Router Fundamentals

Introduction Cisco Router

CPU and memory management LAN interface WAN interface

Tools and techniques for basic router configuration Describe the purpose and basic operation of the IOS Identify various IOS features Identify the methods to establish a command-line interface (CLI)

session with the router Move between the user command executive (EXEC) and privileged

EXEC modes Establish a HyperTerminal session on a router Log into a router Use the help feature in the command line interface

Routers

Router is a dedicated computer system have both LAN and WAN interfaces. to segment or interconnect LANs.

Routers are the backbone devices of large intranets and of the Internet.

Operate at Layer 3 of the OSI model, making decisions based on network addresses.

Two main functions of routers are selection of best path and switching of packets to the proper interface.

Routers accomplish this by building routing tables and exchanging information with other routers

CPU and RAM Central Processing Unit (CPU)

CPU executes instructions in the operating system OS specially written for router

Among these functions are system initialization, routing functions, and network interface control.

1st generation of Cisco Router use Motorola 68020 CPU High-end routers may have multiple CPUs.

Random Access Memory (RAM) Cisco router use static RAM for performance RAM is used for

routing table information fast switching cache running configuration packet queues.

The contents of RAM are lost when power is removed

Flash Memory Flash memory is used for storage of a full Cisco IOS

software image. Some early version of IOS has a size of 16Mbytes normally acquires the default IOS from flash memory. Flash is

programmable Allows updating of IOS software without replacing the ROM chip These images can be upgraded by loading a new image into flash. Retained on power down Multiple versions of IOS can be stored

Flash is relatively slow In most routers an executable copy of the IOS is transferred to RAM

during the boot process. similar to boot from Hard disk In other routers the IOS may be run directly from flash.

NVRAM and ROM Nonvolatile random-access memory

(NVRAM) Small size. Stores backup/startup

configuration files Content is not lost when router is

powered down or restarted

ROM Contains small house-keeping programs

POST (Power On Self Test) are hardware diagnostics during router bootup and loading the Cisco IOS software from flash to RAM

bootstrap program (loads the Cisco IOS) ROMs are not erasable. They can only

be upgraded by replacing the ROM chips in the sockets.

Ports / Interfaces The three basic types of

connections on a router are LAN interfaces WAN interfaces Management ports.

The LAN and WAN connections provide network connections through which frame packets are passed.

The management ports provides a text-based connection for the configuration and troubleshooting of the router

LAN and WAN interface of Routers Routers can be used to segment or interconnect

LANs. Two main functions of routers

are selection of best path and switching of packets to the proper interface.

Routers accomplish this by building routing tables and exchanging information with other routers.

Routers are the backbone devices of large intranets and of the Internet.

Router operates at Layer 3 of the OSI model, making decisions based on network addresses.

Routers have both LAN and WAN interfaces. Located on motherboard or on a separate module Connections through which packets enter and exit

Management Port Connections The common management interfaces two ports

console (CON) port auxiliary (AUX) port.

These are EIA-232 asynchronous serial ports. The computer must run a terminal emulation program to provide a text-

based session with the router. Through this session the network administrator can manage the device.

The console port is recommended for this initial configuration. The CON port is preferred over the AUX port for troubleshooting. This is

because it displays router startup, debugging, and error messages by default.

The console port can be used for disaster and password recovery procedures.

Once the initial configuration is entered through the CON or AUX port, the router can be connected to the network for troubleshooting or monitoring

Console Port

All Cisco routers include a 232 asynchronous serial console port (RJ-45).

Cables and adapters are needed to connect a console terminal to the console port.

To connect a PC running terminal emulation software to the console port, use the RJ-45 to RJ-45 rollover cable with the female RJ-45 to DB-9 adapter

Connecting LAN Interfaces In most LAN environments, the router is connected

to the LAN using an Ethernet or Fast Ethernet interface.

The router is a host that communicates with the LAN via a hub or a switch. A straight-through cable is used to make this connection.

In some cases the Ethernet connection of the router is connected directly to the computer or to another router. For this type of connection, a crossover cable is required.

The correct interface must be used. If the wrong interface is connected, damage can result to the router or other networking devices.

Cisco Internetwork Operating SystemTM (IOS) Like a computer, the router can not operate with out

an operating system. Cisco calls there the IOS. Its functions are: Basic routing and switching functions Reliable and secure access to networked resources Network scalability

When a Cisco router powers up, it performs a power-up self test. During this self test, the router executes diagnostics from

ROM on all hardware modules These diagnostics verify the basic operation of the CPU,

memory, and network interface ports. After verifying the hardware functions, the router proceeds with software initialization.

Router Start up steps

Checks hardware - POST Loads bootstrap

A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation.

Loads operating system The location is disclosed in the boot field of the configuration register. When it is loaded and operational, the operating system locates the hardware

and software components and lists the results on the console terminal. Loads configuration file

The configuration file saved in NVRAM is loaded into main memory and executed one line at a time.

Start routing processes, supply addresses for interfaces Set up mode

Should use setup to bring up a minimal configuration

Router Start up steps (2)

Establish a HyperTerminal session All Cisco routers include a 232 asynchronous

serial console port (RJ-45). Cables and adapters are needed to connect

a console terminal to the console port. A console terminal is an ASCII terminal or

PC running terminal emulation software such as HyperTerminal.

To connect a PC running terminal emulation software to the console port, use the RJ-45 to RJ-45 rollover cable with the female RJ-45 to DB-9 adapter

Command line interface The two basic modes : User and Privileged

modes. User mode

Limited mode used for checking the routers status, looking at routing tables

You cannot configure the routerOnce you’ve typed the password to enter user

mode, you will see the > prompt. The word “Router” will be the name of the router.

Command line interface (2) Privileged mode

Does everything User mode doesFull power to configure the router In user mode, you enter the command “enable”

and then the privileged password

Switch between user & privilege mode

To return to the user EXEC mode from the privileged EXEC mode, the disable command or exit may be entered.

To return to the privileged EXEC mode from the global configuration mode, type exit or Ctrl-Z.

Ctrl-Z may also be used to return directly to the privileged EXEC mode from any sub-mode of global configuration.

– router#disable

router>exit

Global Configuration mode ROUTER#CONFIGURE TERMINAL ROUTER(CONFIG)# The global configuration mode can only be

accessed from the privileged EXEC mode. The following are specific modes that can also be accessed from the global configuration mode: Set the Hostname Set enable password Set enable secret password Set console and virtual terminal passwords Set routed and routing protocols Configure interfaces with IP addresses, subnet mask

Show command show version

show IOS software image, version,indicates configuration register settings, bootstrap ROM version, Router up time, last restart method,system image file and location, and router platform

show startup-config displays the backup configuration file

show running-config displays the active configuration file

show flash shows information about the Flash memory device

show interfaces displays statistics for all interfaces configured on the router

show protocols shows the status of all configured Layer 3 protocols

Getting Help on a Command

To get a list of commands available in either user mode or privileged mode, enter a ? at the prompt.

Router> ? Router# ? The ? can be used with a

partial command to learn all the available commands that match what you entered.

Summary Router

LAN interfaces: Ethernet, fast-ethernet, token-ring WAN interfaces: serial Management console: aux, console

Functions of Routers Path determination and switch packet to the designated

interface

Cisco Routers IOS User (EXEC) mode, Privileged (Enable) mode Basic house keeping command: erase, reload, show