Indirect DNS server connection

For points with Location2 set to 1, the interface indirectly measures DNS Server response times of the default nameserver. To find out the IP address of this nameserver, use the nslookup at the Windows command prompt. For example,

C:> nslookup
Address: 192.168.100.45

Entries in the InstrumentTag determine whether the interface performs a hostname to IP address lookup (for example, INPUT=www.anothercompany.com in the InstrumentTag) or an IP address to hostname lookup (for example, INPUT=192.168.10.100 in the InstrumentTag). The interface uses the function gethostbyname() for the former and gethostbyaddr() for the latter. The response time measured by the interface is the amount of time required for these functions to complete. If these functions fail, the interface writes the value Bad Input. If the interface does not receive a reply within a user-specified timeout duration, it writes I/O Timeout.

If the PI point is of type String, TCPResponse writes the value of the translation; for example, 192.168.10.100. Otherwise, TCPResponse writes the response time value. However, the Windows operating system caches the results from gethostbyname() and gethostbyaddr(). In addition, these functions will not directly connect to the default nameserver if the HOSTS file (located typically in C:\Windows\System32\drivers\etc) contains the necessary information for hostname/IP address translation. Therefore, in order to accurately measure DNS Server response time, the user should use the method presented in the topic: Direct DNS server connection.