Hi, DNS belongs to TCP/IP Suite and thus it falls under TCP/IP Model. From a functional perspective, DNS is clearly part of application layer which is the layer 4. It's invoked by the application layer and rides on top of the transport layer (UDP). In addition, Layer 3 doesn't know what is a host name and it only deals with IP Addresses.

In the example, I mention that both the layer 3 and 4 is managed by OS itself. This means that normal users (not privileged user) cannot interrupted the DNS query. AND only privileged users can interrupt the three way handshake.

FYI, a privileged user is someone who has administrative access to critical systems. For example, root in Linux. Where you cannot perform certain important and critical function in terminal and need the sudo command in order to perform that certain critical function.

Please feel free to refer to other source and reference as this is my personal view and understandings. and I am still in the progress of learning. Thanks