8. internal components of router
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Transcript of 8. internal components of router
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Introduction to Router’s Internal Components
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Internal Components
RAM NVRAM Flash ROM
InterfacesConsoleAuxiliary
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RAM
Temporary storage for router configuration files
RAM content is lost on power down or restartStores...
Routing tables ARP cache Fast switching cache Packet buffering
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NVRAM
Non-volatile RAMStores backup/startup configuration filesContent is not lost when router is powered
down or restarted.
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Flash
EEPROM (Electronically Erasable Programmable Read-Only Memory)
Holds the Cisco IOS (Internetworking Operating System)
Allows updating of software without replacing the Flash chip
Multiple versions of IOS can be storedRetained on power down
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ROM
Contains POST (Power On Self Test)A bootstrap program
(loads the Cisco IOS)And mini-operating system software:
Backup, trimmed down version of the IOS Upgrades require installing new chip set
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Interfaces
Network connections through which packets enter and exit the router
Attached to the motherboard or as separate modules on “modular” routers.
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As the router is booted, the following is loaded into RAM’s Working Storage.
RAM Specifics
CommandExecutive
InternetworkOperating
System(IOS)
ProgramsActiveConfig
FileTables Buffers
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Programs include the bootstrap program that • tests the equipment (POST) • and locates the IOS.
RAM Specifics
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RAM Specifics
Once the IOS is located by the bootstrap program, it is loaded in to RAM.
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RAM Specifics
Part of the IOS is the Command EXEC. This is the program that translates the commands you type into a language that the IOS can understand.
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RAM Specifics
Once the IOS is initialized, it looks for an active configurations file (usually in NVRAM) and loads it. This file tells the router specifically what to do.
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RAM Specifics
The tables are loaded from the configuration file including...• ARP Tables• Routing Tables
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RAM Specifics
Finally, all leftover memory in RAM is used as the buffer for processing incoming and outgoing packets.
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Router Status Commands
“Show” commands yield status information about various router components, as shown on the next slides...
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Example Show Commands
show version displays:
configuration of the system hardware IOS version names and sources of configuration files the current setting of the configuration register
(used in password recovery)
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show running-config displays the active configuration file loaded in
RAM
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show startup-config displays the backup configuration file stored in
NVRAM # copy run start
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show protocols displays the status of all configured Layer 3 protocols displays the status of all interfaces
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show ip route displays the routes to all networks known to the router
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show controller displays information about each interface controller.
Key: shows whether serial interface is DTE or DCE (setting determined by the connected cable).
Important mainly in Cisco lab, where some routers are configured DCE.
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