ntp

[yaredo70]

Hi All,

I wanted to configure the NTP server in our network. The network is isolated from any outside connection. No router. Can I set up one of the switches as an NTP server and the other will sync with that switch?

Thanks, 

Yared.

[M02@rt37 · Accepted solution]

Hello @yaredo70,

Yes, you can set up one of the switches as an NTP server and have the other switches sync their time with that NTP server within your isolated network.

You should set the clock on the designated NTP master switch before activating it as the NTP server.

switch# clock set hh:mm:ss day month year

Configure this switch as server NTP:

switch(config)# ntp master 1

On the other switches that you want to sync with the NTP server, configure them as NTP clients:

switch(config)# ntp server <NTP_Server_IP>

->By default, Cisco switches sync their time with the NTP server every 64 seconds. You can adjust this interval using the 'ntp update-calendar' command followed by the desired interval in seconds:

switch(config)# ntp update-calendar 300

Do #sh ntp status to check the time sync on clients.

Also please note that NTP uses UDP port 123, so make sure that any firewall or access control lists within your isolated network allow NTP traffic between the devices.

[yaredo70]

Thank you for your quick reply. I will try and let you know if I have issues. 

[M02@rt37]

You're welcome @yaredo70.

Thanks.

[Leo Laohoo]

---

@yaredo70 wrote:
The network is isolated from any outside connection. No router. Can I set up one of the switches as an NTP server and the other will sync with that switch?

---

Is this network "air gapped"? 

If this is air gapped, a cheap Raspberry Pi can be configured to be a Stratum 1 NTP server.  

Otherwise, getting a Cisco appliance to become an "NTP server" will not be a good idea because the in-built clock will, eventually, drift after a few hours of getting energized.