This is CCNA Presentation

1. © 2003, Cisco Systems, Inc. All rights reserved.

2. 2

3. Data Networks
Sharing data through the use of floppy disks is not an efficient
or cost-effective manner in which to operate businesses.
Businesses needed a solution that would successfully address
the following three problems:
• How to avoid duplication of equipment and resources
• How to communicate efficiently
• How to set up and manage a network
Businesses realized that networking technology could
increase productivity while saving money.
3

4. Networking Devices
Equipment that connects directly to a network segment is
referred to as a device.
These devices are broken up into two classifications.
• end-user devices
• network devices
End-user devices include computers, printers, scanners, and
other devices that provide services directly to the user.
Network devices include all the devices that connect the end-
user devices together to allow them to communicate.
4

5. Network Interface Card
A network interface card (NIC) is a printed circuit board
that provides network communication capabilities to and
from a personal computer. Also called a LAN adapter.
5

6. Networking Device Icons
6

7. Repeater
A repeater is a network device used to regenerate a signal.
Repeaters regenerate analog or digital signals distorted by
transmission loss due to attenuation. A repeater does not
perform intelligent routing.
7

8. Hub
Hubs concentrate
connections. In other words,
they take a group of hosts
and allow the network to see
them as a single unit.
This is done passively,
without any other effect on
the data transmission.
Active hubs not only
concentrate hosts, but they
also regenerate signals.
8

9. Bridge
Bridges convert network transmission data formats as well as
perform basic data transmission management. Bridges, as
the name implies, provide connections between LANs. Not
only do bridges connect LANs, but they also perform a check
on the data to determine whether it should cross the bridge or
not. This makes each part of the network more efficient.
9

10. Workgroup Switch
Workgroup switches add
more intelligence to data
transfer management.
Switches can determine
whether data should remain
on a LAN or not, and they
can transfer the data to the
connection that needs that
data.
10

11. Router
Routers have all capabilities of the previous devices. Routers
can regenerate signals, concentrate multiple connections,
convert data transmission formats, and manage data
transfers.They can also connect to a WAN, which allows them
to connect LANs that are separated by great distances.
11

12. “The Cloud”
The cloud is used in diagrams to represent where the
connection to the internet is.
It also represents all of the devices on the internet.
12

13. Network Topologies
Network topology defines the structure of the network.
One part of the topology definition is the physical topology,
which is the actual layout of the wire or media.
The other part is the logical topology,which defines how the
media is accessed by the hosts for sending data.
13

14. Physical Topologies
14

15. Bus Topology
A bus topology uses a single backbone cable that is
terminated at both ends.
All the hosts connect directly to this backbone.
15

16. Ring Topology
A ring topology connects one host to the next and the last host
to the first.
This creates a physical ring of cable.
16

17. Star Topology
A star topology connects all cables to a central point of
concentration.
17

18. Extended Star Topology
An extended star topology links individual stars together by
connecting the hubs and/or switches.This topology can extend
the scope and coverage of the network.
18

19. Hierarchical Topology
A hierarchical topology is similar to an extended star.
19

20. Mesh Topology
A mesh topology is implemented to provide as much
protection as possible from interruption of service.
Each host has its own connections to all other hosts.
Although the Internet has multiple paths to any one
location, it does not adopt the full mesh topology.
20

21. LANs, MANs, & WANs
One early solution was the creation of local-area network
(LAN) standards which provided an open set of guidelines for
creating network hardware and software, making equipment
from different companies compatible.
What was needed was a way for information to move
efficiently and quickly, not only within a company, but also
from one business to another.
The solution was the creation of metropolitan-area networks
(MANs) and wide-area networks (WANs).
21

22. Examples of Data Networks
22

23. LANs
23

24. Wireless LAN Organizations
and Standards
In cabled networks, IEEE is the prime issuer of standards for
wireless networks. The standards have been created within the
framework of the regulations created by the Federal
Communications Commission (FCC).
A key technology contained within the 802.11 standard is Direct
Sequence Spread Spectrum (DSSS).
24

25. Cellular Topology for Wireless
25

26. WANs
26

27. SANs
A SAN is a dedicated, high-
performance network used to
move data between servers
and storage resources.
Because it is a separate,
dedicated network, it avoids
any traffic conflict between
clients and servers.
27

28. Virtual Private Network
A VPN is a private network that is constructed within a public network
infrastructure such as the global Internet. Using VPN, a telecommuter
can access the network of the company headquarters through the
Internet by building a secure tunnel between the telecommuter’s PC
and a VPN router in the headquarters.
28

29. Bandwidth
29

30. Measuring Bandwidth
30

31. 31

32. Why do we need the OSI Model?
To address the problem of networks increasing in size
and in number, the International Organization for
Standardization (ISO) researched many network
schemes and recognized that there was a need to
create a network model that would help network
builders implement networks that could communicate
and work together and therefore, released the OSI
reference model in 1984.
32

33. Don’t Get Confused.
ISO - International Organization for Standardization
OSI - Open System Interconnection
IOS - Internetwork Operating System
The ISO created the OSI to make the IOS more
efficient. The “ISO” acronym is correct as shown.
To avoid confusion, some people say “International
Standard Organization.”
33

34. The OSI Reference Model
7 Application The OSI Model will be
used throughout your
6 Presentation
entire networking
5 Session career!
4 Transport
3 Network
Memorize it!
2 Data Link
1 Physical
34

35. Layer 7 - The Application Layer
7 Application This layer deal with
networking applications.
6 Presentation
5 Session Examples:
4 Transport • Email
• Web browsers
3 Network
2 Data Link PDU - User Data
1 Physical
35

36. Layer 6 - The Presentation Layer
7 Application This layer is responsible
for presenting the data in
6 Presentation
the required format which
5 Session may include:
4 Transport • Encryption
• Compression
3 Network
2 Data Link PDU - Formatted Data
1 Physical
36

37. Layer 5 - The Session Layer
7 Application This layer establishes,
manages, and terminates
6 Presentation
sessions between two
5 Session communicating hosts.
4 Transport
Example:
3 Network • Client Software
2 Data Link ( Used for logging in)
1 Physical PDU - Formatted Data
37

38. Layer 4 - The Transport Layer
7 Application This layer breaks up the data
from the sending host and
6 Presentation
then reassembles it in the
5 Session receiver.
4 Transport
It also is used to insure
3 Network reliable data transport
2 Data Link across the network.
1 Physical
PDU - Segments
38

39. Layer 3 - The Network Layer
7 Application Sometimes referred to as the
“Cisco Layer”.
6 Presentation
5 Session Makes “Best Path
4 Transport Determination” decisions
based on logical addresses
3 Network (usually IP addresses).
2 Data Link
PDU - Packets
1 Physical
39

40. Layer 2 - The Data Link Layer
7 Application This layer provides reliable
transit of data across a
6 Presentation
physical link.
5 Session
4 Transport Makes decisions based on
physical addresses (usually
3 Network MAC addresses).
2 Data Link
PDU - Frames
1 Physical
40

41. Layer 1 - The Physical Layer
This is the physical media
7 Application through which the data,
6 Presentation represented as electronic
signals, is sent from the
5 Session
source host to the
4 Transport destination host.
3 Network
Examples:
2 Data Link • CAT5 (what we have)
1 Physical • Coaxial (like cable TV)
• Fiber optic
PDU - Bits 41

42. OSI Model Analogy
Application Layer - Source Host
After riding your new bicycle a few times in
NewYork, you decide that you want to give it to a
friend who lives in Munich,Germany. 42

43. OSI Model Analogy
Presentation Layer - Source Host
Make sure you have the proper directions to
disassemble and reassemble the bicycle.
43

44. OSI Model Analogy
Session Layer - Source Host
Call your friend and make sure you have his
correct address.
44

45. OSI Model Analogy
Transport Layer - Source Host
Disassemble the bicycle and put different pieces
in different boxes. The boxes are labeled
“1 of 3”, “2 of 3”, and “3 of 3”. 45

46. OSI Model Analogy
Network Layer - Source Host
Put your friend's complete mailing address (and
yours) on each box.Since the packages are too
big for your mailbox (and since you don’t have
enough stamps) you determine that you need to
go to the post office. 46

47. OSI Model Analogy
Data Link Layer – Source Host
NewYork post office takes possession of the
boxes.
47

48. OSI Model Analogy
Physical Layer - Media
The boxes are flown from USA to Germany.
48

49. OSI Model Analogy
Data Link Layer - Destination
Munich post office receives your boxes.
49

50. OSI Model Analogy
Network Layer - Destination
Upon examining the destination address,
Munich post office determines that your
boxes should be delivered to your written
home address. 50

51. OSI Model Analogy
Transport Layer - Destination
Your friend calls you and tells you he got all 3
boxes and he is having another friend named
BOB reassemble the bicycle. 51

52. OSI Model Analogy
Session Layer - Destination
Your friend hangs up because he is done talking
to you.
52

53. OSI Model Analogy
Presentation Layer - Destination
BOB is finished and “presents” the bicycle to
your friend. Another way to say it is that your
friend is finally getting him “present”.53

54. OSI Model Analogy
Application Layer - Destination
Your friend enjoys riding his new bicycle in
Munich.
54

55. Host Layers
7 Application These layers
only exist in the
6 Presentation
source and
5 Session destination host
4 Transport computers.
3 Network
2 Data Link
1 Physical
55

56. Media Layers
7 Application
6 Presentation
5 Session
4 Transport
These layers manage
3 Network
the information out in
2 Data Link the LAN or WAN
1 Physical between the source
and destination hosts.
56

57. 57

58. 58

59. Data Flow Through a Network
59

60. 60

61. LAN Physical Layer
Various symbols are used to represent media types.
The function of media is to carry a flow of information
through a LAN.Networking media are considered
Layer 1, or physical layer, components of LANs.
Each media has advantages and disadvantages.
Some of the advantage or disadvantage comparisons
concern:
• Cable length
• Cost
• Ease of installation
• Susceptibility to interference
Coaxial cable, optical fiber, and even free space can
carry network signals. However, the principal medium
that will be studied is Category 5 unshielded twisted-
pair cable (Cat 5 UTP)
61

62. Unshielded Twisted Pair (UTP) Cable
62

63. UTP Implementation
EIA/TIA specifies an RJ-45 connector for UTP cable.
The RJ-45 transparent end connector shows eight colored wires.
Four of the wires carry the voltage and are considered “tip” (T1 through T4).
The other four wires are grounded and are called “ring” (R1 through R4).
The wires in the first pair in a cable or a connector are designated as T1 & R1
63

64. Connection Media
The registered jack (RJ-45) connector and jack are the most
common.
In some cases the type of connector on a network interface
card (NIC) does not match the media that it needs to connect
to.
The attachment unit interface (AUI) connector allows different
media to connect when used with the appropriate transceiver.
A transceiver is an adapter that converts one type of
connection to another.
64

65. Ethernet Standards
The Ethernet standard specifies that each of the pins on an
RJ-45 connector have a particular purpose. A NIC transmits
signals on pins 1 & 2, and it receives signals on pins 3 & 6.
65

66. Remember…
A straight-thru cable has T568B on both ends. A crossover (or
cross-connect) cable has T568B on one end and T568A on the
other. A console cable had T568B on one end and reverse T568B
on the other, which is why it is also called a rollover cable.
66

67. Straight-Thru or Crossover
Use straight-through cables for the following cabling:
• Switch to router
• Switch to PC or server
• Hub to PC or server
Use crossover cables for the following cabling:
• Switch to switch
• Switch to hub
• Hub to hub
• Router to router
• PC to PC
• Router to PC
67

68. Sources of Noise on Copper Media
Noise is any electrical energy on the
transmission cable that makes it difficult for a
receiver to interpret the data sent from the
transmitter. TIA/EIA-568-B certification of a cable
now requires testing for a variety of types of
noise.Twisted-pair cable is designed to take
advantage of the effects of crosstalk in order to
minimize noise. In twisted-pair cable, a pair of
wires is used to transmit one signal.The wire pair
is twisted so that each wire experiences similar
crosstalk. Because a noise signal on one wire
will appear identically on the other wire, this
noise be easily detected and filtered at
receiver.Twisting one pair of wires in a cable
also helps to reduce crosstalk of data or noise
signals from adjacent wires. 68

69. Shielded Twisted Pair (STP) Cable
69

70. Coaxial Cable
70

71. Fiber Optic Cable
71

72. Fiber Optic Connectors
Connectors are attached to the fiber ends so that the fibers can
be connected to the ports on the transmitter and receiver.
The type of connector most commonly used with multimode fiber
is the Subscriber Connector (SC connector).On single-mode
fiber, the Straight Tip (ST) connector is frequently used
72

73. Fiber Optic Patch Panels
Fiber patch panels similar to the patch panels used with copper
cable.
73

74. Cable Specifications
10BASE-T
The T stands for twisted pair.
10BASE5
The 5 represents the fact that a signal can travel for approximately
500 meters 10BASE5 is often referred to as Thicknet.
10BASE2
The 2 represents the fact that a signal can travel for approximately
200 meters 10BASE2 is often referred to as Thinnet.
All 3 of these specifications refer to the speed of transmission at 10
Mbps and a type of transmission that is baseband, or digitally
interpreted. Thinnet and Thicknet are actually a type of networks,
while 10BASE2 & 10BASE5 are the types of cabling used in these
networks.
74

75. Ethernet Media Connector Requirements
75

76. LAN Physical Layer Implementation
76

77. Ethernet in the Campus
77

78. WAN Physical Layer
78

79. WAN Serial Connection Options
79

80. Serial Implementation of DTE & DCE
When connecting directly to a service provider, or to a
device such as a CSU/DSU that will perform signal clocking,
the router is a DTE and needs a DTE serial cable.
This is typically the case for routers.
80

81. Back-to-Back Serial Connection
When
performing a
back-to-back
router scenario
in a test
environment,
one of the
routers will be a
DTE and the
other will be a
DCE.
81

82. Repeater
A repeater is a network device used to regenerate a signal.
Repeaters regenerate analog or digital signals distorted by
transmission loss due to attenuation.Repeater is a Physical
Layer device
82

83. The 4 Repeater Rule
The Four Repeater Rule for 10-Mbps Ethernet should be
used as a standard when extending LAN segments.
This rule states that no more than four repeaters
can be used between hosts on a LAN.
This rule is used to limit latency added to frame travel by
each repeater.
83

84. Hub
Hubs concentrate
connections.In other words,
they take a group of hosts
and allow the network to see
them as a single unit.
Hub is a physical layer
device.
84

85. Network Interface Card
The function of a NIC is to connect a host device to the network medium.
A NIC is a printed circuit board that fits into the expansion slot on the motherboard or
peripheral device of a computer. The NIC is also referred to as a network adapter.
NICs are considered Data Link Layer devices because each NIC carries a
unique code called a MAC address.
85

86. MAC Address
MAC address is 48 bits in length and expressed as twelve hexadecimal
digits.MAC addresses are sometimes referred to as burned-in addresses
(BIA) because they are burned into read-only memory (ROM) and are
copied into random-access memory (RAM) when the NIC initializes.
86

87. Bridge
Bridges are Data Link layer devices.Connected host
addresses are learned and stored on a MAC address
table.Each bridge port has a unique MAC address
87

88. Bridges
88

89. Bridging Graphic
89

90. Switch
Switches are Data Link
layer devices.
Each Switch port has a
unique MAC address.
Connected host MAC
addresses are learned and
stored on a MAC address
table.
90

91. Switching Modes
cut-through
A switch starts to transfer the frame as soon as the destination MAC
address is received. No error checking is available.
Must use synchronous switching.
store-and-forward
At the other extreme, the switch can receive the entire frame before
sending it out the destination port. This gives the switch software an
opportunity to verify the Frame Check Sum (FCS) to ensure that the
frame was reliably received before sending it to the destination.
Must be used with asynchronous switching.
fragment-free
A compromise between the cut-through and store-and-forward modes.
Fragment-free reads the first 64 bytes, which includes the frame header,
and switching begins before the entire data field and checksum are read.
91

92. Full Duplex
Another capability emerges when only two nodes are connected. In a network that
uses twisted-pair cabling, one pair is used to carry the transmitted signal from one
node to the other node. A separate pair is used for the return or received signal. It is
possible for signals to pass through both pairs simultaneously. The capability of
communication in both directions at once is known as full duplex.
92

93. Switches – MAC Tables
93

94. Switches – Parallel Communication
94

95. Microsegmentation
A switch is simply a bridge with many ports. When only one node is connected to a
switch port, the collision domain on the shared media contains only two nodes.
The two nodes in this small segment, or collision domain, consist of the switch port
and the host connected to it. These small physical segments are called micro
segments.
95

96. Peer-to-Peer Network
In a peer-to-peer network, networked computers act as equal partners, or peers.
As peers, each computer can take on the client function or the server function.
At one time, computer A may make a request for a file from computer B, which
responds by serving the file to computer A. Computer A functions as client, while B
functions as the server. At a later time, computers A and B can reverse roles.
In a peer-to-peer network, individual users control their own resources. Peer-to-
peer networks are relatively easy to install and operate. As networks grow, peer-to-
peer relationships become increasingly difficult to coordinate.
96

97. Client/Server Network
In a client/server arrangement, network services are located on a dedicated
computer called a server.
The server responds to the requests of clients.
The server is a central computer that is continuously available to respond to
requests from clients for file, print, application, and other services.
Most network operating systems adopt the form of a client/server relationship.
97

98. 98

99. Why Another Model?
Although the OSI reference model is universally
recognized, the historical and technical open standard
of the Internet is Transmission Control Protocol /
Internet Protocol (TCP/IP).
The TCP/IP reference model and the TCP/IP protocol
stack make data communication possible between any
two computers, anywhere in the world, at nearly the
speed of light.
The U.S. Department of Defense (DoD) created the
TCP/IP reference model because it wanted a network
that could survive any conditions, even a99
nuclear war.

100. Don’t Confuse the Models
7 Application
6 Presentation Application
5 Session
4 Transport Transport
3 Network Internet
2 Data Link Network
1 Physical Access
100

101. 2 Models
Side-By-Side
7 Application
6 Presentation Application
5 Session
4 Transport Transport
3 Network Internet
2 Data Link Network
1 Physical Access
101

102. The Application Layer
The application
layer of the
TCP/IP model
handles high-
level protocols,
issues of
representation,
encoding, and
dialog control.
102

103. The Transport Layer
The transport layer provides transport services from
the source host to the destination host. It constitutes
a logical connection between these endpoints of the
network. Transport protocols segment and
reassemble upper-layer applications into the same
data stream between endpoints.
The transport layer data stream provides end-to-end
transport services. 103

104. The Internet Layer
The purpose of the Internet layer is to
select the best path through the network for
packets to travel. The main protocol that
functions at this layer is the Internet
Protocol (IP). Best path determination and
packet switching occur at this layer.
104

105. The Network Access Layer
The network access layer is also called the host-to-
network layer. It the layer that is concerned with all of the
issues that an IP packet requires to actually make a
physical link to the network media. It includes LAN and
WAN details, and all the details contained in the OSI
physical and data-link layers. NOTE: ARP & RARP work
at both the Internet and Network Access Layers.
105

106. Comparing TCP/IP & OSI Models
NOTE: TCP/IP transport layer using UDP does not always guarantee
reliable delivery of packets as the transport layer in the OSI model does.
106

107. Introduction to the Transport Layer
The primary duties of the transport layer, Layer 4 of the OSI
model, are to transport and regulate the flow of information from
the source to the destination, reliably and accurately.
End-to-end control and reliability are provided by sliding
windows, sequencing numbers, and acknowledgments.
107

108. More on The Transport Layer
The transport layer provides transport services from the
source host to the destination host.
It establishes a logical connection between the endpoints of
the network.
• Transport services include the following basic services:
• Segmentation of upper-layer application data
• Establishment of end-to-end operations
• Transport of segments from one end host to another
end host
• Flow control provided by sliding windows
• Reliability provided by sequence numbers and
acknowledgments 108

109. Flow Control
As the transport layer sends data segments, it tries to ensure that data is not lost.
A receiving host that is unable to process data as quickly as it arrives could be a
cause of data loss.
Flow control avoids the problem of a transmitting host overflowing the buffers in
the receiving host.
109

110. 3-Way Handshake
TCP requires connection establishment before data transfer begins.
For a connection to be established or initialized, the two hosts must
synchronize their Initial Sequence Numbers (ISNs).
110

111. Basic Windowing
Data packets must be
delivered to the
recipient in the same
order in which they
were transmitted to
have a reliable,
connection-oriented
data transfer.
The protocol fails if
any data packets are
lost, damaged,
duplicated, or
received in a different
order.
An easy solution is to
have a recipient
acknowledge the
receipt of each packet
before the next packet
is sent. 111

112. Sliding Window
112

113. Sliding Window
with Different Window Sizes
113

114. TCP Sequence & Acknowledgement
114

115. TCP
Transmission Control Protocol (TCP) is a connection-oriented Layer 4
protocol that provides reliable full-duplex data transmission.
TCP is part of the TCP/IP protocol stack. In a connection-oriented
environment, a connection is established between both ends before the
transfer of information can begin.
TCP is responsible for breaking messages into segments, reassembling
them at the destination station, resending anything that is not received,
and reassembling messages from the segments.TCP supplies a virtual
circuit between end-user applications.
The protocols that use TCP include:
• FTP (File Transfer Protocol)
• HTTP (Hypertext Transfer Protocol)
• SMTP (Simple Mail Transfer Protocol)
• Telnet 115

116. TCP Segment Format
116

117. UDP
User Datagram Protocol (UDP) is the connectionless transport protocol
in the TCP/IP protocol stack.
UDP is a simple protocol that exchanges datagrams, without
acknowledgments or guaranteed delivery. Error processing and
retransmission must be handled by higher layer protocols.
UDP uses no windowing or acknowledgments so reliability, if needed, is
provided by application layer protocols. UDP is designed for applications
that do not need to put sequences of segments together.
The protocols that use UDP include:
• TFTP (Trivial File Transfer Protocol)
• SNMP (Simple Network Management Protocol)
• DHCP (Dynamic Host Control Protocol)
• DNS (Domain Name System) 117

118. UDP Segment Format
118

119. Well Known Port Numbers
The following port numbers should be memorized:
NOTE:
The curriculum forgot to mention one of the most important port numbers.
Port 80 is used for HTTP or WWW protocols. (Essentially access to the internet.)
119

120. URL
120

121. SNMP – Managed Network
121

122. 122

123. Base 2 Number System
101102 = (1 x 24 = 16) + (0 x 23 = 0) + (1 x 22 = 4) +
(1 x 21 = 2) + (0 x 20 = 0) = 22
123

124. Converting Decimal to Binary
Convert 20110 to binary:
201 / 2 = 100 remainder 1
100 / 2 = 50 remainder 0
50 / 2 = 25 remainder 0
25 / 2 = 12 remainder 1
12 / 2 = 6 remainder 0
6 / 2 = 3 remainder 0
3 / 2 = 1 remainder 1
1 / 2 = 0 remainder 1
When the quotient is 0, take all the remainders in
reverse order for your answer: 20110 = 110010012
124

125. 125

126. Network and Host Addressing
Using the IP address of the
destination network, a router can
deliver a packet to the correct
network.
When the packet arrives at a
router connected to the
destination network, the router
uses the IP address to locate the
particular computer connected to
that network.
Accordingly, every IP address has
two parts. 126

127. Network Layer Communication Path
A router forwards packets from the originating network to the
destination network using the IP protocol. The packets must
include an identifier for both the source and destination networks.
127

128. Internet Addresses
IP Addressing is a hierarchical structure.An IP address combines two
identifiers into one number. This number must be a unique number,
because duplicate addresses would make routing impossible.The
first part identifies the system's network address.The second part,
called the host part, identifies which particular machine it is on the
network.
128

129. IP Address Classes
IP addresses are divided into classes to define the large,
medium, and small networks.
Class A addresses are assigned to larger networks.
Class B addresses are used for medium-sized networks, &
Class C for small networks.
129

130. Identifying Address Classes
130

131. Address Class Prefixes
To accommodate different size networks and aid in classifying these networks, IP
addresses are divided into groups called classes.This is classful addressing.
131

132. Network and Host Division
Each complete 32-bit IP address is broken down into a network part
and a host part. A bit or bit sequence at the start of each address
determines the class of the address. There are 5 IP address classes.
132

133. Class A Addresses
The Class A address was designed to support extremely large
networks, with more than 16 million host addresses available.
Class A IP addresses use only the first octet to indicate the
network address. The remaining three octets provide for host
addresses.
133

134. Class B Addresses
The Class B address was designed to support the needs of
moderate to large-sized networks.A Class B IP address uses
the first two of the four octets to indicate the network address.
The other two octets specify host addresses.
134

135. Class C Addresses
The Class C address space is the most commonly used of the
original address classes.This address space was intended to
support small networks with a maximum of 254 hosts.
135

136. Class D Addresses
The Class D address class was created to enable multicasting in an
IP address. A multicast address is a unique network address that
directs packets with that destination address to predefined groups of
IP addresses. Therefore, a single station can simultaneously transmit
a single stream of data to multiple recipients.
136

137. Class E Addresses
A Class E address has been defined. However, the Internet
Engineering Task Force (IETF) reserves these addresses for
its own research. Therefore, no Class E addresses have been
released for use in the Internet.
137

138. IP Address Ranges
The graphic below shows the IP address range of the first octet
both in decimal and binary for each IP address class.
138

139. IPv4
As early as 1992, the Internet Engineering
Task Force (IETF) identified two specific
concerns: Exhaustion of the remaining,
unassigned IPv4 network addresses and the
increase in the size of Internet routing tables.
Over the past two decades, numerous
extensions to IPv4 have been developed.
Two of the more important of these are
subnet masks and classless interdomain
routing (CIDR).
139

140. Finding the Network Address with ANDing
By ANDing the Host address of 192.168.10.2 with 255.255.255.0
(its network mask) we obtain the network address of 192.168.10.0
140

141. Network Address
141

142. Broadcast Address
142

143. Network/Broadcast Addresses
at the Binary Level
An IP address that has binary 0s in all host bit positions is
reserved for the network address, which identifies the network.
An IP address that has binary 1s in all host bit positions is
reserved for the broadcast address, which is used to send data
to all hosts on the network. Here are some examples:
Class Network Address Broadcast Address
A 100.0.0.0 100.255.255.255
B 150.75.0.0 150.75.255.255
C 200.100.50.0 200.100.50.255
143

144. Public IP Addresses
Unique addresses are required for each device on a network.
Originally, an organization known as the Internet Network Information
Center (InterNIC) handled this procedure.
InterNIC no longer exists and has been succeeded by the Internet Assigned
Numbers Authority (IANA).
No two machines that connect to a public network can have the same IP
address because public IP addresses are global and standardized.
All machines connected to the Internet agree to conform to the system.
Public IP addresses must be obtained from an Internet service provider
(ISP) or a registry at some expense.
144

145. Private IP Addresses
Private IP addresses are another solution to the problem of the
impending exhaustion of public IP addresses.As mentioned, public
networks require hosts to have unique IP addresses.
However, private networks that are not connected to the Internet may
use any host addresses, as long as each host within the private
network is unique.
145

146. Mixing Public and
Private IP Addresses
Private IP addresses can be intermixed, as shown in the graphic, with
public IP addresses.This will conserve the number of addresses used for
internal connections. Connecting a network using private addresses to
the Internet requires translation of the private addresses to public
addresses. This translation process is referred to as Network Address
Translation (NAT).
146

147. Introduction to Subnetting
Subnetting a network means to use the subnet mask to divide the
network and break a large network up into smaller, more efficient and
manageable segments, or subnets.
With subnetting, the network is not limited to the default Class A, B, or
C network masks and there is more flexibility in the network design.
Subnet addresses include the network portion, plus a subnet field and
a host field.The ability to decide how to divide the original host portion
into the new subnet and host fields provides addressing flexibility for
the network administrator.
147

148. The 32-Bit
Binary IP Address
148

149. Numbers That Show Up In
Subnet Masks (Memorize Them!)
149

150. Addressing with Subnetworks
150

151. Obtaining an Internet Address
151

152. Static Assignment of an IP Address
Static assignment
works best on small
networks.
The administrator
manually assigns and
tracks IP addresses
for each computer,
printer, or server on
the intranet.
Network printers,
application servers,
and routers should be
assigned static IP
addresses. 152

153. ARP
(Address Resolution Protocol)
Host A
ARP Request - Broadcast to all hosts
SIEMENS
NIXDORF
„What is the hardware address for IP address 128.0.10.4?“
ARP Reply
SIE NS
ME
NIXDORF
SIEMENS
NIXDORF
Host B
IP Address: 128.0.10.4
HW Address: 080020021545
153
Fig. 32 How does ARP work? (TI1332EU02TI_0004 The Network Layer, 47)

154. 154
Fig. 33 The ARP command (TI1332EU02TI_0004 The Network Layer, 47)

155. 1 Network = 1 Broadcast Domain
A B host B would reply
Broadcast: ARP request
2 Networks = 2 Broadcast Domains
A B no one would reply
Router
Broadcast: ARP request
155
Fig. 34 Proxy-ARP concept (TI1332EU02TI_0004 The Network Layer, 49)

156. A
B
A
B
Router R
I take care, to forward
IP packets to B
Broadcast Message to all:
If your IP address matches “B” Yes, I know the destination
then please tell me your network, let me give you my
Ethernet address Ethernet address
156

157. RARP
Reverse Address Resolution Protocol (RARP) associates a known MAC addresses
with an IP addresses.
A network device, such as a diskless workstation, might know its MAC address but not
its IP address. RARP allows the device to make a request to learn its IP address.
Devices using RARP require that a RARP server be present on the network to answer
RARP requests.
157

158. BootP
The bootstrap protocol (BOOTP) operates in a client-server environment and only
requires a single packet exchange to obtain IP information.
However, unlike RARP, BOOTP packets can include the IP address, as well as
the address of a router, the address of a server, and vendor-specific information.
One problem with BOOTP, however, is that it was not designed to provide
dynamic address assignment. With BOOTP, a network administrator creates a
configuration file that specifies the parameters for each device.The administrator
must add hosts and maintain the BOOTP database.
Even though the addresses are dynamically assigned, there is still a one to one
relationship between the number of IP addresses and the number of hosts.
This means that for every host on the network there must be a BOOTP profile
with an IP address assignment in it. No two profiles can have the same IP
address.
158

159. DHCP
Dynamic host configuration protocol (DHCP) is the successor to BOOTP.
Unlike BOOTP, DHCP allows a host to obtain an IP address dynamically without the
network administrator having to set up an individual profile for each device.
All that is required when using DHCP is a defined range of IP addresses on a DHCP
server.As hosts come online, they contact the DHCP server and request an address.
The DHCP server chooses an address and leases it to that host.
With DHCP, the entire network configuration of a computer can be obtained in one
message.
This includes all of the data supplied by the BOOTP message, plus a leased IP
address and a subnet mask.
The major advantage that DHCP has over BOOTP is that it allows users to be mobile.
159

160. 160

161. Introduction to Routers
A router is a special type of computer. It has the same basic components as a
standard desktop PC. However, routers are designed to perform some very specific
functions. Just as computers need operating systems to run software applications,
routers need the Internetwork Operating System software (IOS) to run configuration
files. These configuration files contain the instructions and parameters that control the
flow of traffic in and out of the routers. The many parts of a router are shown below:
161

162. RAM
Random Access Memory, also called dynamic RAM (DRAM)
RAM has the following characteristics and functions:
• Stores routing tables
• Holds ARP cache
• Holds fast-switching cache
• Performs packet buffering (shared RAM)
• Maintains packet-hold queues
• Provides temporary memory for the configuration file of
the router while the router is powered on
• Loses content when router is powered down or restarted
162

163. NVRAM
Non-Volatile RAM
NVRAM has the following characteristics and functions:
• Provides storage for the startup configuration file
• Retains content when router is powered down or
restarted
163

164. Flash
Flash memory has the following characteristics and
functions:
• Holds the operating system image (IOS)
• Allows software to be updated without
removing and replacing chips on the processor
• Retains content when router is powered down
or restarted
• Can store multiple versions of IOS software
Is a type of electronically erasable, programmable
ROM (EEPROM) 164

165. ROM
Read-Only Memory
ROM has the following characteristics and functions:
• Maintains instructions for power-on self test
(POST) diagnostics
• Stores bootstrap program and basic operating
system software
• Requires replacing pluggable chips on the
motherboard for software upgrades
165

166. Interfaces
Interfaces have the following characteristics and functions:
• Connect router to network for frame entry and exit
• Can be on the motherboard or on a separate module
Types of interfaces:
• Ethernet
• Fast Ethernet
• Serial
• Token ring
• ISDN BRI
• Loopback
• Console
• Aux 166

167. Internal Components of a 2600 Router
167

168. External Components of a 2600 Router
168

169. External Connections
169

170. Fixed Interfaces
When cabling routers for serial connectivity, the routers will either have
fixed or modular ports. The type of port being used will affect the syntax
used later to configure each interface. Interfaces on routers with fixed
serial ports are labeled for port type and port number.
170

171. Modular Serial Port Interfaces
Interfaces on routers with modular serial ports are labeled for port type, slot, and port
number.The slot is the location of the module.To configure a port on a modular card, it is
necessary to specify the interface using the syntax “port type slot number/port number.” Use
the label “serial 0/1,” when the interface is serial, the slot number where the module is
installed is slot 0, and the port that is being referenced is port 1.
171

172. Routers & DSL Connections
The Cisco 827 ADSL router has one asymmetric digital
subscriber line (ADSL) interface. To connect a router for DSL
service, use a phone cable with RJ-11 connectors. DSL
works over standard telephone lines using pins 3 and 4 on a
standard RJ-11 connector.
172

173. Computer/Terminal Console Connection
173

174. Modem Connection to Console/Aux Port
174

175. HyperTerminal Session Properties
175

176. Establishing a
HyperTerminal Session
Take the following steps
to connect a terminal to
the console port on the
router:
First, connect the
terminal using the RJ-45
to RJ-45 rollover cable
and an RJ-45 to DB-9 or
RJ-45 to DB-25 adapter.
Then, configure the
terminal or PC terminal
emulation software for
9600 baud, 8 data bits,
no parity, 1 stop bit, and
no flow control. 176

177. Cisco IOS
Cisco technology is built around the Cisco
Internetwork Operating System (IOS), which is the
software that controls the routing and switching
functions of internetworking devices.
A solid understanding of the IOS is essential for a
network administrator.
177

178. The Purpose of Cisco IOS
As with a computer, a router or switch cannot function without
an operating system. Cisco calls its operating system the
Cisco Internetwork Operating System or Cisco IOS.
It is the embedded software architecture in all of the Cisco
routers and is also the operating system of the Catalyst
switches.
Without an operating system, the hardware does not have any
capabilities.
The Cisco IOS provides the following network services:
• Basic routing and switching functions
• Reliable and secure access to networked resources
• Network scalability 178

179. Router Command Line
Interface
179

180. Setup Mode
Setup is not intended as the mode for entering complex protocol features in the
router. The purpose of the setup mode is to permit the administrator to install a
minimal configuration for a router, unable to locate a configuration from another
source.
In the setup mode, default answers appear in square brackets [ ] following the
question. Press the Enter key to use these defaults.
During the setup process, Ctrl-C can be pressed at any time to terminate the
process. When setup is terminated using Ctrl-C, all interfaces will be
administratively shutdown.
When the configuration process is completed in setup mode, the following options
will be displayed:
[0] Go to the IOS command prompt without saving this config.
[1] Return back to the setup without saving this config.
[2] Save this configuration to nvram and exit.
Enter your selection [2]: 180

181. Operation of Cisco IOS Software
The Cisco IOS devices have three distinct operating environments or
modes:
• ROM monitor
• Boot ROM
• Cisco IOS
The startup process of the router normally loads into RAM and executes
one of these operating environments. The configuration register setting can
be used by the system administrator to control the default start up mode for
the router.
To see the IOS image and version that is running, use the show version
command, which also indicates the configuration register setting.
181

182. IOS File System Overview
182

183. Initial Startup of Cisco Routers
A router initializes by loading the bootstrap, the operating system, and a
configuration file.
If the router cannot find a configuration file, it enters setup mode.
Upon completion of the setup mode a backup copy of the configuration file
may be saved to nonvolatile RAM (NVRAM).
The goal of the startup routines for Cisco IOS software is to start the router
operations. To do this, the startup routines must accomplish the following:
• Make sure that the router hardware is tested and functional.
• Find and load the Cisco IOS software.
• Find and apply the startup configuration file or enter the setup
mode.
When a Cisco router powers up, it performs a power-on self test (POST).
During this self test, the router executes diagnostics from ROM on all
hardware modules. 183

184. After the Post…
After the POST, the following events occur as the router initializes:
Step 1
The generic bootstrap loader in ROM executes. A bootstrap is a simple set of
instructions that tests hardware and initializes the IOS for operation.
Step 2
The IOS can be found in several places. The boot field of the configuration register
determines the location to be used in loading the IOS. If the boot field indicates a
flash or network load, boot system commands in the configuration file indicate the
exact name and location of the image.
Step 3
The operating system image is loaded.
Step 4
The configuration file saved in NVRAM is loaded into main memory and executed
one line at a time. The configuration commands start routing processes, supply
addresses for interfaces, and define other operating characteristics of the router.
Step 5
If no valid configuration file exists in NVRAM, the operating system searches for an
184
available TFTP server. If no TFTP server is found, the setup dialog is initiated.

185. Step in Router Initialization
185

186. Router LED Indicators
Cisco routers use LED indicators to provide status information.
Depending upon the Cisco router model, the LED indicators will
vary. An interface LED indicates the activity of the corresponding
interface. If an LED is off when the interface is active and the
interface is correctly connected, a problem may be indicated. If an
interface is extremely busy, its LED will always be on. The green OK
LED to the right of the AUX port will be on after the system initializes
correctly.
186

187. Enhanced
Cisco IOS Commands
187

188. The show version Command
The show version command displays information about the Cisco IOS
software version that is currently running on the router. This includes the
configuration register and the boot field settings.
The following information is available from the show version command:
IOS version and descriptive information
• Bootstrap ROM version
• Boot ROM version
• Router up time
• Last restart method
• System image file and location
• Router platform
• Configuration register setting
Use the show version command to identify router IOS image and boot
source. To find out the amount of flash memory, issue the show flash
command.
188

189. 189

190. 190

191. Router User Interface Modes
The Cisco command-line interface (CLI) uses a hierarchical structure. This
structure requires entry into different modes to accomplish particular tasks.
Each configuration mode is indicated with a distinctive prompt and allows
only commands that are appropriate for that mode.
As a security feature the Cisco IOS software separates sessions into two
access levels, user EXEC mode and privileged EXEC mode. The privileged
EXEC mode is also known as enable mode.
191

192. Overview of Router Modes
192

193. Router Modes
193

194. User Mode Commands
194

195. Privileged Mode Commands
NOTE:
There are
many more
commands
available in
privileged
mode.
195

196. Specific Configuration Modes
196

197. CLI Command Modes
All command-line interface (CLI) configuration changes to a Cisco router
are made from the global configuration mode. Other more specific modes
are entered depending upon the configuration change that is required.
Global configuration mode commands are used in a router to apply
configuration statements that affect the system as a whole.
The following command moves the router into global configuration mode
Router#configure terminal (or config t)
Router(config)#
When specific configuration modes are entered, the router prompt changes
to indicate the current configuration mode.
Typing exit from one of these specific configuration modes will return the
router to global configuration mode. Pressing Ctrl-Z returns the router to all
the way back privileged EXEC mode. 197

198. Configuring a Router’s Name
A router should be given a unique name as one of the
first configuration tasks.
This task is accomplished in global configuration
mode using the following commands:
Router(config)#hostname Tokyo
Tokyo(config)#
As soon as the Enter key is pressed, the prompt
changes from the default host name (Router) to the
newly configured host name (which is Tokyo in the
example above). 198

199. Setting
the Clock
with Help
199

200. Message Of The Day (MOTD)
A message-of-the-day (MOTD) banner can be displayed on all
connected terminals.
Enter global configuration mode by using the command config t
Enter the command
banner motd # The message of the day goes here #.
Save changes by issuing the command copy run start
200

201. Configuring a Console Password
Passwords restrict access to routers.
Passwords should always be configured for virtual terminal
lines and the console line.
Passwords are also used to control access to privileged EXEC
mode so that only authorized users may make changes to the
configuration file.
The following commands are used to set an optional but
recommended password on the console line:
Router(config)#line console 0
Router(config-line)#password <password>
Router(config-line)#login
201

202. Configuring a Modem Password
If configuring a router via a modem you are most likely
connected to the aux port.
The method for configuring the aux port is very similar to
configuring the console port.
Router(config)#line aux 0
Router(config-line)#password <password>
Router(config-line)#login
202

203. Configuring Interfaces
An interface needs an IP Address and a Subnet Mask to be configured.
All interfaces are “shutdown” by default.
The DCE end of a serial interface needs a clock rate.
Router#config t
Router(config)#interface serial 0/1
Router(config-if)#ip address 200.100.50.75 255.255.255.240
Router(config-if)#clock rate 56000 (required for serial DCE only)
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#int f0/0
Router(config-if)#ip address 150.100.50.25 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#exit
Router#
On older routers, Serial 0/1 would be just Serial 1 and f0/0 would be e0.
s = serial e = Ethernet 203
f = fast Ethernet

204. Configuring a Telnet Password
A password must be set on one or more of the virtual terminal
(VTY) lines for users to gain remote access to the router using
Telnet.
Typically Cisco routers support five VTY lines numbered 0
through 4.
The following commands are used to set the same password
on all of the VTY lines:
Router(config)#line vty 0 4
Router(config-line)#password <password>
Router(config-line)#login
204

205. Examining the show Commands
There are many show commands that can be used to examine the contents of files
in the router and for troubleshooting. In both privileged EXEC and user EXEC
modes, the command show ? provides a list of available show commands. The list
is considerably longer in privileged EXEC mode than it is in user EXEC mode.
show interfaces – Displays all the statistics for all the interfaces on the router.
show int s0/1 – Displays statistics for interface Serial 0/1
show controllers serial – Displays information-specific to the interface hardware
show clock – Shows the time set in the router
show hosts – Displays a cached list of host names and addresses
show users – Displays all users who are connected to the router
show history – Displays a history of commands that have been entered
show flash – Displays info about flash memory and what IOS files are stored there
show version – Displays info about the router and the IOS that is running in RAM
show ARP – Displays the ARP table of the router
show start – Displays the saved configuration located in NVRAM
show run – Displays the configuration currently running in RAM
show protocol – Displays the global and interface specific status of any configured
Layer 3 protocols
205

206. 206

207. 207

208. 208

209. Ethernet Overview
Ethernet is now the dominant LAN technology in the world.
Ethernet is not one technology but a family of LAN
technologies.
All LANs must deal with the basic issue of how individual
stations (nodes) are named, and Ethernet is no exception.
Ethernet specifications support different media, bandwidths,
and other Layer 1 and 2 variations.
However, the basic frame format and addressing scheme is
the same for all varieties of Ethernet.
209

210. Ethernet and the OSI Model
Ethernet
operates in two
areas of the
OSI model, the
lower half of
the data link
layer, known as
the MAC
sublayer and
the physical
layer
210

211. Ethernet Technologies
Mapped to the OSI Model
211

212. Layer 2 Framing
Framing is the Layer 2 encapsulation process.
A frame is the Layer 2 protocol data unit.
The frame format diagram shows different groupings of bits
(fields) that perform other functions.
212

213. Ethernet and IEEE Frame
Formats are Very Similar
213

214. 3 Common Layer 2 Technologies
Ethernet
Uses CSMA/CD logical bus topology
(information flow is on a linear bus)
physical star or extended star (wired as a
star)
Token Ring
logical ring topology (information flow is
controlled in a ring) and a physical star
topology (in other words, it is wired as a
star)
FDDI
logical ring topology (information flow is
controlled in a ring) and physical dual-
ring topology(wired as a dual-ring)
214

215. Collision Domains
To move data between one Ethernet station and
another, the data often passes through a repeater.
All other stations in the same collision domain see
traffic that passes through a repeater.
A collision domain is then a shared resource.
Problems originating in one part of the collision
domain will usually impact the entire collision
domain.
215

216. CSMA/CD Graphic
216

217. Backoff
After a collision occurs and all stations allow the cable to
become idle (each waits the full interframe spacing), then the
stations that collided must wait an additional and potentially
progressively longer period of time before attempting to
retransmit the collided frame.
The waiting period is intentionally designed to be random so
that two stations do not delay for the same amount of time
before retransmitting, which would result in more collisions.
217

218. 218

219. Hierarchical Addressing Using
Variable-Length Subnet Masks
© 2003, Cisco Systems, Inc. All rights reserved. 219

220. Prefix Length and Network
Mask
Range of Addresses: 192.168.1.64 through 192.168.1.79 Fourth Octet
• Have the first 28 bits in common, which is 64 01000000
represented by a /28 prefix length 65 01000001
• 28 bits in common can also be represented in dotted 66 01000010
decimal as 255.255.255.240 67 01000011
68 01000100
Binary ones in the network mask represent network bits in the 69 01000101
accompanying IP address; binary zeros represent host bits 70 01000110
11000000.10101000.00000001.0100xxxx IP Address 71 01000111
11111111.11111111.11111111.11110000 Network 72 01001000
Mask 73 01001001
In the IP network number that accompanies the network 74 01001010
mask, when the host bits of the IP network number are: 75 01001011
• All binary zeros – that address is the bottom of the 76 01001100
address range 77 01001101
• All binary ones – that address is the top of the 78 01001110
address range 220
79 01001111

221. Implementing VLSM
221

222. Range Of Addresses for
VLSM
222

223. Breakdown Address Space
for Largest Subnet
223

224. Breakdown Address Space
for Ethernets at Remote Sites
224

225. Address Space for Serial
Subnets
225

226. Calculating VLSM: Binary
226

227. Route Summarization and
Classless Interdomain Routing
© 2003, Cisco Systems, Inc. All rights reserved. 227

228. What Is Route Summarization?
228

229. Summarizing Within an Octet
229

230. Summarizing Addresses in a
VLSM-Designed Network
230

231. Classless Interdomain Routing
– CIDR is a mechanism developed to alleviate
exhaustion of addresses and reduce routing
table size.
– Block addresses can be summarized into single
entries without regard to the classful boundary of
the network number.
– Summarized blocks are installed in routing
tables.
231

232. What Is CIDR?
• Addresses are the same as in the route summarization figure, except that
Class B network 172 has been replaced by Class C network 192.
232

233. CIDR Example
233

234. 234

235. Anatomy of an IP Packet
IP packets consist of the data from upper layers plus an IP
header. The IP header consists of the following:
235

236. 236

237. 237

238. 238

239. Administrative Distance
The administrative distance is an optional parameter that gives a measure
of the reliability of the route. The range of an AD is 0-255 where smaller
numbers are more desireable.
The default administrative distance when using next-hop address is 1,
while the default administrative distance when using the outgoing interface
is 0. You can statically assign an AD as follows:
Router(config)#ip route 172.16.3.0
255.255.255.0 172.16.4.1 130
Sometimes static routes are used for backup purposes. A static route can
be configured on a router that will only be used when the dynamically
learned route has failed. To use a static route in this manner, simply set the
administrative distance higher than that of the dynamic routing protocol
being used. 239

240. Configuring Default Routes
Default routes are used to route packets with destinations that do
not match any of the other routes in the routing table.
A default route is actually a special static route that uses this format:
ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]
This is sometimes referred to as a “Quad-Zero” route.
Example using next hop address:
Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.4.1
Example using the exit interface:
Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0
240

241. Verifying Static
Route Configuration
After static routes are configured it is important to
verify that they are present in the routing table and
that routing is working as expected.
The command show running-config is used to view
the active configuration in RAM to verify that the static
route was entered correctly.
The show ip route command is used to make sure
that the static route is present in the routing table.
241

242. 242

243. Path Determination Graphic
243

244. Routing Protocol
Router
Switch
Router Router
Router
Router
Switch
What is
an optimal
route ?
244

245. Routing Protocols
Routing protocols
includes the following:
processes for sharing
route information
allows routers to
communicate with
other routers to update
and maintain the
routing tables
Examples of routing
protocols that support
the IP routed protocol
are:
RIP, IGRP,
OSPF, BGP,
and EIGRP.
245

246. 246

247. Routed Protocols
Protocols used at the network layer that transfer data from one host to another across
a router are called routed or routable protocols. The Internet Protocol (IP) and Novell's
Internetwork Packet Exchange (IPX) are examples of routed protocols. Routers use
routing protocols to exchange routing tables and share routing information. In other
words, routing protocols enable routers to route routed protocols.
247

248. 248

249. Autonomous System An Autonomous System (AS) is a group of IP networks, which
has a single and clearly defined external routing policy.
EGP
Exterior Gateway
Protocols are used
for routing between
Autonomous Systems
AS 1000 AS 3000
IGP
Interior Gateway Protocols are
used for routing decisions
AS 2000 within an Autonomous System.
249
Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)

250. Interior Gateway Protocol Exterior Gateway Interior Gateway Protocol
(IGP) Protocol (EGP) (IGP)
AS 1000 AS 3000
EGP
EGP IGP
EGP
AS 2000
250
Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)

251. IGP and EGP
An autonomous system is a network or set of networks under
common administrative control, such as the cisco.com domain.
251

252. Categories of Routing
Protocols
Most routing algorithms can be classified into one of two
categories:
• distance vector
• link-state
The distance vector routing approach determines the direction
(vector) and distance to any link in the internetwork.
The link-state approach, also called shortest path first,
recreates the exact topology of the entire internetwork.
252

253. Distance Vector
Routing Concepts
253

254. Distance Vector Routing (DVR)
Routing table contains the addresses
Destination Distance
of destinations and the distance
192.16.1.0 1 of the way to this destination.
192.16.5.0 1
192.16.7.0 2
2 Hops
1 Hop 1 Hop
Router A Router B Router C Router D
192.16.1.0 Flow of routing 192.16.7.0
information
192.16.5.0
254

255. Routing Tables Graphic
255

256. Distance Vector
Topology Changes
256

257. Router Metric Components
257

258. Distance Vector Routing (DVR)
192.16.3.0
192.16.2.0 192.16.6.0
Router A Router B Router C Router D
192.16.4.0
192.16.1.0 192.16.7.0
192.16.5.0
192.16.1.0 0 L 192.16.2.0 0 L 192.16.4.0 0 L 192.16.6.0 0 L
192.16.2.0 0 L 192.16.3.0 0 L 192.16.5.0 0 L 192.16.7.0 0 L
192.16.4.0 0 L 192.16.6.0 0 L
192.16.1.0 0 L 192.16.2.0 0 L 192.16.4.0 0 L 192.16.6.0 0 L
192.16.2.0 0 L 192.16.3.0 0 L 192.16.5.0 0 L 192.16.7.0 0 L
192.16.3.0 1 B 192.16.4.0 0 L 192.16.6.0 0 L 192.16.5.0 1 C
192.16.4.0 1 B 192.16.1.0 1 A 192.16.3.0 1 B 192.16.4.0 1 C
192.16.5.0 1 C 192.16.2.0 1 B
L Locally connected 192.16.6.0 1 C 192.16.7.0 1 D
258

259. Distance Vector Routing (DVR)
192.16.1.0 0 L 192.16.2.0 0 L 192.16.4.0 0 L 192.16.6.0 0 L
192.16.2.0 0 L 192.16.3.0 0 L 192.16.5.0 0 L 192.16.7.0 0 L
192.16.3.0 1 B 192.16.4.0 0 L 192.16.6.0 0 L 192.16.5.0 1 C
192.16.4.0 1 B 192.16.1.0 1 A 192.16.3.0 1 B 192.16.4.0 1 C
192.16.5.0 2 B 192.16.5.0 1 C 192.16.2.0 1 B 192.16.3.0 2 C
192.16.6.0 2 B 192.16.6.0 1 C 192.16.7.0 1 D 192.16.2.0 2 C
192.16.7.0 2 C 192.16.1.0 2 B
192.16.1.0 0 L 192.16.2.0 0 L 192.16.4.0 0 L 192.16.6.0 0 L
192.16.2.0 0 L 192.16.3.0 0 L 192.16.5.0 0 L 192.16.7.0 0 L
192.16.3.0 1 B 192.16.4.0 0 L 192.16.6.0 0 L 192.16.5.0 1 C
192.16.4.0 1 B 192.16.1.0 1 A 192.16.3.0 1 B 192.16.4.0 1 C
192.16.5.0 2 B 192.16.5.0 1 C 192.16.2.0 1 B 192.16.3.0 2 C
192.16.6.0 2 B 192.16.6.0 1 C 192.16.7.0 1 D 192.16.2.0 2 C
192.16.7.0 3 B 192.16.7.0 2 C 192.16.1.0 2 B 192.16.1.0 3 C
259
Fig. 53 Distribution of routing information with distance vector routing protocol (cont.) (TI1332EU02TI_0004 The Network Layer, 71)

260. RIPv1
Distance Vector Routing Protocol,
classful
Distribution of Routing Tables via broadcast
to adjacent routers
Fig. 59 Properties of RIPv1 (TI1332EU02TI_0004 The Network Layer, 81)
Only one kind of metric:
Number of Hops
Connections with different
bandwidth can not be weighted
Routing loops can occur
-> bad convergence in case of a failure
Count to infinity problem
(infinity = 16)
Maximum network size is limited
by the number of hops 260

261. RIP Characteristics
261

262. RIP-1 permits only a Single Subnet Mask
Port 1
130.24.13.1/24
130.24.13.0/24
RIP-1: 130.24.36.0 RIP-1: 130.24.36.0
130.24.25.0/24 Router A
RIP-1: 130.24.0.0
Port 2 200.14.13.0/24
130.24.36.0/24 200.14.13.2/24
262
Fig. 60 RIP-1 permits only a single subnet mask (TI1332EU02TI_0004 The Network Layer, 83)

263. Router Configuration
The router command starts a routing process.
The network command is required because it enables the
routing process to determine which interfaces participate in the
sending and receiving of routing updates.
An example of a routing configuration is:
GAD(config)#router rip
GAD(config-router)#network 172.16.0.0
The network numbers are based on the network class
addresses, not subnet addresses or individual host addresses.
263

264. Configuring RIP Example
264

265. Verifying RIP Configuration
265

266. The debug ip rip Command
Most of the RIP
configuration
errors involve an
incorrect network
statement,
discontiguous
subnets, or split
horizons. One
highly effective
command for
finding RIP update
issues is the
debug ip rip
command. The
debug ip rip
command
displays RIP
routing updates as
they are sent and
received. 266

267. Routing loops
can occur Problem: Routing Loops
when
inconsistent
routing tables
are not
updated due
to slow
convergence
in a changing
network.
267

268. Problem: Counting to Infinity
268

269. Solution: Define a Maximum
269

270. Solution: Split Horizon
270

271. Route Poisoning
Route poisoning is used by various distance vector protocols in order to
overcome large routing loops and offer explicit information when a subnet
or network is not accessible. This is usually accomplished by setting the
hop count to one more than the maximum.
271

272. Triggered Updates
New routing tables are sent to neighboring routers on a regular basis.
For example, RIP updates occur every 30 seconds.
However a triggered update is sent immediately in response to some
change in the routing table.
The router that detects a topology change immediately sends an update
message to adjacent routers that, in turn, generate triggered updates
notifying their adjacent neighbors of the change.
When a route fails, an update is sent immediately rather than waiting on the
update timer to expire.
Triggered updates, used in conjunction with route poisoning, ensure that all
routers know of failed routes before any holddown timers can expire.
272

273. Triggered Updates Graphic
273

274. Solution: Holddown Timers
274

275. IGRP
Interior Gateway Routing Protocol (IGRP) is a proprietary
protocol developed by Cisco.
Some of the IGRP key design characteristics emphasize
the following:
• It is a distance vector routing protocol.
• Routing updates are broadcast every 90 seconds.
• Bandwidth, load, delay and reliability are used to
create a composite metric.
275

276. IGRP Stability Features
IGRP has a number of features that are designed to enhance its stability, such as:
• Holddowns
• Split horizons
• Poison reverse updates
Holddowns
Holddowns are used to prevent regular update messages from inappropriately
reinstating a route that may not be up.
Split horizons
Split horizons are derived from the premise that it is usually not useful to send
information about a route back in the direction from which it came.
Poison reverse updates
Split horizons prevent routing loops between adjacent routers, but poison reverse
updates are necessary to defeat larger routing loops.
Today, IGRP is showing its age, it lacks support for variable length subnet masks
(VLSM). Rather than develop an IGRP version 2 to correct this problem, Cisco has
built upon IGRP's legacy of success with Enhanced IGRP. 276

277. Configuring IGRP
277

278. Routing Metrics Graphics
278

279. Link State Concepts
279

280. Link State Topology Changes
280

281. Link State Routing (LSR)
LSP: LSP:
„My links to SPF „My links to R1 and R3 are
R2 and R4 are up“ up.
Routing My link to R2 is down.“
Table
Router 1 Router 4
Router 2 Router 3
LSP: „My links to LSP: „My links to
R1 and R3 are up, R2 and R4 are up.“
my link to R4 is down.“
LSP....link state packet
SPF... shortest path first 281

282. Link State Concerns
282

283. Link State Routing (LSR)
1
Router A Router C 4
2 2 Router E
1
4
Router B Router D
Link State Database
B-2 A-2 A-1 C-2 C-4
C-1 D-4 D-2 B-4 D-1
E-4 E-1
Router A Router B Router C Router D Router E
A B C D
B C A D D A E C B
D C E E B A
E
283

284. Link State Routing Features
Link-state algorithms are also known as Dijkstras algorithm or as SPF (shortest path first)
algorithms.
Link-state routing algorithms maintain a complex database of topology information.
The distance vector algorithm are also known as Bellman-Ford algorithms. They have
nonspecific information about distant networks and no knowledge of distant routers.
A link-state routing algorithm maintains full knowledge of distant routers and how they
interconnect. Link-state routing uses:
• Link-state advertisements (LSAs)
A link-state advertisement (LSA) is a small packet of routing information
that is sent between routers.
• Topological database
A topological database is a collection of information gathered from LSAs.
• SPF algorithm
The shortest path first (SPF) algorithm is a calculation performed on the
database resulting in the SPF tree.
• Routing tables – A list of the known paths and interfaces. 284

285. Link State Routing
285

286. Comparing Routing Methods
286

287. OSPF (Open Shortest Path First)
Protocol
© 2003, Cisco Systems, Inc. All rights reserved. 287

288. OSPF is a Link-State Routing
Protocols
– Link-state (LS) routers recognize much more information
about the network than their distance-vector
counterparts,Consequently LS routers tend to make more accurate
decisions.
– Link-state routers keep track of the following:
• Their neighbours
• All routers within the same area
• Best paths toward a destination
288

289. Link-State Data Structures
– Neighbor table:
• Also known as the adjacency database
(list of recognized neighbors)
– Topology table:
• Typically referred to as LSDB
(routers and links in the area or network)
• All routers within an area have an identical LSDB
– Routing table:
• Commonly named a forwarding database
(list of best paths to destinations)
289

290. OSPF vs. RIP
RIP is limited to 15 hops, it converges slowly, and it sometimes chooses
slow routes because it ignores critical factors such as bandwidth in route
determination. OSPF overcomes these limitations and proves to be a
robust and scalable routing protocol suitable for the networks of today.
290

291. OSPF Terminology
The next several slides explain various OSPF terms
-one per slide.
291

292. OSPF Term: Link
292

293. OSPF Term: Link State
293

294. OSPF Term: Area
294

295. OSPF Term: Link Cost
295

296. OSPF Term: Forwarding Database
296

297. OSPF Term: Adjacencies Database
297

298. OSPF Terms: DR & BDR
298

299. Link-State Data Structure:
Network Hierarchy
•Link-state routing requires a hierachical
network structure that is enforced by OSPF.
•This two-level hierarchy consists of the
following:
• Transit area (backbone or area 0)
• Regular areas (nonbackbone areas)
299

300. OSPF Areas
300

301. Area Terminology
301

302. LS Data Structures: Adjacency
Database
– Routers discover neighbors by exchanging
hello packets.
– Routers declare neighbors to be up after checking
certain parameters or options in the hello packet.
– Point-to-point WAN links:
• Both neighbors become fully adjacent.
– LAN links:
• Neighbors form an adjacency with the DR and BDR.
• Maintain two-way state with the other routers (DROTHERs).
– Routing updates and topology information are only passed
between adjacent routers.
302

303. OSPF Adjacencies
Routers build logical adjacencies between each other
using the Hello Protocol. Once an adjacency is formed:
• LS database packets are exchanged to synchronize
each other’s LS databases.
• LSAs are flooded reliably throughout the area or network
using these adjacencies.
303

304. 304

305. Open Shortest Path First
Calculation
•Routers find the best paths to destinations by
applying Dijkstra’s SPF algorithm to the link-state
database as follows:
– Every router in an area has the identical
link-state database.
– Each router in the area places itself into
the root of the tree that is built.
– The best path is calculated with respect to the
lowest total cost of links to a specific destination.
– Best routes are put into the forwarding database.
305

306. OSPF Packet Types
306

307. OSPF Packet Header Format
307

308. Neighborship
308

309. Establishing Bidirectional
Communication
309

310. Establishing Bidirectional
Communication (Cont.)
310

311. Establishing Bidirectional
Communication (Cont.)
311