DNS

Description

The DNS feature supports distributed DNS testing and monitoring of your DNS servers.

Running a DNS test provides information about the response times of your DNS servers from different locations. High DNS response times translate into high response times for all services that use DNS to resolve IP addresses, such as web surfing.

When you start a DNS test, the Test Agents will send a request to resolve a lookup address, and collect statistics on response times.

DNS primarily uses User Datagram Protocol (UDP) on port number 53 to serve requests. DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. More information on DNS in general is available in Wikipedia.

Setting up a test or monitoring

To run DNS measurements you need to have at least one Netrounds Test Agent installed. If you haven't already done the installation, consult our quick start guides for various types of Test Agents in the section Netrounds Test Agents.

Traffic will be initiated by the Test Agents, and the DNS server will respond using the same ports. This setup makes it possible to run tests also when the Test Agents are located behind NAT.

Create a new DNS test or monitoring and fill in the mandatory parameters below: 

Parameters

Tests only

  • Duration (seconds): The duration of this test step in seconds. Min: 30 s. Max: 604800 s. Default: 60 s.
  • Fail threshold (seconds): The maximum number of errored seconds (ES) that may occur without triggering a fail for this test step. Default: 0.
  • Wait for ready: Time to wait before starting the test. The purpose of inserting a wait is to allow all Test Agents time to come online and acquire good time sync. Min: 1 min. Max: 24 hours. Default: "Don't wait", i.e. zero wait time.

General

  • Clients: Specify the Test Agents you want to use in the test or monitoring.
  • DNS server: The DNS server to query and test. Leave this empty to use the interface default, which is usually the DNS you have been provided via DHCP.
  • Lookup name: The domain name to look up, e.g. "google.com". Lookups of this domain name will recur periodically.
  • DNS record type: The type of DNS record to look for. The record types supported by Netrounds are as follows (a complete list can be found in Wikipedia):
    • A (IPv4 address; default)
    • AAAA (IPv6 address)
    • CNAME (canonical name)
    • MX (email)
    • PTR (pointer)
    • NS (name server)
    • SOA (start of authority)
    • SRV (service)
    • TXT (text)
  • Time between requests (s): The time to wait between consecutive DNS requests. Default: 10 ms.

Threshold for errored seconds (ES)

  • Timeout (ms): If no response to the DNS request is obtained within this time, Netrounds will indicate an errored second. Default: 50 ms.

Advanced

  • Request lifetime (ms): The maximum time Netrounds will wait for a response before the DNS request is cancelled. Default 200 ms.
  • Response code: Here you can specify an expected response code from the DNS server. If the actual response code does not match this one, a "Response" errored second is triggered. Possible response codes are: NOERROR, REFUSED, NXDOMAIN, SERVFAIL, and NOTAUTH. Default: NOERROR.
  • Expected response: Here you can specify an expected response from the DNS server. If the actual response does not match this, a "Response" errored second is triggered. If the response consists of multiple answers, one of them must match.
  • Recursive requests: Set the Recursion Desired flag in DNS requests. Default: Enabled.
  • Delayed start (seconds): (Tests only) Time by which to delay the start of the test within a test step. Default: 0 s.

SLA thresholds (monitorings only)

  • SLA Good: Threshold for good fulfillment of service level agreement. Default: 99.95%.
  • SLA Acceptable: Threshold for acceptable fulfillment of service level agreement. Default: 99.5%.

Result metrics

  • Response time average (ms): Average response time during the selected time period, that is, the average time taken to receive an answer from the DNS server.
  • Response time min (ms): Minimum DNS response time.
  • Response time max (ms): Maximum DNS response time.
  • ES timeout: Number of errored seconds triggered because no DNS response was obtained before the Timeout period expired.
  • ES response: Number of errored seconds triggered because the DNS response code differs from Response code or the response differs from Expected response.
  • ES total: Aggregated errored seconds, taking into account all types of error.
  • SLA: Service level agreement fulfillment for the test or monitoring: equal to (100 – ES total) %.
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