Articles & Guides
Useful resources for web developers and system administrators
Networking
Fix ERR_EMPTY_RESPONSE: Server Returned No Data
ERR_EMPTY_RESPONSE means the server closed the connection with no reply. Learn the causes — backend crash, proxy timeout, WAF — and fix it via nginx and php-fpm logs.
SSL/TLS
ERR_SSL_VERSION_OR_CIPHER_MISMATCH: Find the Cause and Fix It
ERR_SSL_VERSION_OR_CIPHER_MISMATCH means no shared TLS version or cipher. openssl tests, nginx, Apache, IIS and Cloudflare fixes, plus old router admin pages.
Networking
TSPU, DPI and Traffic Throttling: How It Works
How TSPU and DPI work, how throttling differs from a full block and an outage, the signs that reveal it, and how to run external availability diagnostics.
HTTP
451 Unavailable For Legal Reasons: Meaning (RFC 7725)
HTTP 451 Unavailable For Legal Reasons (RFC 7725): access refused due to a legal demand such as a court order or blocklist. How it differs from 403.
Networking
How Roskomnadzor Blocks Websites: EAIS, TSPU, DPI
How Roskomnadzor blocks websites: the EAIS register, TSPU under Law 90-FZ, DPI filtering, and the difference between IP, DNS and DPI blocking.
HTTP
401 Unauthorized Error: Meaning (RFC 9110) and How to Fix
401 Unauthorized: the request had no valid credentials. Read WWW-Authenticate, send a fresh token or API key, and fix it in curl, Postman or nginx.
HTTP
400 Bad Request: Causes and Fixes (Chrome, nginx, API)
400 Bad Request means the server rejected a malformed request. Usual fixes: clear the site's cookies, fix JSON or Content-Type, raise nginx header limits.
Monitoring
RKN Blocklist 2026: 131,361 Domains Blocked in Russia
Russia's RKN blocklist in numbers: 131,361 domains in the official registry, 1.47M+ in operator lists, 70% outside .ru, 19% of top global sites.
Monitoring
Security Headers Across Russia's Top Sites: a 50-Site Study
Enterno.io scanned 50 of Russia's top sites: only 2% use CSP, 25% use HSTS, and 57% score an F on security headers — while SSL/TLS hygiene is excellent.
Monitoring
Mail Server Monitoring: MX/SMTP/Blacklist
Mail server monitoring: checking MX, SMTP ports 25/465/587, TLS via openssl, blacklist status and alerts. Set up continuous mail monitoring in enterno.io.