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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter8 Administering the Swi tc h 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 shou l d form associations.
Accurate timekeeping is possible by exchanging NTP messages between ea ch pa ir o f d evices wi th an
association. However, in a LAN environment, NTP can be configured to use IP broadcast messages
instead. This alternative reduces configuratio n complexi ty because each device c an simply be co nfigured
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 has procedures for both sending and receiving NTP
broadcast packets.
Beginning in privileged EXEC mode, follow these steps to configure the switch to send NTP broadcast
packets to peers so that they can synchronize their clock to the switch:
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(config)# interface gigabitethernet0/1
Switch(config-if)# ntp broadcast version 2
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify the interface to send NTP broadcast packets, and enter
interface configuration mode.
Step3 ntp broadcast [version number] [key keyid]
[destination-address]Enable 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.
Step4 end Return to privileged EXEC mode.
Step5 show running-config Verify your entries.
Step6 copy running-config startup-config (Optional) Save your entries in the configuration file.
Step7 Configure the connected peers to receive NTP broadcast packets as
described in the next procedure.