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Cisco™ CCNA : IOS

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Internal memory components of a cisco router

ROM : Memory containing micro-code for basic functions to start and maintain the router.

RAM/DRAM : Stores the running configuration, routing tables, and packet buffers.

NVRAM : Memory that does not lose information when power is lost. Stores the system’s

configuration file and the configuration register.

Flash Memory : Stores the compressed IOS image.

Router boot configuration commands

boot system ROM : boots from system ROM

boot system flash <IOS file name> : boots

IOS from flash memory

boot system tftp <IOS file name>

<tftp_addr> : boots IOS from a tftp server

Cisco router configurable locations

Console port, Virtual Terminals (vty), Auxiliary port, TFTP server and Network management station

Router modes of operation include

Mode---------------------------> Prompt

user exec---------------------> Router>

Privileged----------------------> Router #

global config------------------> Router(config)#

Interface config--------------> Router(config-if)#

Router passwords

Enable password

Console password

Enable Secret

Virtual terminal password (vty)

Auxiliary password

Three ways router learns to forward packets

1. Static routes : Configured by the administrator manually. Syntax : ip route <ip-addr><mask-addr><ip-addr>

Ex: R1(config)#ip route 192.168.200.0 255.255.255.0 192.168.1.2

2. Default routes : This is used when a route is not known or is infeasible. Syntax : ip route 0.0.0.0 0.0.0.0 <ip-addr>

Ex: R1(config)#ip route 0.0.0.0 0.0.0.0 192.168.1.2

3. Dynamic routes : In dynamic routing, the routing tables are automatically updated.

Dynamic routing uses broadcasts and multicasts to communicate with other routers.

Router Cursor Commands

<ctrl> A: Move to the beginning of the command line

<ctrl> E: Move to the end of the command line

<ctrl> F: Move forward one character, same as using “Right Arrow”

<ctrl> B: Move backward one character, same as using “Left Arrow".

<ctrl> P: Repeat Previous command, same as using “Up Arrow”

<ctrl> N: Repeat Next (more recent) command, same as using "Down Arrow"

<esc> B: Moves to beginning of previous word.

<esc> F: Moves to beginning of next word.

<ctrl>R: Creates new command prompt, followed by all the

characters typed at the last one.

More info

To enable the Cisco IOS to forward packets destined for

obscure subnets of directly connected networks onto the best

route, use "ip classless" command.

By default, Cisco routers support 5 simultaneous telnet sessions.

This number can be configured using IOS commands.

Router Default Boot Sequence for Cisco IOS

1. NVRAM 3. TFTP server

2. Flash (sequential) 4. ROM

The router first looks at Startup Config file in NV

RAM, if not available, it falls back to Flash, then

to TFTP and then to ROM.

Configuration Register Command

Router(config)# config-register 0x10x (where that last x is 0-F in hex), when the last x is: 0 = boot

into ROM Monitor mode; 1 = boot the ROM IOS; 2 - 15 = look in startup-config file in NVRAM.