Learning by Doing: CISCO Certified Network ... - SCN Research

Objectives:
To more fully understand how routers hardware and software work together.
Tools and Materials:
CISCO router
Workstation with Hyperterminal program
(1) rollover cable
Router Boot Sequence
Background:
All routers essentially have 5 types of logic processors: CPU, FLASH, ROM, RAM, and
NVRAM. Finding out information about these devices from CISCO or on the Internet is
problematic, to say the least. Here we will discuss the block diagram of generic routers,
how to identify the components on 2500/2600 router boards (if you dare to open one up),
and how to “see” those processes during the router boot sequence.
Let’s start by looking at a generic block diagram of a router:
CPU FLASH ROM RAM NVRAM
Network
Modules
BUS
I/O Port
MSC
I/O Port
MSC
CPU-Central Processing Unit (usually Motorola)
FLASH-Holds image of OS (ROM-type) (does not erase when off)
ROM-Holds POST and Bootstrap Programs (does not erase when off)
RAM/DRAM-Holds routing tables, packet buffering, etc. (erases when off)
NVRAM-Holds configuration files (does not erase when off)
MSC-Media Specific Converter
The bus is simply a central transmission point for our bits. The top row of components is
physically attached to the motherboard (CPU, NVRAM, etc). The bottom row of
components (I/O Port MSC) is the Ethernet, Aux., serial connections, etc. Notice there
are no “moving” parts in a router. Computer hard drives have moving parts, which
require frequent replacement. Since routers do not have any moving parts they are said to
“last longer.” Let’s turn our discussion to the boot sequence and how all of these
components inter-relate with the software by looking at a boot sequence block diagram:
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