CCNA2 Chapter 5

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CCNA2 Chapter 5
Managing Cisco IOS Software
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Router Startup Sequence

• Bootstrap

from ROM
Determined from config register 0x2102 says to
look in NVRAM for boot system cmds if none then
Default sequence

• locate load IOS

• flash

• TFTP Server

• ROM (subset of IOS)

• locate load configuration file
• or enter Setup mode

• Default sequence

• NVRAM

• TFTP Server

• console

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Loading IOS Software
Use the configuration registers (show version)
that is saved in NVRAM to determine the sequence
( either from flash, ROM monitor, or RAM ). If
NVRAM lacks boot system commands that the router
can use, the system by default uses the the IOS
software in flash memory.
One can modify the sequence via the
configuration-register command
Router configure terminal
Router(config) boot system flash IOS_filename
Router(config) boot system tftp IOS_filename
tftp_address
Router(config) boot system rom
Ctrl-Z
Router copy running-config startup-config
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Boot Options
Remember multiple images can be stored, so
specify name
Specify name of image, plus IP address of server
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Boot System Command

• To find out if there are boot system commands
  configured on a router, enter any one of the
  following commands
• show running-config
• show config
• show startup-config

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Configuration Register
The configuration register is a 16-bit register
located in NVRAM. The lowest four (4) bits of
the register forms the boot field. To ensure that
the upper 12 bits are not changed, first retrieve
the current values of the configuration register
using the show version command. Then use the
config-register command at the global
configuration mode.

• 1 0 2

Configuration Register
0010 0001 0000 0010
Binary
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Configuration Register
There are 3 monitor modes

• ROM monitor 0xnnn0

• ROM 0xnnn1

• from NVRAM 0xnnn2 TO 0xnnnF

NOTE When one enters the ROM monitor mode, use
the b command at the ROM monitor prompt.
For example to enter the ROM mode do
Router(config) config-register 0x2101
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Configuration Register
If the config-register is set to 0x2102 It tells
the router to look in the startup configuration
for boot system commands.
To enter ROM monitor mode Vargas(config)
config-register 0x2100 Vargas(config)
exit Vargas copy run start Destination
filename startup-config? Building
configuration... OK Vargas reload Proceed
with reload? confirm rommon 1 gt
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Trouble Shooting IOS boot failures

• If a router doesnt boot, then the following
  could be the problem
• configuration file has missing or incorrect boot
  system statement
• incorrect configuration register value
• corrupted flash image
• hardware failure
• Possible solutions
• show run, and look for a boot system statement.
  If incorrect, go to global configuration mode
  and put a no in front of the statement.
• show version, and see if the configuration
  register is incorrectly set
• if the flash is corrupted, one will get an error
  message during boot
• none of the above, then it is possibly a
  hardware error.

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Trouble Shooting IOS boot failures
Remember the configuration register is shown in
show version. The configuration register is NOT
displayed by a show run nor show start.
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IOS File System Overview

• There are two (2) types of software required for
  switches and routers to operate
• Operating system (IOS)
• Configuration (configuration of the
  router/switch)
• Running config is in RAM.
• Startup config is in NVRAM.
• IOS image is in flash
• Some of the functions specified by the config
  file are
• IP addresses of the interfaces
• Routing protocols
• Networks to be advertised

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Trouble Shooting IOS boot failures

• Beginning with version 12 of the IOS, a single
  interface to all the file systems that a router
  uses is provided in Cisco IOS File System (IFS).
• Some prefixes used
• Bootflash
• flash
• ftp
• nvram
• rcp
• Slot0
• Slot1
• system
• Tftp

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IOS Naming Convention
C2600-js-l_121-3.bin
Version number (12.13)
File format (relocatable not compressed)
Feature Set (enterprise w/ extended features)
Hardware Platform (2600)
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Backing up Configuration Files
From the router to TFTP

• copy running-config tftp
• at the prompt, enter the IP address of the TFTP
  server
• enter the name to assign to the config file or
  accept default name
• confirm each choice by typing yes each time

From TFTP server to the router

• copy tftp running-config
• at the prompt, select a host or network config
  file
• at the system prompt,enter the IP address of
  TFTP server where the configuration file is
  located
• at the system prompt, enter the name of the
  config file or accept the default name
• confirm the configuration filename the server
  address that the system supplies

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Using TFTP to Upload an IOS

• Before using TFTP to upload an IOS
• Check memory first (show flash)
• Ping the IP address of your TFTP server
• Know the name of the file you are copying from,
  make sure it is in the default directory

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Troubleshooting IOS boot failures
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Backing up Configuration Files
Another way to managing config files is to use
the Transfer command of the HyperTerminal screen.
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Upgrading/Restore IOS Files

• To restore or upgrade the IOS file, backup the
  original file!!!!
• Do the copy flash tftp
• router will prompt for the IP address of the
  TFTP server.
• router will prompt to erase flash if there is
  not sufficient room available
• a series of es will appear to show the erase
  process.
• ! Will be displayed while the file is
  downloaded.
• After the new flash is down loaded it is verified.

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Backing up the IOS to a TFTP Server
It is a good idea to back up the current IOS
before copying a new one, in case the copy fails
- flash is erased BEFORE the actual copy begins.
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Upgrading/Restore IOS Files
If the IOS image in flash has been erased or
corrupted, one can restore the file from the ROM
monitor mode. It is identified by rommon 1 gt As
an example rommon 1 gt boot flashc2600-is-mz.1
21-5
One can also us Xmodem from ROMmon rommon 1 gt
Xmodem -c c2600-is-mz.122-10a.bin
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X-Modem