NTP and Clock
Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over variable-latency data networks. NTP is intended to synchronize all participating computers to within a few milliseconds of Coordinated Universal Time (UTC) and is designed to mitigate the effects of variable network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve better than one millisecond accuracy in local area networks under ideal conditions.
When authentication of incoming NTP packets is enabled, the switch ensures that they come from an authenticated time source before using them for time synchronization on the switch. Authentication keys are created and added to the trusted list.
To add a key to be used for authentication, take the following steps.
Create the key.
switch
(config)# ntp authentication-key1
md5 passwordAdd the key to the trusted list.
switch
(config)# ntp trusted-key1
Assign the key to the server/peer.
switch
(config)# ntp server10.34
.1.1
keyID1
An authentication key may be created and used to authenticate incoming NTP packets. For the key to be used, make sure the following is in place.
It should be shared with the NTP server/peer sending the NTP packet.
It should be added to the trusted list.
NTP authenticate should be enabled on the system
clock set
clock set <hh:mm:ss> [<yyyy/mm/dd>] Sets the time and date. |
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Syntax Description |
hh:mm:ss |
Time |
yyyy/mm/dd |
Date |
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Default |
N/A |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
show clock |
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Notes |
If not specified, the date will be left the same. |
clock timezone
clock timezone [<zone-word> [<zone-word> [<zone-word>] [<zone-word>]]] no clock timezone Sets the system time zone. The time zone may be specified in one of three ways:
The no form of the command resets time zone to its default (GMT). |
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Syntax Description |
zone-word |
Possible forms this could take include: continent, city, continent, country, city, continent, region, country, city, ocean, and/or island. |
Default |
GMT |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
show clock |
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Notes |
ntp
Configures NTP. The no form of the command negates NTP options. |
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Syntax Description |
disable |
Disables NTP. |
enable |
Enables NTP. |
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peer | server |
Configures an NTP peer or server node. |
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IP address |
IPv4 or IPv6 address. |
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version <number> |
Specifies the NTP version number of this peer. Possible values: 3 or 4 |
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Default |
NTP is enabled NTP version number is 4 |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
ntpdate
ntpdate <ip-address> Configures the system clock using the specified SNTP server. |
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Syntax Description |
ip-address |
IP address of SNTP server. |
Default |
N/A |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
This is a one-time operation and does not cause the clock to be kept in sync on an ongoing basis. It will generate an error if SNTP is enabled since the socket it requires will already be in use. |
ntp authenticate
ntp authenticate no ntp authenticate Enables NTP authentication. The no form of the command disables NTP authentication. |
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Syntax Description |
N/A |
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Default |
Disabled |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
ntp authentication-key
ntp authentication-key <key-id> <encrypt-type> [<password>] no ntp authentication-key <key-id> Enables NTP authentication. The no form of the command disables NTP authentication. |
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Syntax Description |
key-id |
Specifies a key ID, whether existing or a new one to be added. Range: 1-65534 |
encrypt-type |
Specifies encryption type to use (md5, or sha1) |
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password |
Password string |
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Default |
Disabled |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
If a password is not entered, a prompt appears requiring that a password is introduced. |
ntp peer disable
ntp peer <ip-address> disable no ntp peer <ip-address> disable Temporarily disables this NTP peer. The no form of the command enables this NTP peer. |
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Syntax Description |
ip-address |
IP address of the peer. |
Default |
Disabled |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
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ntp peer keyID
ntp peer <ip-address> keyID <key-id> no ntp peer <ip-address> keyID <key-id> Specifies the KeyID of the NTP peer. The no form of the command removes key ID configuration from the NTP peer. |
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Syntax Description |
ip-address |
IP address of the peer. |
key-id |
Range: 1-65534 |
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Default |
Disabled |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
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ntp peer version
ntp peer <ip-address> version <ver-num> no ntp peer <ip-address> version <ver-num> Specifies the NTP version number of this peer. The no form of the command defaults NTP to version 4. |
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Syntax Description |
ip-address |
IP address of the peer. |
ver-num |
NTP version. Possible values: 3 or 4 |
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Default |
4 |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
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ntp server disable
ntp server <ip-address> disable no ntp server <ip-address> disable Temporarily disables this NTP server. The no form of the command enables this NTP server. |
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Syntax Description |
ip-address |
IP address of the peer. |
Default |
Disabled |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
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ntp server keyID
ntp server <ip-address> keyID <key-id> no ntp server <ip-address> keyID <key-id> Specifies the KeyID of the NTP server. The no form of the command removes key ID configuration from the NTP server. |
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Syntax Description |
ip-address |
IP address of the peer. |
key-id |
Range: 1-65534 |
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Default |
Disabled |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
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ntp server-role disable
ntp server-role disable no ntp server-role disable |
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Syntax Description |
N/A |
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Default |
N/A |
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Configuration Mode |
Configure terminal |
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History |
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Role |
Admin |
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Example |
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Related Commands |
show ntp |
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Notes |
This command is configurable. |
ntp server trusted-enable
ntp server <ip-address> trusted-enable no ntp server <ip-address> trusted-enable Trusts this NTP server; if authentication is configured this will additionally force all time updates to only use trusted servers. The no form of the command removes trust from this NTP server. |
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Syntax Description |
ip-address |
IP address of the peer. |
Default |
N/A |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
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ntp server version
ntp server <ip-address> version <ver-num> no ntp server <ip-address> version <ver-num> Specifies the NTP version number of this server. The no form of the command defaults NTP to version 4. |
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Syntax Description |
ip-address |
IP address of the peer. |
ver-num |
NTP version. Possible values: 3 or 4 |
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Default |
4 |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
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ntp trusted-key
ntp trusted-key <key(s)> no ntp trusted-key <key(s)> Adds one or more keys to the trusted key list. The no form of the command removes keys from the trusted key list. |
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Syntax Description |
key(s) |
Range: 1-65534 |
Default |
Disabled |
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Configuration Mode |
config |
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History |
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Example |
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Related Commands |
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Notes |
Keys may be separated with commas without any space, or they may be set as a range using a hyphen. |
show clock
show clock Displays the current system time, date and time zone. |
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Syntax Description |
N/A |
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Default |
N/A |
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Configuration Mode |
Any command mode |
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History |
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Example |
Time: 02:48:41 |
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Related Commands |
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Notes |
show ntp
show ntp Displays the current NTP settings. |
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Syntax Description |
N/A |
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Default |
N/A |
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Configuration Mode |
Any command mode |
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History |
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Example |
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Related Commands |
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Notes |
show ntp configured
show ntp configured Displays NTP configuration. |
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Syntax Description |
N/A |
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Default |
N/A |
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Configuration Mode |
Any command mode |
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History |
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Example |
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NTP enabled: yes |
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Related Commands |
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Notes |
show ntp keys
show ntp configured Displays NTP keys. |
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Syntax Description |
N/A |
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Default |
N/A |
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Configuration Mode |
Any command mode |
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History |
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Example |
NTP Key 1 |
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Related Commands |
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Notes |