TCP Open Briefly hangs LabVIEW

[Norbert_B]

I bear in mind that nslookup uses internal lookup tables it caches. There is some kind of command to reset those tables. I would expect nslookup to perform equally if it really queries the network.....

Norbert

[dan_u]

Even after flushing the DNS cache (ipconfig /flushdns) I get an immediate response from nslookup. The DNS server definitely does not take 2.2s to respond, else it would also take so long for valid addresses.

[Norbert_B]

Well, following Microsofts documentation on NSLookUp, there are several options to use this method. I assume that the way you are using it will query only one DNS server. There are obviously options to query more than one server.

I am not sure what "String To IP" does internally, but reading the LV 2014 help on this reveals that there are different modes:

If String To IP is in single output mode, the net address is the first result returned by the operating system resolver. If String To IP is in multiple output mode, the result is an array of all IP network addresses returned by the operating system resolver. If the node fails to convert the string, the result is a value of zero in single output mode or an empty array in multiple output mode.

To switch between single output and multiple output modes, right-click the node and select Multiple output from the shortcut menu.

Maybe this is some source for the long dealy?

Norbert

[dan_u]

Maybe. I'm using the single output mode of String to IP. I used the multiple output mode to get the multiple IP adresses of the local machine (having multiple network connections) in other applications.

The String to IP documentation does not specify what and how many DNS servers it queries, but since it says it uses the OS resolver it should use the same DNS servers as nslookup. I'm still puzzled.

[rolfk]

I have no idea what nslookup uses. But I'm pretty sure String To IP (whose internal function is also used by TCP Open and friends when passed a non-numeric IP adress) does call into ws2_32.getaddrinfo() because this is the only means to allow for multiple addresses to be returned. nslookup may link into lower level winsock APIs that are not documented.