How to set up a Cisco router to act as an NTP server?

Step 1 Log in to the router.

Step 2 Enter configuration mode:

router# configure terminal

Step 3 Create the key ID and key value:

router(config)# ntp authentication-key key_ID md5 key_value

The key ID can be a number between 1 and 65535. The key value is text (numeric or character). It is encrypted later.

Example:

router(config)# ntp authentication-key 100 md5 attack


Note The sensor only supports MD5 keys.

Note Keys may already exist on the router. Use the show running configuration command to check for other keys. You can use those values for the trusted key in Step 4.
Step 4 Designate the key you just created in Step 3 as the trusted key (or use an existing key):

router(config)# ntp trusted-key key_ID

The trusted key ID is the same number as the key ID in Step 3.

Example:

router(config)# ntp trusted-key 100

Step 5 Specify the interface on the router that the sensor will communicate with:

router(config)# ntp source interface_name

Example:

router(config)# ntp source FastEthernet 1/0

Step 6 Specify the NTP master stratum number to be assigned to the sensor:

router(config)# ntp master stratum_number

Example:

router(config)# ntp master 6

The NTP master stratum number identifies the server's relative position in the NTP hierarchy. You can choose a number between 1 and 15.