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39-2
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
—
Release 8.1
78-15486-01
Chapter 39 Configuring NTP
Default NTP Configuration
The communications between machines running NTP, known as associations, are usually statically
configured; each machine is given the IP addresses of all machines with which it should form
associations. An associated pair of machines can keep accurate timekeeping by exchanging NTP
messages between each other. However, in a LAN environment, you can configure NTP to use IP
broadcast messages. With this alternative, you can configure the machine to send or receive broadcast
messages, but the accuracy of timekeeping is marginally reduced because the information flow is
one-way only.
Cisco’s implementation of NTP does not support stratum 1 service; it is not possible to connect to a radio
or atomic clock. We recommend that you obtain the time service for your network from the public NTP
servers available on the IP Internet.
If the network is isolated from the Internet, Cisco’s NTP implementation allows a machine to be
configured so that it acts as though it is synchronized using NTP, when it actually has determined the
time using other methods. Other machines synchronize to that machine using NTP.
Default NTP Configuration
Table 39-1
shows the default NTP configuration.
Configuring NTP on the Switch
The following sections describe how to configure NTP.
Enabling NTP in Broadcast-Client Mode
Enable the switch in NTP broadcast-client mode if an NTP broadcast server, such as a router, regularly
broadcasts time-of-day information on the network. To compensate for any server-to-client packet
latency, you can specify an NTP broadcast delay (a time adjustment factor for the receiving of broadcast
packets by the switch).
Table 39-1 Default NTP Configuration
Feature
Default Value
Broadcast client mode
Disabled
Client mode
Disabled
Broadcast delay
3000 microseconds
Time zone
Not specified
Offset from UTC
0 hours
Summertime adjustment
Disabled
NTP server
None specified
Authentication mode
Disabled