If an invalid configuration is entered, a warning message is displayed and the configuration is not committed. This will happen if:
A multicast address is used but no NTP response is found.
An NTP server address is used, but that server does not respond properly to NTP.
To prevent against NTP spoofing attacks from rogue servers, NTP has a private key encryption scheme whereby NTP servers are associated with a private key that is used by the client to verify their identity. These keys are not used to encrypt traffic, and they are not used to authenticate the client -- they are only used by the NTP client (that is, the appliance) to authenticate the NTP server. To associate a private key with an NTP server, the private key must first be specified. Each private key has a unique integer associated with it, along with a type and key. The type must be one of the following:
After the keys have been specified, an NTP server can be associated with a particular private key. For a given key, all of the key number, key type and private key values must match between client and server for an NTP server to be authenticated.