ntp server


ntp server <IP-ADDR> [key <KEY-NUM>] [minpoll <MIN-NUM>] [maxpoll <MAX-NUM>][burst | iburst] [prefer] [version <VER-NUM>]

no ntp server <IP-ADDR>

no ntp server <IP-ADDR> [burst] [iburst] [prefer] [key-id <KEY-NUM>]


Defines an NTP server to use for time synchronization, or updates the settings of an existing server with new values. Up to eight servers can be defined.

The no form of this command removes a configured NTP server.

Command context



server <IP-ADDR>

Specifies the address of an NTP server as a DNS name, an IPv4 address (x.x.x.x), where x is a decimal number from 0 to 255, or an IPv6 address (xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx), where x is a hexadecimal number from 0 to F.

When specifying an IPv4 address, you can remove leading zeros. For example, the address becomes

When specifying an IPv6 address, you can use two colons (::) to represent consecutive zeros (but only once), remove leading zeros, and collapse a hextet of four zeros to a single 0. For example, this address 2222:0000:3333:0000:0000:0000:4444:0055 becomes 2222:0:3333::4444:55 .

key <KEY-NUM>

Specifies the key to use when communicating with the server. A trusted key must be defined with the command ntp authentication-key and authentication must be enabled with the command ntp authentication. Range: 1 to 65534.

minpoll <MIN-NUM>

Specifies the minimum polling interval in seconds, as a power of 2. Range: 4 to 17. Default: 6 (64 seconds).

maxpoll <MAX-NUM>

Specifies the maximum polling interval in seconds, as a power of 2. Range: 4 to 17. Default: 10 (1024 seconds).


Send a burst of packets instead of just one when connected to the server. Useful for reducing phase noise when the polling interval is long.


Send a burst of six packets when not connected to the server. Useful for reducing synchronization time at startup . Range: 1 to 4094.


Make this the preferred server.

version <VER-NUM>

Specifies the version number to use for all outgoing NTP packets. Range: 3 or 4.




Defining the ntp server pool.ntp.org, using iburst, and NTP version 4.

switch(config)# ntp server pool.ntp.org iburst version 4

Removing the ntp server pool.ntp.org.

switch(config)# no ntp server pool.ntp.org

Defining the ntp server my-ntp.mydomain.com and makes it the preferred server.

switch(config)# ntp server my-ntp.mydomain.com prefer