Cisco Sg3008 Manual

							Administration
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Cisco Small Business 200, 300 and 500 Series Managed Switch Administration Guide (Internal Version)  72
 
Administration: Time Settings
Synchronized system clocks provide a frame of reference between all devices on 
the network. Network time synchronization is critical because every aspect of 
managing, securing, planning, and debugging a network involves determining 
when events occur. Without synchronized clocks, accurately correlating log files 
between devices when tracking security breaches or network usage is 
impossible.
Synchronized time also reduces confusion in shared file systems, as it is important 
for the modification times to be consistent, regardless of the machine on which the 
file systems reside. 
For these reasons, it is important that the time configured on all of the devices on 
the network is accurate.
NOTEThe device supports Simple Network Time Protocol (SNTP) and when enabled, the 
device dynamically synchronizes the device time with time from an SNTP server. 
The device operates only as an SNTP client, and cannot provide time services to 
other devices. 
This section describes the options for configuring the system time, time zone, and 
Daylight Savings Time (DST). It covers the following topics: 
•System Time Options
•SNTP Modes
•Configuring System Time 
						

							Administration: Time Settings
System Time Options
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System Time Options
System time can be set manually by the user, dynamically from an SNTP server, or 
synchronized from the PC running the GUI. If an SNTP server is chosen, the manual 
time settings are overwritten when communications with the server are 
established.
As part of the boot process, the device always configures the time, time zone, and 
DST. These parameters are obtained from the PC running the GUI, SNTP, values 
set manually, or if all else fails, from the factory defaults. 
Time
The following methods are available for setting the system time on the device:
•Manual—You must manually sets the time.
•From PC—Time can be received from the PC by using browser information. 
The configuration of time from the computer is saved to the Running 
Configuration file. You must copy the Running Configuration to the Startup 
Configuration in order to enable the device to use the time from the 
computer after reboot. The time after reboot is set during the first WEB login 
to the device.
When you configure this feature for the first time, if the time was not already 
set, the device sets the time from the PC. 
This method of setting time works with both HTTP and HTTPS connections.
•SNTP—Time can be received from SNTP time servers. SNTP ensures 
accurate network time synchronization of the device up to the millisecond by 
using an SNTP server for the clock source. When specifying an SNTP server, 
if choosing to identify it by hostname, three suggestions are given in the GUI:
-time-a.timefreq.bldrdoc.gov
-time-b.timefreq.bldrdoc.gov
-time-c.timefreq.bldrdoc.gov
After the time has been set by any of the above sources, it is not set again by the 
browser.
NOTESNTP is the recommended method for time setting.  
						

							Administration: Time Settings
SNTP Modes
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Time Zone and Daylight Savings Time (DST )
The Time Zone and DST can be set on the device in the following ways:
•Dynamic configuration of the device through a DHCP server, where:
-Dynamic DST, when enabled and available, always takes precedence 
over the manual configuration of DST. 
-If the server supplying the source parameters fails, or dynamic 
configuration is disabled by the user, the manual settings are used.
-Dynamic configuration of the time zone and DST continues after the IP 
address lease time has expired.
•Manual configuration of the time zone and DST becomes the Operational 
time zone and DST, only if the dynamic configuration is disabled or fails.
NOTEThe DHCP server must supply DHCP option 100 in order for dynamic 
time zone configuration to take place.
SNTP Modes
The device can receive the system time from an SNTP server in one of the 
following ways:
•Client Broadcast Reception (passive mode)
SNTP servers broadcast the time, and the device listens to these 
broadcasts. When the device is in this mode, there is no need to define a 
Unicast SNTP server.
•Client Broadcast Transmission (active mode)—The device, as an SNTP 
client, periodically requests SNTP time updates. This mode works in either 
of the following ways:
-SNTP Anycast Client Mode—The device broadcasts time request 
packets to all SNTP servers in the subnet, and waits for a response.
-Unicast SNTP Server Mode—The device sends Unicast queries to a list 
of manually-configured SNTP servers, and waits for a response. 
The device supports having all of the above modes active at the same time and 
selects the best system time received from an SNTP server, according to an 
algorithm based on the closest stratum (distance from the reference clock). 
						

							Administration: Time Settings
Configuring System Time
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Configuring System Time
Selecting Source of System Time
Use the System Time page to select the system time source. If the source is 
manual, you can enter the time here. 
!
CAUTIONIf the system time is set manually and the device is rebooted, the manual time 
settings must be reentered.
To define system time:
STEP 1Click Administration > Time Settings > System Time.
The following fields are displayed:
•Actual Time (Static)—System time on the device. This shows the DHCP 
time zone or the acronym for the user-defined time zone if these were 
defined.
•Last Synchronized Server—Address, stratum and type of the SNTP server 
from which time was last taken.
STEP  2Enter these parameters:
Clock Source Settings—Select the source used to set the system clock. 
•Main Clock Source (SNTP Servers)—If you enable this, the system time is 
obtained from an SNTP server. To use this feature, you must also configure a 
connection to an SNTP server in the SNTP Interface Settings page. 
Optionally, enforce authentication of the SNTP sessions by using the SNTP 
Authentication page.
•Alternate Clock Source (PC via active HTTP/HT TPS sessions)—Select to 
set the date and time from the configuring computer using the HTTP 
protocol.
NOTEThe Clock Source Setting needs to be set to either of the above in 
order for RIP MD5 authentication to work. This also helps features that 
associate with time, for example: Time Based ACL, Port, 802.1 port 
authentication that are supported on some devices. 
						

							Administration: Time Settings
Configuring System Time
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Manual Settings—Set the date and time manually. The local time is used when 
there is no alternate source of time, such as an SNTP server:
•Date—Enter the system date. 
•Local Time—Enter the system time.
Time Zone Settings—The local time is used via the DHCP server or Time Zone 
offset.
•Get Time Zone from DHCP—Select to enable dynamic configuration of the 
time zone and the DST from the DHCP server. Whether one or both of these 
parameters can be configured depends on the information found in the 
DHCP packet. If this option is enabled, y o u  m u s t  a l s o  e n a b l e  D H C P  c l i e n t  o n  
the device. 
NOTEThe DHCP Client supports Option 100 providing dynamic time zone 
setting. 
•Time Zone from DHCP—Displays the acronym of the time zone configured 
from the DHCP server. This acronym appears in the Actual Time field
•Time Zone Offset—Select the difference in hours between Greenwich 
Mean Time (GMT) and the local time. For example, the Time Zone Offset for 
Paris is GMT +1, while the Time Zone Offset for New York is GMT – 5. 
•Time Zone Acronym—Enter a user-defined name that represents the time 
zone you have configured. This acronym appears in the Actual Time field.
Daylight Savings Settings—Select how DST is defined:
•Daylight Savings—Select to enable Daylight Saving Time.
•Ti m e  S e t  O f f s e t—Enter the number of minutes offset from GMT ranging from 
1—1440. The default is 60.
•Daylight Savings Type—Click one of the following:
-
USA—DST is set according to the dates used in the USA.
-
European—DST is set according to the dates used by the European 
Union and other countries that use this standard.
-
By Dates—DST is set manually, typically for a country other than the USA 
or a European country. Enter the following parameters:
-
Recurring—DST occurs on the same date every year.
Selecting 
By Dates allows customization of the start and stop of DST: 
						

							Administration: Time Settings
Configuring System Time
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-From—Day and time that DST starts. 
-To—Day and time that DST ends. 
Selecting 
Recurring allows different customization of the start and stop of 
DST:
•From—Date when DST begins each year.
-
Day—Day of the week on which DST begins every year.
-
Week—Week within the month from which DST begins every year.
-
Month—Month of the year in which DST begins every year.
-
Ti m e—The time at which DST begins every year.
•To—Date when DST ends each year. For example, DST ends locally every 
fourth Friday in October at 5:00 am. The parameters are:
-
Day—Day of the week on which DST ends every year.
-
Week—Week within the month from which DST ends every year.
-
Month—Month of the year in which DST ends every year.
-
Ti m e—The time at which DST ends every year.
STEP  3Click Apply. The system time values are written to the Running Configuration file.
Adding a Unicast SNTP Server
Up to 16 Unicast SNTP servers can be configured. 
NOTETo specify a Unicast SNTP server by name, you must first configure DNS server(s) 
on the device (see DNS Settings). In order to add a Unicast SNTP server, check the 
box to enable SNTP Client Unicast.
To add a Unicast SNTP server:
STEP 1Click Administration > Time Settings > SNTP Unicast.
STEP  2Enter the following fields:
•SNTP Client Unicast—Select to enable the device to use SNTP-predefined 
Unicast clients with Unicast SNTP servers.