Routing Protocols and Concepts – Chapter 1 potx

ƒ NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file ƒ NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file.. Router

Introduction to Routing

and Packet Forwarding g

Routing Protocols and Concepts – Chapter 1

ƒ Identify a router as a computer with an OS and de y a ou e as a co pu e a OS a d

hardware designed for the routing process.

ƒ Demonstrate the ability to configure devices and Demonstrate the ability to configure devices and

apply addresses.

ƒ Describe the structure of a routing table Describe the structure of a routing table.

ƒ Describe how a router determines a path and

switches packets switches packets

Router as a Computer

ƒ Describe the basic purpose of a router esc be e bas c pu pose o a ou e

-Computers that specialize in sending packets over the data network

They are responsible for interconnecting networks by selecting the best path for a packet to travel and forwarding packets to their destination

ƒ Routers have many of the same hardware and software components that are found in other computers p p

Router as a Computer

ƒ Router components and their functions” p

ƒCPU - Executes operating system instructions

ƒ such as system initialization, routing functions, and switching functions.

ƒRandom access memory (RAM) RAM stores the instructions and data needed

ƒRandom access memory (RAM) -RAM stores the instructions and data needed

to be executed by the CPU RAM is used to store these components:

– Operating System : The Cisco IOS (Internetwork Operating System) is copied into RAM during bootup g p

– Running Configuration File : This is the configuration file that stores the configuration commands that the router IOS is currently using.

– IP Routing Table g : This file stores information about directly connected and y remote networks It is used to determine the best path to forward the packet.

– ARP Cache : This cache contains the IPv4 address to MAC address mappings, similar to the ARP cache on a PC The ARP cache is used on

h h LAN i f h E h i f routers that have LAN interfaces such as Ethernet interfaces.

– Packet Buffer : Packets are temporarily stored in a buffer when received on an interface or before they exit an interface.

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

Router as a Computer

ƒ Router components and their functions” ou e co po e s a d e u c o s

ƒ Read-only memory (ROM) - Holds diagnostic software used

when router is powered up Stores the router’s bootstrap program.

p g

–ROM is a form of permanent storage Cisco devices use ROM to store:

–The bootstrap instructions

–Basic diagnostic software

–Scaled-down version of IOS

–Scaled-down version of IOS

ROM uses firmware, which is software that is embedded inside the integrated circuit

– Firmware includes the software that does not normally need to

be modified or upgraded, such as the bootup instructions

– ROM does not lose its contents when the router loses power

or is restarted

R t C t

Router as a Computer

ƒ Router components and their functions”

ƒNon-volatile RAM (NVRAM) - Stores startup configuration This may include IP

addresses (Routing protocol Hostname of router)

ƒ NVRAM (Nonvolatile RAM) does not lose its information when power is turned off This is in contrast to the most common forms of RAM, such as DRAM, that requires continual power to maintain its information

ƒ NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file

ƒ NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file

ƒ All configuration changes are stored in the running-config file in RAM, and with few exceptions, are implemented immediately by the IOS

ƒ To save those changes in case the router is restarted or loses power, the running-config must be copied to NVRAM where it is stored as the startup-config file NVRAM retains its must be copied to NVRAM, where it is stored as the startup-config file NVRAM retains its contents even when the router reloads or is powered off.

ƒFlash memory - Contains the operating system (Cisco IOS)

ƒIn most models of Cisco routers, the IOS is permanently stored in flash memory and copied into RAM during the bootup process, where it is then executed by the CPU

ƒFlash consists of SIMMs or PCMCIA cards, which can be upgraded to increase the amount of flash memory

increase the amount of flash memory

ƒInterfaces - There exist multiple physical interfaces that are used to connect network

Examples of interface types:

-Ethernet / fast Ethernet interfaces -Serial interfaces

-Management interfaces

Router as a Computer

ƒ Router components ou e co po e s

Internetwork Operating System

ƒ The operating system software used in Cisco routers is known as Cisco

Internetwork Operating System (IOS)

Internetwork Operating System (IOS)

– Cisco IOS is a multitasking operating system that is integrated with routing, switching, internetworking, and telecommunications functions.

ƒ Although the Cisco IOS may appear to be the same on many routers,Although the Cisco IOS may appear to be the same on many routers,

there are many different IOS images

– An IOS image is a file that contains the entire IOS for that router Cisco creates many different types of IOS images, depending upon the model of the router and the features within the IOS.

the router and the features within the IOS

– Typically the more features in the IOS, the larger the IOS image, and therefore, the more flash and RAM that is required to store and load the IOS

ƒ Although some routers provide a graphical user interface (GUI), the

command line interface (CLI) is a much more common method of

configuring Cisco routers

– The CLI is used throughout this curriculum.

ƒ Upon bootup the startup config file in NVRAM is copied into RAM and

ƒ Upon bootup, 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 Any changes entered by the network administrator are stored in the running- config and are immediately implemented by the IOS

config and are immediately implemented by the IOS

Overview - Managing Cisco IOS Software (cont)

Overview Managing Cisco IOS Software (cont)

Router as a Computer

ƒ Major phases to the ajo p ases o e

router boot-up process

ƒTest router hardwarePower-On Self Test (POST)

Execute bootstrap loaderp

ƒLocate & load Cisco IOS software

Locate IOS-Locate IOS-Load IOS

ƒLocate & load startup configuration file or enter setup mode

-Bootstrap program looks p p gfor configuration file

Stages of the router power-on boot sequence

R t C t

Router as a Computer

ƒ Major phases to the router boot-up process

Step 1 and 2: Test router hardware

P O S lf T t (POST)

• Power-On Self Test (POST)

– During this self-test, the router executes diagnostics from ROM on several hardware components including the CPU, RAM, and NVRAM

• Execute bootstrap loader

– The main task of the bootstrap program is

to locate the Cisco IOS and load it into RAM.

– Note: At this point, if you have a console connection to the router, you will begin to see output on the screen

Step 3 and 4: Locate & load Cisco IOS software

Locate IOS and Load IOS -Locate IOS and Load IOS

– The IOS is typically stored in flash memory, but can also be stored in other places such as a TFTP server.

– If a full IOS image can not be located, a g , scaled-down version of the IOS is copied from ROM into RAM This version of IOS is used to help diagnose any problems and can be used to load a complete version of the IOS into RAM.

– Note: A TFTP server is usually used as a backup server for IOS but it can also be used as a central point for storing and

R t C t

Router as a Computer

Step 5 and 6: Locate & load startup configuration file or enter setup

mode

- After the IOS is loaded, the bootstrap program searches for

the startup configuration file, known as startup-config, in

NVRAM This parameters including:

RAM as the running-config

• The IOS loads the commands in the file, one line at a time

time

– If the startup configuration file does not exist in NVRAM, the

router may search for a TFTP server

• If the router detects that it has an active link to another configured router, it sends a broadcast searching for a configuration file across the active link You will eventually see message like the following one:

• %Error opening tftp://255.255.255.255/network-confg %Error opening tftp://255.255.255.255/network confg (Timed out)

Router as a Computer

ƒ Locate & load startup configuration file or enter setup

mode

– Enter Setup Mode (Optional) If the startup

configuration file can not be located the router

configuration file can not be located, the router

prompts the user to enter setup mode

• Setup mode is a series of questions prompting the user for basic configuration information

Setup mode is not intended to be used to enter complex router configurations and it is not complex router configurations, and it is not commonly used by network administrators

– When booting a router that does not contain a

startup configuration file, you will see the following

question after the IOS has been loaded:

• Would you like to enter the initial configuration dialog? [yes/no]: no

– Setup mode will not be used in this course

to configure the router When prompted to enter setup mode, always answer no If you

e te setup ode, a ays a s e o you answer yes and enter setup mode, you can press Ctrl-C at any time to terminate the setup process.

– When setup mode is not used, the IOS creates a

default running-config.

default running config

• The default running-config is a basic configuration file that includes the router interfaces, management interfaces, and certain default information

Router as a Computer

ƒ Verify the router boot-up process:

show version

-The show version command is used

to view information about the router

during the bootup process

Information includes:

ƒImage name & IOS versionIOS (tm) C2600 Software (C2600 I M) V i 12 2(28)

(C2600-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)

ƒBootstrap version stored in ROM

ƒROM: System Bootstrap, Version 12.1(3r)T2, RELEASE SOFTWARE (fc1)

ƒImage file name & where it was

ƒImage file name & where it was loaded from

ƒSystem image file is

"flash:c2600-i-mz 122-28 bin"flash:c2600 i mz.122 28.bin

ƒSome series of routers, like the

2600, use a fraction of DRAM as packet memory Packet memory is

d f b ff i k tused for buffering packets

ƒTo determine the total amount of DRAM on the router, add both numbers In this example, the Cisco

numbers In this example, the Cisco

2621 router has 60,416 KB (kilobytes) of free DRAM used for temporarily storing the Cisco IOS and other system processes The y pother 5,120 KB is dedicated for packet memory The sum of these numbers is 65,536K, or 64

megabytes (MB) of total DRAM

2 Low-speed serial(sync/async) network interface(s)

ƒ Amount of NVRAM

ƒ32K bytes of non-volatile configuration memory

ƒNVRAM is used to store the startup config file

startup-config file

ƒ Amount of flash

ƒ16384K bytes of processor board System flash (Read/Write)

ƒThis is the amount of flash memory

on the router Flash is used to permanently store the Cisco IOS

Router as a Computer

ƒ Configuration register

show version

ƒ Configuration register is 0x2102

–The last line of the show version

command displays the current

configured value of the software

configuration register in

hexadecimal If there is a second

value displayed in parentheses, it

denotes the configuration register

denotes the configuration register

value that will be used during the

next reload

–The configuration register has

several uses, including password

recovery The factory default setting

for the configuration register is

0x2102 This value indicates that

the router will attempt to load a

Cisco IOS software image from

flash memory and load the startup

configuration file from NVRAM

–Note: The configuration register is

discussed in more detail in a later

course

C fi ti i t

Configuration register

ƒ The order in which the router looks for system

bootstrap depends on the boot field setting in the

register using the show version command

Then use the config-register command, changing

only the value of the last hexadecimal digit

Configuration register (cont )

ƒ To enter the ROM monitor mode, set the configuration

register value to 0xnnn0,

where nnn represents the previous value of the non-boot field

di it

digits

This value sets the boot field bits to 0000 binary

From ROM monitor, boot the operating system manually by

using the b command at the ROM monitor prompt

ƒ To configure the system to boot automatically from ROM

ƒ To configure the system to boot automatically from ROM,

set the configuration register to 0xnnn1,

This value sets the boot field bits to 0001 binary

ƒ To configure the system to use the boot system

commands in NVRAM set the configuration register to

commands in NVRAM, set the configuration register to

any value from 0xnnn2 to 0xnnnF,

These values set the boot field bits to a value between 0010

and 1111 binary

Using boot system commands in NVRAM is the default

Check Configuration Register value (NVRAM)

0 = ROM Monitor mode

1 = ROM IOS

1 ROM IOS

2 - 15 = Boot system from Flash

How a Cisco device locates and loads IOS

The config-register can be Downloaded from:

http:// lilligren com/cisco/do nloads htm

config-register

http://www.lilligren.com/cisco/downloads.htm

Configuration register: 0, 1, and 2 and above

Configuration register: 2102 and 2142

Configuration register: 2102 and 2142

Stages of the router power-on boot sequence

Stages of the router power-on boot sequence

1 ROM

1 POST

2 Bootstrap code executed

1, 2

3 Check Configuration Register value (NVRAM)

0 = ROM Monitor mode

1 = ROM IOS

2 - 15 = Boot system from flash

3

4

2 Check for IOS boot system commands in startup-config file (NVRAM)

If boot system commands in startup-config

a Run boot system commands in order they appear in startup-config to locate the IOS

4

b If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)

3 Locate and load IOS, Default fallback sequence: No IOS boot system commands in startup-config

a Flash (sequential)

b TFTP server (netboot) - The router uses the configuration register value to form a filename from which to boot a default system image stored

on a network server.

c ROM (partial IOS) or keep retrying TFTP depending upon router model

- If no IOS located, get partial IOS version from ROM

4 Locate and load startup-config

a If startup-config found, copy to running-config

b If startup-config not found, prompt for setup-mode

c If setup mode bypassed create a “skeleton” default running config (no startup config)

c If setup-mode bypassed, create a skeleton default running-config (no startup-config)

How a Cisco device locates and loads IOS

How a Cisco device locates and loads IOS

ƒ The router can use its own fallback

sequence to load the software q

The router looks to the boot system

commands saved in NVRAM.

(Tony) The router has its own default

fallback sequence This default sequence

fallback sequence This default sequence

can be interrupted by using the boot

system command and/or config register.

ƒ The settings in the configuration register g g g

enable the following alternatives:

Global configuration mode boot system

commands can be specified to enter

fallback sources.

fallback sources

If NVRAM lacks boot system commands

the system by default uses the Cisco IOS

software in flash memory.

(Tony) No boot system commands (Tony) IOS specified in the boot system does not exist

If flash memory is empty, the router then

If flash memory is empty, the router then

attempts to use TFTP to load an IOS

image from the network.

How a Cisco device locates and loads IOS

U i th b t t d

Using the boot system command

ƒ The three examples show boot system

entries which specify that a Cisco IOS

ft i ill l dsoftware image will load

First from flash memory,

Flash memory – A system image from flash memory can be loaded

flash memory can be loaded

Then from a network server, and

Network server – In case flash memory becomes corrupted, a system

i b l d d f TFTP

image can be loaded from a TFTP server

Finally from ROM:

ROM – If flash memory is corrupted

ROM If flash memory is corrupted and the network server fails to load the image, booting from ROM is the final bootstrap option in software

However the system image in ROM is

However, the system image in ROM is

a subset of the Cisco IOS that lacks the protocols, features of the full Cisco IOS.

Also, if the software has been updated, the router may have an older version

the router may have an older version stored in ROM.

•The command copy running-config startup-config saves the commands in NVRAM.

How a Cisco device locates and loads IOS

• What happen when both config-register and boot

• What happen when both config-register and boot system both exist in the startup-config?

• Which one has the priority? p y

Management Ports

ƒ Routers have physical connectors that are

used to manage the router These connectors

are known as management ports

– Unlike Ethernet and serial interfaces,

management ports are not used for packet

forwarding

ƒ The most common management port is the

console port

The console port is used to connect a terminal

– The console port is used to connect a terminal,

or most often a PC running terminal emulator

software, to configure the router without the

need for network access to that router

– The console port must be used during initial The console port must be used during initial

configuration of the router.

ƒ Another management port is the auxiliary port

– Not all routers have auxiliary ports y p

– At times the auxiliary port can be used in ways

similar to a console port It can also be used to

attach a modem

– Auxiliary ports will not be used in this Auxiliary ports will not be used in this

curriculum.

Routers determine the best path

ƒ Router Interface is a physical connector that

enables a router to send or receive packets

–Each interface connects to a separate network

•different IP network

•different IP network

ƒ Typically, the interfaces connect to various

types of networks, which means that different yp

types of media and connectors are required

Types of router interfaces:

Two major groups of Router Interfaces: LAN & WAN

ƒ LAN Interfaces: such as Ethernet and

FastEthernet

ƒAre used to connect router to LAN network

ƒHas a layer 2 MAC address

ƒa router Ethernet interface participates in the ARP process for that LAN

ƒCan be assigned a Layer 3 IP address

ƒCan be assigned a Layer 3 IP address

ƒUsually consist of an RJ-45 jack

ƒWhen a router is connected to a switch a straight-through cable is

switch, a straight through cable is used

ƒWhen two routers are connected directly through the Ethernet

interfaces or when a PC NIC is

interfaces, or when a PC NIC is connected directly to a router Ethernet interface, a crossovercable is used

f f &

Two major groups of Router Interfaces: LAN & WAN

ƒ WAN Interfaces- such as serial, ISDN, and

ƒUses a layer 3 IP address

ƒ Similar to LAN interfaces each WAN

ƒ Similar to LAN interfaces, each WAN interface has its own IP address and subnet mask, which identifies it as a member of a specific network

ƒThe Layer 2 encapsulation can be of different types,

ƒPPP, Frame Relay, and HDLC (High- , y, ( g Level Data Link Control)

f f &

Two major groups of Router Interfaces: LAN & WAN

ƒ The router in the figure has four

i t f

interfaces

–Each interface has a Layer 3 IP address

and subnet mask that configures it for a

different network

–The Ethernet interfaces also have Layer 2

Ethernet MAC addresses

ƒ The WAN interfaces are using different

Layer 2 encapsulations

–Serial 0/0/0 is using HDLC

–Serial 0/0/1 is using PPP

–Both of these serial point-to-pointBoth of these serial point to point

protocols use a broadcast address for the

Layer 2 destination address when

encapsulating the IP packet into a data link

frame

Routers determine the best path

ƒ A router connects multiple networks p

ƒ This means that it has multiple interfaces that each belong to a

different IP network

ƒ When a router receives an IP packet on one interface it

ƒ When a router receives an IP packet on one interface, it

determines which interface to use to forward the packet onto its

destination

The interface that the ro ter ses to for ard the packet ma be

ƒ The interface that the router uses to forward the packet may be

the network of the final destination of the packet (the network with

the destination IP address of this packet), or it may be a network

connected to another router that is used to reach the destination

connected to another router that is used to reach the destination

network.

ƒ Routers are the network center

-Routers generally have 2 connections:

-WAN connection (Connection to ISP) -LAN connection

Routers determine the best path

ƒ Routers examine a packet’s destination IP address and ou e s e a e a pac e s des a o add ess a d determine the best path by enlisting the aid of a routing table

Routers determine the best path

ƒ 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

ƒ The router uses its routing table to determine the best path to forward the

ƒ The router uses its routing table to determine the best path to forward the packet

– When the router receives a packet, it examines its destination IP address and searches for the best match with a network address in the router's routing table

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

ƒ It is very likely that a router will receive a packet that is encapsulated in

one type of data link frame, such as an Ethernet frame and when

forwarding the packet, the router will encapsulate it in a different type of

data link

Routers determine the best path

ƒ Routers Operate at Layers 1, 2 & 3 ou e s Ope a e a aye s , & 3

– A router makes its primary forwarding

decision at Layer 3, but as we saw earlier, it

participates in Layer 1 and Layer 2

participates in Layer 1 and Layer 2

processes as well

ƒ Router receives a stream of encoded bits

ƒ Bits are decoded and passed to layer 2

ƒ Router de-encapsulates the frame

ƒ Remaining packet passed up to layer 3

-Routing decision made at this layer by examining destination IP address

ƒ Packet is then re-encapsulated & sent out

outbound interface

Routers determine the best path

ƒ PC1 operates at all seven layers, encapsulating the data and sending the frame out as a stream

of encoded bits to R1 its default gateway

of encoded bits to R1, its default gateway.

ƒ R1 receives the stream of encoded bits on its interface The bits are decoded and passed up to Layer 2, where R1 decapsulates the frame The router examines the destination address of the data link frame to determine if it matches the receiving interface, including a broadcast or

multicast address If there is a match with the data portion of the frame, the IP packet is passed

up to Layer 3, where R1 makes its routing decision R1 then re-encapsulates the packet into a

new Layer 2 data link frame and forwards it out the outbound interface as a stream of encoded bits

ƒ R2 receives the stream of bits, and the process repeats itself R2 decapsulates the frame and

passes the data portion of the frame, the IP packet, to Layer 3 where R2 makes its routing

decision R2 then re-encapsulates the packet into a new Layer 2 data link frame and forwards it out the outbound interface as a stream of encoded bits.

ƒ This process is repeated once again by router R3, which forwards the IP packet, encapsulated inside a data link frame and encoded as bits, to PC2

Configure Devices and Apply Addresses

ƒ Implementing Basic Addressing Schemes p e e g as c dd ess g Sc e es

ƒ When designing a new network or mapping an existing network you must provide the following information in

network you must provide the following information in

the form of a document:

-Topology drawing that Illustrates physical connectivity p gy g p y y

– Address table that provides the following information:

ƒ Device name

ƒ Interfaces used

ƒ IP addresses

ƒ Default gateway