When enabling automatic signature updates, it is recommended that you ensure the following configuration guidelines have been met:
â¢The router's clock is set up with the proper relative time.
â¢The frequency for Cisco IOS IPS to obtain updated signature information has been defined.
â¢The URL in which to retrieve the Cisco IOS IPS signature configuration files has been specified.
â¢Optionally, the username and password for which to access the files from the server have been specified.
http://www.cisco.com/en/US/docs/ios/12_4t/12_4t11/ips_v5.html#wp1079125