Allied Telesis AT-S95 WEB - Manual (Page 38)

Page 38
Allied Telesis
AT-S95 Management Software Web Browser Interface User’s Guide
– SNTP — Indicates that the system time is set via an SNTP server.
• System Time — Sets the local clock time. The field format is HH:MM:SS. For example: 21:15:03.
• System Date — Sets the system date. The field format is Day/Month/Year. For example: 04/May/2050
(May 4, 2050).
• Time Zone Offset — The difference between Greenwich Mean Time (GMT) and local time. For example, the
Time Zone Offset for Paris is GMT +1, while the Time Zone Offset for New York is GMT –5.
To set the system clock:
1. Select the system time mode.
2. Define the System Date, System Time and Time Zone Offset fields.
3. Click Apply in each section. The local system clock settings are saved, and the device is updated.
4. Click Save Config on the menu to save the changes permanently.
Configuring SNTP
The device supports the Simple Network Time Protocol (SNTP). SNTP assures accurate network device clock
time synchronization up to the millisecond. Time synchronization is performed by a network SNTP server. The
device operates only as an SNTP client, and cannot provide time services to other systems. The device can poll
the following server types for the server time:
• Unicast
• Anycast
• Broadcast
Time sources are established by stratums. Stratums define the accuracy of the reference clock. The higher the
stratum (where zero is the highest), the more accurate the clock. The device receives time from stratum 1 and
above. The following is an example of stratums:
Stratum 0 — A real time clock (such as a GPS system) is used as the time source.
Stratum 1 — A server that is directly linked to a Stratum 0 time source is used. Stratum 1 time servers provide
primary network time standards.
Stratum 2 — The time source is distanced from the Stratum 1 server over a network path. For example, a Stratum
2 server receives the time over a network link, via NTP, from a Stratum 1 server.
Polling for Unicast Time Information
Polling for Unicast information is used for polling a server for which the IP address is known. T1 - T4 are used to
determine the server time. This is the preferred method for synchronizing device time.
Polling for Anycast Time Information
Polling for Anycast information is used when the SNTP server IP address is unknown. The first Anycast server to
return a response is used to set the time value. Time levels T3 and T4 are used to determine the server time.
Using Anycast time information for synchronizing device time is preferred to using Broadcast time information.
Broadcast Time Information
Broadcast information is used when the server IP address is unknown. When a Broadcast message is sent from
an SNTP server, the SNTP client listens for the response. The SNTP client neither sends time information
requests nor receives responses from the Broadcast server.
Message Digest 5 (MD5) Authentication safeguards device synchronization paths to SNTP servers. MD5 is an
algorithm that produces a 128-bit hash. MD5 is a variation of MD4, and increases MD4 security. MD5 verifies the
integrity of the communication, authenticates the origin of the communication.