Connection and Protocol Errors

SSL protocol errors like "ERR_SSL_PROTOCOL_ERROR" (Chrome) or "SSL_ERROR_NO_CYPHER_OVERLAP" (Firefox) indicate fundamental communication failures between browsers and servers. These errors suggest configuration mismatches, disabled protocols, or incompatible cipher suites. Unlike certificate errors, protocol errors prevent any secure connection establishment.

Common causes include overly restrictive SSL/TLS protocol configurations, disabled cipher suites creating no overlap between client and server, corrupted SSL configurations or certificate files, firewall or security software interfering with SSL/TLS connections, and server-side issues with SSL/TLS implementation. Time synchronization problems can also manifest as protocol errors when certificate validation fails.

Diagnosis requires analyzing server SSL/TLS configuration. Use nmap --script ssl-enum-ciphers -p 443 yourdomain.com to enumerate supported protocols and ciphers. Compare results against browser requirements - modern browsers require TLS 1.2 minimum. Check server error logs for SSL handshake failures. Test from multiple networks to rule out local interference. Verify system time accuracy, as certificate validation depends on correct timestamps.

Resolution involves updating SSL/TLS configurations to balance security with compatibility. Enable TLS 1.2 and TLS 1.3 while disabling older protocols. Configure cipher suites supporting forward secrecy and authenticated encryption. Remove deprecated options like RC4 or 3DES. Test configuration changes thoroughly before production deployment. Consider using Mozilla's SSL Configuration Generator for recommended settings based on your compatibility requirements.