Cisco ICND1 Flashcard: Router Memory

CCNA exam success (and doing well on the new ICND1 and ICND2 component exams) depends alot on keeping fine details and facts straight, even the mundane details of ROM, Flash, NVRAM, RAM.  The questions are worded a certain way to test your knowledge on a related areas. For example, there could be a question about POST but it is really about which memory is being used.

When a router boots up, it performs a POST, finds and loads the Cisco IOS image software, finds and loads the configurations, runs the software.
ROM - means Read-Only Memory. Stores the router's bootstrap startup program, operating system software, and runs the power-on self test (the POST).  The mini-IOS is also stored here, the basic IO in case of problems with current IOS.

Flash - memory is erasable and reprogrammable read-only, stores the Cisco ISO Software image and is retained after power down and reload.

NVRAM - means non-volatile RAM. Stores the startup configuration. It is writable and permanent, therefore contents of NVRAM are not lost on power down or reload. Since NVRAM holds the startup configuration file, if the NVRAM is empty when the router reloads, you will be prompted to enter setup mode (default).

RAM - means Random-Access Memory. Stores the routing tables, running config.  At system bootup, the IOS loads into RAM and the router uses the startup configuration, which is the reason to remember to do "copy run start" to copy the running-config into the startup-config. Use the shortcut to avoid making a typo with this command. Contents are not retained on power down or reload. Must be fast switching.

Configuration Registers
These digits are binary and hex, and useful to understand when troubleshooting password recovery or IOS upgrades.
0x2102 loads the startup config in NVRAM and the IOS from flash memory, factory default
0x2142 ignores the startup config but loads IOS from flash memory
0x2142 is the mode used for password recovery

When the boot field value of the configuration register could be 0x2 to 0xF, the bootstrap code will parse the startup config file in NVRAM for the boot system command that indicate the name and location of the Cisco IOS image to load. This is the boot plan.

Summary: Finding the Cisco IOS Image
1. Check configuration register
2. Parse configuration for boot system command
3. Default to first file in flash memory
If no valid Cisco IOS image is found in the flash, these actions are taken
4. Attempt to boot from network TFTP server (5 attempts)
5. Boot helper image from  ROM
6. ROMMON when there is no boot helper image or it is corrupt

What to do if you lost your Cisco Router password login.


Cisco Flash
For each Cisco Router purchased, remember to order one with a flash card 128MB or 256MB. I had the mishap with the test router with flash memory of only 64MB which was too small to load an IOS make room for the vlan dat and other things. Cisco issues a Field Notice that covers this same model.

A quick online search lists vendors selling the the Cisco flash cards for $349 made in Thailand or Malaysia by the Cisco manufacturer,  but I found an American website selling them for $68 Made in the USA. They arrived within a week http://kahlon.com/itemdetailpg.asp?itemid=1241198 and they worked just great.
FACT about switches: A Switch learns MAC address to port mapping by monitoring the source address of frames

Study smart and study hard for success on the CCNA exam.