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Monitoring a subnet with DHCP

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Hi,

We would like to monitor an entire subnet. We don't exactly which devices will be connected, but we will gradually find them out with an auto-discovery that will run every hour. However, it looks like PRTG is unable to solve the devices names. Please note that they are not Windows systems and that SNMP cannot be set on them. The DHCP is active on such subnet, so we are wondering if PRTG is able to solve a device name every time a new IP Address is reassigned. Once the auto-discovery has found out all devices, we would like to avoid any alarms in case they are off. If a ping fails, it should be paused if possible.

Thanks Fabrizio

dhcp nameresolution ping subnet

Created on Jun 10, 2020 4:21:33 PM by  fabrigatti (0) 2



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Hello fabrigatti,

we use the Windows API for the name resolution process. Each probe also has a DNS cache. This cache contains every name resolution, which the Probe has received since the last start.

That means, the auto-discovery should be set up to use DNS names, because if the device address is set to an IP, PRTG does not check if it changes. Also, quick changes of the name to IP mapping by the DHCP might not be recognized by PRTG because of the DNS cache. That cache is required for a high-performance operation, PRTG cannot do a new resolution for every sensor scan without risking too many name lookups in the network.

Created on Jun 11, 2020 12:36:23 PM by  Arne Seifert [Paessler Support]



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Ok, so if I understand well in PRTG the names are resolved only if they are Windows machines and through DNS. The NetBIOS resolution should be used in my case since these are non-Windows machines. They get different IP addresses during their life on such network (because of the DHCP), but PRTG won't be able to match the machine name with the actual address every time unless the DNS server name is set on the device itself. Correct?

Created on Jun 11, 2020 1:22:55 PM by  fabrigatti (0) 2

Last change on Jun 12, 2020 2:37:42 PM by  Arne Seifert [Paessler Support]



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If I understand you correctly, that is correct.

Created on Jun 11, 2020 4:31:41 PM by  Arne Seifert [Paessler Support]



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