1 00:00:00,420 --> 00:00:06,660 They often use the analogy to explain the domain name system is that it serves as the phone book for 2 00:00:06,660 --> 00:00:11,610 the Internet by translating human friendly computer host names into IP addresses. 3 00:00:12,520 --> 00:00:18,640 Simply, DNS is a directory of names that match with IP addresses. 4 00:00:19,580 --> 00:00:25,910 As you may know, each device connected to the Internet as a unique IP address with other machines used 5 00:00:25,910 --> 00:00:26,960 to find the device. 6 00:00:28,210 --> 00:00:36,040 DNS servers eliminate the need for humans to memorize IP addresses such as two one two eight zero seven 7 00:00:36,040 --> 00:00:37,450 five one three four. 8 00:00:38,290 --> 00:00:43,120 Think about the websites you visit every day, Google and YouTube, Facebook, Twitter, etc., without 9 00:00:43,120 --> 00:00:48,780 DNS, we would have to reach these sites by using their IP addresses instead of their names. 10 00:00:49,580 --> 00:00:57,140 I think remembering the names is so much easier than remembering the strange numbers, but it's still 11 00:00:57,140 --> 00:01:01,390 possible to reach the computer with that strange number of string as well. 12 00:01:03,090 --> 00:01:07,890 Now, DNS deserves to have far more time spent on it. 13 00:01:08,160 --> 00:01:13,380 It could be a whole course in and of itself, but I just want to explain it simply without going to 14 00:01:13,380 --> 00:01:13,570 deep. 15 00:01:14,560 --> 00:01:20,400 So when you enter the you are L, such as dub, dub, dub, dot, Google dot com into the Web browser, 16 00:01:20,410 --> 00:01:23,980 the request is not directly sent to the Google servers. 17 00:01:24,860 --> 00:01:31,700 Instead, the request goes to the DNA that uses a lookup table to determine the IP address of the website 18 00:01:31,700 --> 00:01:32,750 that is being requested. 19 00:01:33,600 --> 00:01:39,990 Then it forwards this information to the proper servers and returns the information requested to your 20 00:01:40,020 --> 00:01:41,160 specific browser. 21 00:01:42,490 --> 00:01:49,180 DNS server is a computer server which contains a database of public IP addresses and their associated 22 00:01:49,180 --> 00:01:54,430 host names, it translates those common names to IP addresses as requested. 23 00:01:55,380 --> 00:02:01,770 DNS servers run special software and communicate with each other using special protocols. 24 00:02:03,050 --> 00:02:07,070 DNS is a client server network communication system. 25 00:02:08,330 --> 00:02:14,480 DNS clients send their requests to and receive the responses from DNS servers. 26 00:02:15,510 --> 00:02:21,420 The request containing the name and resulting in an IP address being returned from the server are called 27 00:02:21,630 --> 00:02:23,820 forward DNS lookups. 28 00:02:25,180 --> 00:02:32,800 The request containing IP addresses and resulting in the names are called the reverse DNS lookups. 29 00:02:33,790 --> 00:02:40,060 The DNS directorate that matches name to number isn't located all in one place. 30 00:02:41,840 --> 00:02:47,180 Pretty much like the Internet itself, the directory is distributed around the world, stored on domain 31 00:02:47,180 --> 00:02:54,740 name servers that all communicate with each other on a very regular basis to provide updates as well 32 00:02:54,740 --> 00:02:55,790 as redundancies. 33 00:02:56,680 --> 00:03:05,620 With more than 332 million domain names listed by the end of 2017, a single directory would be very 34 00:03:05,620 --> 00:03:06,340 large indeed. 35 00:03:08,300 --> 00:03:14,120 So when you type mailed out Google dot com into your browser, your browser sends a query over the Internet 36 00:03:14,120 --> 00:03:15,110 to find a Web site. 37 00:03:15,920 --> 00:03:20,360 It's a query seeking to match the domain name with its corresponding IP address. 38 00:03:21,630 --> 00:03:25,380 So let's follow the path of this question over the Internet infrastructure. 39 00:03:27,250 --> 00:03:35,470 The first server your query interacts with is the DNS resolver, which can be operated by your ISP Internet 40 00:03:35,470 --> 00:03:42,730 service provider, a resolver is basically responsible for initiating and sequencing the queries that 41 00:03:42,730 --> 00:03:45,430 ultimately lead to a full resolution. 42 00:03:46,900 --> 00:03:52,690 Domain name resolvers determine the domain name servers responsible for the domain name in question 43 00:03:53,110 --> 00:03:56,240 by a sequence of queries, starting with the rightmost. 44 00:03:56,260 --> 00:03:58,450 In other words, top level domain label. 45 00:03:59,970 --> 00:04:06,510 Assuming the resolver has no cash records to accelerate the process, which is the worst case scenario, 46 00:04:07,320 --> 00:04:11,700 the resolution process starts with a query to one of the root servers. 47 00:04:12,820 --> 00:04:19,480 The root servers are running all over the world, and each one knows DNS information about top level 48 00:04:19,480 --> 00:04:22,720 domains or TMD such as dot com. 49 00:04:24,260 --> 00:04:30,650 So to begin answering your query, the resolver asks a root server for DNA information about dot com. 50 00:04:32,180 --> 00:04:37,060 So there are 13 sets of root servers and more than 300 locations around the world. 51 00:04:38,750 --> 00:04:46,130 Each tailed DNS name server stores the address information for second level domains within the top level 52 00:04:46,130 --> 00:04:48,170 domain dot dotcom in our example. 53 00:04:49,110 --> 00:04:57,270 The second level domain is Google dot com, when your query reaches the detailed server, the TLD server 54 00:04:57,270 --> 00:05:03,750 answers with the IP address of the domain name server, which will provide the next piece of the puzzle. 55 00:05:04,900 --> 00:05:08,380 So this is the final step of a dress resolution. 56 00:05:09,470 --> 00:05:13,790 The recursive resolver sends the query to the domain name server. 57 00:05:14,610 --> 00:05:22,110 This DNS server knows the IP address for the full domain mail that Google dot com, and that answer 58 00:05:22,110 --> 00:05:24,990 is returned to the recursive resolver. 59 00:05:26,380 --> 00:05:32,050 Now that the recursive resolver knows the IP address for the domain name in your query, the recursive 60 00:05:32,050 --> 00:05:35,770 resolver tells the browser what the IP address is. 61 00:05:36,880 --> 00:05:44,500 So finally, your browser can send a request to the Web site to retrieve the website's content using 62 00:05:44,500 --> 00:05:46,150 the IP address it just learned. 63 00:05:46,990 --> 00:05:54,270 This whole process might seem, well, complicated, it certainly sounds odd to talk it up, but really 64 00:05:54,290 --> 00:05:55,570 takes very little time at all.