A network is a set of connected devices that exchange data using agreed rules called protocols. When you open a website, several protocols work together: names are looked up, packets are routed, and a connection carries a request and response.
1. TCP/IP and ports
IP (Internet Protocol) addresses and moves packets between networks. IPv4 addresses look like 192.0.2.10; IPv6 addresses are longer and written in hexadecimal. An IP address identifies a network interface at a point in time, not necessarily a person or a permanent device.
TCP (Transmission Control Protocol) provides an ordered, reliable byte stream: it tracks delivery and retransmits missing data. UDP sends independent datagrams with less delivery machinery, which can suit voice, video, or DNS. Neither protocol is encryption.
A port identifies an application endpoint on a device. IP plus transport protocol plus port helps deliver traffic to the right service. Ports 443 and 80 are commonly used for HTTPS and HTTP; the number alone does not prove which application is actually listening.
An IP address answers “which network endpoint?” A port answers “which application endpoint?” A protocol defines how they communicate.
2. DNS: names to addresses
The Domain Name System is a distributed directory. A resolver looks up records such as an A record for an IPv4 address, AAAA for IPv6, or MX for mail servers. Caching speeds up repeat lookups; cached answers can remain until their time-to-live expires.
DNS normally helps find an address; it does not establish that a site is trustworthy. A familiar-looking domain can still lead somewhere unsafe, so check the actual domain and the browser's security indicators.
Look up a public domain you recognize: run nslookup example.com in Windows, macOS, or Linux. Compare the returned addresses later; DNS answers can vary by location, provider, or time.
3. HTTP: requests and responses
HTTP is a request-and-response protocol used by web clients and servers. A request includes a method (such as GET to retrieve or POST to submit), a path, headers, and sometimes a body. The response contains a status code, headers, and often content. For example, 200 indicates success, 404 indicates a missing resource, and 500 indicates a server error.
Plain HTTP does not protect the contents from observers on the network. HTTPS is HTTP carried inside a TLS-protected connection. Encryption protects data in transit, but does not make a dishonest website honest or protect a compromised endpoint.
4. TLS: protecting a connection
Transport Layer Security (TLS) helps provide confidentiality, integrity, and server authentication. During setup, the client and server negotiate compatible settings, the server presents a certificate, and both sides establish shared session keys. Modern TLS uses asymmetric cryptography during setup and efficient symmetric encryption for ongoing traffic.
A certificate connects a public key to a domain identity through a certificate authority. Browsers check things such as the domain name, validity period, and trust chain. A padlock means the connection is protected as expected; it is not a review of the site's intentions or content.
Encryption protects data while it travels. Access control decides who may use a service. Backups help recover data. No one safeguard replaces the others.
5. Routing: choosing a path
A router forwards IP packets between networks. It consults a routing table, which contains destination networks and next hops. Your device usually sends traffic for outside its local network to a default gateway, often a home or office router. The internet is a collection of independently operated networks that exchange routes.
Packets can take different paths, and network tools reveal only partial information. Firewalls, address translation, and routing policy can hide or change what a path looks like.
Inspect the route to a domain you use. Windows: tracert example.com. macOS/Linux: traceroute example.com (some systems may need the utility installed). Run this only for ordinary connectivity learning; missing hops are common and do not by themselves mean an attack.
6. Firewalls: filtering traffic
A firewall applies rules to network traffic. Rules may consider source and destination addresses, ports, protocols, connection state, or application identity. Host firewalls run on devices; network firewalls help protect boundaries between networks. A common principle is default deny: allow only traffic required for a clear purpose.
Firewalls reduce exposure, but they do not replace updates, strong authentication, endpoint protection, or monitoring. An allowed connection can still carry unwanted content, and a rule that is too broad can weaken protection.
Practice and recap
On your own device, open a familiar HTTPS website. Describe the sequence: DNS resolves a name; IP routing moves packets; TCP or another transport carries data; TLS protects the connection; HTTP exchanges requests and responses; firewalls apply their configured rules.
- What does a port identify, and how is it different from an IP address?
- Why does a browser use both DNS and TLS?
- What does HTTPS protect—and what does it not guarantee?
- Why can a missing hop in a route trace be normal?
Free learning path and practice
Learn the foundations
- Cisco Networking Academy: Networking Basics — a free, structured introduction to networking.
- Cloudflare Learning Center — free plain-language explainers to revisit as you work through the guide.
Practice in guided labs
- TryHackMe: OSI Model, Network Services, and How the Web Works — guided practice for network layers, services, and web traffic.
- HTB Academy catalogue — search for “Introduction to Networking” and network-enumeration modules; check current access requirements.
Watch networking playlists
- Professor Messer: CompTIA Network+ N10-009 Training Course — a structured networking course from a channel with approximately 1.37M subscribers.
Subscriber counts are approximate and change over time; video view counts vary. This recommendation prioritizes a large audience and a relevant, structured course.
Start with the free course, then use training labs only within their provided scope. Platform room names, availability, and free access can change.
See the standards and compliance guide for the networking and infrastructure controls most relevant to product security.