Introduction to routers in a WAN

What is NVRAM?

This page will provide a brief review of routers.
A router is a special type of computer. It has the same basic components as a standard desktop PC. It has a CPU, memory, a system bus, and various input/output interfaces. However, routers are designed to perform some very specific functions that are not typically performed by desktop computers. For example, routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks.
Just as computers need operating systems to run software applications, routers need the Internetwork Operating System (IOS) software to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. Routers use routing protocols to determine the best path for packets. The configuration file specifies all the information for the correct setup and use of the selected, or enabled, routing and routed protocols on a router.
The main internal components of the router are random-access memory (RAM), nonvolatile random-access memory (NVRAM), flash memory, read-only memory (ROM), and interfaces.
RAM has the following characteristics and functions:

Stores routing tables

Holds ARP cache

Holds fast-switching cache

Performs packet buffering as shared RAM

Maintains packet-hold queues

Provides temporary memory for the configuration file of a router while the router is powered on

Loses content when a router is powered down or restarted


NVRAM has the following characteristics and functions:

Provides storage for the startup configuration file

Retains content when a router is powered down or restarted


You can read some more on my Cisco at this link