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Computer Networking

Learn computer networks, Wi-Fi, routers, IP addressing, network protocols, troubleshooting, and network security through practical guides and step-by-step explanations.

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NETWORKING FUNDAMENTALS

Network Protocols & Architecture

Understand how devices communicate, how network layers work, which protocols use common ports, and how to troubleshoot real connections using practical commands.

Explore OSI Model Start Practice

1. What is a network protocol?

A network protocol is a set of rules that defines how devices exchange information. Protocols specify details such as message formats, addressing, connection behavior, error handling, and communication procedures.

HTTP / HTTPS

Web communication

TCP / UDP

Transport of application data

IP

Addressing and routing

2. What is network architecture?

Network architecture describes how devices, network services, communication protocols, and infrastructure are organized to work together.

Client–Server

A client requests a service, and a server processes the request. Browsers and web servers are a common example.

Peer-to-Peer

Devices can communicate or share resources directly without relying on one central server for every exchange.

Three-Tier Architecture

Applications may separate presentation, application logic, and data storage into distinct tiers.

Network Topology

Describes how devices and links are arranged, such as star, mesh, bus, or ring.

3. OSI Model: All 7 Layers

The OSI model is a reference model used to understand and troubleshoot communication. Real protocols do not always fit neatly into a single layer.

Layer 7: Application

Provides network services to applications.

Examples: HTTP, HTTPS, DNS, SMTP

Opening a website or resolving a domain.

Layer 6: Presentation

Represents, encodes, or transforms application data.

Examples: TLS-related presentation functions, data formats

Character encoding and data serialization.

Layer 5: Session

Describes the establishment and management of communication sessions.

Examples: Session-management concepts

Maintaining a logical dialog between applications.

Layer 4: Transport

Provides transport between application endpoints.

Examples: TCP, UDP

Reliable delivery with TCP or datagrams with UDP.

Layer 3: Network

Handles logical addressing and routing between networks.

Examples: IPv4, IPv6, ICMP

A router forwarding an IP packet.

Layer 2: Data Link

Handles local-link frames and hardware addressing.

Examples: Ethernet, Wi-Fi MAC, ARP

A frame traveling across a local Ethernet network.

Layer 1: Physical

Carries signals across a physical medium.

Examples: Ethernet physical media, radio, fiber

Electrical, optical, or wireless signals.

Remember the order

Top to bottom: Application → Presentation → Session → Transport → Network → Data Link → Physical.

4. TCP/IP Model

The TCP/IP model describes the layers commonly used by Internet communication. It is usually represented using four layers.

4. Application

OSI layers 5–7 (approximately)

Protocols: HTTP, HTTPS, DNS, SSH, SMTP

Data unit: Application data

3. Transport

OSI layer 4

Protocols: TCP, UDP

Data unit: TCP segment / UDP datagram

2. Internet

OSI layer 3

Protocols: IPv4, IPv6, ICMP

Data unit: IP packet

1. Network Access

OSI layers 1–2 (approximately)

Protocols: Ethernet, Wi-Fi

Data unit: Frame and physical signals

5. How data travels across a network

When you open a website, multiple protocols cooperate to establish communication and deliver the requested content.

DNS lookup: The client resolves the website's hostname to an IP address when a suitable cached answer is not already available.
Local delivery: The device uses its routing table and, when necessary, ARP or IPv6 Neighbor Discovery to determine how to send traffic on the local link.
Transport: The application communicates using TCP or UDP, depending on the protocol and connection.
Security: HTTPS commonly uses TLS to protect HTTP communication. HTTP/3 uses QUIC over UDP.
Routing: Routers forward IP packets toward the destination network.
Response: The server sends a response that returns through the network to the client.

6. Encapsulation and data units

Encapsulation occurs when each network layer adds information needed to deliver or process data. The receiving device processes the layers in reverse through decapsulation.

Application data

→

TCP segment

→

IP packet

→

Link frame

→

Signals

This is a simplified TCP-based example. UDP uses a UDP datagram, and actual encapsulation depends on the protocols involved.

7. Common network protocols and ports

These are common default port assignments. Actual services can use different ports, and some protocols do not use TCP or UDP ports.

Protocol	Port	Purpose
HTTP	80/TCP	Transfers web content; unencrypted by itself.
HTTPS	443/TCP	HTTP protected by TLS, usually over TCP.
DNS	53/UDP, TCP	Resolves domain names; TCP is also used in several cases.
DHCPv4	67/UDP, 68/UDP	Assigns IPv4 configuration to clients.
SSH	22/TCP	Secure remote shell and administration.
FTP	21/TCP control	File transfer protocol; standard FTP is not encrypted.
SFTP	22/TCP typically	File transfer over SSH.
SMTP	25/TCP commonly	Mail transfer between mail servers.
IMAP	143/TCP	Accesses and manages email; TLS can be added.
IMAPS	993/TCP	IMAP over TLS.
POP3	110/TCP	Retrieves email; TLS can be added.
POP3S	995/TCP	POP3 over TLS.
NTP	123/UDP	Synchronizes system clocks.
SNMP	161/UDP commonly	Monitors and manages network devices.
RDP	3389/TCP, UDP	Remote Desktop services; configurations vary.
SMB	445/TCP	File and printer sharing, commonly on Windows networks.
LDAP	389/TCP, UDP	Directory access; TCP is common for LDAP queries.
LDAPS	636/TCP	LDAP protected by TLS.
ICMP	No TCP/UDP port	Carries diagnostic and network-control messages.
ARP	No TCP/UDP port	Maps IPv4 addresses to link-layer addresses on a local link.

8. Network devices and their roles

Repeater

Regenerates or repeats signals.

Physical

Hub

Repeats incoming bits to other ports; generally obsolete.

Physical

Switch

Forwards Ethernet frames using MAC address information.

Data Link

Router

Forwards IP packets between networks.

Network

Firewall

Enforces traffic policies using addresses, ports, connections, or application data.

Multiple layers

Access Point

Connects wireless clients to a network.

Network access

Proxy

Relays requests on behalf of clients or servers.

Application (commonly)

Load Balancer

Distributes traffic across backend servers.

Multiple layers

9. Connection-oriented vs connectionless

TCP

Connection-oriented transport.
Provides ordered, reliable byte-stream delivery.
Uses acknowledgements and retransmission mechanisms.
Common for HTTPS over HTTP/1.1 or HTTP/2.

UDP

Connectionless transport.
Does not guarantee delivery or ordering.
Has a smaller transport header.
Common for DNS queries, voice, and real-time traffic.

10. Practical networking commands

Check IP configuration (Windows)

ipconfig /all

Check IP configuration (Linux)

ip addr

Display the routing table

ip route

Test connectivity

ping 1.1.1.1

Trace the route (Windows)

tracert example.com

Trace the route (Linux)

tracepath example.com

Inspect DNS resolution

nslookup example.com

Inspect a TCP connection (Linux)

ss -tun

Test a TCP port (PowerShell)

Test-NetConnection example.com -Port 443

Use systems and services you own or are authorized to test. Command availability differs between Windows and Linux.

11. Hands-on practice

Use these exercises to connect networking theory with real output.

Practice 1: Find your network configuration

ipconfig /all

On Windows, identify the IPv4 address, subnet mask, default gateway, and DNS servers. Compare these values with your router's local network configuration.

Practice 2: Follow a DNS lookup

nslookup example.com

Record the DNS server and the returned addresses. Run the command again and compare the results. Cached answers and load-balanced destinations can affect what you see.

Practice 3: Test HTTPS connectivity

Test-NetConnection example.com -Port 443

Examine the DNS result, remote address, and TcpTestSucceeded field. A successful TCP connection does not by itself prove that TLS negotiation or the website will succeed.

Practice 4: Observe packets in Wireshark

Start a capture on your active network interface.
Run a DNS lookup and visit a website you are allowed to access.
Apply the display filter dns.
Inspect the DNS query and response, then try tcp or tls.
Compare the observed protocols with the OSI and TCP/IP models.

12. Troubleshooting by layer

Physical layer

Check power, cables, Wi-Fi signal, and link status.

Data Link layer

Check Wi-Fi association, VLAN configuration, and local-link reachability.

Network layer

Check IP settings, subnet masks, gateways, and routes.

Transport layer

Check whether the required TCP port is reachable and whether a firewall blocks it.

Application layer

Check DNS, TLS certificates, server responses, and application logs.

13. Network security fundamentals

Prefer encrypted protocols such as HTTPS, SSH, and secure file-transfer services.
Use firewalls to restrict unnecessary inbound and outbound connections.
Keep routers, switches, operating systems, and network services updated.
Segment networks so sensitive systems are not exposed unnecessarily.
Use packet captures and logs together when investigating suspicious activity.
Never assume an open port alone proves that a service is vulnerable.

14. Recommended learning order

Learn IPv4, IPv6, subnet masks, and private IP addresses.
Understand Ethernet, MAC addresses, ARP, and switching.
Study TCP, UDP, ports, and the TCP handshake.
Learn DNS, DHCP, HTTP, HTTPS, and TLS basics.
Practice ping, route tracing, DNS lookup, and port testing.
Use Wireshark to inspect the traffic generated by those exercises.
Study firewalls, network segmentation, and defensive monitoring.

Build your networking foundation

Learn what each protocol does, identify its place in the communication process, and verify your understanding using terminal commands and packet captures. These fundamentals support network administration, troubleshooting, and defensive security.

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Explore More About Networking

Build your networking knowledge with focused guides on network types, IP addressing, Wi-Fi troubleshooting, and defensive network security.

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