discussed separately — most real-world protocols handle these functions within the application layer.
TCP/IP — The Internet's Protocol Suite
While the OSI model is a conceptual framework, TCP/IP is the actual set of protocols that powers the internet. It uses a simpler four-layer model:
All application protocols: HTTP/HTTPS (web), SMTP/IMAP/POP3 (email), FTP/SFTP (file transfer), DNS (name resolution), DHCP (address assignment), SSH (remote access), SNMP (network management). These protocols define what data means and how applications communicate.
TCP and UDP. TCP provides reliable, ordered, byte-stream delivery: connection established via 3-way handshake (SYN, SYN-ACK, ACK), data acknowledged per segment, lost segments retransmitted. Used for web, email, file transfer. UDP sends datagrams with no acknowledgement — used for DNS, VoIP, video streaming, gaming where speed matters more than guaranteed delivery.
The IP protocol provides addressing and routing. Every device on the internet has an IP address. IPv4 uses 32-bit addresses (e.g., 192.168.1.1) — about 4.3 billion total, largely exhausted. IPv6 uses 128-bit addresses (e.g., 2001:db8::1) — effectively unlimited. Packets carry source and destination IP addresses; routers use these to forward packets hop-by-hop toward the destination.
How bits are transmitted on the local network: Ethernet (copper/fibre LAN), Wi-Fi (802.11), fibre optics (SONET/OTN in carrier networks). ARP (Address Resolution Protocol) maps IP addresses to MAC addresses on the local segment, bridging the Network and Data Link layers.
IP Subnetting and Addressing
- Subnet mask — divides an IP address into network portion and host portion; e.g., /24 mask (255.255.255.0) means the first 24 bits are the network, last 8 bits are hosts (up to 254 usable)
- CIDR notation — Classless Inter-Domain Routing writes a subnet as address/prefix-length: 10.0.0.0/8, 192.168.1.0/24, 172.16.0.0/12
- Private ranges — 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 are reserved for internal networks; NAT (Network Address Translation) maps them to public IPs
- DHCP — Dynamic Host Configuration Protocol automatically assigns IP addresses, subnet masks, gateways, and DNS servers to devices when they join a network
- DNS — the Domain Name System translates human-readable names (google.com) to IP addresses (142.250.74.46) via a hierarchy of resolvers, TLD servers, and authoritative nameservers
Routing and Switching
A switch connects devices on the same LAN. When a frame arrives, the switch reads the destination MAC address and looks it up in its MAC address table (learned by reading source MACs of incoming frames). If found, the frame is forwarded only to the correct port — not flooded to all ports. VLANs allow a single physical switch to host multiple isolated logical networks.
A router connects different networks (e.g., your home LAN to the internet). It reads the destination IP address and looks up a route in its routing table — selecting the next-hop router and exit interface. Routing tables are built using static configuration or dynamic routing protocols (OSPF, BGP, EIGRP).
Dynamic protocols allow routers to automatically learn and share routes:
- OSPF (Open Shortest Path First) — a link-state protocol used within enterprise and carrier networks; routers build a complete map of the network topology and calculate shortest paths using Dijkstra's algorithm
- BGP (Border Gateway Protocol) — the routing protocol of the internet; used between autonomous systems (networks owned by different organisations); BGP carries routing information for ~900,000+ prefixes across the global internet
- EIGRP — Cisco-proprietary hybrid protocol; fast convergence within large enterprise networks
More Guides Coming Soon
This section is actively being expanded. Upcoming guides will cover:
- Network Security Basics — firewalls, VPNs, IDS/IPS, and zero-trust architecture
- WAN Technologies — MPLS, SD-WAN, leased lines, and carrier Ethernet
- Wireless Networking — Wi-Fi 6/6E/7 (802.11ax/be), Bluetooth, Zigbee, and unlicensed spectrum
- Network Virtualisation — SDN (Software-Defined Networking), NFV (Network Functions Virtualisation), and virtual switching
- Cloud Networking — VPCs, load balancers, CDNs, and how cloud providers interconnect with the internet