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I'm trying to setup the SNTP of a new Cisco SG300-48 Switch in L3 mode.

So far I have enabled the Main Clock Source (SNTP Servers) option (Administration -> Time Settings), set my time zone and daylight saving settings to match my country.

Also, under SNTP Unicast I have enabled SNTP Client Unicast option and added several NTP public servers (10), all that are currently running (tested using NTP Time Server Monitor by Meinberg in my PC connected to the switch).

The problem is that even after saving the configuration and rebooting the switch all the servers are always with "Down" status. The date and time of the switch is never updated. Somehow the switch is unable to adquire NTP information.

Does anyone knows how to fix it? enter image description here

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Ok, after some research I have discovered that the switch is unable to resolve DNS queries, so I cannot get IP addresses of the NTP servers listed in the picture since they are referenced by name. To confirm that, I've added a NTP server using it's IP address and the switch was able to get time from it.

Since I have a default gateway set to the switch I do not understand why it is unable to resolve DNS queries through the gateway. Do I have to set it mannually?

  • Is there a firewall between the switch and these servers blocking NTP traffic (UDP port 123)? – TheCleaner Feb 13 '15 at 19:11
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    Have you set a default gateway for the switch? – yoonix Feb 13 '15 at 19:12
  • @yoonix how do I do that? – RHaguiuda Feb 16 '15 at 11:58
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    Since you have added the default gateway, did you set the DNS servers on the switch? – Rex Feb 16 '15 at 15:34
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Indeed the switch needs to be able to reach the NTP server by itself:

  • when you set an IP Address for the NTP server, Gateway needs to be set in Administration / Management Interface / IPv4 Interface, check operational default gateway
  • when you set a domain name (FQDN), DNS servers must be set in IP Configuration / Domain Name System / DNS Settings : add at least one DNS server

Yo can use Administration / Traceroute to check that the DNS server is reachable.

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