1-4
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Administering the Switch
Managing the System Time and Date
NTP Version 4
NTP version 4 is implemented on the switch. NTPv4 is an extension of NTP version 3. NTPv4 supports
both IPv4 and IPv6 and is backward-compatible with NTPv3.
NTPv4 provides these capabilities:
• Support for IPv6.
• Improved security compared to NTPv3. The NTPv4 protocol provides a security framework based
on public key cryptography and standard X509 certificates.
• Automatic calculation of the time-distribution hierarchy for a network. Using specific multicast
groups, NTPv4 automatically configures the hierarchy of the servers to achieve the best time
accuracy for the lowest bandwidth cost. This feature leverages site-local IPv6 multicast addresses.
Note You can disable NTP packets from being received on routed ports and VLAN interfaces. You cannot
disable NTP packets from being received on access ports. For details, see the “Disabling NTPv4 Services
on a Specific Interface” section of the “Implementing NTPv4 in IPv6” chapter of the Cisco IOS IPv6
Configuration Guide, Release 12.4T.
For details about configuring NTPv4, see the “Implementing NTPv4 in IPv6” chapter of the Cisco IOS
IPv6 Configuration Guide, Release 12.4T.
Configuring Time and Date Manually
If no other source of time is available, you can manually configure the time and date after the system is
restarted. The time remains accurate until the next system restart. We recommend that you use manual
configuration only as a last resort. If you have an outside source to which the switch can synchronize,
you do not need to manually set the system clock.
Note You must reset this setting if you have manually set the system clock and the stack master fails and
different stack member resumes the role of stack master.
These sections contain this configuration information:
• Setting the System Clock, page 1-4
• Displaying the Time and Date Configuration, page 1-5
• Configuring the Time Zone, page 1-5
• Configuring Summer Time (Daylight Saving Time), page 1-6
Setting the System Clock
If you have an outside source on the network that provides time services, such as an NTP server, you do
not need to manually set the system clock.
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