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I have LAN that must not be on Internet. I have a lot of switches. How to make core switch 4500 series to be some kind of NTP server, and all other switches to adjust their time with this core? Goal would be to set manual time only on core, and all other switches to adjust time with the core. Does anyone know syntax for core and access switches?

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    Aug 7, 2017 at 16:16

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The following is an example of how to configure your devices to point to your 4500 for NTP.

There are a few things that you have to ensure you have on hand:

  1. Know what time-zone the devices are operating in.
  2. Know the local time (or whatever time your equipment is set to according to policy).
  3. A refreshing beverage (in a non-spillable container of course.)

Configs:

4500# config t
4500(config)#ntp master
4500(config)#ntp authenticate 4500(config)#ntp authentication-keys 1 md5 password 4500(config)#int lo0
4500(config-int)#ip address 10.0.0.1 255.255.255.255
4500(config-int)#no shut
4500(config-int)#description Loopback_for_NTP
4500(config-int)#end
4500#clock set hh:mm:ss day name of month year
4500#clock timezone number of hours you are offset from UTC
4500# copy run start

Client#clock set hh:mm:ss day name of month year
Client#clock timezone number of hours you are offset from UTC
Client#config t
Client(config)#ntp authenticate
Client(config)#ntp authentication-key 1 md5 password
Client(config)#ntp server 10.0.0.1 key 1
Client(config)#end Client#copy run start

If I missed anything or someone sees and issue with my configuration, please let me know.

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    Q: why did you set the clock on the client, too? It isn't enough just to set the ntp server IP? Last one: Is clock timezone mandatory? The ntp is local, so doesn't mind about timezone.
    – feligiotti
    Apr 29, 2015 at 8:54
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    1) some NTP clients complain when the drift between clocks is too high. it often doesn't matter but there's always that one time so it doesn't hurt to build the habit. 2) NTP never minds about the timezone. the setting of the timezone only changes how the time is displayed in the logs, etc. It's a convenience feature since internally it's stored in universal coordinated time (or epochal depending on device ). If you prefer viewing UTC you can leave that part out of the config.
    – Stuart Smith
    Apr 29, 2015 at 15:58
  • Thanks Stuart. You covered everything I was going to. Technically you don't need to set the clock on the clients, but NTP has a tendency to get wonky if the client drifts too far from the master. It doesn't happen often, but it can be annoying to troubleshoot (especially in a virtualized environment.)
    – Zack Scaringello
    Apr 30, 2015 at 22:16

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