A CRL is generated by a CA and contains a list of certificates to revoke from the list of certificates that the CA has issued.
Typically, a CA automatically generates a CRL at a specified interval, anywhere from two hours to one year, at which point the new CRL with the list of revoked certificates is available for clients to request.
The CRL itself contains the interval period, which allows clients, such as Centrify Authentication Service, to determine when to request a new CRL. See Retrieving a certificate revocation list and verifying certificates for information about retrieving CRLs.
In addition to automatic generation of a CRL, an administrator can use specific Active Directory utilities that allow them to manually revoke certificates and publish a CRL on the CA. In this case, the CRL-publishing interval is reset so the next automatic publishing operation will occur in the appropriate amount of time.