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Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
OL-30933-01
Chapter 4 Administering the Switch
Managing the System Time and Date
Configuring NTP Broadcast Service
The communications between devices running NTP (known as associations) are usually statically
configured; each device is given the IP addresses of all devices with which it should form associations.
Accurate timekeeping is possible by exchanging NTP messages between each pair of devices with an
association. However, in a LAN environment, NTP can be configured to use IP broadcast messages
instead. This alternative reduces configuration complexity because each device can be configured to
send or receive broadcast messages. However, the information flow is one-way only.
The switch can send or receive NTP broadcast packets on an interface-by-interface basis if there is an
NTP broadcast server, such as a router, broadcasting time information on the network. The switch can
send NTP broadcast packets to a peer so that the peer can synchronize to it. The switch can also receive
NTP broadcast packets to synchronize its own clock. This section provides procedures for both sending
and receiving NTP broadcast packets.
To configure the switch to send NTP broadcast packets to peers so that they can synchronize their clock
to the switch, perform this task:
To disable the interface from sending NTP broadcast packets, use the no ntp broadcast interface
configuration command.
This example shows how to configure a port to send NTP Version 2 packets:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# ntp broadcast version 2
Switch(config-if)# end
Switch#
Command Purpose
Step 1
configure terminal
Enters global configuration mode.
Step 2
interface interface-id
Specifies the interface to send NTP broadcast packets, and enter
interface configuration mode.
Step 3
ntp broadcast [version number] [key
keyid
] [destination-address]
Enables the interface to send NTP broadcast packets to a peer.
By default, this feature is disabled on all interfaces.
• (Optional) For number, specify the NTP version number. The
range is 1 to 3. If you do not specify a version, Version 3 is used.
• (Optional) For keyid, specify the authentication key to use when
sending packets to the peer.
• (Optional) For destination-address, specify the IP address of the
peer that is synchronizing its clock to this switch.
Step 4
end
Returns to privileged EXEC mode.
Step 5
show running-config
Verifies your entries.
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
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