Cisco ASA 5505 Configuration Manual page 274

Setting the Date and Time
Preferred—Sets this server as a preferred server. NTP uses an algorithm to determine which server
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is the most accurate and synchronizes to that one. If servers are of similar accuracy, then the
preferred server is used. However, if a server is significantly more accurate than the preferred one,
the adaptive security appliance uses the more accurate one. For example, the adaptive security
appliance uses a more accurate server over a less accurate server that is preferred.
Interface—Sets the outgoing interface for NTP packets, if you want to override the default interface
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according to the routing table. The system does not include any interfaces, so it uses the admin
context interfaces. If you intend to change the admin context (thus changing the available
interfaces), you should choose None (the default interface) for stability.
• Authentication Key—Sets the authentication key attributes if you want to use MD5 authentication
for communicating with the NTP server.
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Cisco ASA 5500 Series Configuration Guide using ASDM
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Key Number—Sets the key ID for this authentication key. The NTP server packets must also
use this key ID. If you previously configured a key ID for another server, you can select it in the
list; otherwise, type a number between 1 and 4294967295.
Trusted—Sets this key as a trusted key. You must select this box for authentication to work.
Key Value—Sets the authentication key as a string up to 32 characters in length.
Reenter Key Value—Validates the key by ensuring that you enter the key correctly two times.
Chapter 9 Configuring Basic Settings
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