Website Basics

Website common knowledge

Name	Description	Example
Domain name	A human-readable identifier used to identify a server or group of servers. Enter the domain name to access the website	example.com
IP address	An identifier used to uniquely serve the server on the Internet	192.168.1.1
Port	A number that distinguishes different applications on a computer network	e.g. Web service HTTP port is 80 HTTPS port is 443
Domain Name System (DNS)	Responsible for resolving domain names into corresponding IP addresses	example.com resolves to 192.168.1.1
SSL certificate	Used to establish an encrypted connection between a client and a server and to verify the server's identity.	*.example.com, mail.example.com
Access Protocol	Defines the rules for communication between clients and servers. Common access protocols include HTTP and HTTPS, used for normal communication and secure communication respectively. Using HTTPS requires deploying an SSL certificate, otherwise you can only use HTTP	https:// or http://
Access address (URL)	The full address of the website the user is accessing, including protocol, domain name or IP address, port (if not the default port) and path	https://www.example.com:7800/about
Web Server	Used to process client requests and return requested data to the client	Nginx, Apache, IIS, etc.
PHP	Used to process dynamic web pages, such as dynamic data, database queries, etc.	PHP 8.5
Node.js	Used to process dynamic web pages, such as dynamic data, database queries, etc.	Node.js 24.15.0
MySQL	Used to store and manage data	MySql 8.0, MariaDB 10.5

Relationship Between Domain Name and IP Address

A domain name is a human-readable label, while an IP address is the actual numeric identifier of a server on the network. They work together to enable website access:

1. One-to-One:

   One domain name points to one IP address. For example, example.com → 192.168.1.1 . This is the most common setup.

2. One-to-Many:

   One domain name can point to multiple IP addresses (via multiple A records) for load balancing and redundancy. For example, example.com → 192.168.1.1 and 192.168.1.2.

3. Many-to-One:

   Multiple domain names can point to the same IP address. For example, example.com, www.example.com, and blog.example.com all resolve to 192.168.1.1. The web server uses the Host header to distinguish which site to serve.

How It Works

User enters domain name in browser
        ↓
Browser queries DNS server
        ↓
DNS resolves domain to IP address
        ↓
Browser connects to the IP address via HTTP/HTTPS
        ↓
Web server receives the request and identifies the site by the Host header
        ↓
Web server returns the website content

Key Points

• You cannot access a website with only a domain name — the domain must be resolved to an IP address through DNS.

• You can access a website directly via IP address if the server is configured to respond to direct IP requests.

• DNS propagation — After adding or modifying a DNS record, it may take a few minutes to 48 hours for the change to take effect globally.

Access address (URL) disassembly

• For example: https://www.example.com:7800/about

  Name	Example
  Protocol	https:// or http://
  Domain name/IP address	www.example.com or 192.168.1.1
  Port	:7800
  Path	/about

HTTP vs HTTPS

Feature	HTTP	HTTPS
Full Name	HyperText Transfer Protocol	HyperText Transfer Protocol Secure
Port	80	443
Encryption	Data is transmitted in plain text	Data is encrypted via SSL/TLS
Security	Vulnerable to eavesdropping and tampering	Protects data integrity and privacy
SSL Certificate	Not required	Required

• Why use HTTPS?

  Without HTTPS, data transmitted between the browser and server (such as login credentials, form submissions) can be intercepted or modified by third parties. HTTPS ensures data is encrypted during transmission, which is essential for security and is also a ranking factor for search engines like Google.

• How to enable HTTPS:

  Deploy an SSL certificate on the web server. Once configured, the site can be accessed via https://.

Common Ports

Port	Service	Description
80	HTTP	Default port for unencrypted web traffic
443	HTTPS	Default port for encrypted web traffic
22	SSH	Secure remote server management
21	FTP	File transfer protocol
3306	MySQL	MySQL database service
53	DNS	Domain name resolution
25	SMTP	Email sending

SSL certificate

An SSL certificate encrypts data transmitted between a client (browser) and a server, ensuring that sensitive information like passwords and payment details cannot be intercepted. It also verifies the server's identity.

Certificate Types

• *.example.com (Wildcard Certificate):

  A wildcard certificate that matches one level of subdomains, such as www.example.com, mail.example.com. It does not match multi-level subdomains like bb.cc.example.com.

• www.example.com (Single Domain Certificate):

  A certificate that protects a single specific domain, such as www.example.com or example.com. If you need to secure both example.com and www.example.com, you may need a certificate that includes both domains or a wildcard certificate.

• Multi-Domain Certificate (SAN/UCC):

  A single certificate that can protect multiple different domain names, such as example.com, example.org, and mail.example.net. Each domain is listed as a Subject Alternative Name (SAN) in the certificate.

Certificate Validation Methods

• File Validation (HTTP/HTTPS): The Certificate Authority (CA) verifies domain ownership by placing a verification file in the website's root directory and accessing it via HTTP/HTTPS.

• DNS Validation: The CA verifies domain ownership by checking a specific DNS TXT or CNAME record added to the domain's DNS configuration. This method supports wildcard certificates.