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DNS Service

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.

Service Type

TCP/UDP

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 MSP 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 fully qualified domain name (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 the user datagram protocol (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 FQDN that 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.

The illustrations below display the monitoring processes of the DNS server on a private and public network.

Monitoring the DNS Server on a Private Network

Monitoring the DNS Server on a Public Network

To monitor the DNS server, you must add the DNS server as a device and to teh device.

Status Details

Status Detail

Description

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 www.<Web site name>.com.

Round Trip Time (ms)

The time for a request to be sent and received.

DNS Resolution

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.