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Study Guide
Cisco Certified Network Associate 3.0
CCNA 3.0

Version 1
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CCNA FOUNDATIONS .................................................................................................. 4
OSI Model.......................................................................................................................4
Upper Layer .................................................................................................................... 5
Lower Layers .................................................................................................................. 5
Data Link Layer Tasks.................................................................................................... 6
Network Layer Tasks...................................................................................................... 7
Transport Layer Tasks .................................................................................................... 8
LAN Physical Layer Implementations............................................................................ 8
CISCO DEVICE BASICS.............................................................................................. 10
Command Modes.......................................................................................................... 10
Basis Switch Commands............................................................................................... 11
Switch Configuration using the Command Line .......................................................... 11
Basic Router Information.............................................................................................. 12
Common CLI Error Messages ...................................................................................... 12
Basic Router Commands............................................................................................... 13

Address Classes ............................................................................................................ 31
Broadcast....................................................................................................................... 32
Subnetting ..................................................................................................................... 33
Configuring IP Addresses............................................................................................. 35
ROUTING 101 ................................................................................................................ 36
Route Selection ............................................................................................................. 36
Routing Protocols.......................................................................................................... 37
Administrative Distance................................................................................................ 37
Routing Protocol Classes .............................................................................................. 37
RIP ................................................................................................................................ 40
IGRP ............................................................................................................................. 40
ACCESS LISTS .............................................................................................................. 42
Access List Types ......................................................................................................... 42
Access List Guidelines.................................................................................................. 42
Standard IP Access List ................................................................................................ 43
Extended IP Access Lists.............................................................................................. 45
Verifying and Monitoring Access Lists........................................................................ 46
NOVELL INTERNETWORK PACKET EXCHANGE (IPX) PROTOCOL SUITE
........................................................................................................................................... 47
IPX ................................................................................................................................ 47
Encapsulation Types ..................................................................................................... 48
CISCO AND WIDE AREA NETWORK (WAN) ........................................................ 50
WAN Connection Types............................................................................................... 50
WAN Layer 2 Encapsulation........................................................................................ 50
HDLC............................................................................................................................ 51
PPP................................................................................................................................ 51
ISDN ............................................................................................................................. 52
FRAME RELAY............................................................................................................. 54
LMI ............................................................................................................................... 54
Subinterface Connection Types .................................................................................... 55

To assist in remembering the OSI model layers in the proper area you might want to try
either of the following sentences:

All Application
People Presentation
Seem Session
To Transport
Need Network
Data Data Link
Processing Physical

Appliction
(Upper) Layers
Application
Presentation

Presentation layer – determines how data is presented and special processing such as
encryption.
Session Layer – controls the establishment the establishing, managing and terminating
communications sessions between presentation layers.

Lower Layers

The four lower layers are in charge of how data is transferred across a physical wire,
through internetwork devices, to desired end station, and finally to the application on the
other side. Specifically these layers do the following:

Transport – provides for both reliable and unreliable delivery and error correction before
retransmit.
Network – provides logical addressing which device us for path destinations
Data Link – Combines bits into bytes and bytes into frames, provided access to media
using MAC addresses, and error detection.
Physical – responsible to move bits between devices and specifies voltage, wire speed
and pin-out cables.

Encapsulation

The method of passing data down the stack and adding headers and trailers is called
encapsulation. For the each of the lower four layers the unit are as follows:

Transport Segment
Network Packet
Data Link Frame
Physical Bits

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The data link layer has two types of devices: bridges and Layer 2 switches. Layer 2
switching is hardware-based bridging. When a bridge hears a frame on the network it
must decide to filter, flood or copy the frame onto another segment.

This is decided as follows:

1. If the destination in on the same segment it is filtered. That is, if the frame is
from the same segment then it is blocked from going onto segments.
2. If the destination is on another segment it is forwarded to the proper segment.
3. If the destination is not known to the bridge then the bridge will flood the
frame. That is, it is sent to all other segment other than the originating one. Bridged/switched networks have the following characteristics:

1. Each segment is a collision domain.
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2. All devices connected to the same bridge/switch are part of the same
broadcast domain.
3. All segments must use the same data link layer implementation: Ethernet and
all Token Ring.
4. In switched environment, there can be one device per segment, and each
device can send frames at the same time, thus allowing the primary pathway
to be shared.

Network Layer Tasks

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Transport Layer Tasks

For two devices to communicate within a network a connection or session must be
established. The transport layer defines the guidelines for the connection between the
two devices.

The transport layer define the following functions:

• Allows end stations to assemble and disassemble multiple upper-layer segments
into the same transport layer data stream. This is accomplished by assigning
upper-layer application identifiers.

• Allows applications to request reliable data transport between communicating and
systems. This is done through a connection-oriented relationship between the
communicating end systems to accomplish the following:
o Ensure the segments delivered will be acknowledged back to the sender.
o Provide for retransmission of any segments that are not acknowledged.
o Put segments back into their correct sequence order at the receiving
station.
o Provide congestion avoidance and control. LAN Physical Layer Implementations

Cabling exist at the Physical Layer of the OSI model. The CCNA exam focus on the
Ethernet as the physical and data link connections. The term Ethernet refers to a family

connector
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Cisco Device Basics

When a switch or a router is first started 3 operations occur:

Step 1: The power on self-test (POST) is performed. The device finds hardware and
performs hardware checking routines.

Step 2: After the hardware is confirmed functional, the start up routine is performed. The
switch/router looks for and loads the operating system software.

Step 3: After the operating system is loaded, the device will find and apply configuration
settings that are required for network operations. Command Modes

Cisco IOS software uses a command-line interface as its traditional console environment.
There is two default access levels: user EXEC level and privileged EXEC level.

The user EXEC level allows user access to a limited number of basic monitoring
commands.


show version – this command displays information about software version, system
hardware, the names and locations of configuration files, and the boot images. This
command enables you to determine the switch’s current operating system which is
imperative for troubleshooting.

show interface - this command shows the statistics of all of the switch’s interfaces that
are configured. This command can be useful when configuring and troubleshooting the
switch.

show ip - this command shows the current IP configuration of the switch. Switch Configuration using the Command Line

You must switch from the priviledge EXEC mode to the global configuration mode in
order change the parameters of the switch.

switch# conf term
switch(config)#

To configure an interface you must be in the interface configuration mode. You use the
interface command to do this.

switch# interface e0/1
switch(config-if)#

To change the name of the switch you do the following:

switch(config)# hostname testking
testking(config)#

provides a list of commands that begin with a particular character sequence.
For command syntax help, use the ? in the place of a keyword or argument. Include a
space before the ?. Common CLI Error Messages

Error
% Ambiguous command: “show con”

Reason for error
You did not enter enough characters for your switch to recognize the command.

Solution
Reenter the command followed by a question mark (?) with no space between the
command and the question mark. You will be provided with a choice of keywords that
you can enter

Error
% Imcomplete command.

Reason for error
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You did not enter enough of the keywords or values required.

Solution
Reenter the command followed by a question mark (?) with no space between the

Tab Completes a partially entered command if enough characters have
been entered to make it unambiguous.
Basic Router Commands

show version – this commands displays the configuration of the software version, the
router’s hardware, the names and location of the configuration files and the boot images.

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show running-configuration – this commands is used to display the configuration that is
being used by the IOS and that is located in the RAM.

show startup-configuration – this commands displays the backup configuration that is
located in the NVRAM. This is the file that is used to configure the router during startup.

Advance Router Configuration

To make complex and specific configurations for a router you can use the Command
Line. To access these specific configuration modes you must first be in the global
configuration mode. This is achieved by entering the configure terminal command.
Some of the of more popular of these specifc configuration modes are:

Interface – this allows you to enter commands that are responsible to configure
operations on each interface. The prompt for this mode is:


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To add a Message of the Day you would use the banner motd command. Space and a
delimiting character would follow this command. An example follows:

testking(config)#banner motd *
Information Department
You must be authorized to use
this system! * In order to secure your router you can use passwords. Passwords can be used for both the
priviledge EXEC mode and on individual lines. All passwords are case sensitive.

To configure a login password for console terminal you would do the following to set the
password as england:

testking(config)#line console 0
testking(config-line)#login
testking(config-line)#password england

To set a password for an incoming Telnet session you would do the following:

testking(config)#line vty 0 4
testking(onfig-line)#password london

To further secure your router you can provide an enable password. These passwords
restricts access to privilege EXEC mode. To encrypt the enable password you would
need to use the enable secret command. An example of both commands follows:

• Version information. CDP Related Commands

As stated before CDP is enabled by default on Cisco devices. There will be times that
you may want/need to disable it. Two of the reasons for disabling it would be to prevent
CDP information from reaching non-CDP devices and to conserve bandwidth. To
disable CDP at the device level you would issue the no cdp run command at the global
configuration mode. To disable CDP on an interface you would use the no cdp enable
command. To re-enable CDP on an interface you would use the cdp enable command.

show cdp neighbours – this command displays the CDP information for each directly
connected device. The following information will be displayed for each port:

• Neighbor device ID
• Local Interface
• The hold time in seconds
• Neighbor device capability code
• Hardware platform of the neighbor
• Neighbor’s remote port ID
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command or show cdp entry * command.


• Host name
• IP address
• Byte count
• Amount of time the device has been idle
• Connection name assigned to the session

show user – this command displays whether the console port is active, and to list all all
active Telnet sessions, with the IP address or IP alias of the originating host. Local
connections are represented by con and remote connections are represented vty.
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Ctrl-Shift-6, all together, followed by x will suspend the Telnet connection

resume – this command will resume one session. If there was more than one session
before only the last active session will be resumed.

resume sessionnumber (where sessionnumber will be the actual session number) – this
command will resume a specific Telnet session. You can use the show sessions
command to determine the required session number.
To can end a Telnet session you can use the following commands:

exit or logout EXEC command while on the remote device to log out of the console
session.

disconnect EXEC command while on the local device to end the Telnet session. If you
want to disconnect one single session you can use the disconnect sessionnumber (where
sessionnumber will be the actual session number) command.


• RAM – contains the software and data structures that allow the router to function.
• ROM – read only memory. Contains microcode for basic functions to start and
maintain the router
• Flash memory – the primary use is to contain the IOS software image
• NVRAM – this stores the configuration
• Configuration Register – this controls how the router boots up.
• Interfaces

ROM microcode contains:

• Bootstrap code
• POST code
• ROM monitor
• “Partial” IOS show version – this command will be display the configuration register value.

copy running-configuration tftp – this will copy the running configuration to a tftp server.
This will store a copy of the configuration on a location other than the device.

copy running-configuration startup-configuration – this command will move the running
configuration to the startup-configuration (NVRAM). This can be done to save changes
to the configuration.

copy startup-configuration running-configuration – this command will move the startup
configuration (NVRAM) to the running-configuration (RAM).

As previously stated the Flash memory contains the IOS image. To obtain information

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Catalyst 1900 Switch

Functions

This is a Layer 2 device that provides the following functions (bridges provide the same
functionality):

• The devices learn the MAC address for all devices attached to each of its ports.
These addresses are stored in a MAC database.

• When a frame is received the switch will consult its MAC database to establish
through which port the device can be reached. The frame is only sent to that port.

• If your network design includes loops to provide for redundancy it is the switch’s
responsibility to keep the network from coming down but if the Spanning Tree
Protocol is configured then backup paths will be allowed.

• An Ethernet switch discovers addresses and functions like a transparent bridge.
The switch keeps a MAC address table used to track the locality of devices
connected to the switch. It then employs that table to determine which packet
should be forwarded to other segments. Frame Decisions

When a switch receives a frame that is its MAC table, the frame will only be sent to the

the interfaces from transmitting or receiving during normal operations. This can be
achieved through using the Spanning Tree. This will be discussed in greater detail.

Database instability results when multiple copies of a frame arrive one different ports of a
switch. This can be eliminated through a loop avoidance solution would prevent one of
the interfaces from transmitting or receiving during normal operations. This can be
achieved through using the Spanning Tree. This will be discussed in greater detail. A large complex bridged or switched network with multiple switches can cause multiple
loops to occur in the switched network. A loop avoidance mechanism is required to
eliminate this. This is the main reason for the Spanning Tree Protocol.

Spanning Tree Protocol

DEC developed the Spanning Tree Protocol. It is a bridge-to-bridge protocol. IEEE
revised this protocol as the 820.1d specification. The Catalyst 1900 switch uses the IEEE
820.1d specification.

Maintaining a loop-free network is the purpose of the Spanning Tree Protocol. This is
achieved as soon as device finds a loop in the network topology it will block one or more
of the redundant ports. The Spanning Tree Protocol is ever vigilant and is constantly
looking for failures and new additions to the network. When the topology changes,
Spanning Tree Protocol will make the required changes to the ports to avoid total loss
connectivity or the establishment of new loops.

The Spanning Tree Protocol provides a loop free environment by doing the following:

Electing a root bridge – each broadcast domain will have only one root bridge. All of the
ports of the root bridge are called designated ports and are in a forwarding state. A port

100 Mbps 19 10
10 Mbps 100 100 The Catalyst Switch 1900 use the old calculations whereas other Catalyst switches , such
as 2900XL, use the revised calculations Spanning Tree Protocol elections

Root bridge – the switch with the lowest bridge ID.
Root port – the port(s) with the lowest-cost path to the root.
Designated port – all ports on the root bridge are designated ports. On other devices the
designated port is the one that has the lowest cost and then the lower bridge ID.
Blocking – all ports on the segment that are not designated.
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Spanning Tree States

Spanning tree has the following states:

• Blocking
• Listening
• Learning
• Forwarding

• Cut-through – this mode only checks the destination address (DA) and then
begins to forward the frame. This can often reduce the latency from input to
output port. The delay for this mode is the same no matter the size of the frame.
The problem with this mode is that it will forward a frame with an error or a
collision frame.

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• Fragment-free – this mode (also referred to as modified cut-through) reads the
first 64 bytes of the forwarding frame. In this way collisions can be fiilterd out as
they usually occur within the first 64 bytes. The Catalyst 1900 default mode is
fragment free switching. Switch communication

Half-duplex transmission mode implements Ethernet carrier sense multiple access
collisions detect (CMSA/CD). This mode is prone to collisions as one line is used for
both receiving and sending transmissions. A good parallel is a one lane bridge over a
river where cars in one direction must wait for the cars coming the other way are done
before moving.

Full-duplex Ethernet significantly increase bandwidth are separate circuits (of a twisted
pair) are used to transmit and receive frames. This arrangement is collision free.
Therefore you effectively double the wires initial bandwidth. Each full duplex
connection only uses one port. This is achieved by using point-to-point Ethernet and Fast
Ethernet connections.