itacademy routing

7/31/2019 ITAcademy Routing

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Chapter 1 2 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Routing

A Router connects one network two another network

A router is responsible for delivery of packet across different networks

Ensure 24/7 availability

Router use alternate paths in case the primary path fails

Router use Qos prioritization if IP packet to ensure real-time traffic such as

voice and video


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A router connects multiple networks , this means that it has multiple

interfaces that each belong to a different IP network

The interface that the router uses to forward the packet may be thenetwork of the final destination of the packet or it may be a network

connected to another router that used to reach the destination network

LANs are commonly Ethernet networks that contain devices such as PCs ,

Printers, Servers WANs are used to connect networks over a large

geographical area

Routers at the network center


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The primary responsibility of a router is to direct packets destined for local

and remote networks by :

- Determining the best path to send packets- Forwarding packets toward their destination

The router use its routing table to determine the best path to forward the

packet

When the router receives a packet it examine its destination IP address and

searches for the best match with a network address in the routers routing

table

Static Routes and dynamic routing protocols are used by routers to learn

a bout remote networks and build their routing tables

Routers determine the best path


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Like a PC a router also includes :

- Central processing unit

- Random access memory- Read only memory

CPU :CPU executes operating system instructions

RAM :RAMs stores the instructions and data needed to be executed by the CPU

Router CPU and Memory


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Operating system :

The Cisco IOS (internetwork operating system) is copied into ram duringbootup

Running configuration file :

This is the configuration file that stores the configuration commands that

the router IOS is Currently using

All commands configured on the router are stored in the running

configuration file known as running-config

RAM is used to store these components


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IP Routing Table

This file stores information a bout directly connected and remote networks , it

is used to the best path to forward the packet

ARP cache : this cache contains the IPv4 address to MAC address mapping

Packet Buffer : packets are temporarily stored in a buffer when received onan inter face or before they exit an interface

RAM is volatile memory and loses its content when the router is powered

down or restarted


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ROM :

Is a form of permanent storage cisco devices

ROM Store :1 bootstrab instructions

2- Basic diagnostic software

3- Version of IOS

ROM includes the software that does not normally need to be modified orupgraded such as bootup instructions

ROM does not lose its contents when a router loses power or is restarted


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Flash Memory :

Flash memory is nonvolatile computer memory that can be electrically stored

and erased

Flash is used as permanent storage for the operating system cisco IOS

The IOS is permanently stored in flash memory and copied into RAM during

the boot process , where it is then executed by the CPU

Flash memory does not loses its contents when the router loses power or isrestarted


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NVRAM (Nonvolatile RAM ) :

Nonvolatile RAM does not lose its information when power is turned off

NVRAM is used by the cisco IOS as permanent storage of the startupconfiguration file

All configuration changes are stored in the running - config file in RAM , soIOS save those changes is case the router is restarted or loses power the

running-config must be copied to NVRAM where it is stored as the start up

config file


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Internetwork Operating System (IOS)

Cisco IOS has its own user Interface , the common line interface (CLI) is the

much more common method of configuring cisco routers

Upon boot up the startup-config file in NVRAM is copied into RAM and

stored as the running config file

IOS executes the configuration commands in the running-config , and changes

entered by the network administrator are stored in the running-config and areimmediately implemented by the IOS


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Router bootup Process

1- performing the post :

The Power on self test (post) , the post process is used to test the router

hardware

After the post has been completed the router executes the bootstrap program

Loading the bootstrap program :

After the POST the bootstrap program is copied from ROM into the RAM once

in RAM the CPU executes the instructions in the bootstrap program

The main task of the bootstrap program is to locate the cisco IOS and load it

into RAM


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Loading and locating cisco IOS

The cisco IOS stored in Flash Memory

Cisco router copy the IOS into RAM for execution by the CPU

Once the IOS begins to load you may see a string of pounds signs (#) while theimage decompresses

Locating and loading the configuration file

After the IOS is loaded the bootstrap program searches for the startupconfiguration file known as start-config in NVRAM

This file has the previously saved configuration command and parameters

Including ( addresses ,routing information , passwords and other configuration

saved by the network admin


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If the startup configuration file is found in NVRAM the IOS loads it into RAM

The default running config does not contain any interface address, routing

information , passwords or other specific configuration information

Management ports

Routers have physical connectors that are used to manage the router

Unlike Ethernet and serial interfaces , management ports are not used for

packet forwarding

The most common management port is the console port , the console port is

used to configure the router without the need for network access to that

router

Another management port is the auxiliary port , but not all routers have

auxiliary port


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Router interfaces

Refer to physical connectors on the router , who main purpose to receive and

forward packets

For example : a Router usually has fast Ethernet interfaces for connection todifferent LANs and various types of WANs interfaces to connect varity of serial

links including T1, DSL , ISDN

Basic router Configuration

The first prompt the user mode promptRouter>

The second prompt the privileged mode prompt

Router>enable

Router#


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Global configuration mode prompt

Router# conf t

Router(config)#

Router RenameRouter>enable

Router# conf tRouter(config)# hostname r1

R1(config)#


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Examining Router interfaces

Physically connecting a WAN interface

The WAN physical layer describes the interface between the data terminal

equipment (DTE) and the data circuit-terminating equipment (DCE)

The DCE is the service provider and the DTE is the attached device

The router is the DTE device and is connected to a CSU/DSU which is the DCE

device

The DCE device (CSU/DSU) is used to convert the data from the router (DTE

device ) into a form acceptable to the WAN service provider


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The (CSU/DSU) DCE device is also responsible for converting the data from theWAN service provider into a form acceptable by the router (DTE)device

Router is usually connected to the (CSU/DSU) using a serial DTE cable

Serial interfaces require a clock signal to control the timing of the

communication

In most environments the service provider (DCE) device such as (CSU/DSU) will

provide the clock by default

However in a lab environment we are not using any (CSU/DSU) and we don

not have ISP

Configure the clock signal on the serial interface using the clock rate command

You can distinguish DTE from DCE by looking at the connector between the

two cables , the DTE cable has a male connectors and DCE has a femaleconnectors


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You can use the show controllers command to determine which end of thecable is attached to the interface

Example :

R1#show controllers serial0/0/0

The available clock rate in bit per second

1200, 2400, 9600, 19200, 38400, 56000, 64000, 72000, 125000, 148000,

500000, 800000, 1000000, 1300000, 2000000, and 4000000. Some bit rates

might not be available on certain serial interfaces.

Because Serial 0/0/0 interface on R1 has the DCE cable attached, we will

configure that interface with a clock rate.

R1(config)#interface serial 0/0/0

R1(config-if)#clock rate 64000


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Router Interface Configuration

R1>enable

R1# conf t

R1(config)#interface serial 0/0/0R1(config-if)# ip address 192.168.2.1 255.255.255.0

R1(config-if)# no shutdown

R1(config-if)#exit

Verifying basic router configuration

R1#show ip interface brief


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Configuring an Ethernet Interface

R1>enable

R1# conf t

R1(config)#interface fastethernet 0/0

R1(config-if)#ip address 172.16.3.1 255.255.255.0R1(config-if)#no shutdown

Changing IP Address

R1>enable

R1# conf t

R1(config)#interface serial 0/0/0

R1(config-if)# shutdown

R1(config-if)# no ip address


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Introducing the Routing Table

The primary function of a router is to forward a packet toward its destination

network, which is the destination IP address of the packet. To do this, a router

needs to search the routing information stored in its routing table.

A routing table is a data file in RAM that is used to store route information

about directly connected and remote networks.

The routing table contains network/next hop associations.

These associations tell a router that a particular destination can be optimallyreached by sending the packet to a specific router that represents the "next

hop" on the way to the final destination.

The next hop association can also be the outgoing or exit interface to the final

destination.


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Routing table Principals

1- every router makes its decision alone , based on the information it has in its

own routing table

2- the fact that one router has certain information in its routing table does not

mean that other routers have the same information

3- routing information a bout a path from one network to another does not

provide routing information about the reverse or return path


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The command for configuring a static route is ip route

Router(config)#ip route network-address subnet-mask

{ip-address (Next Hop)| exit-interface }

Configuring a static route with the next hop :

R1(config)#ip route 192.168.1.0 255.255.255.0 172.16.2.2

R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2

Configuring a static route with the exit interface :

R1(config)#ip route 192.168.1.0 255.255.255.0 serial0/0/0

R1(config)#ip route 192.168.2.0 255.255.255.0 serial0/0/0


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Modifying static routes

R1(config)#no ip route 192.168.2.0 255.255.255.0 172.16.2.2

Examining Routing Table

R1#Show ip rout

Is used to display the routing table

R1#ping 192.168.2.4


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Dynamic routing Protocols

Routing protocols are used to facilitate the exchange of routing

information between routers

Routing protocols allow routers to dynamically share information about

remote networks and automatically add this information to their own

routing tables

Routing protocols determine the best path to each network which is

then added to the routing table

One of the primary benefits to using a dynamic routing protocols is that

routers exchange routing information whenever there is a topology

change


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Compared to static routing , dynamic routing protocols require less

administrative overhead .

However the expense of using dynamic routing protocols is dedicating

part of routers resources for protocol operation including CPU and

network link bandwidth

The purpose of dynamic routing protocols :

- Discovery of remote networks

- Maintaining up to data routing information

- Choosing the best path to destination networks

- Ability to find a new best path if the current path is no longer a available


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Autonomous system (AS) otherwise known as a routing domain

AS : Is a collection of routers under a common administration

Ex. : companys internal network and an ISPs Network , So we need interior

and exterior routing protocols

Interior gateway protocols (IGP) : are used for intra Autonomous system

routing - routing inside an Autonomous system

Exterior gateway protocols (EGP) : are used for inter- Autonomous system

routing routing between Autonomous systems


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Characteristics ofIGP and EGP routing protocols

IGP s : are used for routing within a routing domain , those networks within the

control of a single organization

An autonomous system is commonly comprised of many individual networksbelonging to companies

An IGP is used to route within the autonomous system and also used to route

with the individual networks themselves

IGPs Include ( RIP , IGRP , EIGRP , OSPF , IS-IS )

Routing protocols uses a metric to determine the best path to a network the

metric used by the routing protocol RIP is a hop count , which is the number of

routers that a packet must traverse in reaching another network


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OSPFProtocol uses a bandwidth to determine the shortest path

EGP : are designed for use between different autonomous systems that are

under the control of different administrations

BGP : is the only currently viable EGP and is the routing protocol used by the

internet

BGP is typically used between ISPs and between a company and ISP


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Interior Gateway Protocols (IGPs) can be Classified as two types :

1- Distance Victor

2- Link state

Distance Victor : means that the routes are advertised as vectors of distance

and direction

- Distance is defined in terms of a metric such as hop count and direction is

simply the next hop router or exit interface

Link state protocol domain :

- Using a link state routing protocol is like having a complete map of the

network topology

- Usually occurring in large networks


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Metric

Purpose of metric :

There are cases when routing protocol learns of more than one route to the

same destination

To select the best path , the routing protocol must be able to evaluate and

differentiate between available paths

For this reason a metric is used

A metric is used to determine which path is most preferable when there are

multiple paths to the same remote networks

Ex.: RIP uses hop count, EIGRP uses a compilation of bandwidth and delay,

OSPF uses bandwidth


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R1(config)#router ?

R1(config)#router rip

R1(config-router)#network 192.168.1.0



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Telnet Command

Router (config)#enable password 123 Enable mode Password

Router(config)#line vty 0-15 Connections

Router(config-line)#password hossam Telnet passwordRouter(config-line)#login

Router(config-line)#do wr

>telnet IP Address in pc command prompt


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RIP v1 RIP v2

Broadcast Multicast

Classful classless

No authentication authentication

Default Route

R1(config)#ip route 0.0.0.0 0.0.0.0 next hop

RIP Protocol Passive InterfaceR1(config)#router rip




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OSPF

- Link state (Bandwidth)

- Link state updates- Neighbors table

- Topology table

- Routing table

- Router ID- Physical port

- Loopback interface


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Area 0

Area 1 Area 2

Topology Table

Internal Router

ABR area border

router

ABR area border

router

Backbone router

Internal Router

Topology Table


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OSPF metric (cost) = 10^8/bandwidth

OSPF Topology

- Point to point hello message 10 s. dead message 40 s

- Broadcast multi-access hello message 10 s. dead message 40 s

- Nonbroadcast multi-access hello message 30 s. dead message 120 s

DR Router and BDR Router


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DR Router and BDR Router (interface number from 0 to 255)

The highest interface number DR and the second BDR

OSPF Multicast protocol

Router(config)#router ospf 1 process number(1-65535)#network 192.168.2.2 0.0.0.255 area 1 c. network wild card area


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Password recovery

1- Reboot Router

2- press ctrl+break

3- change confreg to 0x2142 default= 0x2102

4-reset

DHCP

#Ip dhcp pool hossam

#network 192.168.2.0 255.255.255.0

#default-router 192.168.2.1#do wr

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