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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter7 Administering the Switch
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 pr ivileged EXEC mod e, follow these s teps to disable N TP packets from being received on
an interface:
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 Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Enter interface configuration mode, and specify the interface to disable.
Step3 ntp disable Disable NTP packets from being received on the interface.
By default, all interfaces receive NTP packets.
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.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 ntp source type number 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.
Step3 end Return to privileged EXEC mode.