Key Internet and Computer Network Terms

What this guide is about

When using the internet daily, we frequently encounter various technical terms – IP address, DNS, HTTP, SSL, LAN, routing, protocols, ports, and many others. What do they mean? To understand how the internet and computer networks work, it is useful to familiarize yourself with the meanings of these basic concepts. This article provides a comprehensive yet understandable guide to technical terms aimed at a general audience. Here, we will explain the most important concepts related to computer networks and the internet while avoiding excessive academic jargon. You will learn what a network is, how the internet works, what makes IP addresses and domain names special, how data transmission protocols (e.g., TCP and UDP) operate, the difference between HTTP and HTTPS, what ensures communication security (e.g., SSL/TLS), what LAN and WAN are, how routers work, what port numbers are, firewalls, VPNs, and other important topics. The article is divided into clear sections so you can easily find the topic of interest and delve into the world of networks systematically.

Basic concepts

A computer network is a group of interconnected devices that can exchange data with one another. In simple terms, if you connect two or more computers (or other smart devices) so they can communicate with each other, you create a network. This connection can be realized through various means: wired (e.g., Ethernet cables), wireless (e.g., Wi-Fi, Bluetooth), or even over telephone lines using modems. The network medium is the physical or wireless environment through which signals carrying data travel. For example, data transmitted over copper cables is sent as electrical impulses, over optical cables as light pulses, and in wireless networks as radio waves. Despite the different technical solutions, the purpose of all networks is the same: to ensure that data can travel from one device to another.

The internet is a global network of computer networks. It is often referred to as a “network of networks” because it connects many individual smaller networks into one global system. No single person or organization fully controls the entire internet – it is based on open standards and protocols that allow different types of devices and networks to communicate with each other. Information can reach any corner of the world in just moments because data travels through numerous intermediary nodes and communication lines.

To delve deeper into how the internet and networks operate, it is useful to understand the concept of layers. In network architecture, data transmission is often divided into layers, with each layer performing a specific function: from the physical (signals over cables or air), channel/network (addressing and routing), transport (reliability or speed) to application (browsers, email). The classic model is OSI (7 layers), while the TCP/IP model (simplified 4 layers) is widely used in practice on the internet. Although it is not necessary for an average user to know all the layers in detail, it is worth knowing that such a structure exists – it helps explain how complex network operations are broken down into smaller, more manageable parts.

In summary, a computer network consists of connected devices that can share information, while the internet is a vast amalgamation of networks worldwide, allowing us to communicate, work, and entertain ourselves on a global scale. Next, we will discuss specific terms and components that ensure the operation of this massive network.

LAN, WAN, and others

Computer networks can be classified by coverage area. You will often encounter the terms LAN and WAN, which describe the scale of a network.

LAN (Local Area Network) – is a network with a small geographical coverage. LAN typically connects devices located within a single building or limited area – for example, a home network, an office network, or a computer lab in a school. In a local network, devices can share files, use shared resources (e.g., printers, network drives), and communicate with each other at high speeds due to the short distances involved. A local wireless network is often referred to as WLAN – this is simply a LAN that uses wireless communication (most commonly Wi-Fi). For example, your home Wi-Fi router creates a wireless LAN that connects all home devices (phones, computers, smart TVs).

WAN (Wide Area Network) – is a network that covers a large geographical area. WAN connects multiple local networks and can span cities, countries, or even continents. The best example is the internet itself, which is essentially a massive WAN connecting networks worldwide. A WAN can also be a private organizational network that connects company offices in different cities. Wide area network connections typically use telecommunications infrastructure (optical cables, satellite connections, underwater cables, etc.) to transmit data over long distances. Data transmission in WANs is often slower (due to distances and load) than in LANs, but it covers a much larger area.

In addition to LAN and WAN, literature may mention other terms to describe certain intermediate or specialized networks: for example, MAN (Metropolitan Area Network) – a metropolitan network connecting institutions within a city or region; PAN (Personal Area Network) – a personal network covering a very small distance (e.g., connecting devices around a person using Bluetooth); VPN (Virtual Private Network) – a virtual private network, which we will discuss later in a separate security section. However, LAN (local) and WAN (global) are the primary types that help understand the scope of a network.

Intranet – is a private internal network, usually belonging to an organization, that uses the same technologies as the internet (e.g., websites, email) but is closed to outsiders. Only certain users (e.g., company employees) can access the content of the intranet. It is like a small “internet” within the organization, designed for internal communication. Intranets are usually part of a LAN or WAN but are isolated by firewalls and other security measures.

In summary, a local area network (LAN) covers a small area and features fast connections between nearby devices, while a wide area network (WAN) connects distant locations and enables communication over long distances. The internet is a global WAN that connects many LANs and other networks into one large entity.

Routers, switches, modems

For networks to function, specialized hardware is required. The main network devices encountered by both regular users and system administrators are routers, switches, and modems. Each plays a different role in ensuring data transmission between devices.

Router (also known as a gateway; English: router) – is a device that connects different networks and directs data packets in the appropriate direction. Typically, a router has multiple network interfaces (e.g., one connection to the internet service provider and several connections for the local LAN). Its main task is routing, i.e., selecting the best path for data packets to reach their destination network. A router supports network layer protocols (usually IP) and has an internal routing table – like a map indicating which interface to use to reach specific addresses. Wi-Fi routers often combine several functions in one device: they act as routers (connecting your LAN to the provider’s network), as switches (providing several wired LAN connections), and as wireless access points (broadcasting Wi-Fi). More advanced routers can also perform firewall, NAT (Network Address Translation), and other functions. ([Wikipedia][1])

Switch (English: switch) – is a device designed to connect many devices within a local network. A switch primarily operates at the second (data link) layer of the OSI model: it forwards data frames based on MAC addresses. Each port on a switch is typically connected to a separate device (computer, printer, etc.), and the switch ensures that data packets are sent specifically to the device they are intended for (unlike early hub-type devices that sent data to all).

Modem – is a device that modulates and demodulates signals so that data can be transmitted over a specific communication channel. Today, the term modem encompasses DSL, cable, fiber (ONT), and mobile (4G/5G) modems. Modern home routers often have integrated modem functionality, so a separate device is not needed. Modems “speak the language” between your home network and the internet service provider’s infrastructure.

Digital network addresses

One of the most important elements of the operation of the internet and networks is the IP address. An IP (Internet Protocol) address is a digital identifier that uniquely marks a device on the network. Each packet is labeled with the sender’s and receiver’s IP addresses, and routers use them to determine where to send the packet next.

IPv4 and IPv6: IPv4 is a 32-bit addressing scheme, usually written in four decimal groups (e.g., 192.168.0.10). Due to the growing internet, IPv4 addresses have started to run out, leading to the transition to IPv6 – a 128-bit addressing scheme (written in hexadecimal groups, e.g., 2001:db8::/64), providing an almost inexhaustible address space and other improvements. ([Hostico][2])

Private and public IP addresses: In the IPv4 space, some addresses are reserved for internal networks (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). Such addresses are not routable on the internet – a router with a public IP connects to the internet, performing NAT (translating internal addresses into one or more public ones). This saves addresses and provides an additional layer of security.

Static and dynamic IP addresses: Public IPs can be permanent (static) or temporary (dynamic). Static addresses are suitable for servers and cameras (always the same address), while dynamic addresses are usually assigned to home users (changing after rebooting or at certain intervals).

MAC address: In addition to IP, the MAC (Media Access Control) address is important in networks – a hardware identifier for a network device (48 bits, e.g., 00:1A:2B:3C:4D:5E). MAC is used at the local network level (in switches), while IP addresses are used for global routing.

Summary of IP: IP is a unique “address” on the network; IPv4 is 32 bits, IPv6 is 128 bits; private/public address and NAT mechanisms allow the internet to operate globally and efficiently.

The internet’s “address book”

While computers on the internet recognize each other by numerical IP addresses, it is inconvenient for people to remember them. Therefore, the Domain Name System – DNS (Domain Name System) was created, which somewhat “translates” user-friendly names (e.g., delfi.lt) into IP addresses. DNS is a hierarchical, distributed system with root, top-level (TLD), and authoritative name servers; the browser first queries a resolver (often the provider’s or public DNS), which, if necessary, queries up the hierarchy to an authoritative server that returns the IP.

DNS provides not only A/AAAA records (IP) but also MX (for mail servers), CNAME (for aliases), TXT (for verifications, SPF/DMARC policies), NS (for name servers), and more. Modern systems may additionally use encrypted DNS queries (DoH/DoT), reducing the risk of query interception or redirection. ([domreg.lt][3])

Domain name structure: Domains are read from right to left in hierarchical order: TLD (e.g., .lt, .com), second-level domain (e.g., vu.lt), and finally – subdomains (e.g., naujienos.delfi.lt). Domains are registered with the appropriate registry organizations (in Lithuania, .lt domains are managed by KTU Domreg). ([EUR-Lex][4])

Communication rules

For different devices to understand each other while exchanging data, network protocols exist – a set of agreements and rules that define the format and procedures for data exchange.

IP (Internet Protocol) – is responsible for addressing and routing packets at the network level (packet headers, fragmentation).

TCP (Transmission Control Protocol) – is a transport layer protocol that provides reliable, ordered data streams (three-way handshake, retransmissions, flow/congestion control).

UDP (User Datagram Protocol) – is an alternative to TCP: connectionless, without acknowledgments; therefore, it is faster and suitable for real-time streams (broadcasts, games, DNS queries), where time is more critical than guaranteeing perfect accuracy.

Summary of TCP vs UDP: TCP – reliability and order; UDP – lower latency and overhead costs. There are also modern solutions, such as QUIC (over UDP) and HTTP/3.

From HTTP to email

Application layer protocols are the “rule books” that provide specific functionality. When you browse a website, send an email, or share files, applications communicate using the respective protocols.

HTTP protocol (web)

HTTP (HyperText Transfer Protocol) – is a request-response protocol between the client (browser) and the server. The browser opens a connection (usually TCP), submits a request (GET, POST, etc.), and the server returns a response with a status code (e.g., 200, 404), headers, and content. Evolving versions (HTTP/1.1 → HTTP/2 → HTTP/3) have significantly increased efficiency (multiplexing, header compression, reduced latency via QUIC).

HTTPS and SSL/TLS: secure web connection

HTTPS – is an HTTP connection conducted over an encrypted TLS channel (the historical name “SSL” is still widely used). Using HTTPS, a TLS “handshake” occurs between the browser and the server, the server provides a certificate, keys are agreed upon, and the subsequent stream is encrypted (usually with symmetric encryption). HTTPS uses port 443 by default, while HTTP uses port 80. Browsers mark insecure HTTP and encourage the use of HTTPS even for simple websites.

In addition to HTTP/HTTPS, other common application protocols include: FTP/SFTP (for file transfers), email (SMTP – for sending; POP3/IMAP – for receiving), SSH (for secure remote access), WebSocket (for real-time exchanges over HTTP), DNS (name → IP). Most of these rely on TCP or UDP, and availability is typically determined by ports (see below).

What is the difference between HTTP and HTTPS?

• HTTP transmits data in plain text, while HTTPS transmits it encrypted (TLS); therefore, HTTPS ensures confidentiality and data integrity.
• HTTP uses port 80 by default, while HTTPS uses 443; browsers usually do not display these numbers but use them automatically.
• HTTPS requires a valid certificate confirming the server’s identity; obtaining a certificate today is simple (e.g., Let’s Encrypt or commercial CAs).
• Browsers clearly warn about insecure HTTP, while they show a “lock” for secure connections.

Recommendation: always choose HTTPS – it is the standard that protects user data and reduces the risk of manipulation.

How packets find their way

The internet connects many autonomous networks. Routers – devices that connect these networks – make decisions on where to send the received packet next based on a routing table (like a “map” indicating which neighbor to reach specific IP prefixes). Routing protocols (e.g., BGP between autonomous systems, OSPF internally) are used in the core infrastructure so that routes automatically adapt to network conditions.

Comparison: switching in a local network occurs based on MAC addresses (switches), while routing occurs based on IP addresses between different networks (routers).

NAT (Network Address Translation): almost every home router translates internal private addresses into one public IP. This allows many devices to share one address; moreover, it is impossible to directly access internal devices from the internet without port forwarding or UPnP.

“Doors” to services

A port is a 16-bit number in a TCP/UDP packet that identifies a specific service on a device. A classic analogy: an IP address is the building address, while a port is the apartment number. “Well-known” ports (1–1023) are assigned to standard services (e.g., 80 – HTTP, 443 – HTTPS, 22 – SSH, 25 – SMTP, 53 – DNS), the range 1024–49151 is for registered ports, and 49152–65535 is for dynamic/temporary ports (on the client side).

One server with one IP can provide many different services simultaneously because streams are separated by ports. Firewalls are often configured based on ports – only necessary ones are opened, while others are blocked; if you want to access an internal server from the internet, a port forwarding rule is enabled on the router.

Firewalls and VPNs

Firewall

A firewall is a security measure that filters network traffic based on established rules (source/destination IP, port, protocol, content characteristics). It can be either a specialized network device or software on a computer. Modern (NGFW) firewalls recognize protocols, inspect traffic at a deeper level (DPI), and can prevent known attacks. The Lithuanian equivalent of the term is confirmed in language norms: “router”/“router,” “firewall” (instead of “firewall”).

VPN (Virtual Private Network)

A VPN is a technology that creates an encrypted “tunnel” over the public internet. Remote access (client-to-site) VPN allows a user to connect to the organization’s internal network from anywhere, while site-to-site VPN connects two networks together (e.g., offices in different cities). Commercial VPNs used for user privacy route all traffic through the VPN provider’s server, masking the real IP and encrypting the connection (useful on public “Wi-Fi”).

From a simple user perspective: when a VPN is enabled, part or all of the traffic may be tunneled through the VPN (often using “split tunneling”), so access to local resources or services may change; due to encryption and longer routes, a slight increase in latency may occur.

What we learned

The operation of the internet and computer networks is based on a significant amount of technical concepts and components, but once familiar with the basic terms, the overall picture becomes much clearer. In this article, we discussed what networks and the internet are, the types of networks (from small LANs to the encompassing internet), the roles of network devices (routers, switches, modems), and how each of your devices is identified by an IP address. We learned about two generations of IP addresses – IPv4 and IPv6 – and why the latter emerged due to the shortage of addresses. We reviewed the Domain Name System (DNS), which simplifies browsing the internet daily by converting memorable addresses into numerical IPs.

We also delved into the world of protocols – from the very “languages” of the internet (IP, TCP, UDP) to higher-level protocols that provide us with specific functionality (HTTP allows us to view web pages, SMTP/POP3/IMAP – to send and receive emails, FTP/SFTP – to transfer files, etc.). We understood the importance of security – highlighting HTTPS, which encrypts web traffic thanks to TLS, and discussed concepts such as certificates, public keys, and encryption. We examined the principles of routing – how data packets find their way through numerous intermediary routers to reach their destination, and how the structure of IP addresses and routing protocols assist in this. We explored the concept of ports – like virtual doors that separate different services on one device, and discussed why port management is crucial for security.

Finally, we looked at network security solutions: firewalls, standing guard at the network perimeter or on our own computers, and VPNs – technologies that allow secure tunnels over the internet, ensuring private connections or remote access to internal resources.

All these concepts together form the foundation upon which the technologies we use daily function: browsing websites, messaging, streaming, cloud services, etc. Every time you open a webpage, your computer performs numerous actions invisibly: it learns the server’s IP through DNS, establishes a TCP connection by exchanging packets with routers, possibly sets up TLS encryption, sends an HTTP request, waits for a response, which ultimately arrives in many packets and is assembled into the content displayed on the screen – all of this happens in a fraction of a second.

With an understanding of essential concepts, we can feel more confident using technologies: we know why it is important to use HTTPS websites, why not to publicly open all computer ports, and why the password of our home router and firewall settings are not just formalities but protective layers. It also makes it easier to solve everyday problems: unable to connect to the printer – could the firewall be blocking it? Why is the website unreachable – perhaps DNS issues or a bad route? The realization that the internet is not a mystery but a defined set of terms and rules gives us the ability to rationally seek answers.

Of course, the topic of networks can be much deeper – professionals study routing algorithms, protocol programming, security testing, etc. However, the goal of this guide is to clearly and practically outline the basic terms. We hope that after reading, you have a better mental “map” of the internet: you know what lies behind an IP address or DNS abbreviation, understand what the router on your desk does, why a Wi-Fi network is a LAN, how TCP differs from UDP, what ports are, and why the browser sometimes shows a lock. This knowledge is like having an instruction manual for the world we encounter daily, even though we do not see it. And with an instruction manual, everything becomes simpler.