2.1_Intro to Routing

8/7/2019 2.1_Intro to Routing

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Introduction to Routing and Packet ForwardingRouting Protocols

and Concepts


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Routing Protocolsand Concepts

CISCO CCNA BOOTCAMP


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Router as a Computer

Describe the basic purpose of a routerComputers that specialize in sending packets over thedata network.They are responsible for interconnecting networks byselecting the best path for a packet to travel andforwarding packets to their destination

Routers have many of the same hardware and softwarecomponents that are found in other computers including:

CPURAMROMOperating System


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Router components and their functions

CPU - Executes operating system instructions

such as system initialization, routing functions, and switchingfunctions.

Random access memory (RAM) -RAM stores the instructions and dataneeded to be executed by the CPU.

Read-only memory (ROM) - Holds diagnostic software used when routeris powered up. Stores the routers bootstrap program.

Non-volatile RAM (NVRAM) - Stores startup configuration. This mayinclude IP addresses (Routing protocol, Hostname of router)

Flash memory - Contains the operating system (Cisco IOS)


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Router components


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Internetwork Operating System

The operating system software used in Ciscorouters is known as Cisco Internetwork OperatingSystem (IOS).

Cisco IOS is a multitasking operating systemthat is integrated with routing, switching,

internetworking, and telecommunicationsfunctions.

Although the Cisco IOS may appear to be the sameon many routers, there are many different IOSimages.

An IOS image is a file that contains the entireIOS for that router. Cisco creates many differenttypes of IOS images, depending upon the modelof the router and the features within the IOS.

Typically the more features in the IOS, thelarger the IOS image, and therefore, the more

flash and RAM that is required to store and loadthe IOS.


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Major phases to therouter boot-upprocess

Test router hardware

Power-On Self Test (POST) Execute bootstrap loader

Locate & load Cisco IOSsoftware

Locate IOS

Load IOS

Locate & load startup

configuration file or enter setupmode


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Stages of the router power-on boot sequence


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Verify the router boot-up process:

-The show version command is used to viewinformation about the router during the bootupprocess. Information includes:

Image name & IOS version

IOS (tm) C2600 Software (C2600-I-M),Version 12.2(28), RELEASE SOFTWARE(fc5).

Bootstrap version stored in ROM

ROM: System Bootstrap, Version12.1(3r)T2, RELEASE SOFTWARE (fc1)

Image file name & where it was loaded from

System image file is "flash:c2600-i-mz.122-28.bin"

show version


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Management Ports

Routers have physical connectors that areused to manage the router. Theseconnectors are known as managementports.

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

The most common management port is theconsole port.

The console port is used to connect aterminal, or most often a PC running terminalemulator software, to configure the routerwithout the need for network access to thatrouter.

The console port must be used during initialconfiguration of the router.

.


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Routers determine the best path

Router Interface is a physical connector that enables arouter to send or receive packets

Each interface connects to a separate network

different IP network

Typically, the interfaces connect to various types ofnetworks, which means that different types of media andconnectors are required. Types of router interfaces:

-Ethernet-Fastethernet

-Serial

-DSL

-ISDN

-Cable


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Two major groups of Router Interfaces:LAN & WAN

LAN Interfaces: such as Ethernet andFastEthernet

Are used to connect router to LAN network

Has a layer 2 MAC address

a router Ethernet interface participatesin the ARP process for that LAN.

Can be assigned a Layer 3 IP address

Usually consist of an RJ-45 jack

When a router is connected to aswitch, a straight-through cable isused.

When two routers are connecteddirectly through the Ethernet

interfaces, or when a PC NIC isconnected directly to a router Ethernetinterface, a crossover cable is used.


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Two major groups of Router Interfaces: LAN & WAN

WAN Interfaces- such as serial, ISDN,and Frame Relay

Are used to connect routers toexternal networks thatinterconnect LANs, usually over alarger geographical distance..

Depending on the WAN

technology, a layer 2 address maybe used.

Uses a layer 3 IP addressSimilar to LAN interfaces,each WAN interface has its ownIP address and subnet mask,which identifies it as a memberof a specific network.

TheL

ayer 2 encapsulation can beof different types,PPP, Frame Relay, and HDLC(High-Level Data Link Control).


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Routers examine a packets destination IP address anddetermine the best path by enlisting the aid of a routing table


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The primary responsibility of a router is to direct packets destined forlocal and remote networks by:

Determining the best path to send packets

Forwarding packets toward their destination

The router uses its routing table to determine the best path to forwardthe packet.

When the router receives a packet, it examines its destination IP addressand searches for the best match with a network address in the router'srouting table.

The routing table also includes the interface to be used to forward thepacket. Once a match is found, the router encapsulates the IP packet intothe data link frame of the outgoing or exit interface, and the packet is thenforwarded toward its destination.


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Configure Devices and Apply

Addresses Implementing Basic Addressing Schemes

When designing a new network or mapping an existing network youmust provide the following information in the form of a document:

-Topology drawing that Illustrates physical connectivity

Address table that provides the following information: Device name

Interfaces used

IP addresses

Default gateway


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Addresses Basic Router Configuration A basic router configuration should contain the following:

-Router name - Host name should be unique

-Banner- At a minimum, banner should warn against unauthorized use

-Passwords - Use strong passwords

-Interface configurations

Specify interface type,

IP address and subnet mask.

Describe purpose of interface.

Issue no shutdown command.

If DCE serial interface issue clock rate command.

After entering in the basic configuration the following tasks should be completed

-Verify basic configuration and router operations.

-Save the changes on a router


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AddressesRouter>

Router>enable

Router#

Router#config t

Router(config)#enable secret class

Router(config)#enable password cisco

Router(config)#hostname R1

R1(config)#

R1(config)#line console 0

R1(config-line)#password ciscoR1(config-line)#login

R1(config-line)#exit

R1(config)#line vty 0 4

R1(config-line)#password cisco

R1(config-line)#login

R1(config-line)#exit


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Configure Devices and ApplyAddresses

Configuring a Banner

From the global configuration mode, configure themessage-of-the-day (motd) banner. A delimitingcharacter, such as a "#" is used at the beginning andat the end of the message. The delimiter allows you toconfigure a multiline banner, as shown here.

R1(config)#banner motd #

Enter TEXT message. End with the character '#'.

******************************************

WARNING!! Unauthorized Access Prohibited!!

******************************************


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Limiting Device Access Enable and Enable Secret Passwords

To provide additional security, use enable password orenable secret command to establish authentication beforeaccessing privileged EXEC (enable) mode.

Always use the enable secret command, not the olderenable password command, if possible.

The following commands are used to set the passwords:

Router(config)#enable password password

Router(config)#enable secret password

If no enable password or enable secret password is set,the IOS prevents privileged EXEC access from a Telnetsession.

Without an enable password having been set, aTelnet session would appear this way:

Switch>enable

% No password set Switch>


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Limiting Device Access VTY Password

The vty lines allow access to a router via Telnet.

By default, many Cisco devices support 5 VTY linesthat are numbered 0 to 4.

A password needs to be set for all available vty lines.

The same password can be set for all connections.

However, it is often desirable that a unique passwordbe set for one line to provide a fall-back for

administrative entry to the device if the otherconnections are in use.

The following commands are used to set a password:

Router(config)#line vty 0 4

Router(config-line)#password password

Router(config-line)#login

By default, the IOS includes the login command on the

VTY lines. This prevents Telnet access to the devicewithout first requiring authentication.If, by mistake, the no login command is set, whichremoves the requirement for authentication,unauthorized persons could connect to the line usingTelnet. This would be a major security risk.


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Encrypting Password Display

Another useful command prevents passwords fromshowing up as plain text when viewing theconfiguration files.

This is the service password-encryptioncommand.

This command causes the encryption ofpasswords to occur when a password isconfigured.

The service password-encryption commandapplies weak encryption to all unencryptedpasswords.

This encryption does not apply to passwordsas they are sent over media only in theconfiguration.

The purpose of this command is to keepunauthorized individuals from viewingpasswords in the configuration file.

Once the encryption has been applied, removingthe encryption service does not reverse theencryption.


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Configuring router passwords (cont.)

WARNING

service password-encryption uses a Cisco Level 7 encryption which is very

easy to decrypt.

For the GetPass! software www.boson.com

However, the enable secret uses a stronger encryption method

and cannot be easily hacked.

and !


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Doesnt work for enable secret!


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R1(config)#interface Serial0/0/0

R1(config-if)#ip address 192.168.2.1 255.255.255.0

R1(config-if)#description Ciruit#VBN32696-123 (help desk:1-800-555-1234)

R1(config-if)#no shutdown

R1(config-if)#clock rate 64000

Note: When cabling a point-to-point serial link in our lab environment, oneend of the cable is marked DTE and the other end is marked DCE.

The router that has the DCE end of the cable connected to its serial interfacewill need the additional clock rate command configured on that serialinterface.

This step is only necessary in a lab environment


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The FastEthernet interface needs to beconfiguredR1(config)#interface FastEthernet0/0R1(config-if)#ip address 192.168.1.1

255.255.255.0R1(config-if)#description R1 LANR1(config-if)#no shutdown


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Verify Basic Router Configuration

-Issue the show running-configcommand

displays the current running configuration that is stored in RAM.

-Issuing the copy running-config startup-configcommand

Save the basic router configuration

-Additional commands that will enable you to further verify routerconfiguration are:

Show startup-config - Displays configuration file NVRAM

Show IP route - Displays routing table

Show interfaces - Displays all interface configurations

Show IP int brief- Displays abbreviated interface configurationinformation


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Routing Table Structure

The primary function of a router is to forward a packet toward itsdestination network, which is the destination IP address of thepacket.

To do this, a router needs to search the routing information stored in its routingtable.

Routing Table is stored in ram and contains information:

Directly connected networks - this occurs when a device is connected toanother router interface

Remotely connected networks - this is a network that is not directlyconnected to a particular router

network/next hop associations - about the networks include source ofinformation, network address & subnet mask, and Ip address of next-hoprouter

Show ip route command is used to view a routing table


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The following analogies may help clarifythe concept of connected, static, anddynamic routes:

Directly Connected Routes - To visit aneighbor, you only have to go down thestreet on which you already live. This path

is similar to a directly-connected routebecause the "destination" is availabledirectly through your "connectedinterface," the street.

Static Routes - A train uses the samerailroad tracks every time for a specifiedroute. This path is similar to a static routebecause the path to the destination isalways the same.

Dynamic Routes - When driving a car, youcan "dynamically" choose a different pathbased on traffic, weather, or otherconditions. This path is similar to adynamic route because you can choose anew path at many different points on yourway to the destination.


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Adding a connected network to the routing table

-Router interfaces

Each router interface is a member of a different network

Activated using the no shutdown command

In order for static and dynamic routes to exist in routing table you must

have directly connected networks


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Remote networks are added to therouting table either by configuringstatic routes or enabling a dynamicrouting protocol.

Static routes in the routing table-Includes: network address andsubnet mask and IP address ofnext hop router or exit interface-Denoted with the code S in therouting table-Routing tables must containdirectly connected networksused to connect remotenetworks before static ordynamic routing can be used


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When to use static routes

-When network only consists of a few routers

Using a dynamic routing protocol in such acase does not present any substantialbenefit.

-Network is connected to internet only through

one ISP There is no need to use a dynamic routing

protocol across this link because the ISPrepresents the only exit point to theInternet.

-Hub & spoke topology is used on a largenetwork

A hub-and-spoke topology consists of acentral location (the hub) and multiplebranch locations (spokes), with each spokehaving only one connection to the hub.

Using dynamic routing would beunnecessary because each branch has onlyone path to a given destination-through thecentral location.


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Dynamic routing protocols

-Are used to add remote networks to a routing table

-Are used to discover networks

-Are used to update and maintain routing tables

Automatic network discovery

-Network discovery is the ability of a routing protocol to share informationabout the networks that it knows about with other routers that are alsousing the same routing protocol.

Instead of configuring static routes to remote networks on every router, adynamic routing protocol allows the routers to automatically learn aboutthese networks from other routers.

These networks - and the best path to each network - are added to therouter's routing table and denoted as a network learned by a specific

dynamic routing protocol.

Maintaining routing tables

-Dynamic routing protocols are used to share routing information withother router & to maintain and up date their own routing table.

Dynamic routing protocols not only make a best path determination tovarious networks, they will also determine a new best path if the initial pathbecomes unusable (or if the topology changes)


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Router Paths: Best Path

Whenever multiple paths to reach the same network exist, eachpath uses a different exit interface on the router to reach thatnetwork.

The best path is selected by a routing protocol based onthe value or metric it uses to determine the distance to reacha network.

Metrics can be based on either a single characteristic orseveral characteristics of a path.

Some routing protocols can base route selection onmultiple metrics, combining them into a single metric.

The smaller the value of the metric, the better the path.

Routing protocols, such as RIP, use simple hop-count,which the number of routers between a router and thedestination network.

For example, a router will prefer a path that is 5 hopsaway over a path that is 10 hops away.

Other routing protocols, such as OSPF, determine theshortest path by examining the bandwidth of the links, andusing the links with the fastest bandwidth from a router tothe destination network.


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Router Paths and Packet Switching

A Metric is a numerical value used by routing protocols help determine the bestpath to a destination

The smallerthe metric value the betterthe path

2 types of metrics used by routing protocols are:

-Hop count - this is the number of routers a packet must travel through to getto its destination

Hop count of four indicates that a packet must pass through four routers toreach its destination.

If multiple paths are available to a destination, the routing protocol, suchas RIP, picks the path with the least number of hops.

-Bandwidth - this is the speed of a link also known as the data capacity of alink

OSPF routing protocol uses bandwidth as its metric. The best path to a

network is determined by the path with an accumulation of links that havethe highest bandwidth values, or the fastest links.


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Router Paths: Equal Cost LoadBalancing

You may be wondering what happens if a routing table has twoor more paths with the same metric to the same destinationnetwork.

When a router has multiple paths to a destination network and the value ofthat metric (hop count, bandwidth, etc.) is the same, this is known as anequal cost metric, and the router will perform equal cost load balancing.

Equal cost metric is a condition where a router has multiplepaths to the same destination that all have the same metric

The router will forward

packets using the multiple

exit interfaces listed in the

routing table.


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Router Paths and Packet Switching

Packet forwarding involves two functions:

Path determination function

Switching function

Path determination is a process used by a router to pickthe best path to a destination

One of 3 path determinations results from searching forthe best path

Directly connected network

The destination IP address of the packet is a hostaddress on the same network as this router'sinterface

Remote network

If the destination IP address of the packetbelongs to a remote network, then the packet isforwarded to another router.

No route determined

the packet is discarded


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Router Paths and PacketSwitching

Switching Function of Router is the process used by arouter to switch a packet from an incoming interface toan outgoing interface on the same router.

What does a router do with a packet received from onenetwork and destined for another network?

-A packet received by a router will do the following:Strips offlayer 2 headers.Examines destination IP address located inLayer 3 header to find best route to destination.Re-encapsulates layer 3 packet into layer 2frame.Forwards frame out exit interface.


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2.1_Intro to Routing

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