1 00:00:00,000 --> 00:00:03,650 Before we get too deep into how the domain name system works 2 00:00:03,650 --> 00:00:06,680 we need to understand a couple of terms when working with domains. 3 00:00:06,680 --> 00:00:11,190 One of those terms is called Time To Live or TTL. 4 00:00:11,190 --> 00:00:14,920 Now, this is not just a metaphor for how you should live your life. 5 00:00:14,920 --> 00:00:18,180 This actually specifies the number of seconds, 6 00:00:18,180 --> 00:00:21,260 in which information should be updated. 7 00:00:21,260 --> 00:00:25,270 So your computer might be looking for updates to different information 8 00:00:25,270 --> 00:00:28,200 such as where a specific server is on the internet. 9 00:00:28,200 --> 00:00:32,500 Now, DNS is a very, very distributed system 10 00:00:32,500 --> 00:00:35,100 and this is where the term propagation comes in. 11 00:00:35,100 --> 00:00:38,540 Certain information will be distributed all throughout the globe 12 00:00:38,540 --> 00:00:40,450 and backed up. 13 00:00:40,450 --> 00:00:43,240 Now, when you specify a very low time to live 14 00:00:43,240 --> 00:00:44,310 and a low number of seconds 15 00:00:44,310 --> 00:00:47,810 it will take less time for information to be fetched 16 00:00:47,810 --> 00:00:49,270 and distributed. 17 00:00:49,270 --> 00:00:52,250 When you specify a really high TTL 18 00:00:52,250 --> 00:00:54,580 it will not be looked up as often. 19 00:00:54,580 --> 00:00:58,300 Now as you might imagine, setting a really high time to live 20 00:00:58,300 --> 00:01:01,370 would be very beneficial in certain situations. 21 00:01:01,370 --> 00:01:04,860 This would mean information won't need to be queried as much, 22 00:01:04,860 --> 00:01:07,700 which would be reduced load on your DNS servers. 23 00:01:07,700 --> 00:01:11,050 When you're developing or testing applications 24 00:01:11,050 --> 00:01:14,260 it's useful to set a very low time to live. 25 00:01:14,260 --> 00:01:17,820 This way you can make sure changes get picked up a lot quicker. 26 00:01:17,820 --> 00:01:20,660 When you move into production, it's generally better 27 00:01:20,660 --> 00:01:25,390 to set a high time to live so that clients won't be fetching new information 28 00:01:25,390 --> 00:01:27,220 a lot of the time. 29 00:01:27,220 --> 00:01:30,650 In the case that you're switching servers—for example— 30 00:01:30,650 --> 00:01:34,050 moving your www server from one host to another 31 00:01:34,050 --> 00:01:38,330 it's beneficial to reset the time to live from a high value 32 00:01:38,330 --> 00:01:41,030 to a low value in preparation for the move. 33 00:01:41,030 --> 00:01:44,380 You don't need to worry too much about TTL right now, 34 00:01:44,380 --> 00:01:46,610 but it is something that we'll keep in mind for later.