| An important part of your Cisco CCENT and CCNA | | | | of diagnostic tests designed to verify the basic |
| certification studies is learning the differences between | | | | operation of the network interfaces, memory, and the |
| RAM, ROM, NVRAM, and Flash memory. You better | | | | CPU. |
| know the differences when it comes to working in | | | | Depending on the model or router of switch you're |
| real-life networks as well, because vital Cisco files are | | | | using, you can actually see some of these tests being |
| found in these memory types - and since some of | | | | passed. Here, I've reloaded a Cisco 2950 switch, and |
| these files are lost on a router reload and some are | | | | you can see some of the POSTs being run and |
| not, we better know which is which! | | | | passed at the very beginning of the bootup process. |
| The memory types and functions discussed in this | | | | Initializing flashfs...flashfs[1]: 79 files, 3 directoriesflashfs[1]: |
| section are the same for routers and switches, but to | | | | 0 orphaned files, 0 orphaned directoriflashfs[1]: Total |
| keep from saying "routers and switches" 500 times, I'll | | | | bytes: 7741440flashfs[1]: Bytes used: 5980672flashfs[1]: |
| just say "routers". :) | | | | Bytes available: 1760768flashfs[1]: flashfs fsck took 7 |
| Configuring the routers is a lot of fun, but we've got to | | | | seconds.flashfs[1]: Initialization complete. |
| know what's going on inside the router, too! Cisco | | | | Done initializing flashfs. |
| routers have four different kinds of memory, and while | | | | POST: System Board Test : Passed |
| some of the names are similar, their purpose is totally | | | | POST: Ethernet Controller Test : Passed |
| different. | | | | ASIC Initialization Passed |
| The contents of some of these memory types is kept | | | | POST: FRONT-END LOOPBACK TEST : Passed |
| when the router is reloaded, and others are lost on a | | | | POSTs are particularly effective at detecting major |
| reload. We better know which is which! | | | | problems early in the boot process, such as a broken |
| It's a fair bet that these topics will come up on your | | | | fan. If the POST detects such a problem (usually called |
| CCENT and CCNA exams, and this is also information | | | | an "environmental factor") that would cause the router |
| you've got to know to be a real network admin. Let's | | | | or switch to overheat after booting, the POST will fail, |
| examine these four memory types closely and see | | | | give you a clear message as to why the POST failed, |
| what each one does! | | | | and will then stop the boot process. |
| ROM: Read-Only Memory. ROM stores the router's | | | | But let's speak positively here! |
| bootstrap startup program, operating system software, | | | | After the router passes the POST, it looks for a |
| and power-on diagnostic test programs (POST). | | | | source from which to load a valid Internetwork |
| Flash Memory: Generally referred to simply as "flash", | | | | Operating System (IOS). The router has three sources |
| the IOS images are held here. Flash is erasable and | | | | from which it can load an IOS image, and it's a good |
| reprogrammable ROM. Flash memory content is | | | | idea to know these sources and the order in which the |
| retained by the router on reload. | | | | router will look in each for the IOS image: |
| RAM: Random-Access Memory. Stores operational | | | | 1. Flash memory (the default). |
| information such as routing tables and the running | | | | 2. A TFTP server. (Trivial File Transfer Protocol) |
| configuration file. RAM contents are lost when the | | | | 3. Read-Only Memory (ROM) |
| router is powered down or reloaded. By default, | | | | To change that order, a change must be made to the |
| routers look here first for an Internetwork Operating | | | | configuration register, and we'll talk about that later in |
| System (IOS) file during boot. | | | | the course. It's similar to the Microsoft Registry in that |
| NVRAM: Non-volatile RAM. NVRAM holds the router's | | | | you should never change this value unless you are |
| startup configuration file. NVRAM contents are not lost | | | | sure of the result. |
| when the router is powered down or reloaded. | | | | Once the IOS is found, the router looks for a valid |
| Some important comparisons: | | | | startup configuration file. By default, the router will look |
| RAM contents are lost on reload, where NVRAM and | | | | for the startup configuration file in Non-volatile RAM |
| Flash contents are not. | | | | (NVRAM). |
| NVRAM holds the startup configuration file, where | | | | If no valid startup configuration file is found, the router |
| RAM holds the running configuration file. | | | | enters setup mode, where the router runs the system |
| Let's take a look at the boot process of a Cisco | | | | configuration dialogue, a series of questions involving |
| router, and then talk about the dreaded Setup Mode! | | | | basic router setup. We'll take a look at Setup Mode in |
| The Router Boot Process | | | | the next installment of my exclusive 640-802 CCNA |
| When a Cisco router powers up, it first runs a series | | | | and CCENT certification exam tutorial series! |
| of POSTs (Power-On Self Test). A POST is a series | | | | |