Basic Cisco Router Configuration and Management
Random-Access Memory similar to the function as RAM in PCs. This is where the IOS runs
its processes. It also contains the running configuration, routing and other tables as well as
This Read-Only Memory stores a older 'lite' IOS used to boot the router for the very first time,
or when the Flash memory is erased or corrupted.
This piece of 'flash-able' memory stores the IOS image, the operating system of the router.
In contradiction to normal RAM, Non-Volatile Random-Access Memory is a special type of
memory that doesn't lose its content when the router's power is turned off. It stores the startup
configuration and the configuration register.
The NVRAM has a special location that contains the 16-bit configuration register. Every time
the router boots it reads this value. The config-register value is a hexadecimal value ranging
from from 0x0000 to 0xFFFF and can be set byusing the config-register command. The most
important portion of the configuration register to understand for the exam is the boot field (bit
0 through 3, hexadecimal range 0x0000-0x000F). The boot field value is used to specify from
which location the IOS image should be loaded or bypassed even during startup.
Boot field Meaning
0x0 The router will enter ROM monitor mode and remain at the system bootstrap
0x1 The IOS image stored in ROM will be loaded.
0x2-0xF The router will boot as normal and load the default IOS image stored in Flash
and enables boot system commands.
The remaining 12 bits of the configuration register are used for various functions such as
enabling/disabling the Break function, setting the Console line speed, bypassing NVRAM,
and controlling the broadcast address. To change the configuration register you have to enter
be in global configuration mode. Use the command configure terminal often abbreviated to
conf t in privileged EX