Cisco CCNA Study Guide - Router Alley

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CCNA Study Guide v2.62 – Aaron Balchunas 136 ________________________________________________ Part II The Cisco IOS ________________________________________________ * * * All original material copyright © 2013 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.
CCNA Study Guide v2.62 – Aaron Balchunas 137 Router Memory Components Section 10 - Router Components - Cisco routers (and switches) generally contain four types of memory: • ROM (Read-Only Memory) • Flash • 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 255.255.255.255). 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 powercycled. * * * All original material copyright © 2013 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.
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