By default, CRLs are
issued once every 168 hours (1 calendar week). To specify a value other than
the default value for issuing the CRL, execute the
lifetime
crl command. After the CRL is issued, it is
written to the specified database location as
ca-label. crl,
where
ca-label is the
name of the certificate server.
CRLs can be
distributed through SCEP, which is the default method, or a CRL distribution
point (CDP), if configured and available. If you set up a CDP, use the
cdp-url command
to specify the CDP location. If the
cdp-url command
is not specified, the CDP certificate extension is not included in the
certificates that are issued by the certificate server. If the CDP location is
not specified, Cisco IOS PKI clients automatically request a CRL from the
certificate server with a SCEP GetCRL message. The CA then returns the CRL in a
SCEP CertRep message to the client. Because all SCEP messages are enveloped and
signed PKCS#7 data, the SCEP retrieval of the CRL from the certificate server
is costly and not highly scalable. In very large networks, an HTTP CDP provides
better scalability and is recommended if you have many peer devices that check
CRLs. You may specify the CDP location by a simple HTTP URL string for example,
cdp-url
http://my-cdp.company.com/filename.crl
The certificate
server supports only one CDP; thus, all certificates that are issued include
the same CDP.
If you have PKI
clients that are not running Cisco IOS software and that do not support a SCEP
GetCRL request and wish to use a CDP you may set up an external server to
distribute CRLs and configure the CDP to point to that server. Or, you can
specify a non-SCEP request for the retrieval of the CRL from the certificate
server by specifying the
cdp-url command
with the URL in the following format where
cs-addr is the
location of the certificate server:
cdp-url
http://cs-addr /cgi-bin/pkiclient.exe?operation=GetCRL
Note |
If your
CA is also configured as your HTTP CDP server, specify your CDP
with the
cdp-url
http://cs-addr /cgi-bin/pkiclient.exe?operation=GetCRL
command syntax.
|
It is the
responsibility of the network administrator to ensure that the CRL is available
from the location that is specified through the
cdp-url
command.
In order to force the
parser to retain the embedded question mark within the specified location,
enter Ctrl-v prior to the question mark. If this action is not taken, CRL
retrieval through HTTP returns an error message.
The CDP location may
be changed after the certificate server is running through the
cdp-url
command. New certificates contain the updated CDP location, but existing
certificates are not reissued with the newly specified CDP location. When a new
CRL is issued, the certificate server uses its current cached CRL to generate a
new CRL. (When the certificate server is rebooted, it reloads the current CRL
from the database.) A new CRL cannot be issued unless the current CRL has
expired. After the current CRL expires, a new CRL is issued only after a
certificate is revoked from the CLI.