In this lecture, we'll see why do we use user data from protocol while establishing connections in
DNS?
So the question is, why don't we use TCP instead of Europea being a connection oriented protocol and
more secure than Europe?
The answer lies ahead.
As you can see on the screen, the following are the two diagrams representing the connections for DCP
and UDP in the case of TCBY, the force that this hosty will send the request connection to the server
or be hosted by the replies with confirmed connection.
Horsely again, requests for data and find the host be sensitive.
There are four steps in DCB Connection Fosun needed, whereas in Europe connection there are only two
steps.
Request data and send data.
So we have seen that there are four connections required to establish a single DCB connection, whereas
only two connections or two requests are required for establishing a European connection.
So as you can see, let us consider we are using a TCP connection establishment for DNS resolution.
So your browser sends a request to ISP.
That is the first TCP connection and each DCB connection involves four messages.
Next ISP sends a request to route.
Therefore that comes the second DCB connection.
Then route exchanges messages between early BEARLY exchanges, messages between authentication server
and finally authoritative server replies back to ISP and ISP replies Back to you.
So in short, if we consider the bare minimum of DCB connections, we can see that minimum five TCP
connections need to be established in order to start transmitting data or to start transmitting the
actual message.
So five DCB connection means five times four, which means 20 connection messages need to be sent in
order to start the actual conversation.
So this is a tedious process.
This is a time consuming process.
If we use TCP and therefore Europe is used in such cases.
Europe is much faster than TCP because DCB requires a three way handshake.
And after the three way handshake, finally the actual message begins.
The load on DNS is also an important factor, right?
If there are multiple, if it is not only you who is sending a request to your ISP, but there are millions
of people who will be sending requests to ISP every second.
So DNS servers do not have to keep the connections and therefore UDP is used.
The next point is DNS requests are generally very small and fit well within the UDP segments, and if
they use DCB connections, the space will eventually get wasted.
UDP is not reliable, but in such cases, reliability can be added on application layer, an application
can use UDP and can be reliable using a timeout and reasoned application layer.
Actually, the NSA primarily uses that user data from protocol on board 53 to serve the requests.
DNS queries consist of a single European request from the client, followed by a single European reply
from the server when the length of the answer exceeds, let's say, 512 bytes and both client and server
support DNS, larger Uribe backers are used.
Otherwise, the query is sent again using the transmission control protocol.
So TCBY is used only in rare cases in UDP.
I hope you got the point that because of the load factor and number of connections required, we use
UDP in DNS resolution process.