1 00:00:00,090 --> 00:00:01,680 In this lesson, we're going to cover 2 00:00:01,680 --> 00:00:05,880 the configuration of DHCP and DNS for client services 3 00:00:05,880 --> 00:00:07,860 as well as how these protocols are implemented 4 00:00:07,860 --> 00:00:10,260 on a Linux workstation or server. 5 00:00:10,260 --> 00:00:11,790 Now IP address configuration 6 00:00:11,790 --> 00:00:13,380 is one of the most critical settings 7 00:00:13,380 --> 00:00:15,030 on your network devices. 8 00:00:15,030 --> 00:00:17,790 Workstations, servers, routers, and other components 9 00:00:17,790 --> 00:00:20,430 all have to be properly assigned IP addresses 10 00:00:20,430 --> 00:00:22,560 to be able to participate on the network. 11 00:00:22,560 --> 00:00:25,110 IP address configurations can be set one of two ways, 12 00:00:25,110 --> 00:00:26,400 as I've mentioned before. 13 00:00:26,400 --> 00:00:28,920 You can either do this statically or dynamically. 14 00:00:28,920 --> 00:00:31,890 Now each method has its advantages and disadvantages. 15 00:00:31,890 --> 00:00:34,770 It's important to know when you're going to use each method. 16 00:00:34,770 --> 00:00:37,440 Static IP address configuration means that the settings 17 00:00:37,440 --> 00:00:39,930 are implemented manually by an administrator. 18 00:00:39,930 --> 00:00:42,000 This method increases the risk of mistakes, 19 00:00:42,000 --> 00:00:43,500 but it also ensures that the system 20 00:00:43,500 --> 00:00:45,930 always has the exact same IP address and, 21 00:00:45,930 --> 00:00:48,420 therefore, the same network identity. 22 00:00:48,420 --> 00:00:50,940 Dynamic IP address configuration, on the other hand, 23 00:00:50,940 --> 00:00:52,710 means that the settings on that client 24 00:00:52,710 --> 00:00:54,420 are going to change each time. 25 00:00:54,420 --> 00:00:56,070 Cause every time you boot up the system, 26 00:00:56,070 --> 00:00:58,710 it's going to go to the server, ask for an IP address, 27 00:00:58,710 --> 00:01:01,050 and be given one to use temporarily. 28 00:01:01,050 --> 00:01:03,720 This method does decrease the risk of mistakes, 29 00:01:03,720 --> 00:01:06,120 but it means that system is not always going to have 30 00:01:06,120 --> 00:01:09,150 the same IP address or identity on the network. 31 00:01:09,150 --> 00:01:11,010 Dynamic IP address configurations 32 00:01:11,010 --> 00:01:13,590 are usually going to be appropriate for client machines, 33 00:01:13,590 --> 00:01:14,850 not servers. 34 00:01:14,850 --> 00:01:17,010 Static IPs are normally going to be used 35 00:01:17,010 --> 00:01:19,950 for servers and network print devices. 36 00:01:19,950 --> 00:01:22,380 Now a dynamic host configuration protocol server 37 00:01:22,380 --> 00:01:26,820 or DHCP server contains one or more pools of IP addresses 38 00:01:26,820 --> 00:01:28,410 and related configuration options 39 00:01:28,410 --> 00:01:30,600 that we're going to hand out to our client machines 40 00:01:30,600 --> 00:01:31,830 once they connect. 41 00:01:31,830 --> 00:01:34,530 We call this a lease when we hand it out to them 42 00:01:34,530 --> 00:01:35,790 because we're letting them borrow it 43 00:01:35,790 --> 00:01:37,500 for a given amount of time. 44 00:01:37,500 --> 00:01:38,400 Now, by doing this, 45 00:01:38,400 --> 00:01:41,220 we can save ourself a lot of administrative effort 46 00:01:41,220 --> 00:01:43,080 because this IP address information 47 00:01:43,080 --> 00:01:44,700 doesn't have to be configured statically 48 00:01:44,700 --> 00:01:46,710 on each and every system. 49 00:01:46,710 --> 00:01:48,780 DHCP servers are going to be configured 50 00:01:48,780 --> 00:01:52,050 with a given scope or range of available IP addresses 51 00:01:52,050 --> 00:01:53,850 along with some additional options 52 00:01:53,850 --> 00:01:57,750 like the DNS server's location and the default gateway. 53 00:01:57,750 --> 00:02:00,930 The DHCP service, though, has to be installed on a server 54 00:02:00,930 --> 00:02:03,360 that's going to host this DHCP service 55 00:02:03,360 --> 00:02:04,920 and then allow all the client machines 56 00:02:04,920 --> 00:02:08,039 to lease out those configurations from that server. 57 00:02:08,039 --> 00:02:09,389 These workstations are going to 58 00:02:09,389 --> 00:02:12,960 lease their IP address information from that DHCP server, 59 00:02:12,960 --> 00:02:15,870 and the process really consists of four basic steps 60 00:02:15,870 --> 00:02:17,400 that's initiated by the clients 61 00:02:17,400 --> 00:02:19,860 when they boot up and connect to the network. 62 00:02:19,860 --> 00:02:24,660 These four steps follow the acronym DORA, D-O-R-A. 63 00:02:24,660 --> 00:02:28,980 This stands for discover, offer, request, and acknowledge. 64 00:02:28,980 --> 00:02:30,120 The way this works is that 65 00:02:30,120 --> 00:02:32,190 when the client first connects to the network, 66 00:02:32,190 --> 00:02:35,280 it's going to send out a DHCP discover message. 67 00:02:35,280 --> 00:02:37,290 This is the discover process. 68 00:02:37,290 --> 00:02:38,130 Essentially it says, 69 00:02:38,130 --> 00:02:42,150 hey, is there anybody on this network that's a DHCP server. 70 00:02:42,150 --> 00:02:44,400 If the DHCP server sees that message, 71 00:02:44,400 --> 00:02:46,050 it's going to get that discover message 72 00:02:46,050 --> 00:02:49,440 and then reply with what they call an offer request. 73 00:02:49,440 --> 00:02:51,450 This offer message is going to tell the client, 74 00:02:51,450 --> 00:02:53,220 hey, I'm a DHCP server, 75 00:02:53,220 --> 00:02:56,010 and I'm willing to give you an IP address. 76 00:02:56,010 --> 00:02:57,810 If that client wants to take that offer, 77 00:02:57,810 --> 00:03:01,440 it's going to send back what's called a DHCP request message. 78 00:03:01,440 --> 00:03:04,260 This message is going to say, hey, I'm a client. 79 00:03:04,260 --> 00:03:05,190 You're a server. 80 00:03:05,190 --> 00:03:07,650 I would really like to have one of those IP addresses. 81 00:03:07,650 --> 00:03:09,420 And then the server is going to respond back 82 00:03:09,420 --> 00:03:12,390 with what's called a DHCP acknowledged message. 83 00:03:12,390 --> 00:03:15,330 This message is going to send it back to that client and say, 84 00:03:15,330 --> 00:03:17,820 yes, I understand you want an IP address, 85 00:03:17,820 --> 00:03:19,680 and here is your IP address. 86 00:03:19,680 --> 00:03:22,560 You can have it for the next 24 hours, or seven days, 87 00:03:22,560 --> 00:03:25,530 or 30 days, or whatever that lease time is. 88 00:03:25,530 --> 00:03:28,770 In this message, it's also going to give them their IP address, 89 00:03:28,770 --> 00:03:31,350 their subnet mask, the default gateway, 90 00:03:31,350 --> 00:03:33,630 and the DNS server information. 91 00:03:33,630 --> 00:03:36,510 This is all the information that this client is going to need 92 00:03:36,510 --> 00:03:39,660 to configure itself and be able to connect to the network. 93 00:03:39,660 --> 00:03:42,150 At this point, the client will then configure itself 94 00:03:42,150 --> 00:03:45,120 by taking that IP address and assigning it to its interface, 95 00:03:45,120 --> 00:03:47,040 and connect to the network. 96 00:03:47,040 --> 00:03:48,510 Now, as a system administrator, 97 00:03:48,510 --> 00:03:50,760 it's important to understand where you can configure 98 00:03:50,760 --> 00:03:53,940 your DHCP client on your given Linux system. 99 00:03:53,940 --> 00:03:55,170 To do this, you're going to go 100 00:03:55,170 --> 00:04:00,170 into the /etc/dhcp/dhclient.conf file. 101 00:04:01,860 --> 00:04:05,280 This file enables the configuration of DHCP client settings, 102 00:04:05,280 --> 00:04:08,400 including timeout values, dynamic DNS configurations, 103 00:04:08,400 --> 00:04:10,110 and other things like that. 104 00:04:10,110 --> 00:04:12,450 This file is usually managed and edited 105 00:04:12,450 --> 00:04:14,190 using the network manager. 106 00:04:14,190 --> 00:04:16,500 And this serves as your network configuration service 107 00:04:16,500 --> 00:04:18,300 for all of your different network settings, 108 00:04:18,300 --> 00:04:21,360 including your DHCP client configuration. 109 00:04:21,360 --> 00:04:24,270 Whenever you make changes to the DHCP client configuration 110 00:04:24,270 --> 00:04:25,650 inside the network manager, 111 00:04:25,650 --> 00:04:30,650 it's going to update the /etc/dhcp/dhclient.conf file for you. 112 00:04:32,490 --> 00:04:34,410 I recommend you use the network manager, 113 00:04:34,410 --> 00:04:36,000 either in the command line environment, 114 00:04:36,000 --> 00:04:39,030 the text user interface, or the graphical user interface, 115 00:04:39,030 --> 00:04:42,180 to be able to edit this dhclient.config file 116 00:04:42,180 --> 00:04:45,270 because otherwise, you're likely to make mistakes. 117 00:04:45,270 --> 00:04:49,320 Next, let's talk a little bit about DNS and name resolution. 118 00:04:49,320 --> 00:04:52,380 You might remember that TCP/IP data packets 119 00:04:52,380 --> 00:04:55,890 always need to have a source IP and a destination IP. 120 00:04:55,890 --> 00:04:57,450 So if I want to send something to you 121 00:04:57,450 --> 00:04:59,220 or you want to visit my website, 122 00:04:59,220 --> 00:05:01,320 you would need to know its IP address. 123 00:05:01,320 --> 00:05:03,930 Now the problem is we humans are not very good 124 00:05:03,930 --> 00:05:06,930 at remembering lots of different long series of numbers. 125 00:05:06,930 --> 00:05:08,940 So if I had remember the IP address 126 00:05:08,940 --> 00:05:11,010 for every website I wanted to go to, 127 00:05:11,010 --> 00:05:13,230 that would just be a total pain, 128 00:05:13,230 --> 00:05:15,870 and it would make going on the internet not very fun. 129 00:05:15,870 --> 00:05:17,610 Therefore, there's a system created 130 00:05:17,610 --> 00:05:20,640 called DNS or domain name system. 131 00:05:20,640 --> 00:05:23,010 This allows us to type in user-friendly names 132 00:05:23,010 --> 00:05:24,660 like diontraining.com, 133 00:05:24,660 --> 00:05:26,790 and that gets converted to the IP address 134 00:05:26,790 --> 00:05:28,920 and routes our computer over there. 135 00:05:28,920 --> 00:05:30,570 To set this up on your system, 136 00:05:30,570 --> 00:05:33,360 you need to configure your DNS file. 137 00:05:33,360 --> 00:05:35,790 Now to do this, there is really two methods 138 00:05:35,790 --> 00:05:38,970 to be able to do this names to numbers association. 139 00:05:38,970 --> 00:05:41,070 The first way is the original way it was done 140 00:05:41,070 --> 00:05:43,950 on the internet when the internet was a much smaller place. 141 00:05:43,950 --> 00:05:45,930 And it was where there was a static text file 142 00:05:45,930 --> 00:05:48,150 with all of these links inside of it. 143 00:05:48,150 --> 00:05:51,420 This is called the /etc/hosts file. 144 00:05:51,420 --> 00:05:52,890 If you go into your Linux system 145 00:05:52,890 --> 00:05:57,890 and do cat space /etc/hosts, you'll be able to see 146 00:05:58,200 --> 00:06:01,110 if there's anything in your etc/hosts file. 147 00:06:01,110 --> 00:06:02,730 If you want to have some kind of a link 148 00:06:02,730 --> 00:06:04,890 that overrides everything else on your system 149 00:06:04,890 --> 00:06:08,760 in terms of names, you can put it in the etc/hosts file. 150 00:06:08,760 --> 00:06:10,500 For example, one of my kids 151 00:06:10,500 --> 00:06:12,420 was not doing his homework one night, 152 00:06:12,420 --> 00:06:13,950 and he kept going on YouTube. 153 00:06:13,950 --> 00:06:15,210 So I went into his computer. 154 00:06:15,210 --> 00:06:19,500 I edited his etc/hosts file and added youtube.com, 155 00:06:19,500 --> 00:06:22,860 and redirected it to the IP address of his school's website. 156 00:06:22,860 --> 00:06:24,390 So every time he tried to go to YouTube, 157 00:06:24,390 --> 00:06:26,010 it just pushed him right over 158 00:06:26,010 --> 00:06:27,600 to his school's website instead 159 00:06:27,600 --> 00:06:29,190 because your system is always 160 00:06:29,190 --> 00:06:31,740 going to check the etc/hosts file first 161 00:06:31,740 --> 00:06:33,630 before it goes to the second method, 162 00:06:33,630 --> 00:06:37,050 which is that dynamic database known as DNS. 163 00:06:37,050 --> 00:06:39,510 As I said, in the old days name resolution 164 00:06:39,510 --> 00:06:42,180 can be managed using a single static text file. 165 00:06:42,180 --> 00:06:44,970 And we could just add the different names and numbers in it, 166 00:06:44,970 --> 00:06:45,990 like a phone book. 167 00:06:45,990 --> 00:06:48,570 And we could then go to all the websites we wanted to. 168 00:06:48,570 --> 00:06:50,730 When the internet only had 50 or 100 169 00:06:50,730 --> 00:06:53,610 or a couple of thousand computers, that was manageable. 170 00:06:53,610 --> 00:06:55,830 But today, there are millions and millions of websites 171 00:06:55,830 --> 00:06:57,360 so there's just no way to keep up 172 00:06:57,360 --> 00:06:59,610 with all of the IP address changes, additions, 173 00:06:59,610 --> 00:07:01,230 and deletions that may happen. 174 00:07:01,230 --> 00:07:04,650 So we have to use this dynamic system of DNS instead. 175 00:07:04,650 --> 00:07:07,380 So to use DNS, the way our clients work 176 00:07:07,380 --> 00:07:09,810 is they're going to reach out to a DNS server and say, 177 00:07:09,810 --> 00:07:13,620 I would like to go to this hostname, like diontraining.com. 178 00:07:13,620 --> 00:07:15,780 And then the DNS server will look it up and say, 179 00:07:15,780 --> 00:07:18,090 I know where that is, it's this IP address, 180 00:07:18,090 --> 00:07:20,430 and hand you back the IP address in the background, 181 00:07:20,430 --> 00:07:22,710 and your computer then goes over to that IP address. 182 00:07:22,710 --> 00:07:24,930 That's all DNS does in the background 183 00:07:24,930 --> 00:07:28,350 to resolve a name and give you an IP address in return. 184 00:07:28,350 --> 00:07:30,960 This DNS server contains the resource records 185 00:07:30,960 --> 00:07:33,570 that provides all the answers to these different queries 186 00:07:33,570 --> 00:07:37,170 because diontraining.com isn't just one IP address. 187 00:07:37,170 --> 00:07:39,060 We actually have multiple IP addresses 188 00:07:39,060 --> 00:07:42,660 associated with that name, including our email server, 189 00:07:42,660 --> 00:07:46,110 our web server, our FTP server, and things like that. 190 00:07:46,110 --> 00:07:49,170 So we have to have all these records in a DNS server 191 00:07:49,170 --> 00:07:50,640 that we share with the rest of the world. 192 00:07:50,640 --> 00:07:53,610 And that way, they can know where to find our services. 193 00:07:53,610 --> 00:07:57,150 Now, how does your client know which DNS server to look at? 194 00:07:57,150 --> 00:08:02,150 Well, it does this by looking in the /etc/resolv.conf file. 195 00:08:04,380 --> 00:08:08,340 This is known as the /etc/resolve.config file, 196 00:08:08,340 --> 00:08:10,620 and it's stored locally on each Linux system. 197 00:08:10,620 --> 00:08:12,450 And it tells your system the IP address 198 00:08:12,450 --> 00:08:14,640 of one or more DNS servers. 199 00:08:14,640 --> 00:08:17,040 Now because DNS is so important, 200 00:08:17,040 --> 00:08:18,750 it's really a good idea to have at least 201 00:08:18,750 --> 00:08:23,750 two DNS servers listed inside your /etc/resolv.config file. 202 00:08:24,540 --> 00:08:26,730 Now another place you're going to configure DNS 203 00:08:26,730 --> 00:08:31,730 is inside the /etc/nsswitch.conf file. 204 00:08:32,100 --> 00:08:34,350 This includes a couple of different configuration options 205 00:08:34,350 --> 00:08:35,610 you should be aware of. 206 00:08:35,610 --> 00:08:37,530 For example, there's an option in here 207 00:08:37,530 --> 00:08:40,140 related to name resolution that defines the order 208 00:08:40,140 --> 00:08:41,730 in which name resolution methods 209 00:08:41,730 --> 00:08:43,860 are going to be used on your system. 210 00:08:43,860 --> 00:08:48,210 So should you go to etc/hosts first, then DNS? 211 00:08:48,210 --> 00:08:52,560 Or should you go to DNS first and then /etc/hosts? 212 00:08:52,560 --> 00:08:53,640 Whichever one it is, 213 00:08:53,640 --> 00:08:57,510 you need to configure that inside your nsswitch.config file. 214 00:08:57,510 --> 00:08:59,910 I will tell you, as a matter of best practice, 215 00:08:59,910 --> 00:09:04,140 you should go to /etc/hosts first and then go to your DNS, 216 00:09:04,140 --> 00:09:06,990 which is the dynamic method as your second option. 217 00:09:06,990 --> 00:09:09,210 This is how your system is configured by default. 218 00:09:09,210 --> 00:09:10,560 But if you'd like to change it, 219 00:09:10,560 --> 00:09:15,510 you can do that inside the /etc/nsswitch.config file. 220 00:09:15,510 --> 00:09:17,970 Now to set up your different DNS configurations, 221 00:09:17,970 --> 00:09:19,830 you can manually edit these files, 222 00:09:19,830 --> 00:09:21,750 or you could take the easy way out 223 00:09:21,750 --> 00:09:23,760 and use the network manager tool. 224 00:09:23,760 --> 00:09:25,740 Remember, there's a command line version, 225 00:09:25,740 --> 00:09:28,920 a text-based version, and a graphical user interface version 226 00:09:28,920 --> 00:09:31,380 that you can use to easily configure the IP address 227 00:09:31,380 --> 00:09:34,530 of your DNS servers that you want your client to use. 228 00:09:34,530 --> 00:09:35,940 Now, the last thing I want to talk about 229 00:09:35,940 --> 00:09:37,560 is a couple of command line tools 230 00:09:37,560 --> 00:09:41,070 that you should be aware of to interact with the DNS system. 231 00:09:41,070 --> 00:09:43,470 For example, if you wanted to find out right now 232 00:09:43,470 --> 00:09:46,350 what the IP address is for diontraining.com, 233 00:09:46,350 --> 00:09:48,420 you can do that using your Linux system. 234 00:09:48,420 --> 00:09:49,890 Simply open up your terminal, 235 00:09:49,890 --> 00:09:53,040 type in dig space diontraining.com, 236 00:09:53,040 --> 00:09:56,610 and it's going to return the IP address of diontraining.com. 237 00:09:56,610 --> 00:09:59,430 Dig is one of the ways that you can look up information 238 00:09:59,430 --> 00:10:02,010 on DNS and get that value back. 239 00:10:02,010 --> 00:10:03,660 Another way to get information 240 00:10:03,660 --> 00:10:05,850 is to use a tool called nslookup. 241 00:10:05,850 --> 00:10:08,760 Now, nslookup stands for name server lookup, 242 00:10:08,760 --> 00:10:09,810 and this will allow you to go 243 00:10:09,810 --> 00:10:12,050 and interact with a DNS name server 244 00:10:12,050 --> 00:10:13,980 to be able to get information back. 245 00:10:13,980 --> 00:10:16,500 For example, you might want to use nslookup 246 00:10:16,500 --> 00:10:18,810 to be able to go and look at the DNS records 247 00:10:18,810 --> 00:10:20,730 that are associated with my MX records, 248 00:10:20,730 --> 00:10:23,580 which are mail server records for diontraining.com, 249 00:10:23,580 --> 00:10:27,180 and figure out who am I using as an email service provider. 250 00:10:27,180 --> 00:10:29,220 Another thing you can use is host. 251 00:10:29,220 --> 00:10:31,680 Host is another DNS query tool, 252 00:10:31,680 --> 00:10:34,650 and it does the same type of thing as dig and nslookup, 253 00:10:34,650 --> 00:10:37,380 where you can query a DNS server and get the records back 254 00:10:37,380 --> 00:10:39,750 and look at the IP addresses and the names associated 255 00:10:39,750 --> 00:10:41,730 with each of those different records. 256 00:10:41,730 --> 00:10:44,610 Now, the final tool I want to talk about is whois. 257 00:10:44,610 --> 00:10:46,650 Whois is a command line utility 258 00:10:46,650 --> 00:10:49,260 that's going to allow you to communicate with a whois server, 259 00:10:49,260 --> 00:10:52,350 which actually hosts information about people 260 00:10:52,350 --> 00:10:54,270 who own different domain names. 261 00:10:54,270 --> 00:10:57,420 So if you want to find out who owns diontraining.com 262 00:10:57,420 --> 00:10:59,280 and what our contact information is, 263 00:10:59,280 --> 00:11:01,860 what our mailing address is, and things like that, 264 00:11:01,860 --> 00:11:03,780 that's what whois is used for. 265 00:11:03,780 --> 00:11:07,290 You could type in whois then the name diontraining.com 266 00:11:07,290 --> 00:11:08,970 and it will come back with all the information 267 00:11:08,970 --> 00:11:12,090 that we used to register that with the domain authorities 268 00:11:12,090 --> 00:11:13,980 when we bought that domain. 269 00:11:13,980 --> 00:11:16,020 As you can see, there's lots of different things 270 00:11:16,020 --> 00:11:19,680 you should be aware of when it comes to DHCP and DNS. 271 00:11:19,680 --> 00:11:21,690 Remember, you can configure both of these 272 00:11:21,690 --> 00:11:24,810 on your client using the network manager tool. 273 00:11:24,810 --> 00:11:28,170 When it comes to DHCP, you want to use DHCP assignments 274 00:11:28,170 --> 00:11:29,490 when you're dealing with clients, 275 00:11:29,490 --> 00:11:31,350 but you still want to statically assign things 276 00:11:31,350 --> 00:11:32,970 when you're dealing with servers. 277 00:11:32,970 --> 00:11:34,980 When it comes to DNS, remember, 278 00:11:34,980 --> 00:11:37,050 you can interact with the DNS servers 279 00:11:37,050 --> 00:11:40,500 and get information using dig, nslookup, or host. 280 00:11:40,500 --> 00:11:41,520 If you want to find that information 281 00:11:41,520 --> 00:11:44,583 about who owns that domain, you can use the whois command.