CCNA

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<b>Cisco IOS</b>

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.

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<b>The Purpose of Cisco IOS</b>

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<b>Introduction to Routers</b>

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<b>Router Memory Components </b>

<b>ROM</b>

<b>-</b> <b>Read Only Memory – Bootstrap/POST</b>

<b>FLASH Memory</b>

<b>-</b> <b>IOS Images are kept here</b>

<b>- Erasable reprogrammable ROM</b>

<b>- Contents are kept on Power down or reload</b>

<b>RAM </b>

<b>-</b>

<b> Random Access memory</b>

<b>- Routing Tables</b>

<b>- Running Configuration</b>

<b>- Contents are lost on reboot</b>

<b>NVRAM</b>

<b>-</b>

<b> Start up configuration</b>
<b>- Configuration Register</b>

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<b>ROM</b>

<b>Read-Only Memory</b>

ROM has the following characteristics and functions:



Maintains instructions for power-on self test

(POST) diagnostics



Stores bootstrap program and basic operating

system software

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<b>RAM</b>

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

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<b>NVRAM</b>

<b>Non-Volatile RAM</b>

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

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<b>Flash</b>

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,

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<b>Interfaces</b>

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

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<b>Router Power-On/Bootup </b>

<b>Sequence</b>

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.

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<b>Boot Sequence</b>

<b>ROMMonitor</b>
<b>RXBoot</b>
<b>FLASH</b>
<b>Configuration Register</b>
<b>C-File NVRAM</b>
<b>Y</b>
<b>N</b>
<b>Running</b>
<b>Setup Mode</b>

<b>Checks All interfaces</b>

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<b>After the Post…</b>

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

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

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.

The operating system image is loaded.

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<b>Loading the Cisco IOS Software </b>

<b>From Flash Memory</b>

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<b>Establishing a</b>

<b>HyperTerminal Session</b>

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.

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<b>Router LED Indicators</b>

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<b>Router User Interface Modes</b>

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.

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<b>CLI Command Modes</b>

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#<b>configure terminal (or config t)</b>

Router(config)#

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

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<b>Show Version Command</b>

<b>wg_ro_a#show version</b>

<b>Cisco Internetwork Operating System Software </b>

<b>Compiled Mon 08-Feb-99 18:18 by phanguye</b>

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

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

<b>System restarted by reload</b>

<b>System image file is "flash:c2500-js-l_120-3.bin"</b>

<i><b>(output omitted)</b></i>

<b></b>

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<b>show running-config and </b>

<b>show startup-config Commands</b>

<b>wg_ro_c#show startup-config</b>

<b>Using 1359 out of 32762 bytes</b>
<b>!</b>

<b>version 12.0</b>
<b>!</b>

<b> More </b>
<b>--wg_ro_c#show running-config</b>

<b>Building configuration...</b>
<b>Current configuration:</b>
<b>!</b>

<b>version 12.0</b>
<b>!</b>

<b>--In NVRAM</b>
<b>In RAM</b>

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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

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<b>Command Abbreviation</b>



Show Configuration – sh conf



Configure Terminal – conf t



Line auxillary – line aux

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<b>Configuring a Router’s Name</b>

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)#

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<b>Message Of The Day (MOTD)</b>

A message-of-the-day (MOTD) banner can be displayed on all

connected terminals.

Enter global configuration mode by using the command <b>config t</b>

Enter the command

<b>banner motd # Welcome to Gates Training #</b>.

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<b>Privileged Mode Command</b>

# show startup-config

# show running-config

# show version

# show flash

# show interfaces

# show interfaces s 0

# show history

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<b>Password</b>

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

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<b>Passwords</b>



There are five passwords for Router



Privileged Mode Password – 2



Line Console Password



Auxiliary Port Password

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<b>Privileged Mode Password</b>

Gates(config)# enable password gates

Encrypted privilege mode password

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<b>Line Password</b>

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<b>Aux Port Password</b>

Gates(config)# line aux 0

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<b>Configuring a Telnet Password</b>

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 0

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<b>Telnet Password</b>

Gates(config)# line vty 0 4

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<b>Encrypting Passwords</b>

 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

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<b>Disable Passwords</b>

Gates(config)# no enable password

Gates(config)# no enable secret

For the Console

Gates(config)# line con 0

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<b>LAB – Interface Configuration</b>

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<b>Descriptions</b>



Setting descriptions on an interface is helpful to

the administrator



Only locally significant

R1(config)#<b>int e0</b>

R1(config-if)#<b>description Sales Lan</b>

R1(config-if)#<b>int s0</b>

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<b>Configuring Interfaces</b>

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#<b>config t</b>

R1(config)#<b>int e0</b>

R1(config)#<b>Description Connoted to Host </b>

R1(config-if)#<b>ip address 10.0.0.1 255.0.0.0</b>

R1(config-if)#<b>no shutdown</b>

R1(config-if)#<b>exit</b>

R1(config)#<b>interface serial 0</b>

R1(config-if)#<b>ip address 20.0.0.1 255.255.255.0</b>

R1(config-if)# bandwidth 64

R1(config-if)#<b>clock rate 64000 (required for serial DCE only) </b>

R1(config-if)#<b>no shutdown</b>

R1(config-if)#<b>exit</b>

R1(config)#<b>exit</b>

R1#

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<b>DCE DTE</b>



To find out DCE or DTE

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<b>Viewing Configuration</b>

 To Check the status of interface

#Show IP interface brief
or

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<b>Saving and Erasing Configurations</b>

 To copy RAM to NVRAM

# copy run startup-config

 To remove all configuration

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<b>Objectives</b>



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)

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<b>Routing</b>

The process of transferring data from one local area

network to another

Layer 3 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

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<b>Routing</b>

From

Raj

House #213, 4th Street
Jayanagar, Bangalore

Ram

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

To route, a router needs to know:



Destination addresses



Sources it can learn from



Possible routes

Best route

<b>What is Routing?</b>

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<b>What is Routing? (cont.)</b>

<b>Network</b>
<b>Protocol</b>

<b>Destination</b>
<b>Network</b>

<b>Connected</b>

<b>Learned</b> <b>10.120.2.0172.16.1.0</b>

<b>Exit </b>
<b>Interface</b>

<b>S0</b> <b>Routed Protocol: IP</b>

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<b>Route Types</b>

 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

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<b>IP Routing Process</b>

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

communicate with Host B on a different network

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<b>LAB – Interface Configuration</b>

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<b>Test The Connection</b>

• Host A can ping router R1 and R2

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<b>IP Routing</b>



The different types of routing are:

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<b>Static Routes</b>



<b><sub>Benefits</sub></b>

<sub>No overhead on the router CPU </sub>

<sub>No bandwidth usage between routers </sub>
<sub> Adds security </sub>



<b><sub>Disadvantage</sub></b>

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– <b>R1(config)# iproute DestAddress SNM Nexthop address</b>

<b>R1(config)#ip route </b><i><b>network </b></i><b>[</b><i><b>mask</b></i><b>] </b>

<b>{</b><i><b>address </b></i><b>| </b><i><b>interface</b></i><b>}[</b><i><b>distance</b></i><b>] [permanent]</b>

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 <b>ip route </b>The command used to create the static route.

 <b>destination_network </b>The network you’re placing in the routing table.
 <b>mask </b>The subnet mask being used on the network.

 <b>next-hop_address </b>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.

 <b>exitinterface </b>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

 <b>administrative_distance </b>By default, static routes have an administrative distance

of 1 (or even 0 if you use an exit interface instead of a next-hop address)

 <b>permanent </b>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.

<b>ip route [destination_network] [mask] [next-hop_address or exitinterface]</b>
<b> [administrative_distance] [permanent</b>

<b>Static Route Configuration</b>

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<b>LAB – Static Route Configuration</b>

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

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<b>Verifying Static</b>

<b>Route Configuration</b>

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 <b>show running-config</b> is used to view the

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

The <b>show ip route</b> command is used to make sure that the

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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

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<b>Default Routes</b>

• 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

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<b>Stub Network</b>

<b>ip route 0.0.0.0 0.0.0.0 172.16.2.2</b>

<b>Default Routes</b>

<b>172.16.2.1</b>
<b>SO</b>
<b>172.16.1.0</b>
<b>B</b>
<b>172.16.2.2</b>
<b>Network</b>
<b>A</b> <b>B</b>

This route allows the stub network to reach all known

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<b>Configuring Default Routes</b>

Default routes are used to route packets with destinations that do 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:

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<b>Default Route LAB </b>

<b>Configuration</b>

<b>R2# config t</b>

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<b>What is a Routing Protocol?</b>

 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.

<b>Network</b>

<b>Protocol</b> <b>DestinationNetwork</b>

<b>Connected</b>
<b>RIP</b>
<b>IGRP</b>
<b>10.120.2.0</b>
<b>172.16.2.0</b>
<b>172.17.3.0</b>
<b>Exit </b>
<b>Interface</b>
<b>E0</b>
<b>S0</b>
<b>S1</b>

<b>Routed Protocol: IP</b>

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<b>Autonomous System</b>

Interior Gateway Protocols are
used for routing decisions

Exterior Gateway
Protocols are used
for routing between
Autonomous Systems

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
<sub>AS are identified by numbers</sub>

<b>All Routing protocols are categorized as IGP or EGP</b>

<b>Routing Categories</b>

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<b>IGP</b>
<b>Interior Gateway Protocol</b>

<b>(IGP)</b>
<b>Exterior Gateway </b>
<b>Protocol (EGP)</b>
<b>EGP</b>
<b>EGP</b>
<b>EGP</b>

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An autonomous system is a collection of networks under a

common administrative domain.

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 Distance Vector
RIP V1

IGRP

RIP V2
 Link state

OSPF

 Hybrid

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<b>Classful Routing Overview</b>

Classful routing protocols do 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 1 (RIPv1)

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<b>Classless Routing Overview</b>

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 2 (RIPv2)

EIGRP

OSPF

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• Routers pass periodic copies of routing table to neighbor

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<b>Distance Vector</b>

 Uses Bellman Ford Algorithm

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

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<b>Distance Vector</b>

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

 IGRP - Composite

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<b>Distance Vector</b>

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

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<b>Distance Vector</b>

• IGGRP uses bandwidth and delay as Metric

• RI routing table metric for 192.168.20.1 network will be

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<b>Routing Loops</b>

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• Routers discover the best path to
destinations from each neighbor.

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• Slow convergence produces inconsistent routing.

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• <b>Router A updates its table to reflect the new but </b>
<b>erroneous hop count.</b>

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• <b>Packets for network 10.4.0.0 bounce (loop) between </b>
<b>routers B and C.</b>

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<b>Maximum Hop Count</b>

• 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

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<b>Split Horizon</b>



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

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<b>Route Poisoning</b>

• 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

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<b>Triggered Updates</b>

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.

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<b>Holddowns</b>

• 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

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<b>Pinhole Congestion</b>

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<b>RIP Timers</b>

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

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

• <b>Holddown timer</b> 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

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<b>Routing Information Protocol </b>

<b>(RIP) </b>

 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 1 uses only classful routing, which means that all

devices in the network must use the same subnet mask

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<b>Router Configuration</b>

The <b>router</b> command starts a routing process.

The <b>network</b> 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)#<b>router rip</b>

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<b>RIP Configuration</b>

<b>R1# config t</b>

<b>R1(config)# )#router rip</b>

<b>R1(config)#network 192.168.10.0</b>
<b>R1(config)#network 192.168.20.0</b>

<b>R2# config t</b>

<b>R2(config)#router rip</b>
<b>R2(config)#network 192.168.20.0</b>
<b>R2(config)#network 192.168.30.0</b>
<b>192.168.10.2</b>

<b>R3# config t</b>

<b>R3(config)# )#router rip</b>

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<b>Passive Interface</b>

 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 0

 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

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<b>RIP Version 2 (RIPv2)</b>

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<b>Exercise - RIP Version 2 </b>

<b>Configuration</b>

A B

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<b>Exercise - RIP Version 2 </b>

<b>Configuration</b>

<b>R2# config t</b>

<b>R2(config)#router rip</b>

<b>R2(config)#network 192.168.0.4</b>
<b>R2(config)#network 192.168.0.8</b>
<b>R2(config)#version 2</b>

<b>R1# config t</b>

<b>R1(config)# )#router rip</b>

<b>R1(config)#network 192.168.0.4</b>
<b>R1(config)#network 192.168.0.16</b>
<b>R1(config)#version 2</b>

<b>R3# config t</b>

<b>R3(config)# )#router rip</b>

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<sub>CISCO Proprietary</sub>

<sub>More scalable than RIP</sub>

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Bandwidth
Delay

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<b>IGRP</b>

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.

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<b>IGRP Configuration</b>

<b>R1# config t</b>

<b>R1(config)# )#router igrp 10</b>

<b>R2# config t</b>

<b>R2(config)#router igrp 10</b>

<b>R2(config)#network 192.168.20.0</b>

<b>R2(config)#network 192.168.30.0</b>
<b>192.168.10.2</b>
<b>192.168.20.1</b>
<b>192.168.20.2</b>
<b>192.168.30.1</b>
<b>192.168.30.2</b> <b>192.168.40.1</b>
<b>192.168.40.2</b>

<b>R3# config t</b>

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<b>Verifying the IGRP Routing Tables</b>

LabA#<b>sh ip route</b>

[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.

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<b>Debug Commands </b>

 debug ip igrp events Command

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

 debug ip igrp transactions Command

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