NTP is designed to synchronize the time on a network of machines. NTP runs
over the User Datagram Protocol (UDP), using port 123 as both the source and
destination, which in turn runs over IP. NTP Version 3, RFC 1305, is used to
synchronize timekeeping among a set of distributed time servers and clients. A
set of nodes on a network are identified and configured with NTP and the nodes
form a synchronization subnet, sometimes referred to as an overlay network.
While multiple masters (primary servers) may exist, there is no requirement for
an election protocol. A sample NTP topology is shown in Figure
.
From the
Services > NTP Page, select Enabled for the Network Time Protocol
(NTP) if the network uses NTP
,
. To turn Network
Time Protocol (NTP) off, select Disabled. When NTP is enabled, an NTP Status
field appears. This field indicates whether NTP is synchronized or
unsynchronized. Click Refresh to update this status.
If the network has
a default time server, enter the server IP address or host name in the Time
Server (optional) field.
Cisco Aironet APs do not have a
hardware-supported clock, and they cannot function as an NTP master clock to
which peers synchronize themselves when an external NTP source is not
available. These access points also have no hardware support for a calendar. As
a result, the ntp update-calendar and the ntp master global configuration
commands are not available.
The example below shows how to configure the
AP to synchronize only to devices providing authentication key 42 in the NTP
packets of the device and to configure the AP to synchronize its system clock
with the clock of the peer at IP address 172.16.22.44 using NTP version 2. The
default settings are shown in Figure
.The command
syntax and descriptions are shown in Figures
and
.
AP(config)#ntp authenticate
AP(config)#ntp authentication-key 42 md5
aNiceKey
AP(config)#ntp trusted-key
42
AP(config)#ntp server
172.16.22.44 version 2