ShowDNS Guides
Step-by-Step Guides for
DNS, SSL & Security
Practical walkthroughs with commands, checklists, and screenshots — everything you need to configure, fix, and validate your domain infrastructure.
Featured guides
How to Fix an HSTS Error
Understand why HSTS errors appear and fix NET::ERR_CERT issues as a site owner or visitor.
FeaturedHow to Enable Perfect Forward Secrecy
Configure PFS on Apache and Nginx with ECDHE cipher suites and DH parameters for stronger TLS.
FeaturedHow to Check DNS Propagation
Check DNS propagation after a record change using online tools, dig, and nslookup step by step.
FeaturedHow to Flush DNS Cache
Flush DNS cache on Windows, macOS, Linux, and Chrome browser with step-by-step commands.
FeaturedHow to Create an SPF Record
Build and publish an SPF record for Google Workspace, Microsoft 365, and custom mail servers.
FeaturedHow to Configure DMARC
Set up DMARC from p=none monitoring to p=reject enforcement with a safe, staged rollout plan.
DNS
14How to Check DNS Propagation
Check DNS propagation after a record change using online tools, dig, and nslookup step by step.
How to Fix DNS Propagation Issues
Diagnose and fix slow DNS propagation — from high TTLs and stale caches to resolver delays.
DNS Propagation Time Explained
Understand how long DNS propagation takes, what factors affect it, and how to speed it up.
How to Flush DNS Cache
Flush DNS cache on Windows, macOS, Linux, and Chrome browser with step-by-step commands.
How to Troubleshoot DNS Problems
A complete DNS troubleshooting guide — from NXDOMAIN and SERVFAIL errors to NS misconfigurations.
How to Check Nameservers
Check nameservers for any domain using the ShowDNS NS Lookup, nslookup, dig, and whois.
How to Fix DNS Resolution Errors
Fix NXDOMAIN, SERVFAIL, and connection failures with step-by-step diagnostic commands.
How to Check DNS Records
Query A, AAAA, MX, TXT, CNAME, NS, and SOA records using ShowDNS tools, dig, and nslookup.
How to Change Nameservers
Move DNS to a new provider with zero downtime — export records, reduce TTLs, and verify propagation.
How to Check Domain Health
Complete domain health checklist — DNS, SSL, email auth, security headers, blacklist, and expiry.
Domain Migration Guide
Move a domain to a new hosting or DNS provider with zero downtime — pre-migration checklist included.
Website Downtime Troubleshooting
Diagnose website outages fast — from DNS failures and SSL errors to server crashes and firewall blocks.
How to Enable DNSSEC
Sign your DNS zone, publish the DS record at your registrar, and verify the chain of trust to stop DNS spoofing and cache poisoning.
How to Enable DNS over HTTPS (DoH) in Chrome
Enable DNS over HTTPS in Google Chrome to encrypt your DNS lookups. Turn on Secure DNS, pick a provider, and verify it works step by step.
Security
17How to Fix an HSTS Error
Understand why HSTS errors appear and fix NET::ERR_CERT issues as a site owner or visitor.
How to Enable Perfect Forward Secrecy
Configure PFS on Apache and Nginx with ECDHE cipher suites and DH parameters for stronger TLS.
How to Enable HSTS
Add Strict-Transport-Security on Nginx, Apache, and Cloudflare with a safe staged rollout.
How to Configure CSP
Deploy Content Security Policy in report-only mode, analyse violations, and move to enforcement.
How to Check Security Headers
Audit HTTP security headers using ShowDNS, curl, and browser DevTools — with fixes for missing ones.
Security Headers on Nginx
Add HSTS, CSP, X-Frame-Options, and other security headers to Nginx with config examples.
Security Headers on Apache
Configure HTTP security headers on Apache using .htaccess and httpd.conf with tested examples.
Security Headers on Cloudflare
Set security headers in Cloudflare using Transform Rules, Workers, and Page Rules.
Security Headers on Caddy
Add HSTS, CSP, and other security headers to a Caddy server with minimal Caddyfile config.
Security Headers on IIS
Configure security response headers on IIS using web.config with tested examples for Windows Server.
How to Set X-Frame-Options
Add X-Frame-Options headers on Nginx, Apache, Cloudflare, and IIS to prevent clickjacking.
How to Set X-Content-Type-Options
Prevent MIME sniffing by setting X-Content-Type-Options: nosniff across all major web servers.
How to Set Referrer Policy
Configure the Referrer-Policy header to control how referrer data is shared on your site.
How to Set Permissions Policy
Add Permissions-Policy headers to control browser features like camera, microphone, and geolocation.
How to Set X-XSS-Protection
Learn when and how to configure the legacy X-XSS-Protection header and why CSP replaces it.
How to Set Cross-Origin-Opener-Policy
Add the COOP header on Nginx, Apache, IIS, Caddy, and Cloudflare to isolate your site from cross-origin window attacks.
How to Sign security.txt with PGP
Generate a PGP key with GnuPG, publish the public key under the Encryption field, and cleartext-sign your security.txt so researchers can verify it is authentic.
Email Security
10How to Create an SPF Record
Build and publish an SPF record for Google Workspace, Microsoft 365, and custom mail servers.
How to Configure DMARC
Set up DMARC from p=none monitoring to p=reject enforcement with a safe, staged rollout plan.
How to Setup BIMI
Configure BIMI to display your brand logo in Gmail, Apple Mail, and Yahoo Mail — including VMC.
How to Check MX Records
Verify MX records for email delivery using the ShowDNS MX Lookup tool, dig, and nslookup.
Why Emails Go to Spam
Diagnose and fix email deliverability issues — from missing SPF/DKIM/DMARC to blacklisted IPs.
How to Set Up DKIM
Generate a DKIM key, publish the public key as a DNS record, enable signing, and verify it — for self-hosted servers and major email providers.
How to Set Up MTA-STS
Publish an MTA-STS policy to force inbound mail over valid TLS, add a TLS-RPT record for failure reports, and verify both.
How to Read Your DMARC Reports
Read DMARC aggregate reports end to end — unzip the XML, load it into the analyzer, and interpret sources, SPF/DKIM alignment, dispositions, and spoofing.
How to Set Up DMARC Aggregate Reporting (rua=)
Add a rua= address and start receiving DMARC aggregate reports — mailbox setup, cross-domain authorisation, and confirming reports actually arrive.
Rolling Out DMARC: p=none → quarantine → reject
Stage a DMARC deployment without breaking legitimate mail — inventory senders from aggregate reports, fix alignment, then ramp enforcement with pct.
SSL
3How to Install an SSL Certificate
Install an SSL certificate on Nginx and Apache using Let's Encrypt Certbot or a paid CA.
How to Fix SSL Errors
Fix SSL errors — expired certificates, hostname mismatches, incomplete chains, and mixed content.
How to Check SSL Configuration
Audit your SSL setup — certificate chain, TLS version, cipher suites, OCSP stapling, and HSTS.
SSH
2How to Generate an SSH Key
Generate a secure SSH key pair with ssh-keygen or online, choose the right algorithm, add a passphrase, and install the public key on a server.
How to Convert PPK to PEM
Convert a PuTTY .ppk private key to OpenSSH PEM format so you can use it with ssh, scp, and AWS on Linux and macOS.