Technical Resources

Networking Fundamentals

Networking Fundamentals: TCP/IP, OSI, Subnets, and Protocols

Computer networking is the practice of connecting devices so they can share data. The foundation is the TCP/IP protocol suite, which governs how packets are addressed, routed, and delivered. Understanding IP addressing, subnetting, routing, and switching gives you the framework to configure, troubleshoot, and secure any network.

The OSI model and why it matters

The Open Systems Interconnection (OSI) model divides network communication into seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer has a specific job and interacts with the layers directly above and below it. The model is a conceptual framework, not a rigid implementation, but it gives technicians a common language for isolating problems: a physical-layer issue (bad cable, failed port) is entirely different from a transport-layer issue (TCP session not completing).

In practice, most modern networking is described using the TCP/IP four-layer model: Link, Internet, Transport, and Application. IP operates at the Internet layer, TCP and UDP at the Transport layer, and protocols such as HTTP, DNS, and SMTP at the Application layer. Mapping between the two models is straightforward once you understand what each layer is responsible for.

IP addressing and subnetting

Every device on an IP network needs a unique address. IPv4 addresses are 32 bits long, written as four decimal octets separated by dots (for example, 192.168.1.10). A subnet mask determines which portion of the address identifies the network and which identifies the individual host. CIDR notation (such as /24) expresses the same information more concisely by stating how many bits belong to the network prefix.

Subnetting divides a larger address block into smaller, more manageable networks. The calculation requires understanding binary representation of IP addresses, but the logic is consistent: borrow bits from the host portion to create more network identifiers, at the cost of fewer hosts per subnet. Private address ranges (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) are reserved for internal use and are not routable on the public internet without Network Address Translation (NAT).

Routing, switching, and the path a packet takes

A switch operates at Layer 2 (Data Link) and forwards frames within the same local network using MAC addresses. It maintains a MAC address table and sends traffic only to the port where the destination device is known, rather than flooding every port. VLANs extend the switch's usefulness by creating logical network segments on shared physical infrastructure.

A router operates at Layer 3 (Network) and moves packets between different networks using IP addresses and a routing table. Routes can be configured statically or learned dynamically through routing protocols such as OSPF, BGP, or EIGRP. Understanding the difference between a router and a switch, and knowing where each fits in a network diagram, is fundamental to any networking role and to every major IT certification.

Core protocols every technician should know

DNS (Domain Name System) translates human-readable names like example.com into IP addresses that routers can use. DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses, subnet masks, default gateways, and DNS server addresses to devices when they connect. These two protocols handle most of what goes wrong in a basic connectivity complaint: if a device cannot reach the internet, DNS and DHCP are the first things to verify.

TCP (Transmission Control Protocol) provides reliable, ordered, error-checked delivery by establishing a connection with a three-way handshake before data flows. UDP (User Datagram Protocol) is connectionless and faster, used where some packet loss is acceptable, such as streaming video or DNS queries. HTTP and HTTPS carry web traffic, SMTP and IMAP handle email, and SSH provides encrypted remote access to devices.

Key concepts

  • + OSI model: Seven layers from Physical to Application, each isolating a different aspect of communication.
  • + TCP/IP suite: The actual protocol stack used on the internet; IP addresses packets, TCP ensures reliable delivery.
  • + Subnetting: Divides address space into smaller networks; requires binary math and CIDR notation.
  • + Routing vs switching: Switches connect hosts within a LAN using MAC addresses; routers connect networks using IP addresses.
  • + DNS and DHCP: DNS resolves names to addresses; DHCP assigns addresses automatically at connection time.
  • + TCP vs UDP: TCP guarantees delivery and order; UDP is faster and connectionless, suited to real-time traffic.

Frequently asked questions

What is the difference between a hub, a switch, and a router?
A hub broadcasts every packet to every port, creating collisions and wasting bandwidth; it is obsolete. A switch forwards frames only to the port where the destination MAC address is known, keeping traffic local to its intended recipient. A router connects separate networks and forwards packets based on IP addresses, making decisions about which path to send traffic across.
What is subnetting and why is it used?
Subnetting divides a larger IP address block into smaller networks. It is used to improve security by isolating different groups of devices, to reduce broadcast traffic within each segment, and to use address space more efficiently. A /24 subnet, for example, provides 254 usable host addresses within a single network.
What does DNS do and what happens when it fails?
DNS (Domain Name System) translates domain names like technical-resources.com into IP addresses that routers understand. When DNS fails, devices can still communicate using raw IP addresses, but any name-based request (web browsing, email delivery, most application traffic) will fail with a timeout or 'host not found' error. The first step in diagnosing DNS failure is to check whether the device has a valid DNS server address assigned by DHCP.
What is the purpose of a default gateway?
A default gateway is the IP address of the router a device sends traffic to when the destination is on a different network. Without a properly configured default gateway, a device can communicate with other hosts on its own subnet but cannot reach anything beyond it, including the internet.
What is a VLAN and when would you use one?
A VLAN (Virtual Local Area Network) is a logical network segment created within a physical switch. It separates traffic between groups of devices as if they were on separate physical switches, without the cost of additional hardware. Common uses include separating guest Wi-Fi from corporate traffic, isolating printers or IP cameras, and creating dedicated segments for servers or voice traffic.
What is NAT and why is it needed?
NAT (Network Address Translation) allows multiple devices on a private network to share a single public IP address. The router rewrites the source address of outbound packets to its own public address and keeps a translation table to route incoming responses back to the correct internal device. NAT is what allows a home router with one ISP-assigned address to serve dozens of devices simultaneously.

Related topics

AFFILIATE_SLOT_BOOKS Recommended books on networking

Reserved for affiliate links to recommended technical books and study guides. Not yet wired.

AFFILIATE_SLOT_COURSES Online courses for networking

Reserved for affiliate links to online learning platforms. Not yet wired.

LEAD_SLOT_NEWSLETTER Get networking reference updates

Self-hosted newsletter signup. Not yet wired to an email provider.

Technical Resources publishes vendor-neutral educational information about information technology. It is general reference material, not professional, safety, legal, or warranty advice, and it is not affiliated with, endorsed by, or sponsored by any vendor, certification body, or manufacturer named on the site. Product names, standards, and certification programs are referenced for identification and education only and belong to their respective owners. Technology, standards, exam objectives, and safety guidance change over time, so always verify any decision-critical detail against the current official documentation for your specific hardware, software, standard, or exam before you rely on it. Procedures involving electricity, batteries, or live equipment can be hazardous; follow the manufacturer's instructions and applicable safety codes, and consult a qualified professional when in doubt.