CCNA Routing & Switching:Internal components
1. Introduction to Router’s Internal Components
2. Internal Components RAM NVRAM Flash ROM Interfaces Console Auxiliary
3. RAM Temporary storage for router configuration files RAM content is lost on power down or restart Stores… Routing tables ARP cache Fast switching cache Packet buffering
4. NVRAM Non-volatile RAM Stores backup/startup configuration files Content is not lost when router is powered down or restarted.
5. 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 stored Retained on power down
6. 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
7. Interfaces Network connections through which packets enter and exit the router Attached to the motherboard or as separate modules on “modular” routers.
8. As the router is booted, the following is loaded into RAM’s Working Storage. RAM Specifics Command Executive Internetwork Operating System (IOS) Programs Active Config File Tables Buffers
9. Programs include the bootstrap program that • tests the equipment (POST) • and locates the IOS. RAM Specifics
10. RAM Specifics Once the IOS is located by the bootstrap program, it is loaded in to RAM.
11. 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.
12. 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.
13. RAM Specifics The tables are loaded from the configuration file including… • ARP Tables • Routing Tables
14. RAM Specifics Finally, all leftover memory in RAM is used as the buffer for processing incoming and outgoing packets.
15. Router Status Commands “Show” commands yield status information about various router components, as shown on the next slides…
16. 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)
17. show running-config displays the active configuration file loaded in RAM
18. show startup-config displays the backup configuration file stored in NVRAM # copy run start
19. show protocols displays the status of all configured Layer 3 protocols displays the status of all interfaces
20. show ip route displays the routes to all networks known to the router
21. 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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