Day 15 : Managing OS and Configuration

OS file and Configuration file

Operating System use in Cisco routers and switches is called IOS (Internetwork Operating System). IOS is a monolithic, single-file OS. IOS file is stored in Flash file system.
IOS file can also be saved on a TFTP server.

Configuration on a Cisco router is kept in Non-volatile RAM (nvram). NVRAM retain configuration when the router is power off.
When a router is power on, configuration also stays in RAM. Changes made to configuration only stays in RAM and it is important to save the configuration to NVRAM so that it will not be lost when a router is power cycled.
Configuration can also be saved on a TFTP server.

Configuration in RAM is referred in IOS command as -> running-config.
Configuration in NVRAM is referred in IOS command as -> startup-config.

Command equivalent
write memory (copy running-config startup-config)
write terminal (show running)
write network (copy running-config tftp)

Password recovery (when password is forgotten)

1. Power cycle the router
2. Enter control+break key when the router is starting up (the router will go to ROM Monitor with rommon > prompt)
3. Enter (confreg 0x2142) - to bypass startup configuration where password is kept)
4. Enter "reset" command or power cycle the router
5. After boot is completed, enter "no" at initial startup configuration.
6. Go to Enable mode.
7. Copy configuration from NVRAM to RAM (copy startup-config running-config)
8. Change the forgotten password(s)
9. Change configuration-register value back to 0x2102
10. Save the config.