Answer
Juniper Networks supports RFC3280. Junos OS also has all the required security features of RFC2459 (the predecessor of RFC3280).
Junos OS follows the PKI profile described in RFC3280 and supports:
- Installation of end-entity (EE) or CA certificate
- Encode, including the X.509 or PKCS7, DER or PEM
- Compatibility with X.509 v3 and handling of extensions defined in RFC3280.
For more information, see Understanding Certificates and PKI