The DNS service monitors the DNS server for its availability. The results from monitoring are displayed on the status dashboard under the service and can also be provided in any notifications triggered by the service.
|Instances on a Device||1|
|Device Class||Server - Generic, Workstation - Generic, Other, Printer, Scanner/Camera, Switch/Router, Laptop - Windows, Server - Windows, and Workstation - Windows|
|Monitored By||Windows probe, Central server|
|Scan Interval||5 minutes|
|Timeout Value||The time (in seconds) that the SolarWinds N-central server waits before considering the test a failure. The default is 30 seconds.|
|Port Number||The TCP port number used to monitor the DNS service.|
|FQDN to Resolve||The resolvable FQDN used to determine service availability.|
During the monitoring process, a name server lookup (nslookup) is run at the preset scan intervals to test the availability of the DNS server. If the DNS server returns all of the IP addresses of the specified FQDN, the test is successful.
The nslookup is run using UDP. If a DNS response to the DNS query is too large for the UDP packet, then the service state is displayed as Failed, although the DNS server is functional. For this reason, to receive accurate results of the DNS server's availability, specify an FQDNthat will return fewer IP addresses for the FQDN to Resolve service detail. An FQDN that returns fewer IP addresses has a greater chance of fitting into the UDP packet.
The DNS service can monitor the DNS server through the central server or a Windows probe. If the DNS server is on a public network, the central server is used. If the DNS server is on a private network, a probe is used to send the information received from the DNS server through the firewall to the central server.
To monitor the DNS server, you must add the DNS server as a device and to the device.
|DNS Service Availability||
Determines whether the DNS service is up or down. The DNS service does not use the Warning state.
For example, a DNS test is considered successful if the target DNS server is able to resolve a web site address.
|Round Trip Time (ms)||The time for a request to be sent and received.|
The threshold that determines whether the device name can be resolved.
If an FQDN has been specified, the service searches for its IP address. If the IP address is found, the state will be Normal. Otherwise, it will be Failed, based on the default settings.
If an IP address has been specified, the service checks only the IP address's format. If the format is correct, the state will be Normal. Otherwise, it will be Failed, based on the default settings.