Chapter 7 Administering the Switch

Managing the System Time and Date

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

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.

 

 

 

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

Step 1

 

 

configure terminal

Enter global configuration mode.

Step 2

 

 

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.

Step 3

 

 

end

Return to privileged EXEC mode.

Step 4

 

 

show running-config

Verify your entries.

Step 5

 

 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

 

 

 

The specified interface is used for the source address for all packets sent to all destinations. If a source address is to be used for a specific association, use the source keyword in the ntp peer or ntp server global configuration command as described in the “Configuring NTP Associations” section on page 7-5.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

7-10

OL-9775-02

 

 

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Cisco Systems 3750E manual Configuring the Source IP Address for NTP Packets, Interface interface-id