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Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 7 Administering the Switch
Managing the System Time and Date
If the source IP address matches the access lists for more than one access type, the first type is granted.
If no access groups are specified, all access types are granted to all devices. If any access groups are
specified, only the specified access types are granted.
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:
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.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode, and specify the interface to disable.
Step 3
ntp disable Disable NTP packets from being received on the interface.
By default, all interfaces receive NTP packets.
Step 4
end Return to privileged EXEC mode.
Step 5
show running-config Verify your entries.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.