1 00:00:00,270 --> 00:00:03,480 A Cisco router consists of multiple components. 2 00:00:03,930 --> 00:00:09,660 The major internal components of a Cisco router include a central processing unit or CPU. 3 00:00:10,010 --> 00:00:16,890 The various physical interfaces, such as serial interfaces or FastEthernet interfaces or gigabit interfaces, 4 00:00:17,530 --> 00:00:27,720 random access memory or ram, rom or read only memory, flash memory, as well as N.V. Ram or nonvolatile 5 00:00:27,720 --> 00:00:34,260 RAM. A router is similar to a computer and has several hardware and software components. 6 00:00:34,860 --> 00:00:42,000 So as an example, in a PC today you may have a flash drive or hard drive, and in a similar way, a 7 00:00:42,000 --> 00:00:51,300 router has flash as well as memory and CPU. The router, CPU or central processing unit executes operating 8 00:00:51,300 --> 00:00:57,960 instructions such as system initialization, routing functions and switching functions. 9 00:00:58,450 --> 00:01:06,600 A router may run a routing protocol such as OSPF and when OSPF recalculates the routes to add to the routing 10 00:01:06,600 --> 00:01:10,950 table, the central processing unit needs to do those computations. 11 00:01:11,640 --> 00:01:14,880 The router also has RAM or random access memory installed. 12 00:01:15,510 --> 00:01:17,310 This is very similar to a PC. 13 00:01:18,210 --> 00:01:26,510 RAM is a volatile memory and any data stored in RAM is lost when the routers powered down or restarted. 14 00:01:27,210 --> 00:01:35,490 So in the same way as on a PC, if you're working in Microsoft Word and you lose power to your PC, you'll 15 00:01:35,490 --> 00:01:43,170 lose any changes to the Microsoft Word document if you haven't saved the document to your hard drive. 16 00:01:43,890 --> 00:01:49,860 So if you turn the PC off and you've made some changes without saving them, those changes are lost 17 00:01:49,860 --> 00:01:55,070 because the word changes are only stored in RAM and haven't been written to the hard drive. 18 00:01:55,650 --> 00:02:04,350 So a router has RAM, which is read-write memory and contain software and data structures that allow the 19 00:02:04,350 --> 00:02:05,370 router to function. 20 00:02:05,880 --> 00:02:14,190 Now, in some cases with PCs, when you boot up a PC, the operating system which is stored on the hard 21 00:02:14,190 --> 00:02:16,140 drive is loaded into memory. 22 00:02:17,170 --> 00:02:23,830 That's not always possible because of the size of operating systems and the amount of RAM available 23 00:02:23,830 --> 00:02:24,610 in a PC. 24 00:02:25,480 --> 00:02:35,230 However, a Cisco router today copies the entire Cisco IOS software into RAM during the boot process. 25 00:02:36,040 --> 00:02:39,330 That didn't take place in the past, but that's what happens today. 26 00:02:40,230 --> 00:02:46,320 In a similar way, when you make changes on a router, those changes are written to the running configuration. 27 00:02:47,370 --> 00:02:53,640 The running configuration is stored in RAM, and unless you save that configuration to the startup-config, 28 00:02:54,150 --> 00:02:59,230 which is stored in nonvolatile RAM or NVRAM your changes will be lost. 29 00:03:00,090 --> 00:03:06,450 So the running configuration of a router is stored in RAM and when you save your configuration, it's copied 30 00:03:06,450 --> 00:03:12,780 to the startup-config, which is stored in nonvolatile ram, which means that when the router is turned off, 31 00:03:13,320 --> 00:03:16,710 those configuration changes are saved and not lost. 32 00:03:17,460 --> 00:03:26,430 So NVRAM or Nonvolatile RAM is used to store information such as the startup config, which is not 33 00:03:26,430 --> 00:03:29,860 lost when the router is turned off or loses power. 34 00:03:30,570 --> 00:03:37,440 So the running configuration file is the file that stores the configuration commands that the Cisco 35 00:03:37,440 --> 00:03:43,620 IOS software is currently using on the router typically, all commands that are configured on the 36 00:03:43,620 --> 00:03:45,750 router or stored in the running config. 37 00:03:46,760 --> 00:03:52,880 There are as always, some exceptions to the rule, but generally, the show run command shows you the 38 00:03:52,880 --> 00:03:56,330 configuration that's currently being used by the router. 39 00:03:57,110 --> 00:04:01,400 Once again, NVRAM doesn't lose its information when the router is powered off. 40 00:04:02,090 --> 00:04:09,290 The Cisco IOS software uses NVRAM to permanently store the routers configuration in the startup 41 00:04:09,290 --> 00:04:10,010 config. 42 00:04:10,670 --> 00:04:15,140 When you make changes to the Cisco router using the command line interface. 43 00:04:15,650 --> 00:04:18,079 Those changes are made to the running config. 44 00:04:18,680 --> 00:04:26,330 If you want to save those changes, you need to use commands such as copy running-config, startup-config 45 00:04:26,960 --> 00:04:34,040 to copy the configuration from RAM to NVRAM or from the running-config to the Start-Up config. 46 00:04:37,390 --> 00:04:44,110 Flash memory is nonvolatile computer memory and is used as the permanent storage for the operating system 47 00:04:44,440 --> 00:04:45,610 and other files. 48 00:04:46,210 --> 00:04:50,080 This is very similar to the hard drive or flash drive on PCs today 49 00:04:50,740 --> 00:04:56,950 depending on the size of the flash, multiple copies of the Cisco iOS can be stored in flash. 50 00:04:57,400 --> 00:05:03,730 Other files, such as Music on Hold, which is used in call managing express environments, can also 51 00:05:03,730 --> 00:05:04,810 be stored in flash. 52 00:05:05,410 --> 00:05:13,960 When a Cisco router boots up, it will copy the iOS software from Flash into RAM during the boot process 53 00:05:14,290 --> 00:05:16,660 and then the CPU will execute the iOS. 54 00:05:17,260 --> 00:05:25,900 Some very old models of Cisco routers, such as the 2500 ran the IOS from memory and Flash at the same 55 00:05:25,900 --> 00:05:26,410 time 56 00:05:26,800 --> 00:05:34,630 but these days the entire operating system is copying to RAM and is run from RAM in a similar way to 57 00:05:34,630 --> 00:05:39,950 a hard drive or flash drive on a computer when the router is turned off 58 00:05:40,270 --> 00:05:43,000 Flash memory doesn't lose its contents. 59 00:05:43,600 --> 00:05:46,240 ROM is another form of permanent storage. 60 00:05:47,020 --> 00:05:52,810 This memory contains MICRO code for basic functions to start and maintain the router and includes the 61 00:05:52,810 --> 00:05:57,010 bootstrap code and power on self-test or post. 62 00:05:57,700 --> 00:06:04,720 ROM also contains Rom Monitor or ROMMON, which is used for password recovery and for Router disaster 63 00:06:04,720 --> 00:06:05,950 recovery functions. 64 00:06:06,580 --> 00:06:14,170 ROM is nonvolatile, so the contents are maintained even when the router is turned off or rebooted. 65 00:06:14,830 --> 00:06:20,590 The router also stores the IP routing table, this stores information about directly connected and remote 66 00:06:20,590 --> 00:06:26,050 networks and is used to determine the best path to a local or remote 67 00:06:26,050 --> 00:06:33,520 network. ARP caches are also used by the router and this contains the IPv4 address to MAC address 68 00:06:33,520 --> 00:06:37,300 mappings, which is very similar to the ARP cache on a PC. 69 00:06:37,930 --> 00:06:44,770 The ARP cache on routers is used on Ethernet interfaces and is used, for example, when the router pings 70 00:06:44,950 --> 00:06:51,310 another device on the local subnet, the router will send out an ARP request and when it receives an 71 00:06:51,310 --> 00:06:54,850 ARP response, that information is stored in the ARP cache. 72 00:06:55,360 --> 00:07:02,410 Typically, however, it's populated when PCs are forwarding traffic through a router to a remote destination. 73 00:07:02,740 --> 00:07:09,610 PCs will send an ARP request for their default gateway and the router will reply, and hence the ARP cache 74 00:07:09,610 --> 00:07:10,600 will be populated. 75 00:07:11,110 --> 00:07:17,470 Routers also have packet buffers when packets are received on interfaces they are stored in 76 00:07:17,470 --> 00:07:21,670 buffers, they are also stored in buffers before they exit an interface. 77 00:07:22,090 --> 00:07:29,020 As an example, if an interface is congested, the buffer of the outgoing interface will fill up with 78 00:07:29,020 --> 00:07:33,550 packets in the queue to be processed out of that interface. 79 00:07:34,150 --> 00:07:39,310 A router also has the configuration register, which is stored in NVRAM, 80 00:07:39,940 --> 00:07:42,610 this is used to control how a router boots. 81 00:07:43,120 --> 00:07:50,140 You could configure this value to get a router to boot into ROM MONITOR mode or to bypass the startup-config 82 00:07:50,140 --> 00:07:57,370 config to do a password recovery and can be used for other functions, such as changing the speed of 83 00:07:57,370 --> 00:07:57,940 the console 84 00:07:57,940 --> 00:08:05,380 port. A router has multiple interfaces and may include an auxiliary port which is used in the past for 85 00:08:05,380 --> 00:08:06,580 modem connections. 86 00:08:07,000 --> 00:08:08,440 It'll have a console port. 87 00:08:08,650 --> 00:08:13,180 It may have a USB interface, it may have serial interfaces, 88 00:08:13,180 --> 00:08:20,260 FastEthernet interfaces, gigabit interfaces and may contain other components such as PVDM 89 00:08:20,260 --> 00:08:22,750 which are used in voice environments for trans coding. 90 00:08:23,290 --> 00:08:31,030 These have what are called DSP or digital signal processors to convert analog voice into a digital stream. 91 00:08:31,730 --> 00:08:38,559 Various other types of interfaces and components may be found in routers, and even servers can be installed 92 00:08:38,559 --> 00:08:39,490 in routers today.