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IOS

Internet Operating System (IOS). IOS. Internet Operating System What are its components How does it work. IOS. NVRAM. Flash. TFTP. RAM. Rom. IOS Components. Non Volatile RAM. Random Access Memory. EPROM – Erasable Programmable Memory. Trivial File Transfer Protocol

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IOS

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  1. Internet Operating System (IOS) IOS

  2. Internet Operating System What are its components How does it work IOS

  3. NVRAM Flash TFTP RAM Rom IOS Components Non Volatile RAM Random Access Memory EPROM – Erasable Programmable Memory Trivial File Transfer Protocol Usually a hard disk Read Only Memory

  4. NVRAM Start Flash TFTP RAM Run Rom IOS Components

  5. NVRAM Start Flash TFTP RAM Run Rom IOS Components Memory Memory Configuration IOS Back up server for configs and IOS Memory Memory Loads boot instruction set (bootstrap) to RAM on startup

  6. Router Startup Sequence • Bootstrap ROM loads bootstrap toRAM on start-up Default sequence: • locate & load IOS • flash • TFTP Server • ROM • locate & load configuration file • or enter ‘Setup’ mode • NVRAM • TFTP Server • console

  7. 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

  8. Configuration Register The configuration register is a 16-bit register located in NVRAM. The lowest fourorder bits of the register consists of the boot field.

  9. 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

  10. Configuration Register • If the config-register is set to 0x2102 • It tells the router to look in the startup configuration for boot system commands.

  11. Trouble Shooting - IOS boot failures • If a router doesn’t 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.

  12. 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.

  13. 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

  14. 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:

  15. 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)

  16. 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

  17. Backing up configuration files Another way to managing config files is to use the Transfer command of the HyperTerminal screen.

  18. 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 “e”s 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.

  19. 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 > • As an example: • rommon 1 > bootflash:c2600-is-mz.121-5 • You can also us Xmodem from ROMmon: • rommon 1 > Xmodem -c c2600-is-mz.122-10a.bin

  20. NVRAM Start Flash TFTP RAM Run Rom IOS Components REVIEW Memory Memory Configuration IOS Back up server for configs and IOS Memory Memory Loads boot instruction set (bootstrap) to RAM on startup

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