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Operating Cisco Routers

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Operating Cisco Routers

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Cisco CCNA Study Guide

By Cbrzana

Table Of Contents

Operating Cisco Routers

Access the CLI through Terminal, through dialup device (modem) on Auxiliary port, or by using Telnet.

Console - > Router = Rollover Cable (Pin 1 to Pin 8, Pin 2 to Pin 7, etc)

Modem - > Auxiliary Port = Straight-Through Cable (Pin 1 to Pin 1, etc)

  • Passwords required for Dialup and Telnet access, so first must be set through Terminal

Password Setups

Access From Configuration
Console Line console 0
Password miracle
Auxiliary Line aux 0
Password temple
Telnet Line vty 0 4
Password whoaboy

Vty = Virtual teletypes/terminals, 0 4 designates 0,1,2,3, and 4 connection settings

- > 16 vtys now enabled by default in current IOS


1. User Exec Mode (User Mode)

a. User can look at settings, but not touch

2. Privileged Exec Mode (Privileged Mode)

a. Able to alter (privileged changes can be made)

b. Enable command enters mode

c. Disable command exits mod

3. Configuration Mode

a. Config terminal command

b. Changes take place upon hitting Enter

CLI Help Features

What is typed Result
? All commands for this mode
Help Text describing how to get help
Command ? Describe all first parameter options
Com? List of commands that begin with "Com"
command parm? Help on all parameters that begin with "parm"
Command parm[Tab] Pressing tab either autocompletes the word, or does nothing
Command parm1 ? Lists all the next parameters w/ description

By default, stores last 10 commands in history buffer.

- >To change size, terminal history size x (x is value 0-256)

Enhanced Editing Mode

Keyboard Command Result
Up arrow / Ctrl+P Most recently used command displayed
(P = previous)
Down arrow / Ctrl+N If you have gone too far in history buffer, moves one step towards most recently used command. (N = next)
Left arrow / Ctrl+B Moves cursor back one w/o deleting character.
Right arrow / Ctrl+F Moves cursor forward one w/o deleting character.
Backspace Moves cursor back one and deletes character.
Ctrl+A Acts like "Home" button
Ctrl+E Acts like "End" button
Esc+B Moves cursor back one word
Esc+F Moves cursor forward one word
Ctrl+R Creates new command prompt, and all characters typed since last command prompt was written.

Turn off = no terminal editing

Turn on = terminal editing

Would turn off if running advanced scripts, enhanced editing mode could interfere with.

Debug and Show

Show - > Lists facts about router's operational status that router already knows

Debug - > Tells router to spend some CPU cycles to provide user with additional logging information (Syslog Messages). Can overwhelm router and crash it.

- > View messages on Telnet by Terminal monitor command
- > no debug all turns debugs off

Configuring Cisco IOS Software

Interface command configures specific interfaces

Ex: interface serial 1
  • Prompt changes when you move from one mode to another
  • Enable password or enable secret logins with a password or encrypted password, respectively.
  • If both configured, use enable secret

Banner motd

  1. Text

More Text

  1.  ? Ends "Message of the Day"

Router Memory, Processors, and Interfaces

Different types of memory used:

1. Flash: Holds the IOS Software

2. NVRAM: Startup Configuration

3. RAM: Running Configuration/Working memory

4. ROM: Basic Cisco IOS Software (tells where to find IOS)

  • RAM is only volatile memory of the 4

Show running-config displays contents of RAM (Old = write term)

Show startup-config displays contents of NVRAM (Old = show config)

To copy configuration from one source to another:

copy {tftp | running-config | startup-config} {tftp | running-config | startup-config}

  • copies (from x - > to x)

To erase contents of NVRAM:

1. Write erase

2. Erase startup-config

3. Erase nvram: ? Preferred command to use

To reload router: reload

  • If router reloaded after NVRAM erased, enters setup mode (initial configuration)
  • After settings selected, choose 2 to save settings (saves to both NVRAM and RAM)
  • 0 exits to the command prompt
  • 1 starts the process over again
  • Cntrl+C also exists setup process

Upgrading Cisco IOS Software Image into Flash Memory

1. Obtain IOS Image from Cisco

2. Download to TFTP/FTP Server to default directory

3. Issue copy command from router into Flash memory

a. Copy tftp flash

b. Also needs IP of server, filename of IOS, erase old file, enough space?

4. show flash command verifies new version after installation

5. reload in order to use new IOS

Note: In older version, you needed to boot IOS in ROM so that IOS in Flash was in read/write state. New copy tftp flash command does this automatically

- > process called Rxboot Mode, can't route packets in this mode, but can send/receive. So, TFTP server must either be on same subnet, or have default router mapped to it.

Cisco IOS Boot Sequence

1. Router performs POST, verify/discover hardware

2. Loads and runs bootstrap code from ROM

3. Router finds IOS/other software and loads it

4. Router finds startup-config, loads it into current-config

- > POST code only thing admin can't change

- > Only part typically changed is the location of IOS/software

Operating System Typical Location Purpose
Full-featured IOS Flash All features
Limited-function (Rxboot) ROM Used when Flash memory is broken and need to copy new IOS from TFTP
ROMMON (ROM Monitor) ROM Low-level debugging, password recovery

There are two methods that tell the router what OS to load:

1. Configuration register

a. 16-bit software register, set using config-register global command

b. Default value is hex: 2102

c. Boot field is low order bits: 0 = ROMMON, 1=Rxboot

2. boot system configuration command

a. Used if more than one full-feature IOS exists

b. If no boot system commands, loads first file in Flash memory

Boot System Commands Result
No boot command First file in flash, broadcast TFTP, IOS in ROM, and lastly ROMMON
Boot system ROM IOS from ROM loaded
Boot system Flash First file in FLASH loaded
Boot system Flash filename Specify filename in Flash to load
Boot system tftp filename [Address] Filename loaded from TFTP
Multiple boot commands Load first boot, if fails, load second, etc.

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