1 00:00:00,4 --> 00:00:05,644 The domain name system it really doesn't have a great place to fit in this 2 00:00:05,644 --> 00:00:10,238 architecture. It is the thing that converts user 3 00:00:10,238 --> 00:00:16,100 friendly names like www.umich.edu to, to like a network friendly address. 4 00:00:16,100 --> 00:00:20,379 These network numbers and IP addresses are important, because they are the. 5 00:00:20,379 --> 00:00:24,340 they encode the geography of the, of the connections of the internet. 6 00:00:24,340 --> 00:00:28,66 But we humans really don't care about the geography of the interconnections of the 7 00:00:28,66 --> 00:00:33,209 internet. www.umich.edu or www.facebook.com is what 8 00:00:33,209 --> 00:00:37,489 we want to remember. So I like to kind of think of the, the 9 00:00:37,489 --> 00:00:41,265 the domain name system is kind of like, sort of, somewhere either between the 10 00:00:41,265 --> 00:00:45,100 internet and the transport, or between the internet and the link or somewhere 11 00:00:45,100 --> 00:00:49,880 like in this area. You know, somewhere here. 12 00:00:49,880 --> 00:00:52,600 And it's certainly not in the application layer, it's not the link layer. 13 00:00:52,600 --> 00:00:56,862 It uses the link layer. but basically, it's kind of a little add 14 00:00:56,862 --> 00:01:00,934 on to the side. So the domain name system is for 15 00:01:00,934 --> 00:01:06,177 user-friendly names, okay. So let's talk a little bit about just how 16 00:01:06,177 --> 00:01:10,386 it works, because domain names are what we use all the time and IP addresses are 17 00:01:10,386 --> 00:01:16,239 what computers use all the time. And routers use, routers really have no 18 00:01:16,239 --> 00:01:19,431 knowledge of the domain names, they simply move data based on the IP 19 00:01:19,431 --> 00:01:23,625 addresses. Numeric addresses are tough for people to 20 00:01:23,625 --> 00:01:25,938 remember. I remember in the old days we would have 21 00:01:25,938 --> 00:01:29,972 little post-it notes on our computers and that's how I would keep track. 22 00:01:29,972 --> 00:01:33,248 Oh, there's a new, Minnesota just put up a server, let's put that number on my 23 00:01:33,248 --> 00:01:36,876 little post-it note. So the fact that they were numbers didn't 24 00:01:36,876 --> 00:01:40,159 bother us at all, because there were only 40 of em, but quickly there was more than 25 00:01:40,159 --> 00:01:45,384 40. And each campus even in the early days 26 00:01:45,384 --> 00:01:48,840 would only have one network number but now campuses have 20 or even 40 network 27 00:01:48,840 --> 00:01:52,234 numbers. Multiple groups of addresses, they're 28 00:01:52,234 --> 00:01:54,590 groups of addresses but their many of them. 29 00:01:54,590 --> 00:01:57,428 They get reorganized, you move a server from one place on campus to another like 30 00:01:57,428 --> 00:02:00,94 the, the Michigan web server, it was on our north campus so it would have one 31 00:02:00,94 --> 00:02:05,219 address, it was on our main campus. We'd have another reference and so you 32 00:02:05,219 --> 00:02:09,20 don't people to know what these IP addresses are. 33 00:02:09,20 --> 00:02:13,312 So they invented this notion of a domain name system, the. 34 00:02:13,312 --> 00:02:18,196 the visible name that we could switch the mapping from the name of the IP address 35 00:02:18,196 --> 00:02:22,892 transparently. And so the domain name system is like the 36 00:02:22,892 --> 00:02:27,692 internet's address book and it's a big distributed data base that's fast, it 37 00:02:27,692 --> 00:02:35,320 uses caching so that it's locally fast even if the network is partially down. 38 00:02:35,320 --> 00:02:38,850 IP addresses reflect the technical geography. 39 00:02:38,850 --> 00:02:42,567 And they read right to left, at least to the point where the network number is 40 00:02:42,567 --> 00:02:47,470 kind of the physical attachment point for the campus or business. 41 00:02:47,470 --> 00:02:51,990 And then, this part is the attachment point within that campus or business. 42 00:02:51,990 --> 00:02:56,470 And so, the most specific, the least specific to most specific goes from left 43 00:02:56,470 --> 00:02:59,764 to right. Doman names, on the other sa, hand are 44 00:02:59,764 --> 00:03:04,164 like organizational structure. The least specific is on the far right, 45 00:03:04,164 --> 00:03:08,0 and then it goes more specific as we go left. 46 00:03:08,0 --> 00:03:12,87 So edu means educational institutions, umich.edu means the particular 47 00:03:12,87 --> 00:03:16,710 educational institution University of Michigan, si.umich.edu means the school 48 00:03:16,710 --> 00:03:20,970 of information at the University of Michigan. 49 00:03:20,970 --> 00:03:23,160 Not all schools but just a particular one. 50 00:03:23,160 --> 00:03:26,520 And then dub, dub, dub is a particular server at that school. 51 00:03:26,520 --> 00:03:31,357 And it reads like a posta address. So, if you think that where I teach 2455 52 00:03:31,357 --> 00:03:36,453 North Quad, it's kind of on earth. And it's on the country USA, and it's in 53 00:03:36,453 --> 00:03:40,290 a zip code to the state of Michigan, it's in Ann Arbor. 54 00:03:40,290 --> 00:03:44,50 And then this is the building and then this is the room number in the building. 55 00:03:44,50 --> 00:03:47,858 So we go from very general to very specific. 56 00:03:47,858 --> 00:03:52,90 So, domain names lead, read in a sense right to left. 57 00:03:52,90 --> 00:03:54,759 Phone numbers and IP addresses read left to right. 58 00:03:57,970 --> 00:04:01,830 The other thing that's interesting about domain names is that they're owned. 59 00:04:01,830 --> 00:04:06,648 They're owned from right to left, and so there are sort of, they're a hierarchy, 60 00:04:06,648 --> 00:04:13,940 and basically an organization owns edu. The organization's name is Educause. 61 00:04:13,940 --> 00:04:18,490 It has conferences and other things but one of the things that it does is it owns 62 00:04:18,490 --> 00:04:24,490 in the public trust the name edu. So University of Michigan could go to edu 63 00:04:24,490 --> 00:04:28,870 and say hey could I have umich.edu. And they would say let me think about 64 00:04:28,870 --> 00:04:33,650 that, and then maybe they would give it. And they did, because University of 65 00:04:33,650 --> 00:04:36,800 Michigan, nobody else had it and it seemed like a good name and University of 66 00:04:36,800 --> 00:04:41,864 Michigan was like accredited in higher Education so they will give it to them. 67 00:04:41,864 --> 00:04:44,810 If I want to say like I'm Dr. Chuck and I want to create a Dr. 68 00:04:44,810 --> 00:04:52,570 Chuck University like Dr. Chuck.edu and they go like no, you can't. 69 00:04:52,570 --> 00:04:55,420 You're not a university. You're not a, you're not a educational 70 00:04:55,420 --> 00:05:00,253 institution. So they might say yes, they might say no. 71 00:05:00,253 --> 00:05:04,861 Things like .com and .org, they're kind of a catch as catch can and so the first 72 00:05:04,861 --> 00:05:10,932 one who gets there tends to win. There's, there's some situations where 73 00:05:10,932 --> 00:05:15,28 if, If I got cocacola.com, and had no particular use for it and Coca Cola owned 74 00:05:15,28 --> 00:05:18,740 the trademark Coca Cola, they could take it away from me, unless I had a 75 00:05:18,740 --> 00:05:25,94 legitimate purpose for it. It's hard for me to imagine a legitimate 76 00:05:25,94 --> 00:05:29,189 purpose for Coca Cola, but target.com might be a club for target shooting, and 77 00:05:29,189 --> 00:05:33,158 it would be difficult for Target to say, sorry I got to take your, your target 78 00:05:33,158 --> 00:05:37,1 shooting club away because thats', even though, though it's not as big as 79 00:05:37,1 --> 00:05:43,362 Target's comapny, it it's a legitimate use. 80 00:05:43,362 --> 00:05:48,576 So, at each level, once the University of Michigan is awarded the University of 81 00:05:48,576 --> 00:05:54,970 Michigan It creates a mechanism to a word subdomains within that. 82 00:05:54,970 --> 00:05:58,150 And so, there is actually committee at the University of Michigan. 83 00:05:58,150 --> 00:06:01,270 And if we want, like our learning measurement system is called 84 00:06:01,270 --> 00:06:05,170 ctools.umich.edu, if we want that, we have to go to the committee and convince 85 00:06:05,170 --> 00:06:10,310 them to give it to us. A top level domain within the University 86 00:06:10,310 --> 00:06:13,136 of Michigan. We got one, the School of Information, 87 00:06:13,136 --> 00:06:17,700 where I'm a faculty member, is si.umich.edu and they gave us that one. 88 00:06:17,700 --> 00:06:22,779 I can go to that committee and I could say hey, I want to be drchuck.umich.edu. 89 00:06:22,779 --> 00:06:29,685 And they would say no, you can't. So, then the school of information, where 90 00:06:29,685 --> 00:06:33,910 I teach has si.umich.edu and they have a committee. 91 00:06:33,910 --> 00:06:35,814 And they can give out sub-domains within that. 92 00:06:35,814 --> 00:06:37,391 So, you get the picture. Right? 93 00:06:37,391 --> 00:06:41,698 So, I could go there and I'd say, Hey, can I have drchuck.umich.edu, 94 00:06:41,698 --> 00:06:46,60 si.umich.edu? Drchuck.si.umich.edu. 95 00:06:46,60 --> 00:06:46,282 And it will say, No. But you can have csef. 96 00:06:46,282 --> 00:06:46,581 people.si.unich.edu. So once you own one of these things you 97 00:06:46,581 --> 00:06:49,488 can give out sub domains. I do own Drchuck.com. 98 00:06:49,488 --> 00:07:00,546 Drchuck.com And if there was a high desire for something underneath 99 00:07:00,546 --> 00:07:06,739 drchuck.com. That I could have my own little business 100 00:07:06,739 --> 00:07:08,755 selling domains under Dr. Chuck. 101 00:07:08,755 --> 00:07:11,840 com. nobody seems to want any of those things. 102 00:07:11,840 --> 00:07:16,262 But you know, some people have mail.com and other things and so each one of these 103 00:07:16,262 --> 00:07:21,540 is a new potential for expansion. And so, that's kind of how the domain 104 00:07:21,540 --> 00:07:25,700 name works, right, it is this mapping between these names There is sort of this 105 00:07:25,700 --> 00:07:29,796 right to left ownership of these names and and you have to ask people to get 106 00:07:29,796 --> 00:07:37,103 those names and so that's a real quick overview of the domain name system.