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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 7 Adminis tering the Switch Managi ng the System Ti me and Dat e
You need t o configure only one end of an a ssociati on; the other device can automat icall y establi sh the
associat ion. If you are using the default NTP version (version 3) and NTP sync hronizati on does no t
occur, try using N TP versi on 2. Ma ny NTP se rvers on t he Inte rnet run version 2.
To remove a peer or server association, use the no ntp peer ip-address or the no ntp server ip-address
global configurat ion comm and.
This example shows how to configure the switc h to synchro nize its syste m clock w ith the clock of t he
peer a t I P a ddres s 17 2.1 6. 22.44 using N TP version 2:
Switch(config)# ntp server 172.16.22.44 version 2

Configuring NTP Broadcast Service

The co mmunic ations bet ween devices run ning NTP (k nown as associations) are usually statically
configured; each device is given the IP addresses of a ll devices with whic h it should form associ ations.
Accurat e t imekee ping is po ssible by exch angi ng NTP messa ges be tw ee n ea ch pa ir o f d evices wi th an
associa tion. However, in a LA N environment , N TP can be configure d to use IP b roa dca st m essa ges
instead. This alternative reduces configuration complexity because each device can simply be
configured to send or rece ive broadcast messa ges. However, the inform ation 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 packe ts to a peer so that the peer can synch ronize to it. The switch can also recei v e NTP broadcast
packets to synchronize its own clock. This section provides 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:
Step 3 end Return to privileged EXEC mode.
Step 4 show running-config Verify your e ntrie s.
Step 5 copy running-config startup-config (Optiona l) Save your entries in the co nfigurati on file.
Command Purpose
Command Purpose
Step 1 configure terminal Enter globa l configurati on mode.
Step 2 interface interface-id Specify the interface to send NTP broadcast packets, and enter
interface con figurati on mode.
Step 3 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.
•(Optiona l) For number, specify the NTP version num ber. The
range is 1 to 3. If you do not specify a version, version 3 is used.
•(Optiona l) For keyid, specify the authentication key to use wh en
sending pa ckets to the pe er.
•(Optional) For destination-address, specif y the I P addres s of th e
peer that is synchroni zing its clo ck to this swi tch.
Step 4 end Return to p rivileged EXEC mode.
Step 5 show running-config Verify your e ntrie s.