CCNA2 - 1 -Configuring Network Devices and Introduction to Routing

8/13/2019 CCNA2 - 1 -Configuring Network Devices and Introduction to Routing

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2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1

WELCOME TOCCNA 2

Some important info to follow


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ITE PC v4.0Chapter 1 2 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Before we begin....Practical Sessions

You need to attend your practical session every week to avoid fallingbehind

Online Chapter Tests Will be active for 1 week following the theory lecture

Passing requirements You need to pass

both the CCNA 2 and CCNA 3 online final exam and the skillsexam with 70%

the written exam in November with 50%


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Configuring Network Devices &Introduction to Routing


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The purpose of Cisco IOSSoftware

As with a computer, a router or switch cannot functionwithout an operating system.Cisco calls its operating system the Cisco InternetworkOperating System or Cisco IOS.

The Cisco IOS provides the following network services:Basic routing and switching functionsReliable and secure access to networked resourcesNetwork scalability


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Router user interfaceThe Cisco IOS software uses a command-lineinterface (CLI) as the traditional consoleenvironment.This environment is accessible through several

methods:Console AUX port (modem)Telnet


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Router user interface modes

The IOS provides a command interpreter service known asthe command executive ( EXEC ).

After each command is entered, the EXEC validates andexecutes the command.The levels are user EXEC mode and privileged EXECmode .


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Cisco IOS software features

Although there are numerous IOS images fordifferent Cisco device models and feature sets, thebasic configuration command structure is thesame.

The naming convention for the different Cisco IOSreleases contains three parts:The platform on which the image runsThe special features supported in the imageWhere the image runs and whether it has been


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Operation of Cisco IOS Software

The Cisco IOS devices have three distinct operatingenvironments or modes:

ROM monitorBoot ROM

Cisco IOS


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Troubleshooting command line errorsHelp is at hand.. When in doubt use the ? to see what commandoption are available


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Examining the initial routerbootup


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Device management

Out-of-band management requires a computer to be directlyconnected to the console port or auxiliary port (AUX) of thenetwork device being configured.Use in-band management to monitor and make configurationchanges to a network device over a network connection.


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Establishing a HyperTerminalsession

Take the following steps to connect a terminal to the consoleport on the router:Connect the terminal using the RJ-45 to RJ-45 rollovercable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter.Configure the terminal or PC terminal emulation softwarefor 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow

Rollovercable

Consoleport

Com1 or Com2 serialport

Terminal ora PC with

terminalemulationsoftware

Router

bl h l


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Establishing a HyperTerminalsession

Important: A console connection is not the same as anetwork connection!

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Logging into the router

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Two commands can be used to set a password used toaccess privileged EXEC mode: enable password andenable secret The following are specific modes that can also be accessedfrom the global configuration mode:

InterfaceSubinterfaceLine


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Keyboard help in the router CLI

17


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Keyboard help in the router CLI


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Enhanced editing commands

Ctrl-Z is a command used to back out of configurationmode. This will return the user to the privileged EXECmode prompt.


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Router command history

terminal history size : maximum number ofcommands is 256


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Router as a Computer

The basic purpose of a router-Computers that specialize in sending packets overthe data network. They are responsible forinterconnecting networks by selecting the best path

for a packet to travel and forwarding packets to theirdestinationRouters are the network center

-Routers generally have 2 types of connections:

-WAN connection (Connection to ISP)-LAN connection


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Router as a ComputerData is sent in form of packets between 2 enddevicesRouters are used to direct packet to its destination


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Router as a ComputerRouters examine a packets destination IP address

and determine the best path by enlisting the aid ofa routing table


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Router components and their functions

CPU - Executes operating system instructions

Random access memory (RAM) - Contains the running copy ofconfiguration file. Stores routing table. RAM contents lost when power isoff

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)

Interfaces - There exist multiple physical interfaces that are used toconnect network. Examples of interface types:-Ethernet / fast Ethernet interfaces-Serial interfaces-Management interfaces


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Router components

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Major phases to the router boot-up

Test router hardwarePower-On Self Test

(POST)Execute bootstrap loader

Locate & load Cisco IOSsoftware-Locate IOS-Load IOS

Locate & load startupconfiguration file or entersetup mode-Bootstrap program looks

for configuration file


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Verify the router boot-up process

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

Platform model numberImage name & IOS versionBootstrap version stored in ROMImage file name & where it was loaded fromNumber & type of interfaces

Amount of NVRAM Amount of flashConfiguration register


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Info we can see at boot time


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Router Interfaces

Router Interface is a physical connector that enablesa router to send or receive packetsEach interface connects to a separate networkConsist of socket or jack found on the outside of arouterTypes of router interfaces:

-Ethernet-Fastethernet-Serial-DSL-ISDN

-Cable


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Router InterfacesTwo major groups of Router Interfaces

LAN Interfaces:

Are used to connect router to LANnetworkHas a layer 2 MAC address

Can be assigned a Layer 3 IPaddressUsually consist of an RJ-45 jack

WAN Interfaces

Are used to connect routers to external networks thatinterconnect LANs.

Depending on the WAN technology, a layer 2 addressmay be used.

Uses a layer 3 IP address


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Routers and the Network Layer

Routers use destination IP address to forwardpackets

The path a packet takes is determined after a routerconsults information in the routing table.

After router determines the best path

Packet is encapsulated into a frameFrame is then placed on network medium in form of Bits


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Routers Operate at Layers 1, 2 & 3Router receives a stream of encoded bits

Bits are decoded and passed to layer 2Router de-encapsulates the frameRemaining packet passed up to layer 3

Routing decision made at this layer by examining destination IP

addressPacket is then re-encapsulated & sent out outboundinterface


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Implementing Basic AddressingSchemes

When designing a new network or mapping anexisting network you must provide the followinginformation in the form of a document:

-Topology drawing that Illustrates physical connectivity

Address table that provides the following information:Device nameInterfaces usedIP addresses

Default gateway


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Basic Router Configuration A basic router configuration should contain thefollowing:

-Router name - Host name should be unique-Banner - At a minimum, banner should warnagainst unauthorized use

-Passwords - Use strong passwords-Interface configurations - Specify interfacetype, IP address and subnet mask. Describepurpose of interface. Issue no shutdown

command. If DCE serial interface issue clockrate command. After entering in the basic configuration the followingtasks should be completed

-Verify basic configuration and routeroperations.


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Configure Devices and Apply AddressesVerify Basic Router Configuration

-Issue the show running-config command-Save the basic router configuration by Issuing thecopy running-config startup-config command

-Additional commands that will enable you to furtherverify router configuration are:

Show running-config - Displays configuration currently inRAMShow startup-config - Displays configuration file NVRAMShow IP route - Displays routing tableShow interfaces - Displays all interface configurationsShow IP int brief - Displays abbreviated interfaceconfiguration information


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Routing Table StructureRouting Table is stored in ram and containsinformation about:

Directly connected networks - this occurs when adevice is connected to another router interface

Remotely connected networks - this is a networkthat is not directly connected to a particular routerDetailed information about the networks include

source of information, network address & subnet

mask, and Ip address of next-hop routerShow ip route command is used to view a routingtable


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Routing Table StructureRouter interfaces

Each router interface is a member of a different network Activated using the no shutdown commandIn order for static and dynamic routes to exist inrouting table you must have directly connectednetworks


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Static RoutesStatic routes in the routing table

-Includes: network address and subnet mask and IPaddress of next hop router or exit interface-Denoted with the code S in the routing table

-Routing tables must contain directly connectednetworks used to connect remote networks beforestatic or dynamic routing can be used

When to use static routes

-When network only consists of a few routers-Network is connected to internet only through oneISP-Hub & spoke topology is used on a large network


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Connected and Static routes


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Dynamic routing protocolsDynamic routing protocols

-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-Routers are able discover new networks by sharingrouting table information

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

IP routing protocols. Example of routing protocols include:-RIP-IGRP-EIGRP-OSPF


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Connected. Static and Dynamic


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Routing Table Principles3 principles regarding routing tables:

Every router makes its decisions alone , based onthe information it has in its routing table.Different routing table may contain different

information A routing table can tell how to get to a destinationbut not how to get back


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Effects of the 3 Routing Table Principles

-Packets are forwarded through the network from one routerto another, on a hop by hop basis.

-Packets can take path X to a destination but return via pathY (Asymmetric routing).


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Internet Protocol (IP) packetInternet Protocol (IP) packet format contains fieldsthat provide information about the packet and thesending and receiving hostsFields that are importance for CCNA students:

-Destination IP address-Source IP address-Version & TTL-IP header length-Precedence & type of service-Packet length


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Internet Protocol (IP)


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MAC Layer Frame Format

MAC Frames are also divided into fields. Theyinclude:

-Preamble-Start of frame delimiter-Destination MAC address-Source MAC address-Type/length

-Data and pad-Frame check sequence


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MAC Layer Frame Format


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Router Metrics A Metric is a numerical value used by routing protocols helpdetermine the best path to a destination

The smaller the metric value the better the path2 types of metrics used by routing protocols are:

-Hop count - this is the number of routers a packet must travelthrough to get to its destination-Bandwidth - this is the speed of a link also known as the datacapacity of a link


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Router Paths with Equal MetricsEqual cost metric is a condition where a router has multiplepaths to the same destination that all have the same metricTo solve this dilemma , a router will use Equal Cost LoadBalancing . This means the router sends packets over the multipleexit interfaces listed in the routing table.

Ro ter Paths and Packet


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Router Paths and PacketSwitchingPath determination is a process used by a router to pick the bestpath to a destinationOne of 3 path determinations results from searching for the bestpath

Directly connected networkRemote networkNo route determined


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Router Packet SwitchingSwitching Function of Router is the processused by a router to switch a packet from anincoming interface to an outgoing interface onthe same router.

-A packet received by a router will do thefollowing:

Strips off layer 2 headers.Examines destination IP address located in

Layer 3 header to find best route todestination.Re-encapsulates layer 3 packet into layer 2

frame.Forwards frame out exit interface.

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As a packet travels from one networkingdevice to another

-The Source and Destination IP addresses NEVER change-The Source & Destination MAC addresses

CHANGE as packet is forwarded from onerouter to the next.-TTL field decrement by one until a value ofzero is reached at which point router discardspacket (prevents packets from endlesslytraversing the network)


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A Day in the life of a Packet

PC1 Wants to send something to PC 2 here is part ofwhat happensStep 1 - PC1 encapsulates packet into a frame. Framecontains R1s destination MAC address


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A Day in the life of a Packet Step 2 - R1 receives Ethernet frame.

R1 sees that destination MAC address matches its own MAC.R1 then strips off Ethernet frame.R1 Examines destination IP.R1 consults routing table looking for destination IP.

After finding destination IP in routing table, R1 now looks upnext hop IP address.R1 re-encapsulates IP packet with a new Ethernet frame.R1 forwards Ethernet packet out Fa0/1 interface.


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A Day in the life of a Packet


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A Day in the life of a Packet Path determination and switching function details. PC1 Wants tosend something to PC 2 here is part of what happens

Step 3 - Packet arrives at R2R2 receives Ethernet frameR2 sees that destination MAC address matches its own MACR2 then strips off Ethernet frameR2 Examines destination IPR2 consults routing table looking for destination IP

After finding destination IP in routing table, R2 now looks upnext hop IP addressR2 re-encapsulates IP packet with a new data link frameR2 forwards Ethernet packet out S0/0 interface


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A Day in the life of a Packet Step 4 - Packet arrives at R3

R3 receives PPP frameR3 then strips off PPP frameR3 Examines destination IPR3 consults routing table looking for destination IP

After finding destination IP in routing table, R3 is directly connectedto destination via its fast Ethernet interfaceR3 re-encapsulates IP packet with a new Ethernet frameR3 forwards Ethernet packet out Fa0/0 interface

Step 5 - IP packet arrives at PC2. Frame is decapsulated& processed by upper layer protocols.


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SummaryRouters are computers that specialize in sending data over a network.Routers are composed of:

-Hardware i.e. CPU, Memory, System bus, Interfaces-Software used to direct the routing process

IOSConfiguration file

Routers need to be configured. Basic configuration consists of:-Router name-Router banner-Password(s)-Interface configurations i.e. IP address and subnet mask

Routing tables contain the following information-Directly connected networks-Remotely connected networks-Network addresses and subnet masks-IP address of next hop address


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SummaryRouters determine a packets path to its destinationby doing the following

Receiving an encapsulated frame & examiningdestination MAC address.

If the MAC address matches then Frame is de-encapsulated so that router can examine thedestination IP address.If destination IP address is in routing table or there

is a static route then Router determines next hop IPaddress. Router will re-encapsulate packet withappropriate layer 2 frame and send it out to nextdestination.Process continues until packet reaches destination.Note - only the MAC addresses will change the


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Documents

CCNA2 - 1 -Configuring Network Devices and Introduction to Routing