Articles & Guides
Useful resources for web developers and system administrators
Networking
Fix ERR_CONNECTION_CLOSED: Causes and Solutions
ERR_CONNECTION_CLOSED in Chrome means the server dropped the connection. Causes: TCP RST, antivirus, proxy, MTU, TLS. Fix it as a user and on the server.
Networking
Fix ERR_QUIC_PROTOCOL_ERROR: QUIC / HTTP3 Error Guide
What ERR_QUIC_PROTOCOL_ERROR means in Chrome, why QUIC/HTTP3 fails, and how to fix it: disable the QUIC flag, check UDP/443, the Alt-Svc header and server bugs.
Networking
Your Site Is Blocked in Russia: Owner's Guide
How a site owner can check a block in Russia, tell it from a hosting or DNS failure, find the grounds in the EAIS register, and file an unblocking appeal to Roskomnadzor.
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
Fix ERR_SSL_VERSION_OR_CIPHER_MISMATCH: Causes and Solutions
ERR_SSL_VERSION_OR_CIPHER_MISMATCH explained and fixed: outdated TLS 1.0/1.1, weak ciphers, nginx and Apache config, and openssl and curl verification steps.
Networking
TSPU, DPI and Traffic Throttling: How It Works and How to Check
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
HTTP 451 Unavailable For Legal Reasons Explained
What HTTP 451 means under RFC 7725, how it differs from 403, who returns it, its link to Roskomnadzor blocks, and how to serve 451 with the blocked-by header.
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
HTTP 401 Unauthorized: Causes and Fixes
What HTTP 401 Unauthorized means, the role of WWW-Authenticate and Authorization headers, how it differs from 403, and how to fix expired tokens or sessions.
HTTP
HTTP 400 Bad Request: Causes and Fixes
What HTTP 400 Bad Request means, why it happens (broken cookies, JSON, long URLs) and how to fix it as a user and as a developer, with clear examples.