Study Guide Cisco Certified Network Associate 3.0 CCNA 3.0 Version 1

Data Link Layer Tasks The data link layer provides network traffic with information on where it is to go and what it is to do once it gets there.. You can use the following commands/key

Study Guide

Cisco Certified Network Associate 3.0

CCNA 3.0

Version 1

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

Advance Router Configuration 14

OBTAINING NETWORK INFORMATION 16

CDP 16

CDP Related Commands 16

Telnet Application 17

Router Basics 18

Router components 18

CATALYST 1900 SWITCH 21

Functions 21

Frame Decisions 21

Avoiding Loops 21

Spanning Tree Protocol 22

Spanning Tree Path Cost 23

Spanning Tree Protocol elections 23

Spanning Tree States 24

How Frame Are Sent 24

Switch communication 25

Catalyst 1900 Switch Configuration 25

Configuration commands 26

Virtual LANs 27

TCP/IP 28

TCP Connection Establishment 29

Windowing 29

TCP/IP Internet Layer 29

ICMP 30

IP Addressing Basics 30

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

Obtain Frame Relay Information 56

LABS 57

Lab 1 – Configure a name and passwords for a router 57

Lab 2 – Configuring Router Interfaces 59

Lab 3 – Configuring Static Routes 61

Lab 4 – Configuring RIP and Restoring Configuration 62

Lab 5 – Configuring IGRP 63

Lab 6 – Access List 64

CCNA Foundations

OSI Model

One of the keys to understanding Cisco is the OSI model The OSI model permits

people to understand how internetwork works and it serves as a guideline or framework for creating and implementing network standards, devices, and internetworking schemes Some of the advantages of the OSI model include:

• It allows for the breaking down of complex operation into simple elements;

• Enables engineers to specialize the design and development of modular elements; and

• It provides standards for plug and play and multivendor integration

The OSI reference model has 7 layers:

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

Data Flow

Layers

Media Access Control (MAC) Sublayer Logical Link Control (LLC) Sublayer

Or from the bottom of the OSI model to the top

Please Do Not Throw Sausage Pizza Away

Upper Layer

Upper Layers – The upper layers of the OSI model deal with user interface, data

formatting, and application access Specifically these layers do the following:

Application Layer – this is where the user/applications access the network

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

Collision vs Broadcast Domains

Collision domain is a group of devices connected to the same physical media such that if two devices access the media at the same time, the result is a collision of the two signals Broadcast Domains is a group of devices in the network that receive one another’s

broadcast messages

Data Link Layer Tasks

The data link layer provides network traffic with information on where it is to go and what it is to do once it gets there In order to provide this functions the IEEE data link layer is defined into two sublayers:

1 Media Access Control (MAC) Sublayer (802.3) – This sublayers is responsible for how the data is transported over the physical wire This is the part of the data link layer that communicates downward to the physical layer

The MAC address is a 48-bit address expressed as 12 hexadecimal digits The first 24 bits or 6 hexadecimal digits of the MAC address contain a manufacturer identification or vendor code This can also be called the Organizationally Unique Identifier (OUI) The last 24 bits or 6 hexadecimal are administered by each vendor and often represents the interface serial number

2 Logical Link Control (LLC) Sublayer (802.2) – This sublayer is responsible for

logically identifying different protocol types and then encapsulating them in the order to

be transmitted across the network

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

2 All devices connected to the same bridge/switch are part of the same

Network Layer Tasks

The network layer defines how to transport traffic between devices that are not locally attached in the same broadcast domain In order for this to occur the following is

required:

1 A logical address associated with the source and destination stations

2 A path through the network to reach the desired destination

The logical network address consists of two parts: one part to identify the network and the other to uniquely identify the host

Routers work at the network level The router performs the following tasks:

• Routers identify networks and provide connectivity

• Router do not forward Layer 2 broadcast or multicast frames

• Routers attempt to determine the optimal path through a routed network based on routing algorithms

• Routers strip Layer 2 frames and forward packets based on Layer 3 destination address

• Routers map a single Layer 3 logical address to a single network device;

therefore, routers can limit or secure network traffic based on identifiable

attributes within each packet These options, controlled via access lists, can be applied to inbound or outbound packets

• Routers can be configured to perform both bridging and routing functions

• Routers provide connectivity between different virtual LANs (VLANs) in a switched environment

• Routers can be used to deploy quality of service parameters for specified types of network traffic

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

of LAN implementations The three major categories are:

1 Ethernet (DIX) and IEEE 802.3 – this operates at 10 Mbps over coaxial cable, UTP and fiber

2 100 Mbps Ethernet (IEEE 802.3u) – this is also known as the Fast Ethernet that operates over UTP or fiber

3 1000 Mbps Ethernet – this is known as the Gigabit Ethernet that operates at 1000 Mbps over fiber

Ethernet Cabling Specifications

Segment Length

Topology Connector

10BaseT Cat 3,4,5 UTP,

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

Basis Switch Commands

history – This command will provide you with a list of the contents of the switch’s

substitution buffer You can use the following commands/key strokes to navigate the buffer

Up-arrow button/Ctrl-p – Last (previous) command recall

Down-arrow / Ctrl-n – More recent command to buffer

Switch>show history – Shows commands buffer contents

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

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

switch(config)# hostname testking

testking(config)#

Please note the name change is immediate

You will also need to configure the ip address of the switch this achieved as follows: testking(config)# ip address 10.5.5.11 255.255.255.0

Basic Router Information

When a router is first turned on it will check its NVRAM (nonvolatile random access memory) for a router configuration If one is not found then the operating system starts a question driven initial configuration This is known as the system configuration dialog or setup dialog

To change the configuration of the router you will need to do so in the configuration mode There are two levels of modes:

User mode – often used to check the status of the router

Privileged mode – used to change the routers configuration

Cisco IOS CLI on Cisco routers offers context sentsitive word help and command syntax help:

For word help, use the question mark (?) following one or more characters This

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

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

command and the question mark

$ Invalid input detected at ‘^” marker

Reason for error

The command was entered incorrectly The caret (^) marks the place of the error

Ctrl-a Moves the cursors to the beginning of the line

Ctrl-e Moves the cursors to the end of the line

Ctrl-f Moves the cursors forward one character

Ctrl-b Moves the cursors backward one character

Esc-f Moves the cursors forward one word

Esc-b Moves the cursors backward one word

Ctrl-d Deletes a single character

Ctrl-k Deletes everything to the right of the cursor

Ctrl-x Deletes everything to the left of the cursor

Ctrl-u Deletes a line

Ctrl-r Refreshes the command line and everything typed up to this point Backspace Removes one character to the left of the cursor

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

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:

copy running-configuration startup-configuration – this command will copy the current configuration in the RAM to the NVRAM (backup configuration)

To change the name of the router you would use the hostname command An example follows:

router(config)#hostname testking

testking(config)#

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)#enable password washington

testking(config)#enable secret boston

Obtaining Network Information

In general, CDP provides the following information for each CDP neighbor device:

• Device name and if there is one a domain name

• An address for each supported protocol

• Port identifier That is names of the local and remote ports This is done is

ASCII such as ethernet0

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

To obtain additional information you can use either the show cdp neighbours detail

command or show cdp entry * command

show cdp entry command will display the following information:

• Neighbor device ID

• Layer 3 protocol information

• The device’s platform

• The device’s capabilities

• The local interface type and outgoing remote port ID

• The hold time value in seconds

• OIS type and version

show cdp traffic – this command displays the number of CDP packets sent and received and the number of errors

show cdp interface - this command displays the configuration information and the

interface status of the local device

show sessions – this command shows a list of devices that you are connected to This will allow you to verify Telnet connectivity This commands displays the following for each device:

• 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

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

clear line – this command will close a Telnet session from a foreign host You will need

to use the show user command to determine which users are on the device This will provide you with the lines that need to be disconnected

Other useful TCP/IP tools that you can use are the ping command and the traceroute command The ping command verifies connectivity and traceroute will show the route that packets travel

Router Basics

Booting Sequence of a router

Step 1 – POST

Step 2 – Load and run bootstrap code

Step 3 – Find the IOS software

Step 4 – Load the IOS software

Step 5 - Find the configuration

Step 6 – Load the configuration

Step 7 – Run

Router components

Routers have the following components:

• 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

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

• Total amount of memory on the router

• Memory available

• System image file name

• The size of the file in Flash

The name of the Cisco image file contains different parts An example is

c2500-js-1_120-3.bin

c2500 shows the platform that the image runs

js – j means that this is an enterprise image and s shows an extended capabilities

1 – means the file is not compressed and can be moved

120-3 – represents the version number of the image

.bin – means that this is a binary executable file

copy tftp flash – this command will download a new image from a network server to the Flash memory

• 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

• Without some form of loop avoidance there is a distinct possibility that each switch will flood the network with broadcasts continuously These broadcasts

can lead a broadcast storm that can cause a waste of bandwidth and severely impacts network and host performance

• Many copies of nonbroadcast frames may delivered to the destination device This could cause unrecoverable errors

• MAC address table could become instable as it receives of the same frame being received on different ports

Loop avoidance can address each of these problems

Broadcast storms are 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

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

in a forwarding state can both receive and transmit frames

Each nonroot bridge will have on root port – the root port is the one with lowest cost path

to the root bridge These root ports are in the forwarding state Spanning Tree path cost

is an accumulated cost based on bandwidth If the cost is the same then it is the port with the lowest port number

On each segment there is one designated port – once again the designated port is selected

on the bridge that has the lowest path cost to the root bridge As these ports are in the forwarding state they are responsible for forwarding the traffic of the segment

Nondesignated ports are in a blocking state so as to break a loop in the topology As a result it cannot forward traffic

Devices running the Spanning Tree Protocol exchange Bridge Protocol Data Unit

(BPDU) BPDU are multicast message are sent by default is sent every 2 seconds that contain configuration information including the bridge ID This ID most often contain 2 bytes for priority and 6 bytes that contain the MAC address of the device

Spanning Tree Path Cost

(Reviswed IEEE Specs) Cost (Old IEEE Specs)

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

Forwarding – all designated ports and root ports are in the forwarding state

Spanning Tree States

Spanning tree has the following states:

All ports start in the blocked state These port still receive BPDUs Ports move to the listening state The move to this state to ensure if the transitions it they will not create a loop Next the port will populate its MAC address table in the learning state but will not forward frames Finally the port begin receiving and sending frames once it moves into the forwarding state The default time to move from the blocking state to the forwarding state is 50 seconds The time it takes for a device to transition between the listening to learning and learning to forwarding is called forward delay The default Spanning Tree timers are as follows:

Hello Time 2 seconds

Forward Delay 30 seconds

How Frame Are Sent

Switches have three operating modes to address frame switching:

• Store and Forward – in this mode the switch must first receive all of the frame prior to forwarding it The source and destination destinations are read, the CRC (cyclic redundancy check) is done, filters are applied, and then the frame is

forwarded If an error is discovered the frame is dropped Latency for this mode

is dependent on the size of frame

• 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

• 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

Catalyst 1900 Switch Configuration

This type of switch can be configured three different ways:

• Using the consol port via a menu-driven interface

• Web-based Visual Switch Manager (VSM)

• Using the IOS command-line interface (CLI)

As the CCNA exam deals with the use of the CLI so will this study guide

The default configuration settings of the Catalyst Switch is as follows:

IP address – 0.0.0.0

CDP – Enabled

Switching mode – fragment-free

100BaseT port – auto detect duplex mode

Spanning Tree – Enabled

Console password – none

To configure a specific interface (port) you would do the following:

switch(config)# interface e0/1

switch(config-if)#

To configure the IP address and subnet mask on the switch you would do the following: switch(config)# ip address {address} {mask}

Where address is the IP address and mask is the subnet mask

To configure the default gateway you would do the following:

switch(config)# ip default-gateway {ip address}

IP address is the IP address of the default gateway such as 10.5.5.3

To configure the duplex mode of an interface you would do the following:

switch(config)# interface e0/1

switch(config-if)#duplex {auto|full|full-full-control|half}

auto – sets the duplex mode to autonegotiation This is the default for 100 Mbps TX ports

full – sets the mode to full-duplex

full-flow-control – sets the mode to full-duplex with flow control

half – set the mode to half duplex mode This is default option for 10 Mbps TX ports

show version – user EXEC command to display basic information about hardware and the IOS software version Also included is memory information and uptime

copy nvram tftp – this command will upload the running configuration to a TFTP server copy tftp nvram – downloads the configuration file from the TFTP server

Virtual LANs

A VLAN (Virtual Local Area Network) is a switched network that is logically segmented

by communities of interest without regard to the physical location of users Each port on the Switch can belong to a VLAN Ports in a VLAN share broadcasts Ports that do not belong to that VLAN do not share these broadcasts thus improving the overall

performance of the network VLANs remove the physical constraints of workgroup communications Layer 3 routing provides communications between VLANs In other words users can be in totally different physical locations and still be on the same VLAN Likewise users in the same physical location can be on different VLANs

VLANs provide the following benefits:

• Reduced administration costs from solving problems associated with moves and changes - As users physically move they just have to be re-patched and enabled into their existing VLAN

• Workgroup and network security - You can restrict the number of users in a VLAN and also prevent another user from joining a VLAN without prior approval from the VLAN network management application

• Controlled Broadcast activity - Broadcasts are only propagated within the VLAN This offers segmentation based on logical constraints

• Leveraging of existing hub investments - Existing hubs can be plugged into a switch port and assigned a VLAN of their own This segregates all users on the hub to one VLAN

• Centralized administration control - VLANs can be centrally administrated

Inter-Switch Links (ISL) is a Cisco proprietary protocol used to interconnect switches and to maintain VLAN information as traffic goes between switches ISL provides VLAN capabilities while maintaining full wire-speed performance over Fast Ethernet links in full- or half-duplex mode It operates in a point to point environment

show spantree – this command will display the Spanning Tree Protocol configuration status of the switch

TCP/IP

Another important concept for someone preparing for the CCNA exam is the

Transmission Control Protocol/Internet Protocol (TCP/IP) stack In particular Layer 3 and Layer 4 The TCP/IP model compares to the OSI model as follows:

The TCP/IP application layer enables the following operations:

At the transport layer the following two protocols operate:

TCP – connection orientated protocol/ reliable protocol

UDP – User Datagram Protocol is connectionless and unacknowledged protocol

TCP and UDP both use ports to pass information to the application layers The most common ports used are:

For TCP to establish a connection a three-way handshake must occur That is, the

devices involved in the communication must exchange initial sequence numbers (ISN) and a control bit called SYN (synchronize) There are three steps to establishment of communication:

1 Device 1 sends it SYN to Device 2

2 Device 2 ACK Device 1 SYN and sends it own SYN

3 Device 1 ACK Device 2 SYN and sets ACK and SYN bit

Communication is established

Windowing

TCP controls the flow of data with windowing The receiving device reports how many octets it is prepare to receive, a window, from the sending device TCP window size can change during the duration of the connection Each acknowledgement contains how many bytes the receiving device can receive If the window size is set to zero it means the buffer of the receiving device is full and cannot receive any more data The sending device will not send additional data until an acknowledgement has a window bigger than zero

TCP/IP Internet Layer

The following protocols operate at the Internet Layer of TCP/IP model:

1 Internet Protocol (IP) – is a connectionless protocol that provides for a best effort delivery of datagrams The content of the datagram is not a concern, rather route to a destination is

2 Internet Control Message Protocol (ICMP) – provides control and messaging capabilities

3 Address Resolution Protocol (ARP) – determines the data link layer address (MAC address) of the destination device for known destination IP address

4 Reverse Address Resolution Protocol (RARP) – determines the source

network address (IP address for example) when source data link layer address (MAC Address) is known This is used when a device does not know its own

IP address when it comes onto a network

without going through a router If two hosts have different network ID's, they belong to different segments on the network They must communicate with each other remotely through a router or default gateway

An IP address consists of 32 binary bits, where each bit is either a 0 or 1 We write the 32 bits into four 8-bit numbers (octets) separated by a periods

For Example: 11000001 00001010 00011110 00000010 (IP address in binary form)

To convert the IP address from binary to decimal form, we convert each of the four 8-bit numbers in each octet according to the following table:

Everywhere a 1 appears in the table, the decimal value in that column is added to

determine the decimal value of the entire octet

There are 5 different address classes The decimal notation of the very first octet can distinguish classes The following Address Class table illustrates how you can determine

to which class and address belongs

Class Range of Network Numbers Network Bits Default Subnet Mask

Please note 127 is reserved for local testing The local loopback is 127.0.0.1

The two parts of IP address of 172.16.122.204 is as follows: Network number 172.16 (first 16 bits) and Host number is 122.204 (the remaining 16 bits)

If you are required to determine how many hosts are available for given IP address you can use the following formula:

2N – 2 (where N is the number of bits are in the host portion)

All subnet broadcast

Flooded broadcast are considered local and are represented by 255.255.255.255

Directed broadcast are sent to a particular network and are allowed to transit by a router Directed broadcasts have 1 in the host portion of the address If you want to send a broadcast to the third subnet of the 172.16 network the address would be 172.16.3.255

To send a broadcast to all the subnets of 172.16 network the address would be

172.16.255.255