1 00:00:02,420 --> 00:00:10,790 In this lecture, we'll see why do we use user data from protocol while establishing connections in 2 00:00:10,790 --> 00:00:11,340 DNS? 3 00:00:11,840 --> 00:00:19,490 So the question is, why don't we use TCP instead of Europea being a connection oriented protocol and 4 00:00:19,490 --> 00:00:20,660 more secure than Europe? 5 00:00:21,110 --> 00:00:22,390 The answer lies ahead. 6 00:00:23,780 --> 00:00:30,380 As you can see on the screen, the following are the two diagrams representing the connections for DCP 7 00:00:30,380 --> 00:00:37,730 and UDP in the case of TCBY, the force that this hosty will send the request connection to the server 8 00:00:37,880 --> 00:00:41,630 or be hosted by the replies with confirmed connection. 9 00:00:42,110 --> 00:00:47,460 Horsely again, requests for data and find the host be sensitive. 10 00:00:48,080 --> 00:00:54,710 There are four steps in DCB Connection Fosun needed, whereas in Europe connection there are only two 11 00:00:54,710 --> 00:00:55,130 steps. 12 00:00:55,370 --> 00:00:57,050 Request data and send data. 13 00:00:57,710 --> 00:01:04,400 So we have seen that there are four connections required to establish a single DCB connection, whereas 14 00:01:04,400 --> 00:01:09,320 only two connections or two requests are required for establishing a European connection. 15 00:01:09,740 --> 00:01:16,430 So as you can see, let us consider we are using a TCP connection establishment for DNS resolution. 16 00:01:17,000 --> 00:01:20,320 So your browser sends a request to ISP. 17 00:01:20,810 --> 00:01:27,410 That is the first TCP connection and each DCB connection involves four messages. 18 00:01:28,310 --> 00:01:31,550 Next ISP sends a request to route. 19 00:01:31,790 --> 00:01:35,840 Therefore that comes the second DCB connection. 20 00:01:36,530 --> 00:01:44,150 Then route exchanges messages between early BEARLY exchanges, messages between authentication server 21 00:01:44,360 --> 00:01:51,600 and finally authoritative server replies back to ISP and ISP replies Back to you. 22 00:01:52,250 --> 00:02:00,350 So in short, if we consider the bare minimum of DCB connections, we can see that minimum five TCP 23 00:02:00,350 --> 00:02:08,150 connections need to be established in order to start transmitting data or to start transmitting the 24 00:02:08,150 --> 00:02:09,210 actual message. 25 00:02:09,620 --> 00:02:19,970 So five DCB connection means five times four, which means 20 connection messages need to be sent in 26 00:02:19,970 --> 00:02:22,700 order to start the actual conversation. 27 00:02:23,300 --> 00:02:25,590 So this is a tedious process. 28 00:02:25,610 --> 00:02:27,410 This is a time consuming process. 29 00:02:27,680 --> 00:02:33,740 If we use TCP and therefore Europe is used in such cases. 30 00:02:35,120 --> 00:02:41,570 Europe is much faster than TCP because DCB requires a three way handshake. 31 00:02:41,570 --> 00:02:45,530 And after the three way handshake, finally the actual message begins. 32 00:02:46,400 --> 00:02:50,000 The load on DNS is also an important factor, right? 33 00:02:50,660 --> 00:02:56,540 If there are multiple, if it is not only you who is sending a request to your ISP, but there are millions 34 00:02:56,540 --> 00:03:00,070 of people who will be sending requests to ISP every second. 35 00:03:00,710 --> 00:03:06,540 So DNS servers do not have to keep the connections and therefore UDP is used. 36 00:03:07,490 --> 00:03:14,870 The next point is DNS requests are generally very small and fit well within the UDP segments, and if 37 00:03:14,870 --> 00:03:19,070 they use DCB connections, the space will eventually get wasted. 38 00:03:20,730 --> 00:03:27,630 UDP is not reliable, but in such cases, reliability can be added on application layer, an application 39 00:03:27,630 --> 00:03:33,150 can use UDP and can be reliable using a timeout and reasoned application layer. 40 00:03:35,040 --> 00:03:42,150 Actually, the NSA primarily uses that user data from protocol on board 53 to serve the requests. 41 00:03:42,960 --> 00:03:50,340 DNS queries consist of a single European request from the client, followed by a single European reply 42 00:03:50,340 --> 00:03:58,440 from the server when the length of the answer exceeds, let's say, 512 bytes and both client and server 43 00:03:58,620 --> 00:04:02,340 support DNS, larger Uribe backers are used. 44 00:04:02,760 --> 00:04:08,010 Otherwise, the query is sent again using the transmission control protocol. 45 00:04:08,430 --> 00:04:12,510 So TCBY is used only in rare cases in UDP. 46 00:04:13,110 --> 00:04:20,850 I hope you got the point that because of the load factor and number of connections required, we use 47 00:04:20,850 --> 00:04:23,460 UDP in DNS resolution process.