Cisco router components: Memory types

RAM

Stores packet buffers, ARP cache, routing table, software code and data structures necessary for router operation. Running configuration and decompressed IOS code is stored in RAM

ROM

Contains basic software for hardware testing and initialization

Flash

Stores IOS and backup configuration files. Not volatile

NVRAM (non-volatile RAM)

Saves router configuration

Cisco router components: Software

POST

Power-on Self-Test. Stored in ROM. Checks basic router functions

Bootstrap

In ROM. Initiates router and loads IOS

ROM Monitor

In ROM. Used for tests and troubleshooting. Basic interface for troubleshooting low-level issues

IOS (Internetwork Operating System)

Provides all of the higher-level router functionalities

Configuration Register

• Controls various low-level settings
  • Tells router to load or ignore NVRAM configuration at startup
  • Terminal behaviour (e.g. serial speed)
• Current value can be seen with show version
• Most common settings are:
  • 0x2102 - normal
  • 0x2142 - ignore configuration

Where is the configuration?

• Router always has two configurations
  • running-config
    • In RAM. Shows which parameters are currently in use.
    • show running-config
    • Modified with configure terminal command
  • startup-config
    • In NVRAM. Loaded by router in next reboot
    • This is where the running-config is saved
    • show startup-config

Configuration backups

• You can store configuration in other places
  • In router’s Flash memory
  • In a server, via TFTP
• Can be copied around with copy command
  • copy running-config startup-config
    • or write memory (old style)
  • copy running-config tftp
  • copy startup-config tftp
  • copy startup-config flash:saved-config
  • copy flash:saved-config startup-config

When the router has no configuration....

• It asks Would you like to enter the initial configuration dialog? [yes/no]:
• Just say n (no)
  • otherwise you get a tedious series of questions to answer

Access modes

• User EXEC
  • Limited access. Show interface state, etc.
  • Router>
• Privileged EXEC (enabled mode)
  • Detailed examination, manipulate configuration and files, run tests, debugging, etc.
  • Router#
• ROM Monitor
  • Password recovery and IOS installation
  • rommon 1>

Management input sources

Console

Direct access via serial port

Auxiliary Port

Access via Modem

Virtual Terminals (VTY)

Telnet/SSH

Changing the configuration

• Commands are activated immediately
• Be careful when typing!
• When working on serial console or via Telnet or SSH, commands can be copied from a text file and pasted into the terminal

Changing the configuration (contd)

router>
router>enable
... type password ...
router#
router# configure terminal
router(config)#
... type commands ...
router(config)# end
router# write memory

How to tell where you are

Router> - USER EXEC
Router# -  PRVILEDGED EXEC
Router(config) - Global configuration
Router(config-if) - Interface configuration
Router(config-subif) - Sub-interface configuration
Router(config-route-map) - Route-map configuration
Router(config-router) - Routing protocol configuration
Router(config-line) - Line configuration
rommon 1> - ROM Monitor

Context Help

• Use "?" to obtain a list of commands available in your current configuration mode

  Router(config)#?
  Configure commands:
    aaa                         Authentication, Authorization and Accounting.
    aal2-profile                Configure AAL2 profile
    access-list                 Add an access list entry
    alarm-interface             Configure a specific Alarm Interface Card
    alias                       Create command alias
    appfw                       Configure the Application Firewall policy
    application                 Define application
    archive                     Archive the configuration
    arp                         Set a static ARP entry
    ...
  

Online help

• Use "?" also to see all possible parameters to an incomplete command:

  <Router(config)#username ?
    WORD  User name
  Router#show ?
    aaa                       Show AAA values
    aal2                      Show commands for AAL2
    access-expression         List access expression
    access-lists              List access lists
    accounting                Accounting data for active sessions
    ...
  

Command completion

• Use the Tab key to complete a command

  router(config)#int<TAB>
  router(config)#interface et<TAB>
  router(config)#interface ethernet 0
  router(config-if)#ip add<TAB>
  router(config-if)#ip address n.n.n.n m.m.m.m
  

• You can just type the abbreviated form if it's unambigious

router(config)#int e 0
router(config-if)#ip add n.n.n.n m.m.m.m

Moving faster around the command line

• Move within command history
  • [Cursor Up] - Previous command
  • [Cursor Down] - Next command
• Line editing
  • [Cursor Left] and [Right] - move within the line
  • Ctrl-a : move to beginning of line
  • Ctrl-e : move to end of line
  • Ctrl-k : delete until end of line

Verifying and troubleshooting

show running-config
show run interface f0/0
show ip int brief
debug ip ospf hello / events / adj
show log
show version