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Chapter 7

ECE495 Chapter Notes - Chapter 7: Fast Ethernet, Trivial File Transfer Protocol, Flash Memory

Electrical and Computer Engineering
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Router Components v1.00 – Aaron Balchunas
* * *
All original material copyright © 2007 by
Aaron Balchunas (aaron@routeralley.com),
unless otherwise noted. All other material copyright © of their respective owners.
This material may be copied and used freely, but may not be altered or sold without the expressed written
consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
- Router Components -
Router Memory Components
Cisco routers (and switches) generally contain four types of memory:
ROM (Read-Only Memory)
NVRAM (Non-Volatile RAM)
RAM (Random-Access Memory)
ROM contains a bootstrap program called ROM Monitor (or ROMmon).
When a router is powered on, the bootstrap runs a hardware diagnostic
called POST (Power-On Self Test).
If POST completes successfully, the bootstrap then attempts to locate and
load the Cisco IOS (Internetwork Operating System) stored in Flash
memory. Flash memory can be erased or overwritten, thus making the Cisco
IOS upgradeable. The Cisco IOS is covered in great detail in other guides.
If the bootstrap cannot find the IOS in Flash, a stripped-down version of the
IOS that will be loaded from ROM instead. The contents of ROM cannot be
altered or erased; the entire ROM chip must be replaced if an upgrade/repair
is necessary.
If the bootstrap does find the IOS in Flash, it is loaded into RAM and
attempts to find a Startup Configuration (startup-config) file in NVRAM.
NVRAM is non-volatile, thus its contents will survive a power-cycle.
If the IOS cannot find a startup-config file in NVRAM, it will attempt to
load a configuration file from a TFTP server (this request is broadcasted to If no TFTP server responds, the IOS will enter Initial
Configuration Mode, a series of interactive questions intended for quick
configuration of the router.
If the IOS does find a startup-config file in NVRAM, this file is loaded into
RAM, and becomes the Running Configuration (running-config). RAM is
a volatile memory, and thus its contents will be lost if the router is power-
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