CCNA

The configuration commands start routing processes, supply addresses for interfaces, and define other operating characteristics of the router... Loading the Cisco IOS Software [r]

Cisco IOS

Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching functions of internetworking devices

The Purpose of Cisco IOS

Introduction to Routers

Router Memory Components

ROM - Read Only Memory – Bootstrap/POST

FLASH Memory- IOS Images are kept here

- Erasable reprogrammable ROM

- Contents are kept on Power down or reload

RAM - Random Access memory

- Routing Tables

- Running Configuration

- Contents are lost on reboot

NVRAM - Start up configuration - Configuration Register

ROM

Read-Only Memory

ROM has the following characteristics and functions:

 Maintains instructions for power-on self test

(POST) diagnostics

 Stores bootstrap program and basic operating

system software

RAM

Random Access Memory, also called dynamic RAM (DRAM) RAM has the following characteristics and functions:

 Stores routing tables

 Holds ARP cache

 Performs packet buffering (shared RAM)

 Provides temporary memory for the configuration file of

the router while the router is powered on

NVRAM

Non-Volatile RAM

NVRAM has the following characteristics and functions:

Provides storage for the startup configuration file

Retains content when router is powered down or

restarted

Configuration Register – 16 bit register which decides

Flash

Flash memory has the following characteristics and functions:

 Holds the operating system image (IOS)

 Allows software to be updated without

removing and replacing chips on the processor

 Retains content when router is powered down

or restarted

 Can store multiple versions of IOS software

 Is a type of electronically erasable,

Interfaces

Interfaces have the following characteristics and functions: Connect router to network for frame entry and exit Can be on the motherboard or on a separate module Types of interfaces:

 Ethernet

 Fast Ethernet

 Serial

 ISDN BRI

Router Power-On/Bootup Sequence

1 Perform power-on self test (POST). 2 Load and run bootstrap code.

3 Find the Cisco IOS software. 4 Load the Cisco IOS software. 5 Find the configuration.

6 Load the configuration.

Boot Sequence ROMMonitor RXBoot FLASH Configuration Register C-File NVRAM Y N Running Setup Mode

Checks All interfaces

RAM

14

15 13 1211 10 9 8 7 6 5 4 3 2 1 0 4

8 2 1 8 4 2 1 8 4 2 1 8 4 2 1

After the Post…

After the POST, the following events occur as the router initializes:

Step 1

The generic bootstrap loader in ROM executes A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation

Step 2

The IOS can be found in several places The boot field of the configuration register determines the location to be used in loading the IOS

Step 3

The operating system image is loaded

Step 4

Loading the Cisco IOS Software From Flash Memory

Establishing a

HyperTerminal Session

Take the following steps to connect a terminal to the console port on the router: First, connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter

Router LED Indicators

Router User Interface Modes

The Cisco command-line interface (CLI) uses a hierarchical structure This structure requires entry into different modes to accomplish particular tasks

Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode

CLI Command Modes

All command-line interface (CLI) configuration changes to a Cisco router are made from the global configuration mode Other more specific modes are entered

depending upon the configuration change that is required

Global configuration mode commands are used in a router to apply configuration statements that affect the system as a whole

The following command moves the router into global configuration mode Router#configure terminal (or config t)

Router(config)#

When specific configuration modes are entered, the router prompt changes to indicate the current configuration mode

Show Version Command

wg_ro_a#show version

Cisco Internetwork Operating System Software

IOS (tm) 2500 Software (C2500-JS-L), Version 12.0(3), RELEASE SOFTWARE (fc1) Copyright (c) 1986-1999 by cisco Systems, Inc.

Compiled Mon 08-Feb-99 18:18 by phanguye

Image text-base: 0x03050C84, data-base: 0x00001000 ROM: System Bootstrap, Version 11.0(10c), SOFTWARE

BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE SOFTWARE(fc1) wg_ro_a uptime is 20 minutes

System restarted by reload

System image file is "flash:c2500-js-l_120-3.bin"

(output omitted)

show running-config and

show startup-config Commands wg_ro_c#show startup-config

Using 1359 out of 32762 bytes !

version 12.0 !

More wg_ro_c#show running-config

Building configuration Current configuration: !

version 12.0 !

More

In NVRAM In RAM

Configurations in two locations - RAM and NVRAM •The running configuration is stored in RAM

•Any configuration changes to the router are made to the running-configuration and take effect immediately after the command is entered

•The startup-configuration is saved in NVRAM and is loaded into the router's running-configuration when the router boots up

• To save the running-configuration to the startup configuration, type the following from privileged EXEC mode (i.e at the "Router#" prompt.)

Router# copy run start

Command Abbreviation

Show Configuration – sh conf

Configure Terminal – conf t

Line auxillary – line aux

Configuring a Router’s Name

A router should be given a unique name as one of the first configuration tasks

This task is accomplished in global configuration mode using the following commands:

Router(config)#hostname Gates Gates(config)#

Message Of The Day (MOTD) A message-of-the-day (MOTD) banner can be displayed on all

connected terminals

Enter global configuration mode by using the command config t

Enter the command

banner motd # Welcome to Gates Training #

Privileged Mode Command

# show startup-config # show running-config # show version

# show flash

# show interfaces

# show interfaces s 0 # show history

Password

Passwords restrict access to routers

Passwords should always be configured for virtual terminal

lines and the console line

Passwords are also used to control access to privileged EXEC

Passwords

There are five passwords for Router

Privileged Mode Password – 2

Line Console Password

Auxiliary Port Password

Privileged Mode Password

Gates(config)# enable password gates Encrypted privilege mode password

Line Password

Aux Port Password

Gates(config)# line aux 0

Configuring a Telnet Password

A password must be set on one or more of the virtual

terminal (VTY) lines for users to gain remote access to the router using Telnet

Typically Cisco routers support five VTY lines numbered

Telnet Password

Gates(config)# line vty 4

Encrypting Passwords

 Only the enable secret password is encrypted by default  Need to manually configure the user-mode and enable

passwords for encryption

 To manually encrypt your passwords, use the service

password-encryption command

Router#config t

Disable Passwords

Gates(config)# no enable password Gates(config)# no enable secret

For the Console

Gates(config)# line 0

LAB – Interface Configuration S0 S0 E0 10.0.0.1 10.0.0.2 30.0.0.2

20.0.0.1 20.0.0.2 30.0.0.1

Descriptions

Setting descriptions on an interface is helpful to

the administrator

Only locally significant

R1(config)#int e0

R1(config-if)#description Sales Lan

R1(config-if)#int s0

Configuring Interfaces An interface needs an IP Address and a Subnet Mask to be configured All interfaces are “shutdown” by default

The DCE end of a serial interface needs a clock rate

R1#config t

R1(config)#int e0

R1(config)#Description Connoted to Host

R1(config-if)#ip address 10.0.0.1 255.0.0.0

R1(config-if)#no shutdown

R1(config-if)#exit

R1(config)#interface serial 0

R1(config-if)#ip address 20.0.0.1 255.255.255.0

R1(config-if)# bandwidth 64

R1(config-if)#clock rate 64000 (required for serial DCE only)

R1(config-if)#no shutdown

R1(config-if)#exit

R1(config)#exit

R1#

DCE DTE

To find out DCE or DTE

Viewing Configuration

 To Check the status of interface

#Show IP interface brief or

Saving and Erasing Configurations

 To copy RAM to NVRAM

# copy run startup-config

 To remove all configuration

Objectives

Upon completion of this chapter, you will be

able to complete the following tasks:

Distinguish the use and operation of static and dynamic

routes

Configure and verify a static route

Identify how distance vector IP routing protocols such as

RIP and IGRP operate on Cisco routers

Enable Routing Information Protocol (RIP)

Routing

The process of transferring data from one local area

network to another

Layer devices

Routed protocol Enables to forward packet from one

router to another – Ex – IP, IPX

Routing protocol sends and receives routing

information packets to and from other routers – Ex -RIP, OSPF , IGRP

Routing protocols gather and share the routing

information used to maintain and update routing tables

That routing information is in turn used to route a

Routing

From

Raj

House #213, 4th Street Jayanagar, Bangalore

To

Ram

To route, a router needs to know:

Destination addresses

Sources it can learn from

Possible routes

Best route

What is Routing?

What is Routing? (cont.)

What is Routing? (cont.)

Network Protocol

Destination Network

Connected

Learned 10.120.2.0172.16.1.0

Exit Interface

E0

S0 Routed Protocol: IP

172.16.1.0 10.120.2.0

E0

Route Types

 Static routing - network administrator configures

information about remote networks manually They are used to reduce overhead and for security

 Dynamic routing - information is learned from other

routers, and routing protocols adjust routes automatically

 Because of the extra administrative requirements, static

IP Routing Process

 Step-by-step what happens when Host A wants to

communicate with Host B on a different network

E0 E1

10.0.0.1

10.0.0.2 A B 20.0.0.2

LAB – Interface Configuration S0 S0 E0 10.0.0.1 10.0.0.2 30.0.0.2

20.0.0.1 20.0.0.2 30.0.0.1

Test The Connection

• Host A can ping router R1 and R2

IP Routing

The different types of routing are:

Static Routes

Benefits

No overhead on the router CPU

No bandwidth usage between routers  Adds security

Disadvantage

– R1(config)# iproute DestAddress SNM Nexthop address

R1(config)#ip route network [mask]

{address | interface}[distance] [permanent]

 ip route The command used to create the static route

 destination_network The network you’re placing in the routing table  mask The subnet mask being used on the network

 next-hop_address The address of the next-hop router that will receive the packet

and forward it to the remote network This is a router interface that’s on a directly connected network

 exitinterface You can use it in place of the next-hop address if you want, but it’s

got to be on a point-to-point link, such as a WAN

 administrative_distance By default, static routes have an administrative distance

of (or even if you use an exit interface instead of a next-hop address)

 permanent If the interface is shut down, or the router can’t communicate to the

next-hop router, the route will automatically be discarded from the routing table

ip route [destination_network] [mask] [next-hop_address or exitinterface] [administrative_distance] [permanent

Static Route Configuration

LAB – Static Route Configuration S0 S0 E0 10.0.0.1 10.0.0.2 30.0.0.2

20.0.0.1 20.0.0.2 30.0.0.1

A S0 E0 40.0.0.2 40.0.0.1 B S1

R1# config t

R1(config)#ip route 30.0.0.0 255.0.0.0 20.0.0.2 R1(config)#ip route 40.0.0.0 255.0.0.0 20.0.0.2

R2# config t

R2(config)#ip route 10.0.0.0 255.0.0.0 20.0.0.1 R2(config)#ip route 40.0.0.0 255.0.0.0 30.0.0.2

R3# config t

Verifying Static

Route Configuration

After static routes are configured it is important to verify

that they are present in the routing table and that routing is working as expected

The command show running-config is used to view the

active configuration in RAM to verify that the static route was entered correctly

The show ip route command is used to make sure that the

S0 S0 E0

10.0.0.1

10.0.0.2

30.0.0.2

20.0.0.1 20.0.0.2 30.0.0.1

A S0 E0 40.0.0.2 40.0.0.1 B S1

R1# config t

R1(config)#no ip route 30.0.0.0 255.0.0.0 20.0.0.2 R1(config)#no ip route 40.0.0.0 255.0.0.0 20.0.0.2

R2# config t

R2(config)#no ip route 10.0.0.0 255.0.0.0 20.0.0.1 R2(config)#no ip route 40.0.0.0 255.0.0.0 30.0.0.2

R3# config t

R3(config)#no ip route 10.0.0.0 255.0.0.0 30.0.0.1 R3(config)#no ip route 20.0.0.0 255.0.0.0 30.0.0.1

Default Routes

• Can only use default routing on stub networks

• Stub networks are those with only one exit path out of the network

• The only routers that are considered to be in a stub network are R1 and R3

Stub Network

ip route 0.0.0.0 0.0.0.0 172.16.2.2

Default Routes 172.16.2.1 SO 172.16.1.0 B 172.16.2.2 Network A B

This route allows the stub network to reach all known

Configuring Default Routes

Default routes are used to route packets with destinations that not match any of the other routes in the routing table

A default route is actually a special static route that uses this format: ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]

This is sometimes referred to as a “Quad-Zero” route Example using next hop address:

Default Route LAB Configuration S0 S0 E0 E0 10.0.0.1 10.0.0.2 40.0.0.2 20.0.0.1 20.0.0.2 30.0.0.1 A B S0 S1 30.0.0.2 40.0.0.1

R2# config t

What is a Routing Protocol?

What is a Routing Protocol?

 Routing protocols are

used between

routers to determine paths and maintain routing tables

 Once the path is

determined a router can route a routed protocol

Network

Protocol DestinationNetwork

Connected RIP IGRP 10.120.2.0 172.16.2.0 172.17.3.0 Exit Interface E0 S0 S1

Routed Protocol: IP

172.17.3.0 172.16.1.0 10.120.2.0

E0

Autonomous System

AS 2000

AS 3000

IGP

Interior Gateway Protocols are used for routing decisions

Exterior Gateway Protocols are used for routing between Autonomous Systems

EGP

AS 1000

An Autonomous System (AS) is a group of IP networks, which has a

single and clearly defined routing policy

Group of routers which can exchange updates AS are identified by numbers

All Routing protocols are categorized as IGP or EGP

Routing Categories

IGP Interior Gateway Protocol

(IGP) Exterior Gateway Protocol (EGP) EGP EGP EGP

An autonomous system is a collection of networks under a

common administrative domain

 Distance Vector RIP V1

IGRP

RIP V2  Link state

OSPF

 Hybrid

Classful Routing Overview

Classful routing protocols not include the subnet mask with the route advertisement

Within the same network, consistency of the subnet masks is assumed

Summary routes are exchanged between foreign networks

Examples of classful routing protocols: RIP Version (RIPv1)

Classless Routing Overview

Classless routing protocols include the subnet mask with

the route advertisement

Classless routing protocols support variable-length

subnet masking (VLSM) and subnetting

Examples of classless routing protocols: RIP Version (RIPv2)

EIGRP

OSPF

• Routers pass periodic copies of routing table to neighbor

Distance Vector

 Uses Bellman Ford Algorithm

 It needs to find out the shortest path from one network to other  How to determine which path is best?

Distance Vector

 There are two Distance Vector Protocol, Both uses different metric  RIP – Hops

 IGRP - Composite

192.168.10.1

Distance Vector

 DV protocol are known as Routing by rumor  RIP uses only Hop count

Distance Vector

192.168.10.1

192.168.20.1 56 kbps

1 Mbps 1 Mbps

1 Mbps

56 kbps

• IGGRP uses bandwidth and delay as Metric

• RI routing table metric for 192.168.20.1 network will be

Routing Loops

• Routers discover the best path to destinations from each neighbor

• Slow convergence produces inconsistent routing

• Router A updates its table to reflect the new but erroneous hop count.

• Packets for network 10.4.0.0 bounce (loop) between routers B and C.

Maximum Hop Count

• One way of solving routing loop problem is to define a maximum hop count

• RIP permits a hop count of up to 15, so anything that requires 16 hops is deemed unreachable

Split Horizon

Solution to the Routing Loop problem

Split Horizon is a rule that routing

information cannot be sent back in the direction from which it was received

Had split horizon been used in our

Route Poisoning

• Route Poisoning Usually used in conjunction with split horizon

• Route poisoning involves explicitly poisoning a routing table entry for an unreachable network

• Once Router C learned that network 10.4.0.0 was unavailable it would have immediately poisoned the route to that network by setting its hop count to the routing protocol’s infinity value

Triggered Updates

New routing tables are sent to neighboring routers on a regular basis RIP updates occur every 30 seconds

However a triggered update is sent immediately in response to some change in the routing table

The router that detects a topology change immediately sends an update message to adjacent routers that, in turn, generate triggered updates notifying their adjacent neighbors of the change

Holddowns

• Holddowns are a technique used to ensure that a route recently removed or changed is not reinstated by a routing table update from another route

• Holddown prevents regular update messages from reinstating a route that is going up and down (called flapping)

• Holddowns prevent routes from changing too rapidly by allowing time for either the downed route to come back up

Pinhole Congestion

192.168.10.1

192.168.20.1

1Mbps 1Mbps

56kbps

RIP Timers

• Route update timer Sets the interval (typically 30 seconds) between periodic routing updates

• Route invalid timer Determines the length of time (180 seconds) before a router determines that a route has become invalid

• Holddown timer This sets the amount of time during which routing information is suppressed This continues until either an update packet is received with a better metric or until the holddown timer expires The default is 180 seconds

Routing Information Protocol (RIP)

 Routing Information Protocol (RIP) is a true distance-vector routing protocol

 It sends the complete routing table out to all active interfaces every 30 seconds

 RIP only uses hop count to determine the best way to a remote network

 It has a maximum allowable hop count of 15  AD is 120

 Bellman-ford algorithm

 Works well in small networks, but it’s inefficient on large networks  RIP version uses only classful routing, which means that all

devices in the network must use the same subnet mask

Router Configuration

The router command starts a routing process

The network command is required because it enables the routing process to determine which interfaces participate in the sending and receiving of routing updates

An example of a routing configuration is: Gates(config)#router rip

RIP Configuration S0 S0 E0 E0 192.168.10.1 A B S0 S1

R1# config t

R1(config)# )#router rip

R1(config)#network 192.168.10.0 R1(config)#network 192.168.20.0

R2# config t

R2(config)#router rip R2(config)#network 192.168.20.0 R2(config)#network 192.168.30.0 192.168.10.2 192.168.20.1 192.168.20.2 192.168.30.1 192.168.30.2 192.168.40.1 192.168.40.2

R3# config t

R3(config)# )#router rip

Passive Interface

 Passive-interface command prevents RIP update

broadcasts from being sent out a defined interface, but same interface can still receive RIP updates

R1#config t

R1(config)#router rip

R1(config-router)#network 192.168.10.0 R1(config-router)#passive-interface serial

 Passive-interface command depends upon the routing

protocol

 RIP router with a passive interface will still learn about

the networks advertised by other routers

 EIGRP, a passive-interface will neither send nor receive

RIP Version (RIPv2)

Exercise - RIP Version Configuration

S0 S0

E0

E0

192.168.0.16/29

A B

S0 S1

192.168.0.4/30 192.168.0.8/30

192.168.0.32/28

Exercise - RIP Version Configuration S0 S0 E0 E0 192.168.0.16/29 A B S0 S1 192.168.0.4/30 192.168.0.8/30 192.168.0.32/28

R2# config t

R2(config)#router rip

R2(config)#network 192.168.0.4 R2(config)#network 192.168.0.8 R2(config)#version 2

R1# config t

R1(config)# )#router rip

R1(config)#network 192.168.0.4 R1(config)#network 192.168.0.16 R1(config)#version 2

R3# config t

R3(config)# )#router rip

CISCO Proprietary

More scalable than RIP

Bandwidth Delay

IGRP

Some of the IGRP key design characteristics emphasize the following:  It is a distance vector routing protocol

 Routing updates are broadcast every 90 seconds

 Bandwidth, load, delay and reliability are used to create a composite metric

IGRP Configuration S0 S0 E0 E0 192.168.10.1 A B S0 S1

R1# config t

R1(config)# )#router igrp 10

R2# config t

R2(config)#router igrp 10

R2(config)#network 192.168.20.0 R2(config)#network 192.168.30.0 192.168.10.2 192.168.20.1 192.168.20.2 192.168.30.1 192.168.30.2 192.168.40.1 192.168.40.2

R3# config t

Verifying the IGRP Routing Tables

LabA#sh ip route

[output cut]

I 192.168.50.0 [100/170420] via 192.168.20.2, Serial0/0 I 192.168.40.0 [100/160260] via 192.168.20.2, Serial0/0 I 192.168.30.0 [100/158360] via 192.168.20.2, Serial0/0 C 192.168.20.0 is directly connected Serial0/0

C 192.168.10.0 is directly connected, FastEthernet0/0

• The I means IGRP-injected routes The 100 in [100/160360] is the administrative distance of IGRP The 160,360 is the composite metric The lower the composite metric, the better the route

Debug Commands

 debug ip igrp events Command

 summary of the IGRP routing information that is running on the network

 debug ip igrp transactions Command