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Documentation & Tutorials

Network & Server Diagnostic Guides

Expert tutorials to help you diagnose downtime, debug DNS propagation, interpret HTTP response codes, and protect your digital privacy.

Server Troubleshooting

How to Fix HTTP 502 Bad Gateway & 504 Gateway Timeout

Estimated reading time: 4 mins • Updated October 2026

A 502 Bad Gateway error occurs when one server on the internet (such as a reverse proxy, CDN, or Cloudflare edge node) receives an invalid response or no response from an inbound origin server (like Nginx, Apache, Node.js, or PHP-FPM).

Common Causes & Step-by-Step Fixes:

  1. Origin Web Server Crashed: Check if your PHP-FPM, Node.js, or Nginx process died due to out-of-memory (OOM). Run systemctl status php8.2-fpm or pm2 status on your server.
  2. Origin Firewall Blocking CDN IPs: If using Cloudflare or a reverse proxy, ensure your server firewall (UFW / iptables) allows connections from Cloudflare IP ranges.
  3. DNS Misconfiguration: If you recently moved hosting providers, verify your A record points to the active server IP address.
  4. PHP-FPM Timeout (504): For long-running database queries or heavy scripts, increase max_execution_time and request_terminate_timeout in your server config.
Tip: Use our Global Uptime Checker to test if your server is reachable from multiple geographic locations worldwide.
DNS & Networking

What is DNS Propagation & How to Flush DNS Cache

Estimated reading time: 3 mins • Updated October 2026

When you update a domain's A, CNAME, or Nameserver records, the changes must replicate across recursive DNS servers worldwide. This process is called DNS Propagation and typically takes anywhere from 5 minutes up to 24 hours depending on the TTL (Time to Live) setting.

How to Flush DNS Cache on Your Local Computer:

# Windows (Command Prompt / PowerShell):
ipconfig /flushdns
# macOS (Terminal):
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
# Linux (Ubuntu / Debian with systemd):
sudo systemd-resolve --flush-caches
HTTP Protocol Reference

The Complete HTTP Status Code Cheat Sheet

Estimated reading time: 5 mins • Updated October 2026

HTTP response status codes indicate whether a specific HTTP request has been successfully completed. They are divided into 5 standard classes:

200 OK

The request succeeded. The resource was successfully fetched and transmitted in the message body.

301 Moved Permanently

The URL of the requested resource has been changed permanently. Search engines transfer SEO link equity.

403 Forbidden

The client does not have access rights to the content, often triggered by firewall rules or file permission errors.

404 Not Found

The server cannot find the requested URL. Usually caused by a broken link or removed webpage.

500 Internal Server Error

A generic catch-all server crash code. Inspect your server error logs (e.g. Apache/Nginx error.log) for stack traces.

503 Service Unavailable

The server is temporarily overloaded or undergoing maintenance. Common during sudden traffic spikes.

Cybersecurity & Privacy

Public IP vs. Private IP: What Can Websites Track?

Estimated reading time: 4 mins • Updated October 2026

Every device connected to the internet has a Public IP address assigned by its Internet Service Provider (ISP). Whenever you load a webpage, send an email, or stream video, your public IP is transmitted in the packet headers.

What Websites Can See from Your IP:

  • Your Internet Service Provider (ISP) and Autonomous System Number (ASN).
  • Your approximate physical city, region, postal code, and country.
  • Your connection speed, latency, and router timezone.

How to Mask Your IP Address:

Using a reputable Virtual Private Network (VPN) routes your web traffic through an encrypted tunnel to a remote server, replacing your actual public IP with an anonymous shared IP address.

Check your current public IP exposure