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DNS Lookup Test: Enables or disables the use of a Domain Name Server
(DNS) lookup as a test to verify the integrity of the mobile connection. The test
is successful if a valid reply is received from a DNS server. Typically, this
means the hostname is successfully “resolved” to an IP address by a DNS
server. But even a reply such as “not found” or “name does not exist” is
acceptable as a successful test result, since that demonstrates successful two-
way communication over the mobile connection. When a valid reply is
received, the test completes successfully and immediately.
The DNS servers used in this test for the hostname lookup, are the primary and
secondary DNS servers obtained from the mobile network when the mobile
PPP connection is first established. These addresses can be viewed by going to
Administration > System Information > Mobile.
Note that this DNS test is independent of the normal DNS client configuration
and lookup cache, which is used for other hostname lookups. This test has been
specifically designed to require communication over the mobile connection for
each lookup, and to avoid being “short-circuited” by previously cached
information. Also, this test does not interfere in any way with the normal DNS
client configuration of this device.
Two hostnames may be configured for this test. If the first hostname fails to get
a reply, the same test is attempted for the second hostname. If no reply is
received for either hostname, the test fails. The primary and secondary DNS
names should be fully qualified domain names. Note that the reverse lookup of
an IP address is possible, but that is usually unlikely to succeed in returning a
name. Still, such a reverse lookup can be used to demonstrate the integrity of
the mobile connection.
– Primary DNS Name: The first hostname to look up.
– Secondary DNS Name: The second hostname to look up (if the first hostname
fails).
Repeat the selected link integrity test every N seconds: Specifies the
interval, in seconds, at which the selected test is initiated (repeated). A new test
will be started every N seconds while the mobile connection is established.
This value must be between 10 and 65535. The default is 240.
If the configured interval is less time than it takes a test to complete, the next
test will not be initiated until the previous (current) test has completed.