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Managing the System Time and Date
To remove access control to the switch NTP services, use the no ntp access-group {query-only |
serve-only | serve | peer} global configuration command.
This example shows how to configure the switch to allow itself to synchronize to a peer from access
list 99. However, the switch restricts access to allow only time requests from access list 42:
Switch# configure terminal
Switch(config)# ntp access-group peer 99
Switch(config)# ntp access-group serve-only 42
Switch(config)# access-list 99 permit 172.20.130.5
Switch(config)# access list 42 permit 172.20.130.6
Disabling NTP Services on a Specific Interface
NTP services are enabled on all interfaces by default.
Beginning in privileged EXEC mode, follow these steps to disable NTP packets from being received on
an interface:
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
ntp disable
Step 4
end
Step 5
show running-config
Step 6
copy running-config startup-config
To re-enable receipt of NTP packets on an interface, use the no ntp disable interface configuration
command.
Configuring the Source IP Address for NTP Packets
When the switch sends an NTP packet, the source IP address is normally set to the address of the interface
through which the NTP packet is sent. Use the ntp source global configuration command when you want to
use a particular source IP address for all NTP packets. The address is taken from the specified interface. This
command is useful if the address on an interface cannot be used as the destination for reply packets.
Beginning in privileged EXEC mode, follow these steps to configure a specific interface from which the IP
source address is to be taken:
Command
Step 1
configure terminal
Step 2
ntp source type number
Step 3
end
Step 4
show running-config
Step 5
copy running-config startup-config
Catalyst 3750 Switch Software Configuration Guide
7-10
Purpose
Enter global configuration mode.
Enter interface configuration mode, and specify the interface to disable.
Disable NTP packets from being received on the interface.
By default, all interfaces receive NTP packets.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Purpose
Enter global configuration mode.
Specify the interface type and number from which the IP source address
is taken.
By default, the source address is set by the outgoing interface.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Chapter 7
Administering the Switch
78-16180-02
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