# Date & Time Settings

This page displays time settings for the security device.

## Device Time

The following information appears at the top of the page:

- Up time: indicates the elapsed time (in number of days, hours, minutes, and seconds) since the device was first powered on

- System time: indicates the set time on the device including the date, time (hh:mm:ss), and the GMT timezone (hh:mm)

## Synchronizing the System Clock

This feature synchronizes the system clock with the clock on the administrator's workstation to allow logging to reflect the actual time at which events occur. This feature is especially useful if you are managing the device remotely across timezones. By synchronizing the device system clock with the time on your workstation, logged events reflect your local time and not the time at the physical location of the device.

### To Synchronize the System Clock

1. Click Sync Clock With Client to set the system clock of the NetScreen device to be the same as your workstation.

2. A dialog box asks you if the "Automatically adjust clock for daylight savings changes" option is enabled on your workstation. Click Yes or No, depending on your workstation setting.

3. Click Apply to save your settings.

## Greenwich Mean Time (GMT) Zone

GMT is an internationally accepted standard for calculating time based on International Atomic Time. You set the timezone by specifying the number of hours and minutes by which your local time is behind or ahead of GMT. For example, if your timezone is Pacific Daylight Saving Time, your timezone is 8 hours behind GMT; as a result, you enter -8 in the GMT offset field.

### To Set the Time Zone

1. From the Set Time Zone, select the correct offset from GMT for your local time.

2. Click Apply to save your settings.

## Daylight Saving Time

By default, the Automatically adjust clock for daylight saving changes (DST) option is selected. At 2:00 A.M. on the first Sunday in April, the Daylight Saving Time feature automatically adjusts the clock one hour ahead. At 2:00 A.M. on the last Sunday in October, it adjusts the clock one hour back.

If you use the device in an area that is unaffected by DST, clear this option. If you disable this feature, no time adjustments occur. You can also customize DST based on your specific country or region of the world using recurring and nonrecurring modes.

You can set the DST adjustment to recur on a weekday schedule (for example, the first Sunday in April) or on specific date. You can also set DST adjustment no to recur, in which case you can adjust DST settings only for a single year.

### To set Daylight Saving Time

You can set the DST adjustment to recur on a weekday schedule (for example, the first Sunday in April) or on a specific date. You can also set DST adjustment not to recur, in which case you can adjust DST settings only for a single year.

1. Select one of the following option buttons to choose how DST adjustment recurs: Recurring mode based on weekday; Recurring mode based on day; Non-recurring mode.

2. From the Start at and End at drop-down lists, choose the week, weekday, month, hour, and minute DST should start or end. If you choose, recurring mode based on day or non-recurring mode, choose the day of the month instead of the week. In non-recurring mode, DST settings only apply to the current year, so you do not have to select a year.

3. Enter the Offset, the number of minutes to go forward at the beginning of DST or backwards at the end of DST.

If you want to revert customized settings back to the default DST settings for the U.S., click Set Default.

## Network Time Protocol (NTP)

Network Time Protocol (NTP) is a method by which computers synchronize system clocks on the Internet. To ensure that the device always maintains the right time, it can use NTP to synchronize its system clock with that of an NTP server over the Internet. You can do this manually or you can configure the device to perform this synchronization automatically at specified time intervals.

### Multiple NTP Servers

You can configure up to three NTP servers on a device: one primary server and two backup servers. When you configure the device to automatically synchronize its system clock , it queries each configured NTP server sequentially. The device always queries the primary NTP server first. If the query is not successful, the device then queries the first backup NTP server and so on until it gets a valid reply from one of the NTP servers configured on the device. The device makes four attempts on each NTP server before it terminates the update and logs the failure.

To find an NTP server to which you can synchronize your device, you can refer to various sites on the Internet that maintain lists of NTP public time servers, such as http://www.ntp.org/.

### Secure NTP Servers

You can secure NTP traffic by using an MD5-based checksum to authenticate of NTP packets. To enable NTP traffic authentication, you must assign a unique key ID and a preshared key to each NTP server you configure on a device. The key ID and preshared key serve to create a checksum with which the device and the NTP server can authenticate the data.

There are two types of authentication for NTP traffic: required and preferred.

- Required – When you select Required authentication, the NetScreen device must include the authentication information—key ID and checksum—in every packet it sends to a NTP server and must authenticate all NTP packets it receives from a NTP server. Before authentication can occur between a device and a NTP server, the administrators of the device and the NTP server must first exchange a key ID and a preshared key. They have to exchange these manually and can do so in different ways, such as through e-mail or telephone.

- Preferred – When you select Preferred authentication, the device must first operate as in Required mode by trying to authenticate all NTP traffic. If all attempts to authenticate fail, the device then operates as if you selected no authentication. It sends out packets to a NTP server without including a key id and checksum. Essentially, although there is a preference for authentication, if authentication fails, the
  device still permits NTP traffic.

### Maximum Time Adjustment

When you enable the automatic NTP synchronization feature, you can specify a maximum time adjustment value (in seconds). The value represents the acceptable time difference between the device's system clock and the time received from an NTP server. The device only adjusts its clock with the NTP server time if the time difference between its clock and the NTP server time is within the maximum time-adjustment value that you set.

### To Enable and Configure NTP

1. Select Automatically synchronize with an Internet Time Server (NTP).

2. In the Update system clock every _ minutes field, enter how often (in minutes), you want the NetScreen device to synchronize its system clock with the NTP server. The value range is 1 to 1440 minutes (1 minute to 24 hours).

3. In the Maximum time adjustment field, enter a value (in seconds). The default value for this feature is 3 seconds and the range is 0 (no limit) to 3600 (one hour).

4. Optionally, you can select an authentication mode, Required or Preferred, if you want the NetScreen device to authenticate NTP traffic.

5. Enter the IP address or domain name of one or more NTP servers, beginning with the Primary server and then the backup servers. If you enabled authentication, also provide a unique server key ID and preshared key for each NTP server that you configure.

6. Click Apply to save your settings.

Note: You can only synchronize the system clock manually using the CLI. For more information on how to do this, refer to the ScreenOS CLI Reference Guide or the Concepts & Examples ScreenOS Reference Guide.