Certificate CN Referencing Hostnames or Private IP Addresses

Mozilla Firefox classifies using a private IP address as the Common Name (CN) on a certificate as a "problematic practice" (, and Google Chrome also displays an error when an IP address is used as a CN. The result of using a private IP address as a CN is when a user attempts to browse the website, the user receives an error.

  • The error from Chrome is "NET:ERR_CERT_COMMON_NAME_INVALID"

  • The error from Firefox is "(Error code: sec_error_unknown_issuer)"

The recommended configuration is to use an FQDN as the CN, and specify the IP address as a SAN. 


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