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I manage a mid-sized Industrial automation network. I have roughly 10 client machines and 4 server machines. Up until now, we didn’t have a GPS clock in the network. One of the machines, server-A, was working as a time server & NTP was used to sync other machines.

Now that we are installing this new GPS clock I need to configure server-A to receive the time from the GPS clock so that all the Clients + Servers will get time-synced with the GPS clock.

We have manageable Cisco switches in the network and I want to know if I need to plan to do time sync for the switches as well? I did not think so, but I am not sure. Can you please explain why time sync is required on managed switches and what may go wrong if these switches do not have synchronized times?

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 16 '17 at 22:07
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Your network devices (routers, switches, etc.) should be using NTP to keep their times synchronized. The primary benefit is for the logs and troubleshooting. When you look in the logs on your syslog server while trying to troubleshoot network problems, your job will be much more difficult if the times are not synchronized.

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  • And kerberos, should it be in use anywhere, for authentication, is incredibly time sensitive – Tom O'Connor Feb 15 '17 at 21:18
  • When using certificates it's also desirable to have the correct time, to be able to correctly check a certificate's validity. – hertitu Feb 15 '17 at 23:30
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Another reason: if the time of a HTTPS client is significantly different from the time of a HTTPS server, the connection may not work. I have observed this once, when a laptop had time that was off by probably several months. No HTTPS site worked. Fixing the time allowed HTTPS to work. I'm not sure if this was connected to certificate validity or something else, but the effect of HTTPS not working with severely incorrect time is true.

Of course, in a typical switch lifetime of 10 years or so, it is unlikely that the clock of a switch would be severely off so much that HTTPS does not work. This also applies only if the switch implements HTTPS. Some insecure managed switches may support only HTTP.

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  • The time on a switch has nothing to do with HTTPS. A switch is a transparent device that operates at layer-2, and it knows nothing about application-layer protocols such as HTTPS, and a server has no idea what time a switch has because a switch does not communicate with the server. – Ron Maupin Feb 21 '17 at 18:12
  • I meant managed switches, where the management interface is accessed with HTTPS. If the switch has the notion of time, it almost certainly is a managed switch. – juhist Feb 21 '17 at 19:18
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    OK. Most network engineers don't use HTTP or HTTPS to manage network devices. That is usually too limiting to properly manage a switch or router. – Ron Maupin Feb 21 '17 at 20:04

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