CISCO CCNA Certification knowledge to pass the exam
Knowledge of OSI Reference Model
Identify and describe the functions of each of the seven layers of the
OSI reference model.

Open Systems Interconnection (OSI)
OSI consists of two environments; the OSI environment, which is made up
of seven
layers of OSI protocols and the local system environment, which is the
end computer
system. The reason for dividing the environment in this way was to avoid
interfering with
the innovation of the design and implementation of computer systems. OSI
facilitates a
vehicle to communicate between dissimilar or similar computer based
systems. The local
computer system environment has a closed operating system and performs
its designed
functions within these bounds. All application processes that do not
communicating with other systems to complete its tasks, will provide, the
end result with
out any problems. However when an application process needs to
communicate with
another application process located in a remote system, both systems must
become open
to the OSI environment Many operations and concepts are involved in this
process. There
is interaction between peer entities within a layer and interaction
between layers.
Important concepts to understand OSI Layering are:
Each layer performs unique and specific task

A layer only has knowledge of its immediately adjacent layers

A layer uses services of the layer below

A layer performs functions and provides services to the layer above

A layer service is independent of the implementation

The Application layer is unique among the seven layers in that, it has no
layer above. The
application consists of `Service Elements’ that are incorporated within
the application
process when it needs to become a part of the OSI environment.

Each layer contains a logical groupings of functions that provide
specific services for
facilitating a communication. A function, or a group of functions, making
up a functional
unit is a logical entity that accepts one or more inputs (arguments) and
produces a single
output (value) determined by the nature of the function. Functions can be
grouped in a collective unit, which is then defined as (N) layer having
(N+1) layer an upper layer
boundary and (N-1) layer as a lower boundary. The N layer receives
services from N-1
layer and provides services to N+1 layer.
Layer 7 is the APPLICATION layer: provides services directly to
applications. Responsible for
identifying and establishing the availability of the intended partner,
and required resources. It is also
responsible for determining if there exist sufficient communication
resources to reach the remote
Layer 6 is the PRESENTATION layer: Data encryption, decryption,
compression and decompression
are functions of this layer. It does this by using Abstract Syntax
Notation 1 (ASN.1) ASN.1
standardization allows differing computer architectures to exchange data
that are from differing
computer architectures.
Layer 5 is the SESSION layer: facilitates a dialog between communicating
systems and controls the
dialog. Offers three different dialogs, simplex, half-duplex and full
duplex. Session is set up by
connection establishment, data transfer and connection release.
Layer 4 is the TRANSPORT layer: Segments data and also reassembles data
from upper layers.
Delivers data in a connection and connection less modes. Includes simplex
(one way) half duplex (both
ways one at a time) full duplex (both ways simultaneously). Also flow
control and error recovery.
Layer 3 is the NETWORK layer: Establishes a connection between two nodes
by physical and logical
addressing. Includes routing and relaying data through internetworks.
This layer’s primary function is
to deliver packets from the source network to the destination network.
Layer 2 is the DATA LINK layer: Ensures hardware addressing of the
device, and delivery to the
correct device. Translates data messages from upper layers to frames,
enabling hardware to transmit
upper layer messages as a bit stream. Provides flow control to the layer
2. Also carries a Frame Check
Sequence to make sure the frame received is identical to the one

Logical Link Control (LLC) Sublayer of the Data Link Control layer
provides flexibility to Network
Layer and the Media Access Control (MAC) layer. It runs between Network
Layer and the MAC
sublayer of the data Link Layer.

Media Access Control (MAC) Sub Layer of the Data Link Layer is
responsible for framing. It builds
frames from the 1s and 0s that the Physical Layer picks up from the wire.
Layer 1 is the PHYSICAL layer: Which transmits the raw bit stream and
includes electrical signaling
and hardware interface.

Describe connection orientated network service and connection less
network service.
Identify the key difference between them.
Department of Defense (DOD) model is analogous to the OSI model and is
the model
used in the TCP/IP protocol suite. Following are the layers of the DOD
DOD Model
Analogous to
OSI Model
Host to Host

Network Access
Data Link

At the transport layer of OSI and the Host to Host layer of DOD, there is
a connection
establishment process with the end system. This is a very impotent
process where the
sending system decides whether to use a reliable link, which is
connection orientated,
resource intensive or to use an unreliable link, connection less access
to the end system
with very much less resource utilization.
The two protocols involved in the connection establishment of the end
system is
Transmission Control Protocol (TCP) for reliable connection and User
Protocol UDP for unreliable connection.
TCP is defined in the RFC 793 and defines a reliable, connection
orientated full duplex
byte stream for a user process. TCP creates a CONNECTION orientated
service by
contacting the end system and establishing a set of guidelines both can
support. Such
agreements as how much data segments can be transferred before an
acknowledgement is
received. TCP takes large blocks of data coming from upper layers and
segments them.
Then it adds numbers to the segments so the end system can sequence them
at arrival and
assemble the original block before sending it to the upper layer. When
TCP creates a
connection between two end systems, it is called a VIRTUAL CIRCUIT. This
circuit is created at the time the one system needs to send a data stream
to the end system
and takes it down when the data transfer is completed.


UDP is defined in RFC 768. It is the protocol that does not consume
system resources as
much as TCP but it unreliable and transfers data to the destination
system with out
establishing a connection and hence, connectionless protocol. UDP sends
data to the
destination system in numbered segments same as TCP but it can not
retransmit erred
segments if they get lost or damaged.

Key differences between connection orientated network service and
connection less network service.

Packet header:
Connection orientated service
Connection less service

Source Port, Destination Port
Source Port, Destination Port

Sequence number
No Sequence Number

Acknowledgement Number
No Acknowledgement number

Data offset
No data offset

Length of data
Variable length of data

No flags

No window

Check sum
Check sum

Urgent pointer
No Urgent pointer

Options and Padding
No Options and Padding

Both TCP and UDP use the concept of ports and sockets to identify a
connection between
two communicating computers. A connection-orientated service is mainly
used for secure
and reliable data transfer, where the requirement is also transfer of
data in timely manner.
If the underlying network, drops data packets because the network is
congested or the end
system buffers overflow, a connection orientated service can recover, but
the connection
less service cannot recover from such faults because, once the data frame
leaves the
sending systems buffer, it is cleared by the sending system and there are
acknowledgement sent to the sending system. To get the high reliability
with the
connection orientated system, large amount of system resources has to be
allocated for
buffers and CPU time. As for the connection less service it is analogous
to mailing a
letter and is not resource intensive. The buffers can be much smaller
because the frame
that is transmitted does not have to wait for an acknowledgment before
been discarded.

CPU utilization is much less for connectionless service because of the
windowing mechanism.

Describe Data Link addresses and Network Address, and identify the key
Data Link addresses are the source address and the destination address of
the 48 bit BIA
of the hardware NIC card. At each interface these addresses change
because, on route to
the destination a frame has to pass may INC cards. Address Resolution
Protocol (ARP)
finds the MAC address when it moves to a different segment. Network layer
address has
a source and a destination address, which are end points of the
transmitting and receiving
systems. It provides routing and relaying functions to achieve it goal.
It provides a
transparent path to the transport layer for a best end to end packet
delivery service.

(4) Identify at least three reasons why industry uses a layered model
Layered model avoids interfering with the innovation of design and
implementation of
computer systems
Facilitates communication between dissimilar systems
Allow changes to one layer with out changing other layers
Facilitate systematic network trouble shooting
Reduce the complexity of networking into more manageable layers and sub

Define and explain the five conversion steps of data encapculation
User information is converted to data
Data is converted to segments
Segments are converted to packets or datagrams
Packets or datagrams are converted to frames
Frames are converted to bits (1s and 0s)

Define Flow Control and describe the three basic methods used in networkig
Flow control stops a sending station from flooding the receiver station
buffers, if it has no
resources to match the speed of data arriving from the receiving station.
Once the buffers
are emptied at the receiver, it sends a message to the transmitter to
start sending again. It
is called windowing and controls how much data is transmitted from one
end to the other.
Has a fixed window say 7, the transmitting station sends seven packets
before waiting for
an acknowledgement packet. Once the acknowledgement is received at the
receiver, it
sends another seven packets.
Window size of one. Every packet sent to the receiver has to be
acknowledged before the
transmitter can send the next packet.

Variable window, if the receiving station for some reason finds difficult
to catch up with
buffer emptying, it then tells receiver to reduce the window size and the
sender does so.

List the key internetworking functions of the OSI network layer and how
they are
performed in a router.
Network layer of the OSI seven layer model conations many protocols that
a router use
to evaluate the best route it should take and it is updated regularly so
the best route is
available for the packet to be transported. Network layers primary
function is to send
packets from the originating network to destination network. After the
router has decided
the best path from source to the destination network, the router switches
the packet to it.
This is known as packet switching. Essentially, this is forwarding the
packet received by
the router on one network interface (NIC card), or port to the port that
connects to the
best path through the network cloud. An internetwork must continually
designate all
paths of its media connections. All routers in the internetwork cloud are
connected by
media (cables), each line connecting a router to another is numbered.
Routers use these
numbers as network addresses. These addresses posses and convey important
about the path of the media connections. They are used by routing
protocols to pass
packets from a source onward towards to its destination. The network
layer creates a
composite “network map” and a communication strategy model by combining
information about the sets of links into an internetwork with path
discrimination, path
switching and route processing functions. It can also use these addresses
to provide relay
capability and to interconnect independent networks. Routers using
network layer
protocols streamline network performance by not letting unnecessary
broadcasts get into
the internetwok cloud.

Knowledge of WAN protocols
Differentiate between the following WAN services: FRAME RELAY, ISDN/LAPD,

Frame relay is used to connect large number of sites in the network
because it is
relatively inexpensive to do so. The service provider gives you a frame
relay circuit and
is charged for the amount of data and the bandwidth you use as oppose to
T1 circuit that
charges with a flat monthly rate whether you use partial bandwidth or the
full bandwidth
regardless. Frame relay is a high performance WAN protocol that operates
at the Data
Link layer and the Physical layer of the OSI model.
Integrated Services Digital Network (ISDN) is designed to run over
existing telephone
networks. It can deliver end to end digital service carrying voice and
data. ISDN operates
at OSI model, physical layer, data link layer and network layer. It can
carry multimedia
and graphics with all other voice, data services. ISDN supports all upper
layer protocols
and you can choose PPP, HDLC or LAPD as your encapsulation protocol. It
has two
offerings, Primary rate which is 23B+D channels. 23, 64 kbps and one
64kbps mainly
used for signaling. The other is the Basic Rate which has 2B+D channels
two 64kbps and
one 16kbps.
At data link layer ISDN supports two protocols; LAPB and LAPD. LAPB is
used to
mainly transfer data from upper layers and has three types of frames.
I-Frames carry
upper layer information and carries out sequencing, flow control, error
detection and
recovery. S- Frames carry control information for the I-frame. LAPD
provides an additional multiplexing function to the upper layers
enabling number of network entities
to operate over a single physical access. Each individual link procedure
independently of others. The multiplex procedure combines and distributes
the data link
channels according to the address information of the frame. Each link is
associated with a
specific Service Access Point (SAP), which is identified in the part of
the address field.
High Level Data Link Control (HDLC) is a bit oriented data link layer
frame protocol
that has many versions similar to LAP, LAPB, and LAPD. CISCO routers
encapsulation is HDLC, but it is proprietary to CISCO.
Point to Point Protocol (PPP) is a Data Link Layer protocol that can be
used over ether
asynchronous (dial up) or synchronous (ISDN) lines. It uses Link Control
Protocol (LCP)
to build and maintain data link connections. Included in PPP is the
protocols, PAP and CHAP, and data compression. It supports IP, IPX,
DECnet and OSI/CLNS.
Recognize key Frame Relay terms and features

Frame Relay is a high performance WAN protocol that operates at the
physical and data
link layer of the OSI reference model. It was originally designed to
operate on ISDN
circuits, but today it is used on variety of network interfaces. To
configure Frame Relay
on a CISCO router, we have to specify it as an encapsulation on a serial
interface. There
are only two encapsulation methods are available, CISCO, the default and
the type IETF.
A frame Relay connection between CISCO devices the type: CISCO is used
and between
a CISCO device and a non CISCO device type IETF is used.
#encapsulation frame relay cisco or #encapsulation frame relay ietf
Frame Relay virtual circuits are identified by Data Link Connection
Identifiers (DLCI).
DLCIs are issued by the Frame Relay service provider. It is used to map
IP addresses at
each end of the virtual circuit. Local Management Interface (LMI) was
developed by
CISCO and others to enhance the CCITT-ITU standard with protocol features
allowed internetworking devices communicate easily with a Frame Relay
network. LMI
messages provide current DLCI values, global or local significance of the
DLCI values
and the status of virtual circuits. CISCO supports three types of LMIs:
CISCO which is
the default, ANSI and Q933A.

List commands to configure, maps and subinterfaces

To configure DLCI (config-if) #frame-relay interface-dlci 16
Any number from 0 to 4292967295 can be as the DLCI number.
To configure LMI
(config-if)#frame-relay lim-type q933a
Subinterfaces can have multiple virtual circuits on a single serial
interface and treat each
virtual circuit as a separate interface. The advantage of using
subinterfaces is that you can
assign different network layer characteristics each subinterface and
virtual circuit, such as
IP routing on one virtual circuit and IPX routing on another.
(config)# int s0.16 The serial interface s0 configured with a
subinterface 16
There are two types of subinterfaces, point to point and multipoint.
Point to point is used
when a single virtual circuit connect one router to another. Multipoint
is used when the
router is in the middle of star virtual circuits.

Map command is used to map IP devices address at the end of the virtual
circuits to
DLCIs so that they can communicate. There are two types of mapping: Use
Frame Relay
map command and use inverse-arp function. Example of Frame Relay map
#int s).16
#encap frame relay ietf
#no inverse-arp
#ip address
#frame relay map ip 30 cisco broadcast

Example of Frame Relay inverse-arp command:
#int s0.16
#encap frame-relay ietf
#ip address
List commands to monitor Frame Relay operation on the router

In the user mode key in the following:
Router>sho frame ?
show frame relay IP statics
show frame relay lmi statics
show frame relay map table
show frame relay pvc statics
route show frame relay route
traffic show frame relay protocol statics

Identify PPP operations to encapsulate WAN data on CISCO routers

Point to Point Protocol (PPP) is a data link protocol that can be used on
(dial up) or synchronous ISDN circuits. It uses Link Control Protocol
(LCP) to build and
maintain data link connections. Some features included in PPP are:
Authentication Protocol (PAP) and Challenge Handshake Password
Protocol (CHAP). Data compression and multiprotocols such as IP, IPX ,
DECnet and OSI/CLNS are supported. Encapsulate PPP on the router
#int s0
#encapsulate ppp
State a relevant use and context for ISDN networking

Integrated Services Digital Network (ISDN) can run on existing telephones
lines to
provide an end to end digital service for both domestic and business
uses. ISDN can
carry, in addition to voice and data, multimedia as well. ISDN can used
as a backup
circuit for high speed network links. CISCO routers can be configured to
dial up on an ISDN link when the main network link goes down.
Identify ISDN protocols, function groups, reference points and channels

ISDN protocols were defined by CCITT (now ITU-T), and there are three
protocols that
define the complex transmission issues:
Protocol specifications beginning with latter E, specify ISDN on the
existing telephone network, ie;
Analog lines.

Protocol specifications beginning with letter I, specify concepts,
terminology and services.
Protocol specifications beginning with letter Q, specify trunk switching
and signaling.

Describe CISCO’s Implementation of ISDN BRI

ISDN Basic Rate Interface (BRI), service provides two B channels and D
channel, which
is also known as 2B+D. B channels operate at 64 kbps and carries user
information where
D channel operates at 16 kbps and usually carry control and signaling
information. D
channel signaling protocol spans the OSI reference model’s, Physical
layer, Data link
layer and the Network layer. The two 64 kbps lines can be used as a
single 128 kbps
channel. To place a call on ISDN is similar to placing a call on Plain
Old Telephones
(POTS). For ISDN network to identify a call placed on its network, you
must use
directory numbers and Service Profile Identifiers (SPID)s. These two
items are given to
you by the service provider. Directory number is a telephone number you
will use when
you call. The SPID is a number the telephone uses to identify equipment
on your ISDN
connection. Majority of switches in US are either AT&T 5ESS, 4ESS or
Telcom DMS 100. Attaching a CISCO router to ISDN needs either a Network
Termination 1 or an ISDN modem. If router has a BRI interface, (called
Terminal End
Point 1) then it is ready to be connected to the ISDN network.
Router#config t
Router(config)#isdn switch-type basic-dms100
Router(config)#int bri0
Router(config-if)#encap ppp
Router(config-if)#isdn spid 775456721
Router(config-if)#ppp authentication chap

Log in to a router in user and privilege mode

CISCO IOS software has a command interpreter called Exec. Exec has two
levels of
access: User mode and privilege mode. These two levels serve as for
access into the
different levels of commands. In user mode one can only do: Check router
connecting to remote devices, making temporary changes to terminal
settings and
viewing basic system information. In the privilege mode you can change the
configuration of the router and get detail reports of router status. Test
and run debug
operations. Access global configuration modes.
When you first log into a router, press ENTER and you will be in the Exec
mode. At the
prompt it will ask if you need a password. Router> This is the User mode
as stated above
very little can be done at this level. When you type in Enable:
Router>Enable and press
return it will ask for the password. Once you key in the correct
password, your in the
privilege mode. Now the prompt will show you Router#.
Use the context-sensitive help facility

One can receive help on any command by typing ? after the command. In the
example: Router# clock ? you typed in clock a space and the question
mark, and pressed
enter. Reply was as follows: set
Set the time and date. Now you want to know what
format to enter. So you put another question after the set as follows:
Router# clock set ?.
Now you will get the format in the reply as follows: hh:mm:ss: Current
Time (hh:mm:ss)
Use the command history and editing features

The user interface comes in with an editing feature to help you type in
commands. One can turn off editing by typing terminal no editing and
again turn it on
by typing terminal editing.
The router keeps the last ten commands you entered during your console or
session, in a special memory buffer called command history. One can
recall commands
from the command history buffer and reuse them or modify slightly to save
on typing. To
see all the commands type the following at the command prompt Router#show
and press enter. All commands you typed in will be shown. To increase the
size of the
command history buffer you type the following: Router#terminal history
size 100. This
will increase the size to 100 lines from the default value. VT 100
terminal emulation
gives use of up down and side arrows in addition to the other keys as
shown below:
Move to the beginning of the command line
Move to the end of the command line
CTRL+F (or right arrow)
Move one character forward
CTRL+B (or left arrow)
Move one character backward
CTRL+P (or up arrow)
Repeat previous command entry
CTRL+N (or down arrow)
Most recent command recall
Move backward one word
Move forward one word

Examine router elements (RAM,ROM,CDP,show)

CISCO routers use the following type of memory:
Random Access Memory (RAM) stores the running configuration when the
router is running and it is
cleared when switched off. Also provides cashing, routing tables and
packet buffering. The IOS
operates from RAM
Flash Memory is an electrically erasable, re-programmable ROM that holds
the operating system
image and microcode. This facilitates the upgrades to the operating
system with out replacing the chips
on the motherboard.
Read Only Memory (ROM) is used by the router to store bootstrap program,
operation system software
and Power On Self Test (POST). The ROM chips are installed in sockets on
the router’s motherboard,
so that they can be replaced or upgraded. ROM holds the smaller version
of IOS and is loaded during
power up so the router can boot up.
Nonvolatile RAM (NVRAM) This memory does not loose its information when
the router is powered
down. Stores the systems start up configuration file and the virtual
configuration register.

Cisco Discovery Protocol (CDP) is CISCO’s proprietary protocol that
allows you to
access configuration on other routers with a single command. By running
Sub Network
Access Protocol (SNAP) at the data link layer, two devices running
different Network
Layer protocols can communicate and learn about each other. These devices
include all
LAN and some WANs. CDP starts by default on any router version 1.3
earlier and
discovers neighboring CISCO routers running CDP by doing a Data Link
broadcasts. It
does not matter what protocol is running at the network layer. Once CDP
has disproved a
router, it can then display information about the upper layer protocols,
such as IP and
IPX. The router caches the information it receives from its CDP
neighbors. Any time a
router receives up dated information that a CDP neighbor has changed, it
discards the old
information in favor of the broadcast.
There are many show commands available for the administrator to manage
the router.
They can be found by typing at the command prompt Router#sh ?.
Manage configuration files from the privilege exec mode.

When the router is powered up, it does a self-test, then a loads the IOS
image, and finds
the configuration file and loads it. Startup configuration is in NVRAM
and the operating
system places it on to the RAM. To manage configuration files you must be
in privilege
mode. At start up you will be in user mode. To get to the privilege mode
do the
following: Router>enable, if passwords are enabled then enter them when
asked. Now
your in privilege mode. Router#. By typing config t you can modify
configuration files.
Following are commands for starting and saving configurations:

Show startup-config
Shows the configuration that will loaded when the router boots.
Show running-config
Show the configuration that is currently loaded to RAM and is running
Erase startup-config This command will erase the configuration in
NVRAM and put you in to the initial configuration dialog
This command will reload the startup-config to
This command starts the initial configuration dialog

Software version 10.3 and earlier should run the following router
Show config
Same as show startup-config
Write term
Same as show running-config
Write erase
Same as erase startup-config
Write mem
Same as copy running-config startup config

Control router password, identification and banner

There are five different passwords that is used to secure CISCO routers
and they are as
Enable secret
is a cryptographic password used in version 10.3 and up. It has precedence
over the enable password when it exists. One can configure this password,
ether during
the setup mode or by typing the following:
Router#config t
Router(config)#enable secret kit (kit is the password you entered)
Enable password
is used when there is no enable secret and when you are using older
software, and some older images. The administrator manually encrypts it.
One can set
this password during the setup process or by typing the following:
Router#config t
Router(config)#enable password athul (athul is the password)
If both passwords are present, both passwords can not be the same

Virtual Terminal Password
is used for Telnet sessions with the router. You can change
the password at any time , but it must be specified or you will not be
able to telnet in to
the router. The password can be set up as follows:
Router#config t
Router(config)#line vty 0 4
Router(config-line)#password kit (kit is the password)
Line vty 0 4 specifies the number of telnet sessions allowed in router.
One can also setup
a different password each line by typing line vty [port number]
Auxiliary Password
is used to setup a password for the auxiliary port. This port is used
to connect a modem to the router for remote console connection. It is set
as follows:
Router#config t
Router(congfig)#line aux 0
Router(config-line) #password kit (kit is the password)

Console Password
is used to setup a password for the console port. It can be set up as
Router#config t
Router(config)$line con 0
Router(config-line)#password kit (kit is the password)

Entering a Banner
The banner added will be displayed when ever any one logs in to the CISCO
router. The
command to enter is banner #.motd. Message of the day (motd) has to start
with a
delimiting character. Type as follows: Router(config)#banner motd k (k is
the delimiter)
Now enter the text message and end with the character `k’. So we enter
the following: If
you are not authorized log out immediately
K(and press enter)
(22) Identify the main CISCO IOS commands for router startup.

Router’s configuration files contain the configuration of the router.
There are two basic
configuration files for each router: startup and running. Startup
configuration is held in
NVRAM and is accessed when router is started. The startup configuration
is placed in
RAM for the router to run. Following command will display the startup
Router#sh star

Enter the initial configuration using the setup command

Setup command facility is an interactive facility that allows you to
perform first time
configuration and other basic configuration procedure on the router. The
command parser
allows you to make detail changes to your configuration. However, some
configuration changes do not require granularity provided by the command
parser. In this
case you can use the setup command facility to make major enhancements to
configuration. Set up can make add a protocol suite, to make major
addressing schemes
changes, or configure a newly installed interface. Setup command facility
provides you
with a high level view of the configuration and guides you through the
change process. If you are not familiar with CISCO products and the
command parser,
the setup command facility is a particularly valuable tool, because it
asks you questions
required to make configuration changes. To start setup, key in the
Router#setup and press enter.

Copy and manipulate configuration files

Binary executable IOS image is held in flash memory. IOS image is the
binary program
that parses and executes the configuration, while IOS configuration tells
the device its
current configuration. You can copy the content of the flash to a TFTP
server by entering
the following command Router#copy flash tftp
One can copy TFTP server to flash memory by typing Router#copy tftp
flash. An
interactive dialog begins and asks whether to erase the entire content of
the flash before
copying the file. Content of the flash memory can be displayed by the
Router>sh flash
One can copy the current configuration from a router to a TFTP server by
Router#copy run tftp.
Or telnet to the router, copy a TFTP configuration file to running
conflagration by typing
the following command: Router#copy run
List the commands to load CISCO IOS software from: flash memory,
TFTP server, or ROM.
One can specify where the router should look for the CISCO IOS software
to create a fall
back in case one configuration does not load or one needs to load from a
TFTP server. To
load the CISCO IOS from a TFTP server, use the following command string:
Boot system TFTP ios_filename TFTP_ipaddress. There are three places that
router can look for the a valid IOS: flash, TFTP server or ROM. Following
will load the IOS from flash and ROM
Router(config)#boot flash
Router(config)#boot rom
(26) Prepare to backup, upgrade and load a backup CISCO IOS image
Use the TFTP server to backup the IOS image. Type the following command
at the
command prompt: Router(config) copy flash tftp. Flash memory can be used
to upgrade
the IOS without physically changing the EEPROM. To load a backup image
can be
carried out from TFTP server, flash and ROM. Typing the following command
will cause
the router to try the other alternatives if the flash configuration does
not come up.
boot system flash ios_filename
boot system TFTP ios_filename
boot system rom
Prepare the initial configuration of your router and enable IP
When you power up the router, it does a POST and finds and loads the IOS
image, the
operation system for the router. Before the router can function, as you
want it to, it needs
to finds its configuration and apply it. If the router does not find a
configuration file and it
is not configured to find one on the network, it will begin the setup
dialog. The setup is
menu driven and all you have to do is to answer the questions. Setup
dialog will let you
get the router up and running with a very basic configuration. It will
allow you to give a
host name, set both password and secret password, enable any network
layer protocols
assign appropriate addresses to router interfaces and enable dynamic
routing protocols.
Every CISCO router has a 16 bit configuration register, which is stored
in a secial
memory location in NVRAM. This register controls number of functions and
some of
which are listed below:
Force the system in to the bootstrap program
Select a boot source and default boot file name
Enable or disable the console Break function
Set the console terminal baud rate
Load operating software from ROM
Enable booting from a TFTP server

The configuration register boot field is the portion of the configuration
register that
determines whether the router loads an IOS image, and if so where to get
it from. The
least significant four bits, 0 through 3, make up the boot field. If the
boot field is 0x0 (all
four bits set to zeros) then the router will enter ROM monitor mode. If
the boot field
value is set to 0x1 (binary 0001) the router will boot from the image in
ROM. If the boot
field value is 0x2 through 0xF (binary 0000 through 1111) then the router
will follow the
normal boot sequence and will look for the boot system commands in the
file on the NVRAM.. Type Router# sh ver, will display the configuration
register value
currently in effect and the value that will be used at the next reload.
Display line in the
discussion is displayed on the screen is as follows:
Configuration register is 0x142 (will be 0x102 at next reload)
You can place special commands in the router’s configuration file that
will instruct it
where to find the IOS image. If you do not specify a file name, the
router will load the
first valid file it finds in the flash memory. Following are the boot
Router(config)#boot system flash
Boots from flash
Router(config)#boot system tftp Boots from a TFTP server
with ip address
Router(config)#boot system ROM
Boots from ROM (this is last resort if nothing
works and should be changed after the flash is corrected)
Network Protocols
Monitor Novell IPX operation on the router

Once you have IPX configured and running, following show commands can be
used to
verify and track router is communicating correctly:
Router#sh ipx servers. This command will show the content of the SAP
table. Server
name, IPX address, port, route, hops and interface.
Router#sh ipx route This command will display the IPX routing table
entries that the
router knows about. The router reports networks to which is connected to
directly and
also the networks that it has learned since coming on line.

If you were to up parallel IPX paths between routers, by default, the
CISCO routers will
not learn about these paths. The router will learn a single path to the
destination and
discard alternative parallel, equal cost paths. If you need more than one
parallel path to a
destination then the router has to be configured Router(config)#ipx
maximum paths 2 (up
to 512).
Router#sh ipx traffic. This command will display a summary of the number
of IPX
packets received and transmitted by the router. Summary will show IPX,
update packets.
Router#sh ipx int e0
The debug IPX command will display IPX packets as its running through your
Router#debug ipx routing can have two commands, debug routing activity or
routing events. Since debug IPX command is CPU intensive, it should be
switched off as
soon as monitoring process is over as shown: Router#undebug ipx routing
Describe two parts of network addressing, then identify the parts in
specific protocol
address examples.

The 32 bit structure of the IP address is comprised of a network address
and host address.
Number of bits assigned to each of these components varies with the
address class.
IP addressing is analogues to the address of a letter. Street address is
analogues to the
network address and the house number is analogues to the host address.
The concept of
subnetting allows the network portion of the address to be subdivided in
to number of
logical sections; subnets. With subnetting the two part IP address
becomes a three part
address, a network address, subnetwork address and a host address.
In Class A address, the most significant bit of the first octet is set to
0 and first octet is set
for the network address, leaving 24 bits for the host address. This
corresponds to possible
network addresses of 0 to 127. The reserved values are 0 and 127, leaving
1 to 126 for
network addressing in class A.
In Class B address, the most significant bit and one after it is set to
10 leaving 16 bits for
the network address and 16 bits for the host address. This corresponds to
network address of 128 to 191.
In Classes C address, the most significant bit and two bits after are set
to 110 leaving 24
bits for network address and 8 bits for host address. This corresponds to
possible network
address of 192 to 223.
Class D and Class E is not required for the CCNA examination.
Create different classes of IP addresses (and subnetting)

For the subnet address scheme to work, every host on the network must
know which part
of the host address will be used as the subnet address. This is
accomplished by assigning
a subnet mask to each host. Following are the subnet masks for each Class
Class A
default subnet mask
Class B default subnet mask
Class C,net,node default sunet mask

Configure IP addresses
Following commands will configure the IP address for the Ethernet
interface 0
Router#config t
Router(config)#int e0
Router(config-if)#ip address
Router(config-if)#no shut

Verify IP addresses

Router#sh ip int e0 will display the following:
Ethernet0 is up, line protocol is up
Internet address is
Broadcast address is
Also many other interface details
List required IPX addresses and encapsulation type

IPX performs functions at layer 3 and 4 of the OSI model. It controls the
assignment of
IPX addresses (software addressing) on individual nodes, governs packet
delivery across
networks, and make routing decisions based on information provided by
protocols, RIP or NLS. IPX is a connectionless protocol and it does not
require an
acknowledgement from the destination node. To communicate with upper layer
protocols, IPX uses sockets. These are similar to TCP/IP ports, in that
they are used to
address, multiple independent applications running on the same machine.
Sequence Packet eXchange (SPX) is a connection-orientated protocol as
oppose to IPX.
Through it upper layers can be assured that the data was delivered from
the source to the
destination. SPX works by creating virtual circuits or connections
between machines,
with each connection having a specific connection ID, included in the SPX
Routing Information Protocol (RIP) is a distance vector routing protocol
used to discover
IPX routes through internetworks. It employs ticks (1/8 th of a second)
and the hop count
(number of routers between nodes) as metric for determine preferred
Service Advertising Protocol (SAP) allows servers to advertise the
services they provide
on the network. There are three types of SAP packets defined: Periodic
updates, service
quires and service response.
Netware Link Services Protocol (NLSP) is an advanced link state routing
intended to replace Novell RIP and SAP.
Netware Core Protocol (NCP) provides clients with server resources such
as file access,
security and printing.

IPX addressing is somewhat different from IP addressing. The
administrator assigns the
network part of the address and the node part is automatically assigned.
IPX address has
80 bits or 10 bytes. It is divided in to network address, which is 4
bytes and the node
address which is the remaining 6 bytes. An example of an IPX address is
as follows:
0000.7C80.0000.8609.33E9. The first 8 hex digits (0000.7C80) represents
the network
part of the address, next 8 hex digits (0000.8609) represents the node
part of the address
and the last 4 hex digits (33E9) represents the socket.
Encapsulation or framing is the process of taking packets from upper
layer protocols and
building frames to transmit across the network. Encapsulation takes IPX
datagarms from
Layer 3 and builds frames at layer 2 to transmit on one of the supported
Encapsulation on following media is as follows:
Cisco Keyword

Netware Frame:
novell-ether (default
Netware 3.11)



Token Ring

Netware Frame:
sap (default)



Netware Frame:
snap (default)



Enable the Novell IPX protocol and configure interfaces

First you enable IPX routing and after you enable IPX protocol on each
interface as
Router(config)#ipx routing
Router(config)#int e0
Router(config-in)#ipx network 2100
You can add multiple frame types to the same interfaces follows: using
the old way
Router(config)#int so
Router(config-in)#ipx netwok 3200 encap hdlc sec

Next is to use the current method:
Router(config)#int e0.100
Router(config-subif)#ipx network 2300 sap
Identify functions of the TCP/IP Transport layer

The Transport layer protocol equivalent to the layer in the DOD model is
the Host to
Host protocol. Its main purpose is to shield the upper layer applications
from the
complexities of the network. Transmission Control Protocol (TCP) and the
Datagram Protocol (UDP) operate at this layer. TCP is a
connection-orientated protocol,
which means that it first establishes a connection on a virtual circuit
between source and
destination, before sending user data. UDP is a connection less protocol,
which means the
source is not concerned whether the datagram it sent to the destination,
did arrive there or
not. TCP and UDP both receive large chunks of data form the upper layers
and they
break them down to manageable segments so that they can be transmitted to
destinations. Each segment is numbered so that at the destination they
can be
reassembled. Only TCP keeps tract of this reassembly process, by
requesting the missing
segment from the source. If a segment is missing from a UDP transmission,
destination does not have a mechanism request it from the source.
Therefore UDP is a
unreliable protocol. TCP carries out error checking, and requests a
retransmission, also
through a windowing mechanism it controls the data flow so that receiver
buffers are not
flooded by the source. TCP is a full duplex, connection orientated,
reliable and accurate
Identify the functions of the TCP/IP network layer protocol.

At network layer, the TCP/IP protocol suit has the Internet Protocol (IP)
in operation. The
function of IP includes, packet routing and providing a single network
interface to the
upper layers. The lower layers do not carry out any routing and routing
occurs at the IP
internet layer. To route, IP looks at each packet’s IP address, then
using a routing table it
decides where a packet is to be sent next, choosing the best path. All
hosts on a network
has an IP address and it contains the required routing information to
enabling the packet
to travel to the destination. IP receive data segments from the next
upper layer, which is
the Host to Host layer and fragments them to datagrams or packets. Each
datagram is
assigned an IP address of the sender and the IP address of the recipient.
Each machine
that receives the datagram makes a routing decision based upon the
packet’s destination
IP address. The IP packet has a header and in it there is a field which
carries an IP type
number. This number indicate the socket number that the IP datagram
should use to pass
the data to upper layer which is the Host to Host layer. Data travelling
on the internet
layer is, either a TCP datagrma or a UDP datagram.

Identify Functions performed by ICMP

Internet Control Message Protocol (ICMP)is a management protocol and a
service provider for IP. Its messages are carried as IP datagrams. RFC
1256 ICMP Router
Discovery Messages is an annex to ICMP, which affords hosts extend
capability in
discovering routes to gateways. Periodically, router advertisements are
announced over
the network, reporting IP addresses for its network interfaces. Hosts
listens for these
network infomercials to acquire route information. A router solicitation
is a request for
immediate advertisement and may be sent by a host when it starts up.
Following are some
common events and messages that ICMP relates to:
Destination Unreachable: If a router cannot send an IP address any
further, it uses ICMP to send a
message back to the sender advertising it of the situation. For example
if the router receives a packet
destined to a network that the router does not know about, it will send
an ICMP Destination
Unreachable message back to the sending station.
Buffer full: If a router’s memory buffer for receiving in coming
datagrams is full, it will use ICMP to
send out this message.
Hops: Each IP datagram is allotted a certain number of routers that it
may go through, called Hops. If it
reaches its limit of hops before arriving at its destination, the last
router to receive that datagram
deletes it. The executioner router then uses ICMP to send an message to
the originator that the
datagram is dead.
Ping: Packet Internet Groper uses ICMP echo message to check the physical
connectivity of machines
on an internetwork.

Configure IPX access lists and SAP filters to control basic Novell traffic

Similar to IP access lists IPX has two types of access lists: Standard
IPX Access Lists and
Extended IPX Access lists.
Standard IPX access lists allow or deny packets based on source and
destination IPX
addresses. Template to enter standard IPX access lists is as follows:
Access-list (number from 800 to 899) (permit or deny) (source network IPX
(destination network IPX number)
Following example will show how the access list will permit or deny
access to IPX
Router#config t
Router(config)#access-list 810 permit 30 10
Router(config)#int e0
Router(config-if)#ipx access-group 810 out

810 correspond to the 800 to 899 range. This access-list mean that any
network other than
30 will be denied access network 10. If we wanted to allow access all
networks to 10
other than 50 the access-list entry will be as follows:
Router(config)#access-list 810 deny 50 10
Once we configure the access-list we must apply it to the interface, and
it applied as
Router(config)#int e0
Router(config-if)#ipx access-group 810 out
Which means that the above restriction is applied to the interface
Ethernet 0, IPX
outgoing packets from the router to the network.
Extended IPX access lists can filter based on the following: Source
network, source node,
destination network, destination node, IPX protocol (SAP, SPX etc) and
IPX sockets.
Template to enter the extended IPX access list is as follows:
access-list (number, 900 to 999) permit or deny (protocol) (source IPX
network number)
(source socket) (destination IPX network number) (destination socket)
Following example will show how the extended access list will permit or
deny IPX
network access using extended access lists
Router(config)#access-list 910 deny ­1 50 0 10 0
This means that the access is denied to any IPX protocol type from IPX
network 50 on all
sockets to enter IPX network 10 on all sockets.
If you want to let any network access any network, any protocol and on
any socket the
entry will be as follows:
Router(config)#access-list 910 permit ­1 ­1 0 ­1 0
Again once the access list is configured it has to be applied the
interface as follows:
Router(config)int e0
Router(config-if)#access-group 910 out

IPX SAP filters are used to control access IPX devices. The template for
IPX SAP filters are as follows: access-list (number 1000 to 1099) (permit
or deny)
(source network.node address of the server) (service type)
Source address here is the IXP internal address for example
Router(config)#access-list 1010 permit 0000.7c80.0000.33e9 0
Access list 1010 is in the range, 1000 to 1099 reserved for IPX SAP
filters. This IPX
SAP filter will allow packets from 0000.7c80.0000.8609.33e9 to enter the
interface and be included in SAP updates across the network. The last
entry is the service
type and we entered 0, which means all services should be allowed.
Now that we created the SAP filter, lets apply it to the interface for it
to be operational.
We apply it to the interface as follows:
Router(config)#int e0
Router(config-if)#ipx input­sap-filter 1010

(39) Add the RIP routing protocol to your configuration

Route Information Protocol (RIP) is a distance vector routing protocol
that practices
classfull routing, which is used to discover the cost of a given route in
terms of hops and
stores that information on a routing table.
The router can then consult the table to select the least costly most
efficient route to a
destination. It gathers information by watching for routing table
broadcasts by other
routers and updating its own table in the event that a change occurs. RIP
routing tables
has following minimum entries: IP destination address, A metric (1 to 15)
indicative of
the total cost in hops, of a particular route to a destination, IP
address of a the next router
that a datagram would reach , on the path to its destination, A maker
signaling recent
changes to a route, Timers, which are used to regulate performance,
Flags, which indicate
whether the information about the routers has recently changed,
Hold-downs used to
prevent regular update messages from reinstating a route that is no
longer functional,
Split horizon used to prevent routing loops. A poison reverse updates
used to prevent
routing loops. RIP sends out routing updates at regular intervals and
whenever a network
topology changes occurs. And uses the following timers to regulate its
Routing table update timer typically 30 seconds
Route invalid timer 90 seconds
Route flush timer 240 seconds
To add RIP routing to a router type in the following:
Router#config t
Router(config)#router rip
Router#wr mem (write to the running configration)
(40) Add the IGRP routing protocol to your configuration

Interior Gateway Routing Protocol (IGRP) is a CISCO proprietary, distance
interior routing protocol that was designed by CISCO to overcome the
presented by RIP. IGRP hop count is 255 as oppose to RIP’s limited 15
hop count.
IGRP advertises three types of routes:
Interior: These are routes between subnets. If a network is not subnetted
then IGRP will
not advertise the interior routes.
System: These are routes to networks within an Autonomous System. They
are derived
from directly connected interfaces, other IGRP routes, or access servers.
They do not
include subnet information.
Exterior: These are routes to networks out side of the Autonomous System.
They are
considered when identifying a gateway of last resort. The gateway of last
resort is chosen
from the list of exterior routes that IGRP provides.
Type in the following to add IGRP routing
Router(config)#router igrp 10 (10 is the Autonomous System number it can
be any
number from 1 to 65535)
Router#wt mem
(41) Explain the services of separate and integrated multiprotocol routing

A separate protocol routing is when the routing device, eg: a switch uses
a routing table
based on MAC address, and can accommodate only one encapsulation type.
This type of
routing is carried out at the data link, MAC sublayer.
Multiprotocol routing is carried out mostly by routers and similar
devices because, the
routing decisions are made at network layer and the routing tables are at
network layer.
At network layer there can exist, many different protocols and with them
comes their
own associated routing tables. So a router can have a IP routing table,
IPX routing table
and a Apple Talk routing table.
A bridge or a switch connects two or more physical networks into a single
network, where as routers connects two or more logical networks and
routes between
them using information that is built by routing protocols and kept in
routing tables. The
advantage of a router as compared to a bridge or a switch is that it
physically and
logically breaks a network in to multiple manageable pieces, allows for
control of routed
packets, and routes network layer protocols at the same time.
List problems that each routing type encounters when dealing with
topology changes and
describe techniques to reduce the number of these problems.

Describe the benefits of network segmentation with routers
Routers filter by both the hardware and network addresses. Routers only
forward packets
to the network segment that the packet is destined for. The benefits of
segmentation could be summarized as follows:
Manageability: Multiple routing protocols give the flexibility of
designing for optimum
requirements of the network.
Increased functionality: CISCO routers addresses the issues of flow
control, error control
congestion control and fragmentation, Also efficient control over packet
Multiple active paths: Using the protocols DSAPs, SSAPs and path metrics,
routers can
make informed routing decisions as well as interpret the next layer
protocol. CISCO
routers can have more than on active link between routers.

Network Security
(44) Configure standard and extended access lists to filter IP

Access lists are used to control access via a router to the network or
from the network to
another network or to a device attached to the router. Packet filtering
is performed by the
access lists, to either, entering packets to the router, or exiting
packets from the router.
Apart from providing security to the network, access lists provide
valuable static on
packet flow.
Access lists are a list of conditions that the network designer can
enforce to get total
control of access to the network and exit from the network. When you
apply the access
list to the router interface, it has the total control of packets
entering and leaving the
interface. Configuring the Standard IP access list and applying to the
interface is as
follows: First you configure the access list then you apply it to the
Configure access list as follows using the template:
Access-list (number) (permit or deny) (source address)
Router(configt)#access-list 10 permit
Access list number for standard IP access list is any number from 1 to 99
Now we apply it to the interface as follows:
Router(config)#int e0
Router(config-if)#access-group 10 out
out at the end of the command means that the restriction is for the
packets going out of
the e0 interface.
(45) Monitor and verify selected access lists

Router#sh access ­1 Will show all the access lists running on the router.
example will show the output;
Extended access list 110
Permit tcp host eq 8080 (34 matches)
What the above two lines show is as follows: first line gives the access
number, which is
110 an extended IP access list (any number from 100 to 199). The second
line shows the
number of packets that matched.
Router#sh ip access-list Will show only the IP access lists as shown below
Extended IP access list 110
Permit tcp host host eq 8080 (15 matches)
If the log command was used on the access list the console will then
display the
Access list number, Source address, Source port, Destination address
Destination address,
Number of packets.
When monitoring access lists it is important to find out which interface
an access list
applied to. The two commands to display this information is
Router#sh int e0 and Router#sh run
LAN Switching
(46) Describe the advantage of LAN segmentation

A single Ethernet LAN will work well for a limited number of users
attached to the
Ethernet. As time goes by and the number of users attached to the
Ethernet increases and
the number of people want to get on the network at the same time also
Congestion begins to creep in and the user access to the network begins
to slow down.
The remedy for this situation is to segment the LAN in to manageable
parts so that each
part or segment has a amount of users attached to it so that it will get
congested even if
all the users access simultaneously. There are many ways to do this
(47) Describe LAN segmentation using Bridges

Physical segmentation: You can segment by bridges and routers. Bridges
segment at the
MAC address of the Data Link layer. A bridge will first look at a routing
table and match
the packet to a segment and forwards it.
(48) Describe LAN segmentation using Routers

Routers use the network layer to segment the network with network layer
address and the
MAC address of the interface. The routing table will give the MAC address
and the
network layer addressing protocol address. eg IP address, IPX address or
apple Talk
Describe LAN segmentation using Switches

LAN switches uses at line speed by using the destination MAC address. In
order to
ensure that the packet is forwarded to the correct port, cut through
switching is used. Cut
through looks at the in coming frame FCS has passed it as error free, it
looks at the
destination MAC address and starts to forward before the full packet is
received. Cut
through switching greatly improves the throughput.
Name and describe two switching methods

The two switching methods or modes are Store and Forward, and Cut Through.
With Store and Forward switching method, the LAN router copies the entire
frame in to
its buffer and checks the following and discards the frame if they are
not correct:
A CRC error, if the frame is runt (less than 64 bytes including the CRC)
or a giant (more
than 1518 bytes including CRC). The frame has no errors then the router
looks up the
routing table and sends to the correct interface for transmission down
the line. Latency
due to this error checking varies with the length of the frame.
Cut Through switching, the LAN switch copies only the destination address
to its buffers
(six bytes after the preamble). It then looks at the destination address
on the switching
table, determines the outgoing interface and submits it to the correct
interface for
transmission down the line. Cut through switching reduce latency because,
first it does
not copy the complete frame to the buffer and secondly it starts to
transmitting the frame
as soon as it locate the destination address from the routing table.
Describe full and half duplex Ethernet operation

Full duplex can transmit and receive simultaneously, but to do so one
needs a CISCO
switch that has a full duplex interface. The end user needs a full duplex
NIC card so that
it can be connected to the switch full duplex switch interface. Full
duplex Ethernet uses
point to point connections and it is collusion free transmission. This is
because it does not
share bandwidth with any other device. The frames sent by two nodes can
not collide
because they are on physically separate transmit and receive circuits. If
you have a full
duplex 10 Mbps Ethernet operating on the same switch port it can
theoretically have a
throughput of 20 Mbps.
Half duplex will send and receive, one at a time. When the transmitter is
transmitting his
receiving circuit is in active. Same with the receiver, when his
receiving circuit is active
his transmitting circuit is inactive.

Describe the congestion problem in Ethernetworks

Ethernet device gets access to the network by listening to the signals on
the cable. If no
one is transmitting then the device starts to transmit. If two devices
start to transmit at the
same time a collusion will occur and each station will back off and
retransmit the frame
later. This is good for a small number of devices attached to the network
but when there
are too many devices gets attached, the collisions become more frequent
and delays

Describe the benefits of network segmentation with bridges

Bridges segment the network by the MAC address of the data link layer. By
segmenting a
logical network in to multiple physical segments, it ensures network
availability, scalability and manageability.

Describe the benefits of network segmentation with switches.

Just like bridges LAN switches use destination MAC address in order to
ensure that the
packet gets to the right out going port. Switches are similar to bridges
with more ports
attached to it.

Describe the features and benefits of fast Ethernet

Fast Ethernet is the IEEE 802.3u standard also known as 100 Base T. It is
10 times faster
because the bit rate is 100 Mbps instead of 10 Mbps for 10 Base T. This
standard defines
the physical layer and the data link layer, and uses the same CSMA/CD
technology as 10 Base T. The other standards associated with Fast
Ethernet are as
follows: 100 Base FX which is 100 Mbps two strand multi mode 50/125 or
micron fiber optic cable. 100 Base T4 can use CAT 3,4,or 5 cabling with
RJ 45
connector. 100 Base TX can use CAT 5 or 100 ohm two pair shielded twisted
pair or type
1 cable.
Benefits of fast Ethernet can listed as follows:
100 Base T is 10 times faster as 10 Base T
Existing cabling and network equipment can be used
10 Mbps and 100 Mbps can exist on the same cable media
It uses tried and tested CSMA/CD
Migration to 100 Mbps from 10 Mbps does not create any problems

Describe the guide lines and distance limitations of Fast Ethernet

To exist on the same cable media, 10 Base T and 100 Base T, the time
slots should be the
same. Standard defined round trip is shorter for 100 Base T. Therefore
distance between transmitter and receiver is shorter for 100 Base T.
Maximum distance
between end nodes for 100 Base TX is 100 meters and for 100 Base FX is
412 meters

Distinguish between Cut Through and Store and Forward LAN switching

Cut through switching, the LAN switching device copies destination
address to its in put
buffer and looks at the destination switching table for the destination
address. As soon as
it finds the destination address, it starts to transmit the frame to the
destination. This
reducers the latency associated with store and forward
Store and forward switching, the LAN switching device copies the entire
frame to its in
put buffer and does a CRC check, runt check and a giant check on the
frame. If any of
them checks gives errors then the frame is dropped, if not it looks at
the routing table and
locates the destination address and sends the frame to the appropriate
interface to transmit
it down the line. All these checks take time and latency time increases
for store and
forward switching.
Describe the operation of Spanning Tree Protocol and its benefits

IEEE 802.1d standard defines the Spanning Tree Protocol and was developed
to prevent
routing loops in a network. If a router, a switch or a hub has more than
one path to the
same destination, then a routing loop problem could occur. To prevent
this, the spanning
tree protocol is executed between devices to detect and logically block
redundant paths
on the network. For fault networks there should be redundant links
between devices, and
to be loop free it should also execute the spanning tree protocol.
Describe the benefits of virtual LANs

Virtual LAN (VLAN) is a logical group of end users and resources
connected to defined
ports on a switch. This logical group communicates at layer 2 and layer 3
to establish the
Virtual LAN. Most beneficial asset in implementing is the functional
group. It is secure
because on out side of the VLAN group can get access to the group and the
members of
the group can not go out side of the group. Next item is that if a member
of the VLAN
group is moved from one floor to another, no set ups are required because
the member
can go to the next floor be connected to a different switch with a port
that is in the same
VLAN group. Because VLAN operates at layer 2 and 3, broadcasts can be
Following are the primary benefits of VLAN: Broadcast control, Functional
groups and

Define and describe the function of the MAC address

Media Access Control (MAC) address is the hardware address of the
interface and it is
burned in to the NIC card. This is a unique number issued by IEEE to the
It is 6 bytes long and the first 24 bits represents the vendor and next
24 bits represents the
serial number of the NIC card. This hardware address is used by the MAC
layer of the
Data Link layer to identify uniquely, the LAN device, to the network

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