NSLookup, how to set to TCP from UDP?

Question

_{Thursday, August 18, 2016 2:31 PM}

Hi there,

By default when you run the NSLOOKUP queries, it is using the UDP protocol. But based on the help "Nslookup /set port" it should be possible to use TCP also, but how ?

Petri

All replies (2)

_{Friday, August 19, 2016 7:44 AM ✅Answered | 2 votes}

Slightly strange answer. How did you manage to believe that I'm not trusting to the programs? And if you are looking for Microsoft's help site, they are stating very clearly that TCP should be an option.

But anyway, my own search lead me to the page: "Using the TCP for DNS lookups". And that really makes NSLOOKUP to use the TCP for the queries.

Petri

_{Thursday, August 18, 2016 2:51 PM}

DNS lookups always uses UDP in normal circumstances. From https://en.wikipedia.org/wiki/Domain_Name_System#Protocol_transport

DNS primarily uses the User Datagram Protocol (UDP) on port number 53 to serve requests.<sup class="reference" id="cite_ref-rfc1035_3-5">[3]</sup> DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. The Transmission Control Protocol (TCP) is used when the response data size exceeds 512 bytes, or for tasks such as zone transfers. Some resolver implementations use TCP for all queries.

I suggest you trust NSLookup and other applications to be smart enough to know how they should behave.

Best regards, George