Answer
The Junos OS device does not support multiple certificates with the same subject name (or distinguished name [DN]) on a single Junos OS device. Therefore, we recommend using a separate subject name for every key pair to avoid confusion. Some CAs also have limitations on supporting multiple key pairs for the same subject name.
Additionally, the Junos OS device does not auto-generate CN (common name) values such as a fully qualified domain name (FDQN) and serial number. The FQDN or any other CN values must be specified during the certificate request procedure.
For more information, see Understanding Certificates and PKI