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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 4 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
Switch(config)# end
Switch#

Disabling NTP Services on a Specific Interface

NTP services are enabled on all interfaces by default.
To disable NTP packets from being received on an interface, perform this task:
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. To use a particular source IP address for all NTP
packets, use the ntp source global configuration command. 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.
To configure a specific interface from which the IP source address is to be taken, perform this task:
Command Purpose
Step 1 configure terminal Enters global configuration mode.
Step 2 interface interface-id Enters interface configuration mode, and specify the interface to disable.
Step 3 ntp disable Disables NTP packets from being received on the interface.
By default, all interfaces receive NTP packets.
To reenable receipt of NTP packets on an interface, use the
no ntp disable interface configuration command.
Step 4 end Returns to privileged EXEC mode.
Step 5 show running-config Verifies your entries.
Step 6 copy running-config startup-config (Optional) Saves your entries in the configuration file.
Command Purpose
Step 1 configure terminal Enters global configuration mode.
Step 2 ntp source type number Specifies the interface type and number from which the IP source address
is taken.
By default, the source address is set by the outgoing interface.
Step 3 end Returns to privileged EXEC mode.
Step 4 show running-config Verifies your entries.
Step 5 copy running-config startup-config (Optional) Saves your entries in the configuration file.