Cisco Router Hardware

Hardware Components

There are 7 major internal components of a router:

• CPU
• RAM
• NVRAM
• Flash
• ROM
• Console

• Interfaces

CPU
The CPU performs functions just as it does in a normal PC. It executes commands given by the IOS using other hardware components. High-end routers may contain multiple processors or extra slots to add more CPUs later.

RAM
Random Access Memory; this component is dynamic. Meaning, its content changes constantly. The main role of the RAM is to: hold the ARP cache, Store routing tables, hold fast-switching cache, performs packet buffering, and hold queues. It also provides temporary memory for the configuration file of the router while the router is powered on. However, the RAM loses content when router is restarted or powered off. This component is upgradeable!

NVRAM
Nonvolatile RAM is used to store the startup configuration files. This type of RAM does not lose its content when the router is restarted or powered off.

Flash
Flash memory is very important because it saves your ass if you screw up the operating system configuration. It holds the Cisco IOS image file, as well as backups. This flash memory is classified as an EEPROM (Electronically Erasable Programmable Read Only Memory). The flash ROM is upgradeable in most Cisco routers.

ROM
The ROM performs the same operations as a BIOS. It holds information about the systems hardware components and runs POST when the router first starts up. This component can be upgraded by "unplugging" the chip and installing a new one. A ROM upgrade ensures newer versions of the IOS.

Console
The console consists of the physical plugs and jacks on the router. The purpose of the console is to provide access for configurations.

Interfaces
The interfaces provide connectivity to LAN, WAN, and Console/Aux. They can be RJ-45 jacks soldered onto the motherboard, transceiver modules, or card modules. Cisco routers, especially the higher-end models, can be configured in many different ways. They can use a combination of transceivers, card modules and onboard interfaces.