Configuring The Source Ip Address For Ntp Packets - Cisco Catalyst 4500 Series Configuration Manual

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:
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

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
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
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
4-10
Purpose
Enters global configuration mode.
Enters interface configuration mode, and specify the interface to 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.
Returns to privileged EXEC mode.
Verifies your entries.
(Optional) Saves your entries in the configuration file.
Purpose
Enters global configuration mode.
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.
Returns to privileged EXEC mode.
Verifies your entries.
(Optional) Saves your entries in the configuration file.
Chapter 4 Administering the Switch
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