1 00:00:00,150 --> 00:00:01,380 Domain Name System 2 00:00:01,380 --> 00:00:05,613 or commonly referred to as DNS is for human convenience. 3 00:00:06,630 --> 00:00:09,300 A computer doesn't care what the actual name 4 00:00:09,300 --> 00:00:10,680 of Google.com is. 5 00:00:10,680 --> 00:00:12,900 All it is looking for is IP addresses 6 00:00:12,900 --> 00:00:14,940 when it comes to networking. 7 00:00:14,940 --> 00:00:18,180 DNS makes it easier for us as human beings 8 00:00:18,180 --> 00:00:22,110 to look up locations of different website addresses 9 00:00:22,110 --> 00:00:24,810 or maybe even resource locations. 10 00:00:24,810 --> 00:00:27,150 But again, the system does not care. 11 00:00:27,150 --> 00:00:28,890 So in this walkthrough, we're going to go through 12 00:00:28,890 --> 00:00:32,580 how to configure a DNS client by making an entry 13 00:00:32,580 --> 00:00:36,240 to allow us to connect to one of our partner computers 14 00:00:36,240 --> 00:00:38,840 without having to reference the IP address directly. 15 00:00:39,690 --> 00:00:42,000 Okay. First, we're going to look at the host name, 16 00:00:42,000 --> 00:00:44,400 which we know is also at the end of the prop, 17 00:00:44,400 --> 00:00:45,750 server 01, that's who I am. 18 00:00:46,890 --> 00:00:50,520 Now I've set up another VM on this network 19 00:00:50,520 --> 00:00:52,083 and it's going to be server 02. 20 00:00:52,980 --> 00:00:55,533 So let's just look at my current IP address. 21 00:01:01,170 --> 00:01:04,533 Okay. I am currently 10.0.2.15. 22 00:01:05,790 --> 00:01:10,113 And my partner is going to be 10.0.2.16. 23 00:01:11,040 --> 00:01:12,750 Now important file that we're going to need 24 00:01:12,750 --> 00:01:17,013 to reference sometimes is the Etc/resolve.config file. 25 00:01:18,960 --> 00:01:23,040 This file just merely points the system to DNS servers 26 00:01:23,040 --> 00:01:25,080 so that we know where to resolve 27 00:01:25,080 --> 00:01:26,460 all the different DNS things 28 00:01:26,460 --> 00:01:29,400 that we're going to be using throughout our searches 29 00:01:29,400 --> 00:01:32,250 or when we're trying to access certain systems 30 00:01:32,250 --> 00:01:33,093 by their name. 31 00:01:34,470 --> 00:01:37,200 If you see the last one, very common reference 32 00:01:37,200 --> 00:01:39,780 is Google 8.8.8.8. 33 00:01:39,780 --> 00:01:42,060 So again, this file just letting system know, 34 00:01:42,060 --> 00:01:46,560 Hey, whenever you're looking for an IP address 35 00:01:46,560 --> 00:01:49,170 use these IP addresses and they will resolve 36 00:01:49,170 --> 00:01:51,390 the domain name for us. 37 00:01:51,390 --> 00:01:52,223 All right. 38 00:01:53,460 --> 00:01:54,390 Now, next we're going to look at 39 00:01:54,390 --> 00:01:56,820 the Etc host configuration file. 40 00:01:56,820 --> 00:02:00,780 That is our local maintenance of our own DNS server. 41 00:02:00,780 --> 00:02:02,670 So again, this file's going to reference 42 00:02:02,670 --> 00:02:05,730 IP addresses to names, and we're typically going to use this 43 00:02:05,730 --> 00:02:07,560 for our local server 44 00:02:07,560 --> 00:02:10,470 for names that haven't been registered globally 45 00:02:10,470 --> 00:02:14,490 for DNS servers to add them to their databases. 46 00:02:14,490 --> 00:02:16,890 So we're going to modify our local copy 47 00:02:16,890 --> 00:02:20,610 to include the IP address of our partner IP address. 48 00:02:20,610 --> 00:02:22,610 So let's see what this looks like first. 49 00:02:26,490 --> 00:02:30,450 Again, we see it reference our loop back IP address 50 00:02:30,450 --> 00:02:33,390 which is 127.0.0.1. 51 00:02:33,390 --> 00:02:38,280 So anytime the system sees any of those domain names 52 00:02:38,280 --> 00:02:40,230 it's going to reference that to that IP address. 53 00:02:40,230 --> 00:02:43,470 So it's going to know how to actually get to a location. 54 00:02:43,470 --> 00:02:45,810 'Cause remember, the system does not care about a name 55 00:02:45,810 --> 00:02:48,390 when it comes to the packet configuration 56 00:02:48,390 --> 00:02:51,540 when we're sitting out TCP IP packets. 57 00:02:51,540 --> 00:02:53,970 This source and destination IP addresses 58 00:02:53,970 --> 00:02:55,443 are mandatory requirements. 59 00:02:56,520 --> 00:03:00,060 So our partner server is going to be server 02, 60 00:03:00,060 --> 00:03:02,360 but let's try to ping it and see what happens. 61 00:03:04,980 --> 00:03:07,320 We see that it's letting us know that 62 00:03:07,320 --> 00:03:09,630 it can't resolve the domain name, 63 00:03:09,630 --> 00:03:10,983 but we can ping the IP address. 64 00:03:10,983 --> 00:03:14,283 It's going to be 10.0.2.16. 65 00:03:15,870 --> 00:03:18,120 Okay. So we're getting a solid response back. 66 00:03:20,280 --> 00:03:22,673 Now next we're going to ahead and modify this file. 67 00:03:23,880 --> 00:03:24,713 Use the Vim. 68 00:03:31,650 --> 00:03:33,540 So let's add the IP address. 69 00:03:33,540 --> 00:03:37,593 Go to insert mode 10.0.2.16. 70 00:03:38,880 --> 00:03:41,163 I'm going to call it the server 02. 71 00:03:44,910 --> 00:03:47,310 So again, anytime we type in server 02 72 00:03:47,310 --> 00:03:49,460 the system will know what to resolve there. 73 00:03:50,490 --> 00:03:52,413 Ping server 02. 74 00:03:55,830 --> 00:03:57,780 And now we have a server response back. 75 00:03:58,980 --> 00:04:01,410 Again, DNS is very simple. 76 00:04:01,410 --> 00:04:04,293 It's just a mapping of a name to an IP address. 77 00:04:05,370 --> 00:04:07,350 And we can see in the responses, 78 00:04:07,350 --> 00:04:11,700 if you look at the ping output, after server 02, 79 00:04:11,700 --> 00:04:16,680 it has 10.0.2.16, just for our reference as well. 80 00:04:16,680 --> 00:04:19,079 Okay. So now we're going to test the host function. 81 00:04:20,130 --> 00:04:22,440 And again, this is going to give some key information 82 00:04:22,440 --> 00:04:25,113 about a website and we'll use Google, favorite site. 83 00:04:26,760 --> 00:04:30,660 So this host command, it resolves the domain name 84 00:04:30,660 --> 00:04:33,090 and it gives us the IP address for it. 85 00:04:33,090 --> 00:04:35,280 It's going to give us the IPV4 version 86 00:04:35,280 --> 00:04:37,203 as well as the IPV6 version. 87 00:04:38,340 --> 00:04:39,390 That's simple enough. 88 00:04:40,230 --> 00:04:42,540 Now last I'm going to do is use the NS lookup command. 89 00:04:42,540 --> 00:04:44,040 And again, that's going to give us information 90 00:04:44,040 --> 00:04:47,283 specifically about domain name servers. 91 00:04:48,300 --> 00:04:50,283 So Google is a popular one. 92 00:04:54,270 --> 00:04:57,300 And again, Google has mini alias IP addresses. 93 00:04:57,300 --> 00:04:59,640 So there'll be multiple different IP addresses 94 00:04:59,640 --> 00:05:03,300 to reference Google 'cause Google has so many servers, 95 00:05:03,300 --> 00:05:05,670 they're distributed across the internet 96 00:05:05,670 --> 00:05:08,340 for load balance purposes. 97 00:05:08,340 --> 00:05:10,170 Okay. We went through how to configure 98 00:05:10,170 --> 00:05:12,390 and DNS configuration file, 99 00:05:12,390 --> 00:05:15,480 which for the host file under the Etc folder. 100 00:05:15,480 --> 00:05:18,390 We went through the process of understanding how 101 00:05:18,390 --> 00:05:20,550 when you have the configuration file set correctly 102 00:05:20,550 --> 00:05:23,940 we can use the DNS name and we don't, 103 00:05:23,940 --> 00:05:25,710 you have to use the IP address. 104 00:05:25,710 --> 00:05:27,000 When a DNS server goes down, 105 00:05:27,000 --> 00:05:30,450 a lot of times connectivity could be a huge issue 106 00:05:30,450 --> 00:05:32,310 because a lot of the systems that we set up 107 00:05:32,310 --> 00:05:37,170 we set them up to use domain names and not IP addresses. 108 00:05:37,170 --> 00:05:39,150 So if connectivity becomes the issue, 109 00:05:39,150 --> 00:05:40,770 one of the things you definitely need to look at 110 00:05:40,770 --> 00:05:42,510 is your DNS. 111 00:05:42,510 --> 00:05:44,110 I'll see you in the next lesson.