IOS

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IOS

• Internet Operating System (IOS)

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IOS

• Internet Operating System
• What are its components
• How does it work

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IOS Components
Non Volatile RAM
Random Access Memory
EPROM Erasable Programmable Memory
Trivial File Transfer Protocol Usually a hard disk
Read Only Memory
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IOS Components
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IOS Components
Memory
Memory
Configuration
IOS
Back up server for configs and IOS
Memory
Loads boot instruction set (bootstrap) to RAM on
startup
Memory
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Router Startup Sequence

• Bootstrap

ROM loads bootstrap to RAM on start-up
Default sequence

• locate load IOS

• flash

• TFTP Server

• ROM

• locate load configuration file
• or enter Setup mode

• NVRAM

• TFTP Server

• console

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Locating IOS Software (Operating System)
Use the configuration register that is saved in
NVRAM to determine the sequence. (show version)
provides the register address If NVRAM does not
contain boot system commands that the router can
use, the system by default will then go to flash
memory.
You 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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Configuration Register
The configuration register is a 16-bit register
located in NVRAM. The lowest four order bits of
the register consists of the boot field.
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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 enter
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.
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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
• incorrect boot system statement
• incorrect configuration register value
• corrupted flash image
• hardware failure
• Possible solutions
• do a s run, and look for a boot system
  statement. If incorrect, go to
• global configuration mode and put a no in front
  of the statement.
• do a s version, and see if the configuration
  register is incorrectly set
• if the flash is corrupted, an error message
  during boot will appear
• none of the above, then it is possibly a
  hardware error. Call TAC.

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Trouble Shooting - IOS boot failures
Remember the configuration register is shown in
show version (s ver). The configuration register
is NOT displayed in show run or show start.
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IOS File System Overview

• There are two types of software required for
  switches routers to operate
• Operating system (IOS)
• Configuration
• IOS image is in flash
• Running config is in RAM.
• Startup config is in NVRAM.
• Some of the functions specified by the config
  file are
• IP addresses of the interfaces
• Routing protocols
• Networks to be advertised
• NOTE To restore a previously good copy of the
  config file which is in NVRAM type copy start run

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IOS File System Overview

• Beginning with version 12 of the IOS, a single
  interface to all the file systems that a router
  uses is provided in the 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-1_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 assigned 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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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

• If you restore or upgrade the IOS file, backup
  the original file first!!!!
• Do 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.
• a series of !s will be displayed while the
  file is downloading.
• After the new flash successfully down loads it is
  then verified.

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Upgrading/restore IOS files
If the IOS image in flash has been erased or
corrupted, you can restore the file while in ROM
monitor mode. It is identified by rommon 1 gt As
an example rommon 1 gt boot flashc2600-is-mz.1
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You can also us Xmodem from ROMmon rommon 1 gt
Xmodem -c c2600-is-mz.122-10a.bin
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IOS Components REVIEW
Memory
Memory
Configuration
IOS
Back up server for configs and IOS
Memory
Loads boot instruction set (bootstrap) to RAM on
startup
Memory