1 00:00:00,930 --> 00:00:01,740 What time is it? 2 00:00:03,150 --> 00:00:09,990 I'm sure you agree that time is of great importance in the real world and the same is true for networking. 3 00:00:10,580 --> 00:00:18,270 If I asked you to have a meeting with me tomorrow at 9 a.m., one of the first questions is 9:00 4 00:00:18,330 --> 00:00:24,170 AM, in which time zone I'm based in the U.K., but you may be based elsewhere. 5 00:00:24,780 --> 00:00:31,980 So we're talking about 9:00 a.m. Eastern Time in the US or perhaps Pacific Time or are we talking 6 00:00:31,980 --> 00:00:34,050 about 9:00 a.m. U.K. time. 7 00:00:34,560 --> 00:00:37,560 Time is also of great importance when troubleshooting networking. 8 00:00:38,070 --> 00:00:40,350 In this example, I've got three routers, router 9 00:00:40,390 --> 00:00:41,840 1, router 2 and router 3. 10 00:00:42,750 --> 00:00:52,410 And as an example, if I type Conft and then Control zed or control z, notice the time on this router. 11 00:00:52,920 --> 00:00:59,160 The Syslog message is saying that the router was configured by the console, but this router thinks 12 00:00:59,160 --> 00:01:02,640 it's in the year 2030, so it's done a bit of time travel. 13 00:01:05,290 --> 00:01:12,760 This router thinks that it's in the year 2002, so it's stuck in the past. I've got a router with the 14 00:01:12,760 --> 00:01:16,500 correct time in the UK, but the wrong date. 15 00:01:17,350 --> 00:01:20,220 This router thinks that it's based in the future. 16 00:01:21,100 --> 00:01:24,840 This router has the correct time currently in the UK. 17 00:01:25,630 --> 00:01:26,590 This one doesn't. 18 00:01:27,370 --> 00:01:31,060 This router, however, has the wrong date and so does this router. 19 00:01:33,150 --> 00:01:40,780 Now, this becomes even more important when we're trying to troubleshoot an issue on the network. In this 20 00:01:40,780 --> 00:01:50,550 example, I'll enable OSPF on router 2 it's already enabled on the other routers in the network. 21 00:01:56,410 --> 00:02:04,180 So we can see that a relationship was formed in the year 2030 and according to this side a neighbor 22 00:02:04,180 --> 00:02:12,070 relationship was formed in the year 2002, it's going to be very difficult to troubleshoot any kind 23 00:02:12,070 --> 00:02:15,910 of issue taking place between the router in this network 24 00:02:17,160 --> 00:02:20,970 because the date and time is not synchronized on the routers. 25 00:02:22,170 --> 00:02:25,910 Now you can manually configure time on the routers. 26 00:02:26,130 --> 00:02:31,230 So I could use the clock command as an example and set the time 27 00:02:32,510 --> 00:02:33,320 on the routers 28 00:02:34,950 --> 00:02:43,800 but that's not going to scale very well if I have many, many routers and in addition 29 00:02:44,250 --> 00:02:53,220 clocks drift, so we ideally want to ensure that all the clocks on all the devices are synchronized to an atomic clock 30 00:02:53,220 --> 00:02:53,580 somewhere. 31 00:02:54,480 --> 00:03:00,630 The protocol used for synchronization of time is Network Time Protocol or NTP. 32 00:03:01,170 --> 00:03:10,200 At the moment, if I type show NTP status on router 1, we can see that NTP is not enabled, NTP is 33 00:03:10,230 --> 00:03:13,020 not enabled by default on Cisco routers and switches. 34 00:03:13,470 --> 00:03:17,730 You need to configure the devices to talk to a time source. 35 00:03:18,300 --> 00:03:23,070 Now in this example, I don't have an atomic clock which I can draw my time from. 36 00:03:24,160 --> 00:03:29,290 You can, as an example, get NTP from various servers on the Internet. 37 00:03:29,980 --> 00:03:36,730 Here's some examples of NTP servers available in the United Kingdom just do a search in Google or your 38 00:03:36,730 --> 00:03:43,840 favorite search engine for various NTP services available online for security reasons, you might prefer 39 00:03:43,840 --> 00:03:50,190 to get time from a local active directory server in your network rather than directly off the Internet. 40 00:03:50,680 --> 00:03:55,840 But in this network, what we'll do is configure router 3 as a master or what's called a stratum 41 00:03:55,840 --> 00:03:58,930 router, NTP has different levels 42 00:03:59,350 --> 00:04:05,260 the lower the number, the closer you are to a atomic clock source. 43 00:04:06,790 --> 00:04:13,630 So on router 3, you would use a command, now I'm good right now because I want to set up some other values 44 00:04:13,630 --> 00:04:20,920 first, but you would specify a stratum value for the router once again, the lower the number, 45 00:04:21,070 --> 00:04:23,440 the closer you are to an atomic source. 46 00:04:24,160 --> 00:04:33,250 NTP uses a hierarchy of stratums where a router or a device was stratrum 3 would get its time from 47 00:04:33,250 --> 00:04:40,000 a device with a lower number like 1 or 2, time would then be pushed across the network to multiple 48 00:04:40,000 --> 00:04:41,860 devices from one level to another. 49 00:04:42,970 --> 00:04:51,640 NTP is once again used for clock synchronization between network devices or computer systems over a data 50 00:04:51,640 --> 00:04:55,240 network such as the Internet or our little network 51 00:04:55,240 --> 00:04:58,210 in this example, it's been around for a long time. 52 00:04:58,540 --> 00:05:04,930 So since the 1980s, it uses UDP port or user datagram protocol port 53 00:05:04,930 --> 00:05:12,700 No one 123 time can be sent using unicast broadcasts or multi costs. 54 00:05:13,970 --> 00:05:22,130 Here's a picture of a US Naval master clock, which has a stratum of zero. 55 00:05:22,130 --> 00:05:27,860 providing time to many other devices using a hierarchal system. 56 00:05:28,520 --> 00:05:35,720 Stratum 0 devices are very high precision time devices that have atomic clocks, GPS clocks or other 57 00:05:35,870 --> 00:05:37,250 and so forth and so on. 58 00:05:37,910 --> 00:05:45,230 Stratum 0 devices are very high precision time devices that have atomic clocks, GPS clocks or other 59 00:05:45,230 --> 00:05:46,100 radio clocks. 60 00:05:46,680 --> 00:05:54,680 They are known as reference clocks in NTP. Stratum 1 are synchronized to within a few microseconds 61 00:05:54,680 --> 00:05:57,200 and are attached to stratum 0 devices. 62 00:05:57,680 --> 00:06:03,710 They are referred to as primary time servers and then time filters down to other devices. 63 00:06:04,130 --> 00:06:11,120 So stratum 2 devices will carry stratum 1 and stratum 3 will carry stratum 2 and that will 64 00:06:11,120 --> 00:06:13,490 continue up to the maximum of 15.