Simpo PDF Merge and Split Unregistered Version - http://www.simpopdf.com Introduction to Routing doc

Simpo PDF Merge and Split Unregistered Version -

Introduction to Routing
and Packet Forwarding
g

Routing Protocols and Concepts – Chapter 1

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

1


Simpo PDF Merge and Split Unregistered Version -

Objectives
Identify a router as a co pu e with a OS a d
de y ou e
computer
an
and
hardware designed for the routing process.
Demonstrate the ability to configure devices and
apply addresses.
Describe the structure of a routing table
table.

Describe how a router determines a path and
switches packets

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

2


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer
Describe the bas c purpose o a router
esc be e basic pu pose of 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

Routers have many of the same hardware and software
components that are found in other computers
p
p
including:
–CPU

–RAM
–ROM
–Operating System
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

3


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer
Router components and their functions”
p
CPU - Executes operating system instructions
such as system initialization, routing functions, and switching functions.

Random 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
g
p
into RAM during bootup.
–Running Configuration File: This is the configuration file that stores the
configuration commands that the router IOS is currently using.
–IP Routing Table: This file stores information about directly connected and

g
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
routers that h
h have LAN i
interfaces such as E h
f
h
Ethernet i
interfaces.
f
–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.
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

4


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer

Router co po e s a d their functions”
ou e components and e u c o s
Read-only memory (ROM) - Holds diagnostic software used
when router is powered up. Stores the router’s bootstrap
p g
program.
–ROM is a form of permanent storage.
Cisco devices use ROM to store:
–The bootstrap instructions
–Basic diagnostic software
–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.
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

5


Router components and their functions”
Non-volatile RAM (NVRAM) - Stores startup configuration. This may include IP
addresses (Routing protocol Hostname of router)

protocol,
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.
NVRAM is used by the Cisco IOS as permanent storage for the startup configuration file
file.
All configuration changes are stored in the running-config file in RAM, and with few
exceptions, are implemented immediately by the IOS.
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
NVRAM,
file
contents even when the router reloads or is powered off.

Flash memory - Contains the operating system (Cisco IOS)

In 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.
Flash consists of SIMMs or PCMCIA cards, which can be upgraded to
increase the amount of flash memory
memory.
Interfaces - There exist multiple physical interfaces that are used to connect network.
Examples of interface types:
-Ethernet / fast Ethernet interfaces
-Serial interfaces
-Management interfaces
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

6

Simpo PDF Merge and Split Unregistered Version -

Router
R t as a C
Computer
t


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer
Router co po e s
ou e components

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

7

Simpo PDF Merge and Split Unregistered Version -

Internetwork Operating System
The operating system software used in Cisco routers is known as Cisco
Internetwork Operating System (IOS)
(IOS).
– Cisco IOS is a multitasking operating system that is integrated with routing,
switching, internetworking, and telecommunications functions.

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.
– 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.

Although some routers provide a graphical user interface (GUI), the
command li i t f
d line interface (CLI) i a much more common method of
is
h
th d f
configuring Cisco routers.
– The CLI is used throughout this curriculum.

Upon bootup the startup config file in NVRAM is copied into RAM and
bootup,
startup-config
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 runningconfig and are immediately implemented by the IOS.
IOS
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

8


Simpo PDF Merge and Split Unregistered Version -

Overview - Managing Cisco IOS Software (cont)

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

9


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer

Major p ases to the
ajo phases o e
router boot-up process
Test router hardware
Power-On Self Test
(POST)
Execute bootstrap loader
p
Locate & load Cisco IOS
software
-Locate IOS
Locate
-Load IOS
Locate & load startup
configuration file or enter
setup mode
p program looks
-Bootstrap p g
for configuration file
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

10


Simpo PDF Merge and Split Unregistered Version -

Stages of the router power-on boot sequence

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

11


Simpo PDF Merge and Split Unregistered Version -

Router
R t as a C
Computer
t
Major phases to the router boot-up process

ITE PC v4.0
Chapter 1

Step 1 and 2: Test router hardware
•Power-On Self Test (POST)
P
O S lf T t
–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
–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
loading the IOS.
© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

12


Simpo PDF Merge and Split Unregistered Version -

Router
R t as a C
Computer
t
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:
•interface addresses
interface
•routing information
•passwords
•any other configurations
y
g
–If the startup-config, is located in NVRAM, it is copied into
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
tftp://255.255.255.255/network confg
(Timed out)
ITE PC v4.0
Chapter 1

•%Error opening tftp://255.255.255.255/cisconet.cfg
(Timed out)
© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

13


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer
Locate & load startup configuration file or enter setup
mode
–Enter Setup Mode (Optional). If the startup
configuration file can not be located, the router
located
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
configurations,
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
e te
enter setup mode, a ays a s e no. If you
ode, always answer o
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.
running config.
•The default running-config is a basic
configuration file that includes the router
interfaces, management interfaces, and certain
default information.
•The default running-config does not contain any
Th d f lt
i
fi d
t

t i
interface addresses, routing information,
passwords, or other specific configuration
information.
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

14


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer

show version

Verify the router boot-up process:
-The show version command is used
to view information about the router
during the bootup process.
Information includes:
Image name & IOS version
IOS (tm) C2600 Software
(C2600-I-M), V i 12.2(28),
(C2600 I M) Version 12 2(28)
RELEASE SOFTWARE (fc5).

Bootstrap version stored in ROM
ROM: System Bootstrap,
O S
Version 12.1(3r)T2, RELEASE
SOFTWARE (fc1)
Image file name & where it was
loaded from
System image file is
"flash:c2600-i-mz 122-28 bin"
flash:c2600 i mz.122 28.bin
ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

15


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer

show version

Verify the router boot-up process:
Platform model number
CPU
Amount of RAM

Some series of routers, like the
2600, use a fraction of DRAM as
packet memory. Packet memory is
used f b ff i packets.
d for buffering
k t
To determine the total amount of
DRAM on the router, add both
numbers. In this example, the Cisco
2621 router has 60,416 KB
(kilobytes) of free DRAM used for
temporarily storing the Cisco IOS
y
processes. The
and other system p
other 5,120 KB is dedicated for
packet memory. The sum of these
numbers is 65,536K, or 64
megabytes (MB) of total DRAM.

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

16

Simpo PDF Merge and Split Unregistered Version -

Router as a Computer

show version

Verify the router boot-up process:
Number & type of interfaces
2 FastEthernet/IEEE 802.3
interface(s)
2 Low-speed serial(sync/async)
network interface(s)

Amount of NVRAM
32K bytes of non-volatile
configuration memory.
NVRAM is used to store the
startup-config file
startup config file.

Amount of flash
16384K bytes of processor board
System flash (Read/Write)
This is the amount of flash memory
on the router. Flash is used to
permanently store the Cisco IOS.

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

17


Simpo PDF Merge and Split Unregistered Version -

Router as a Computer

show version

Configuration register
Configuration register is 0x2102

ITE PC v4.0
Chapter 1

–The last line of the show version
command displays the current
configured value of th software
fi
d l
f the ft
configuration register in
hexadecimal. If there is a second
value displayed in parentheses, it
denotes the configuration register
value that will be used during the

next reload.
–The configuration register has
g
g
several uses, i l di password
l
including
d
recovery. The factory default setting
for the configuration register is
0x2102. This value indicates that
the
th router will attempt t l d a
t
ill tt
t to load
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.
© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

18


Simpo PDF Merge and Split Unregistered Version -

Configuration register
C fi
ti
i t
The order in which the router looks for system
bootstrap depends on the boot field setting in the
g
g
configuration register.
The default configuration register setting can be
changed with the global configuration mode
command config-register.
Use a hexadecimal number as the argument for this
command.

The configuration register is a 16-bit register in
NVRAM.
The lowest four bits of the configuration register form
the boot field.
To ensure that the upper 12 bits are not changed,
first retrieve the current values of the configuration
register using the show version command.
Then use the config-register command, changing
only the value of the last hexadecimal digit.

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

19


Simpo PDF Merge and Split Unregistered Version -

Configuration register (cont.)
(cont )
To enter the ROM monitor mode, set the configuration
register value to 0xnnn0,
where nnn represents the previous value of the non-boot field
digits.
di it
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.

To configure the system to boot automatically from ROM
ROM,
set the configuration register to 0xnnn1,
This value sets the boot field bits to 0001 binary.

To configure the system to use the boot system
commands in NVRAM set the configuration register to
NVRAM,
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
2 - 15 = Boot system from Flash

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

20


Simpo PDF Merge and Split Unregistered Version -

How a Cisco device locates and loads IOS
The config-register can be Downloaded from:
/>lilligren com/cisco/do nloads htm
Demo http://
config-register

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

21


Simpo PDF Merge and Split Unregistered Version -

Configuration register: 0, 1, and 2 and above

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

22


Simpo PDF Merge and Split Unregistered Version -

Configuration register: 2102 and 2142

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

23


Simpo PDF Merge and Split Unregistered Version -

Configuration register
1

Router(config)#config-register value

2

3

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

24


1.

ROM

1, 2

1. POST
2. Bootstrap code executed
3. Check Configuration Register value (NVRAM)

3

0 = ROM Monitor mode
1 = ROM IOS
2 - 15 = Boot system from flash

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

ITE PC v4.0
Chapter 1

© 2007 Cisco Systems, Inc. All rights reserved.

Cisco Public

25

Simpo PDF Merge and Split Unregistered Version -

Stages of the router power-on boot sequence