1 00:00:00,000 --> 00:00:03,940 There are 3 different types of top-level domains or TLDs. 2 00:00:03,940 --> 00:00:07,640 There are country code top-level domains like .us, 3 00:00:07,640 --> 00:00:11,060 .uk, .il as well as a ton more. 4 00:00:11,060 --> 00:00:15,940 There are also generic top-level domains, which you're probably pretty familiar with. 5 00:00:15,940 --> 00:00:22,110 These are things like .com, .net, .org, .gov as well as many, many more. 6 00:00:22,110 --> 00:00:25,930 And finally there are infrastructure top-level domains, 7 00:00:25,930 --> 00:00:29,230 which we'll get into a little bit later on in the course. 8 00:00:29,230 --> 00:00:33,420 Now, there are some constraints with top-level domains. 9 00:00:33,420 --> 00:00:35,750 They can never be all numeric. 10 00:00:35,750 --> 00:00:40,910 Now, when you look at a website like www.example.com 11 00:00:40,910 --> 00:00:43,240 you'll see that it's 3 different levels. 12 00:00:43,240 --> 00:00:45,340 The top-level domain, 13 00:00:45,340 --> 00:00:46,960 domain, and the subdomain. 14 00:00:46,960 --> 00:00:51,020 You might be wondering how many different levels you can have in a domain name. 15 00:00:51,020 --> 00:00:55,160 The answer is there can be 127 levels 16 00:00:55,160 --> 00:00:58,210 each of them being up to 63 characters. 17 00:00:58,210 --> 00:01:01,370 However, that could quickly get out of control. 18 00:01:01,370 --> 00:01:06,600 So the full domain name is limited to 253 characters of text, 19 00:01:06,600 --> 00:01:11,470 and the domain name must use the ASCII character set 20 00:01:11,470 --> 00:01:15,040 and has limitations called the LDH Rule, 21 00:01:15,040 --> 00:01:18,830 which stands for letters, digits, and hyphens. 22 00:01:18,830 --> 00:01:23,060 This means you can use the letters A through Z in lower case or upper case, 23 00:01:23,060 --> 00:01:25,550 the numbers 0 through 9, 24 00:01:25,550 --> 00:01:27,580 as well as a hyphen. 25 00:01:27,580 --> 00:01:31,430 And the domain name cannot start or end with a hyphen.