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DNS Server Test
The DNS Server test has been designed to monitor the availability
and performance of a particular DNS server.
When you configure the test, you are asked for the DNS server
address. You can supply either the fully qualified hostname
(eg: dns0.mydomain.com) or it's IP address.
The test is performed by querying the DNS server for it's
own address, which it will always know without the need for
consulting other servers.
Because DNS uses UDP as the transport protocol, there is
no such thing as a "connection time". However, at Nexus Watch
we feel that it is important to try and distinguish between
network response and server response as much as is possible.
The DNS Server Test therefore has a sub-test that performs
an ICMP echo ("ping") of the DNS server at the same time.
Because a ping packet will not involve any processing by DNS
software (such as "Bind"), it gives a metric for the performance
of the network between Nexus Watch and the server.
Please note however, that depending upon the configuration
of the server and the network to it, ICMP packets may be given
different priority or may even be blocked. This sub-test is
therefore of most value when you know the network configuration
by your DNS server.
The test configuration also allows you to specify what to
do if you don't get a response. The very nature of UDP as
a transport protocol can mean that not getting a response
first time is acceptable (as it is a connectionless protocol).
You can configure the amount of time to wait for a DNS response
(the "timeout"). You can also configure how many times to
retry (the "retry" value), and how much to increase the timeout
by between retries (the "timeout multiplier"). Only after
retrying the specified amount of times will Nexus Watch generate
an event if there is still no response.
Nexus Watch will repeat the test at intervals set by the
Polling Interval field on the test configuration page.
You may configure error and threshold events to watch out
for, and optionally have Nexus Watch send you an alert if
it sees them.
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