IOS Internetwork Operating System

IOS modes and ROM monitor Router>EXEC mode Router#Priviledge mode Router(config)#Global config m Router(config-if)#Interface config m rommon >ROM Monitor

EXEC mode Example commands: show, clear, ping, traceroute, ssh, telnet, … Switch from EXEC to Priviledge mode Router> enable Router#

Priviledge mode Example commands: configure, debug, write … + all EXEC commands Switch to Configuration mode Router# configure terminal Router(config)#

Configuration mode Example commands: interface Router(config-if)# router Router(config-router)# Navigation: Router(config-if)#exit Go 1 level back in Config mode Router(config)#end Escape from Config mode

Configuration Start-up configuration saved in NVRAM, permanent memory Running configuration saved in RAM Changes only in running configuration will get lost after reload!

Router start-up The Power-On Self Test (POST) checks the router’s hardware. When the POST completes successfully, the System OK LED indicator comes on. The router checks the configuration register to identify where to load the IOS image from. A setting of 0×2102 means that the router will use information in the startup- config file to locate the IOS image. If the startup-config file is missing or does not specify a location, it will check the following locations for the IOS image: 1. Flash (the default location) 2. TFTP server 3. ROM (used if no other source is found) The router loads the configuration file into RAM (which configures the router). The router can load a configuration file from: 1. NVRAM (startup-configuration file) 2. TFTP server 3. If a configuration file is not found, the router starts in setup mode.

ROM mon rommon > How to enter ROM mon mode? configuration-register (ie. 0x2120) escape sequence at the start-up CTRL+]

ROM mon How to boot IOS from ROM mon? rommon 1 >confreg 0x2102 rommon 2 >reset or rommon 1> boot flash:ios-image-file.bin