1 00:00:01,070 --> 00:00:07,190 So the boot field, this last value, determines how the router will boot. 2 00:00:09,880 --> 00:00:19,540 That consists of four binary bits which either set on or off a value of 0 means ROM monitor, a value 3 00:00:19,540 --> 00:00:27,880 of 1 means boot into RX boot in the old days or today means boot using the first operating system 4 00:00:27,880 --> 00:00:28,450 in flash. 5 00:00:29,930 --> 00:00:32,659 Setting it to 2 or a greater number, 6 00:00:34,010 --> 00:00:41,570 such as F or E, in other words, anything from 2 to F means normal boot. 7 00:00:43,960 --> 00:00:51,790 So this value is set to 2 or greater means normal boot, so in other words, enables default booting 8 00:00:51,790 --> 00:00:52,770 from flash memory. 9 00:00:53,290 --> 00:00:58,870 You can override that by using the boot system commands in the running-config of a router. 10 00:00:59,650 --> 00:01:04,750 So on a router, you could use the boot system command to specify that a different operating system is 11 00:01:04,750 --> 00:01:05,950 used as an example. 12 00:01:06,280 --> 00:01:10,370 So the router would boot from a TFTP server as an example. 13 00:01:11,350 --> 00:01:20,350 So in other words, on the router, you could use a command such as boot system and tell the router to 14 00:01:20,350 --> 00:01:29,020 boot its operating system or for TFTP server or an FTP server as an example, rather than booting the 15 00:01:29,020 --> 00:01:30,490 operating system from Flash. 16 00:01:32,730 --> 00:01:40,140 When a router boots up, it goes through a series of steps which include loading the Cisco iOS software 17 00:01:40,140 --> 00:01:47,220 from Flash or if specified from somewhere else, such as an FTP server into the RAM of the router, 18 00:01:47,880 --> 00:01:56,400 the router will also load the configuration stored in startup-config and apply that and use it as the running 19 00:01:56,400 --> 00:01:56,990 config. 20 00:01:57,630 --> 00:02:02,910 So here these steps that are takes when booting up, the first thing it does is perform the 21 00:02:02,910 --> 00:02:04,870 power on self-test or post. 22 00:02:05,490 --> 00:02:12,180 This is a series of hardware tests that verify that all the components of a Cisco router are functional, during 23 00:02:12,180 --> 00:02:12,540 the test 24 00:02:12,540 --> 00:02:14,940 the router also determines which hardware is present. 25 00:02:15,480 --> 00:02:19,400 This executes from microcode that is stored in the system 26 00:02:19,410 --> 00:02:19,830 ROM. 27 00:02:21,040 --> 00:02:21,940 So here's our router 28 00:02:22,990 --> 00:02:28,900 and here's our APC, I'm going to do an immediate reboot on the router. 29 00:02:37,740 --> 00:02:43,690 So you can see the router is booting up and then is loading the operating system. 30 00:02:44,430 --> 00:02:48,730 Now it's going to do a power and self-test, but that's not very clear on this router. 31 00:02:49,290 --> 00:02:53,640 So what I'm going to do is show you the power and self-tests on a Cisco switch. 32 00:02:54,390 --> 00:02:58,320 So I'll do a reboot on the Cisco switch 33 00:03:07,040 --> 00:03:07,610 and 34 00:03:08,530 --> 00:03:12,160 you can see the 2950 boot loader is being used. 35 00:03:15,510 --> 00:03:18,420 It's now loading the operating system from Flash 36 00:03:21,530 --> 00:03:28,490 and what I'd like to show you here is notice the power and self-tests that are shown on the switch, so you 37 00:03:28,490 --> 00:03:34,010 can see clearly that power and self-test have been passed on the switch 38 00:03:36,160 --> 00:03:42,660 and then the switch boots up and the interfaces come up. So scrolling back notice power and self-test, 39 00:03:43,000 --> 00:03:44,200 power and self-test 40 00:03:45,480 --> 00:03:52,980 can see the operating systems loaded and then the switch is ready to start. Now something similar is taking 41 00:03:52,980 --> 00:03:54,300 place on a router. 42 00:03:55,440 --> 00:03:57,870 We just don't see it as clearly in the output here 43 00:04:02,150 --> 00:04:07,880 but here's the output when I reloaded the router, you can see ROM monitors initialized the program, 44 00:04:07,880 --> 00:04:09,200 loads are taking place. 45 00:04:09,650 --> 00:04:12,350 The operating system is being decompressed and loaded. 46 00:04:14,490 --> 00:04:21,630 So the first step on a router is to perform a power-on Self-test, the router then loads and runs the 47 00:04:21,630 --> 00:04:27,390 bootstrap code, which is used to perform subsequent events, such as locating the Cisco iOS software 48 00:04:27,840 --> 00:04:34,020 and loading it into RAM and running it after the Cisco iOS software is loaded and running. 49 00:04:34,410 --> 00:04:40,980 The bootstrap code is not used until the next time the router is reloaded or power cycled. 50 00:04:42,840 --> 00:04:50,250 So on this 1841 router, we can see that the bootstrap code is loading the operating system 51 00:04:53,360 --> 00:04:57,590 and here we can see which version of operating system has been loaded into RAM.