The DNS UDP Monitor tests a DNS Server's ability to respond to a record query, as well as its level of responsiveness.
The DNS UDP Monitor uses the Universal Datagram Protocol, which is the primary (more efficient) method of communication with DNS Servers. UDP does not require acknowledgement of packets received as does TCP.
ipMonitor measures round trip time by sending a query for a root server "A Record" (a.root-servers.net) to the specified DNS Server and then waiting for a response.
The Monitor test will pass if the Monitor receives a valid positive or negative response within the required timeout period.
The DNS UDP Monitor tests that the:
- DNS Server is "up and running"
- DNS Server is able to process and respond to a query
- Response makes a complete round trip within a specific number of seconds
The Test Parameters dialog box is used to specify the location of the DNS Server you want to monitor and any parameters required to connect to it.
IP Address
Specify the IP Address of the DNS Server you want to monitor.
UDP Port
Specify the UDP Port number that the target DNS Server responds on. By default, the standard Port Number used for DNS UDP communication (Port 53) is already entered.
DNS Entry to Query
The DNS over UDP Monitor is hard coded to query for the 'a.root-servers.net' root server "A" Record.
When the Monitor is in an Up state, test results are reported as shown in the example below:
rtt - Round-Trip Time. This value indicates the time it took the test packet to reach the monitored resource and return a response to ipMonitor. Round-trip time is measured in milliseconds (ms).
When the Monitor is in a Warn, Down, or Lost state, the Last Result field indicates the problem encountered. Different Monitor types generate specific Error Codes in accordance with the technical capabilities of the Monitor. Refer to the Error Codes section of this document for details.
You will need to use the DNS - QA Monitor if your DNS server does not have the 'a.root-servers.net' record. The DNS - QA Monitor can be used to:
- Test multiple DNS servers using the OR Boolean operator
- Perform a lookup against a specific Domain Name
- Test the lookup results against a list of IP addresses
- Return a pass result if any IP address in the list is resolved, or if a single IP address is resolved
For information on settings common to all Monitor types, such as Identification, Timing, Notification Control and Recovery Parameters, refer to General Monitor Settings.
The following error codes are generated by the DNS UDP Monitor. Error codes are displayed in Real-time Reports and Historical Reports. They can also be added to Alerts using Tokens.
| Message | Details |
|---|---|
| Configuration information for this item is missing some required fields | A required element for Monitor connectivity or testing was not supplied to ipMonitor. |
| Unable to connect to the remote device | The specified address to the connection-based Service is unavailable. |
| Could not obtain an IP address for the remote device | The supplied address was not a valid IP address OR the Server Domain Name could not be translated into an IP address. The Server Domain Name may refer to a local machine name or a fully qualified domain name. |
| The remote device timed out before sending a response | The resource being monitored did not respond within the maximum allowable time. |
For information on other features and concepts related to those discussed in this article, refer to the following ipMonitor resources:
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Last Updated: March 30, 2007 | What did you think of this topic?