Chabot College
ELEC 99.08
Router Components & “Show” Commands
CISCO NETWORKING ACADEMY
Internal Components
RAM
Console
Auxiliary
CISCO NETWORKING ACADEMY
NVRAM Flash
Interfaces
ROM
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
CISCO NETWORKING ACADEMY
NVRAM
• Non-volatile RAM
• Stores backup/startup configuration
files
• Content is not lost when router is
powered down or restarted.
CISCO NETWORKING ACADEMY
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
CISCO NETWORKING ACADEMY
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
CISCO NETWORKING ACADEMY
Interfaces
• Network connections through which
packets enter and exit the router
• Attached to the motherboard or as
separate modules on “modular”
routers.
CISCO NETWORKING ACADEMY
RAM Specifics
As the router is booted, the following
is loaded into RAM’s Working Storage.
Internetwork
Operating
System
NVRAM (IOS)
Flash
ROM
RAM
Command
Executive
RAM
Console
Interfaces
Active
Auxiliary
Programs
CISCO NETWORKING ACADEMY
Config
File
Tables
Buffers
RAM Specifics
Programs include the bootstrap program that
• tests the equipment (POST)
• and locates the IOS.
RAM
Programs
CISCO NETWORKING ACADEMY
RAM Specifics
Once the IOS is located by the bootstrap
program, it is loaded in to RAM.
Internetwork
Operating
System
(IOS)
RAM
Programs
CISCO NETWORKING ACADEMY
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.
Internetwork
Operating
System
(IOS)
RAM
Command
Executive
Programs
CISCO NETWORKING ACADEMY
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.
Internetwork
Operating
System
(IOS)
RAM
Command
Executive
Programs
CISCO NETWORKING ACADEMY
Active
Config
File
RAM Specifics
The tables are loaded from the configuration file
including...
• ARP Tables
• Routing Tables
Internetwork
Operating
System
(IOS)
RAM
Command
Executive
Programs
CISCO NETWORKING ACADEMY
Active
Config
File
Tables
RAM Specifics
Finally, all leftover memory in RAM is used as the
buffer for processing incoming and outgoing
packets.
Internetwork
Operating
System
(IOS)
RAM
Command
Executive
Programs
CISCO NETWORKING ACADEMY
Active
Config
File
Tables
Buffers
Router Status Commands
• “Show” commands yield status
information about various router
components, as shown on the next
slides...
CISCO NETWORKING ACADEMY
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)
CISCO NETWORKING ACADEMY
Example Show Commands
show version
Try it now with Router e-SIM:
– Start Router e-SIM
– Give all your routers a configuration:
• click SHOW DONE
• in the row of SET buttons at the bottom, click A, B, C, D, E
• click HIDE DONE
– Login - Password - cisco
– Enable privileged mode: Secret Password: class
CISCO NETWORKING ACADEMY
Example Show Commands
show running-config
– displays the active configuration file loaded in RAM
Try it now with Router e-SIM
CISCO NETWORKING ACADEMY
Example Show Commands
show startup-config
– displays the backup configuration file stored in NVRAM
Try it now with Router e-SIM:
• Your router will not have a startup configuration until you
save the running configuration to the startup file:
Lab_A# copy run start
• Now try show start again
CISCO NETWORKING ACADEMY
Example Show Commands
show interfaces
– displays statistics for all interfaces configured on the
router
Try it now with Router e-SIM.
CISCO NETWORKING ACADEMY
Example Show Commands
show protocols
– displays the status of all configured Layer 3 protocols
– displays the status of all interfaces
Try it now with Router e-SIM.
CISCO NETWORKING ACADEMY
Example Show Commands
show ip route
– displays the routes to all networks known to the router
Try it now with Router e-SIM.
CISCO NETWORKING ACADEMY
Example Show Commands
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.
Router e-SIM doesn’t understand this command,
so you’ll need to try it on a real router...
CISCO NETWORKING ACADEMY
Router#show interfaces
Router#show version
Router#show flash
RAM
NVRAM
Flash
Internetwork Operating System
Router#show processes CPU
Router#show protocols
Tables
and
Buffers
Router#show ip route
Router#show buffers
Router#show running-config
CISCO NETWORKING ACADEMY
Interfaces
Active
Programs Configuration
File
Backup
Operating
Configuration
Systems
File
Router#show startup-config