Cisco Certification – Basics of Cisco Routers

Cisco has quite a few totally different routers, amongst them are the favored 1600 sequence, 2500 sequence and 2600 sequence. The ranges begin from the 600 sequence and go as much as the 12000 sequence (now we’re speaking about some huge cash). All of the above gear runs particular software program known as the Cisco Internetwork Working System or IOS. That is the kernel of their routers and most switches. Cisco has created what they name Cisco Fusion, which is meant to make all these gadgets run the identical working system.

We’re going to start with the essential parts which make up a Cisco router (and switches) and I shall be explaining what they’re used for, so seize that tea or espresso and let’s get going !

The essential parts of any Cisco router are

  1. Interfaces
  2. The Processor (CPU)
  3. Internetwork Working System (IOS)
  4. RXBoot Picture
  5. RAM
  6. NVRAM
  7. ROM
  8. Flash reminiscence
  9. Configuration Register

Now I simply hope you have not seemed on the record and thought “Stuff this, it appears to be like arduous and complex” as a result of I guarantee you, it is much less painful than you may suppose ! In truth, when you learn it a few instances, you will see that all of it straightforward to recollect and perceive. Interfaces These enable us to make use of the router ! The interfaces are the assorted serial ports or ethernet ports which we use to attach the router to our LAN. There are a variety of various interfaces however we’re going to hit the essential stuff solely. Listed here are a few of the names they’ve given a few of the interfaces: E0 (first Ethernet interface), E1 (second Ethernet interface). S0 (first Serial interface), S1 (second Serial interface), BRI 0 (first B channel for Primary ISDN) and BRI 1 (second B channel for Primary ISDN).

It’s important to join a digital telephone to an ISDN line and since that is an ISDN router, it has this feature with the router. I ought to, nonetheless, clarify that you do not usually get routers with ISDN S/T and ISDN U interfaces collectively. Any ISDN line requires a Community Terminator (NT) put in on the buyer’s premises and also you join your gear after this terminator. An ISDN S/T interface does not have the NT gadget in-built, so that you want an NT gadget to be able to use the router. Alternatively, an ISDN U interface has the NT gadget in-built to the router.

Other than the ISDN interfaces, we even have an Ethernet interface that connects to a tool in your LAN, often a hub or a pc. If connecting to a Hub uplink port, then you definitely set the small change to “Hub”, but when connecting to a PC, you might want to set it to “Node”. This change will merely convert the cable from a straight by (hub) to a x- over (Node):

The Config or Console port is a Feminine DB9 connector which you join, utilizing a particular cable, to your computer systems serial port and it permits you to instantly configure the router.The Processor (CPU) All Cisco routers have a predominant processor that takes care of the primary features of the router. The CPU generates interrupts (IRQ) to be able to talk with the opposite digital parts within the router. The routers make the most of Motorola RISC processors. Often the CPU utilisation on a traditional router would not exceed 20 %.


The IOS is the primary working system on which the router runs. The IOS is loaded upon the router’s bootup. It often is round 2 to 5MB in dimension, however generally is a lot bigger relying on the router sequence. The IOS is presently on model 12, and so they periodically releases minor variations each couple of months e.g 12.1 , 12.3 and so forth. to repair small bugs and likewise add additional performance.

The IOS provides the router its varied capabilities and will also be up to date or downloaded from the router for backup functions. On the 1600 sequence and above, you get the IOS on a PCMCIA Flash card. This Flash card then plugs right into a slot positioned in the back of the router and the router hundreds the IOS “picture” (as they name it). Often this picture of the working system is compressed so the router should decompress the picture in its reminiscence to be able to use it.

The IOS is likely one of the most important components of the router, with out it the router is just about ineffective. Simply take into account that it isn’t essential to have a flash card (as described above with the 1600 sequence router) to be able to load the IOS. You’ll be able to truly configure most routers to load the picture off a community tftp server or from one other router which could maintain a number of IOS photographs for various routers, wherein case it’s going to have a big capability Flash card to retailer these photographs.

The RXBoot Picture

The RXBoot picture (often known as Bootloader) is nothing greater than a “cut-down” model of the IOS positioned within the router’s ROM (Learn Solely Reminiscence). In case you had no Flash card to load the IOS from, you’ll be able to configure the router to load the RXBoot picture, which might provide the capacity to carry out minor upkeep operations and produce varied interfaces up or down.


The RAM, or Random Entry Reminiscence, is the place the router hundreds the IOS and the configuration file. It really works precisely the identical manner as your laptop’s reminiscence, the place the working system hundreds together with all the assorted applications. The quantity of RAM your router wants is topic to the dimensions of the IOS picture and configuration file you might have. To offer you a sign of the quantities of RAM we’re speaking about, most often, smaller routers (as much as the 1600 sequence) are proud of 12 to 16 MB whereas the larger routers with bigger IOS photographs would want round 32 to 64 MB of reminiscence. Routing tables are additionally saved within the system’s RAM so you probably have giant and complicated routing tables, you’ll clearly want extra RAM ! Once I tried to improve the RAM on a 1600 router, I unscrewed the case and opened it and was amazed to discover a 72 pin SIMM slot the place you wanted to connect the additional RAM. For many who do not know what a 72 pin SIMM is, it is principally the kind of RAM the older Pentium socket 7 CPUs took, again in ’95. Such a reminiscence was changed by at this time’s customary 168 pin DIMMs or SDRAM.The

NVRAM (Non-Unstable RAM)

The NVRAM is a particular reminiscence place the place the router holds its configuration. Whenever you configure a router after which save the configuration, it’s saved within the NVRAM. This reminiscence will not be huge in any respect in comparison with the system’s RAM. On a 1600 sequence, it is just 8 KB whereas on greater routers, just like the 2600 sequence, it’s 32 KB. Usually, when a router begins up, after it hundreds the IOS picture it’s going to look into the NVRAM and cargo the configuration file to be able to configure the router. The NVRAM will not be erased when the router is reloaded and even switched off.

ROM (Learn Solely Reminiscence)

The ROM is used to start out and preserve the router. It incorporates some code, just like the Bootstrap and POST, which helps the router do some fundamental checks and bootup when it is powered on or reloaded. You can not alter any of the code on this reminiscence because it has been set from the manufacturing unit and is Learn Solely.

Flash Reminiscence

The Flash reminiscence is that card I spoke about within the IOS part. All it’s, is an EEPROM (Electrical Eraseable Programmable Learn Solely Reminiscence) card. It matches right into a particular slot usually positioned in the back of the router and incorporates nothing greater than the IOS picture(s). You’ll be able to write to it or delete its contents from the router’s console. Often it is available in sizes of 4MB for the smaller routers (1600 sequence) and goes up from there relying on the router mannequin.

Configuration Register

Maintaining issues easy, the Configuration Register determines if the router goes in addition the IOS picture from its Flash, tftp server or simply load the RXBoot picture. This register is a 16 Bit register, in different phrases has 16 zeros or ones. A pattern of it in Hex can be the next: 0x2102 and in binary is: 0010 0001 0000 0010.

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