1. TCP/IP Basics
Chapter 7

2. Objectives
• Describe how the Internet Protocol works
• Explain CIDR and subnetting
• Describe the functions of static and dynamic
IP addresses

3. Overview

4. Moving up the OSI Layers
• Chapters 3 through 6 detailed Layers 1 and 2
• Ethernet network technology
• Now explore the software side of networking
– Individual rule is a protocol
– A protocol suite is a set of rules
• Begin with Internet Protocol (IP) of TCP/IP

5. Three Parts to Chapter 7
• IP in Depth
• CIDR and Subnetting
• Using IP Addresses

6. IP in Depth

7. IP in Depth
• TCP/IP suite supports both simple and
complex networks
– Small LAN
– Multiple LANs interconnected into a WAN

8. • TCP/IP on LAN over Ethernet
– On small network, sending computer broadcasts
using MAC address ff-ff-ff-ff-ff-ff to obtain
recipient’s MAC address
– Broadcasting is disastrous to a large network

9. Figure 7.2 PC broadcasting for a MAC address

10. Figure 7.3 Broadcasting won’t work for the
entire Internet

11. • TCP/IP on LAN over Ethernet
– IP addressing overcomes limits of Ethernet MAC
addresses
• Unique IP address per host
• Unique address per logical network
• Communicate between LANs without broadcasts

12. • IP Addresses (IPv4 only]
– 32-bit value
• Example: 11000000101010000000010000000010
• Broken into four groups of eight
11000000.10101000.00000100.00000010
• Each 8-bit value convertsed into a decimal number
between 0 and 255

13. • Binary to Decimal Conversion
Binary Decimal Binary Decimal
00000000 0 11111000 248
00000001 1 11111001 249
00000010 2 11111010 250
00000011 3 11111011 251
00000100 4 11111100 252
00000101 5 11111101 253
00000110 6 11111110 254
00000111 7 11111111 255
00001000 8
skip a bunch skip a bunch

14. • IP Addresses (IPv4 only]
– Converted:
11000000101010000000010000000010
is displayed as 192.168.4.2 in dotted decimal
notation (dotted-octet numbering system)
– Know how to convert dotted decimal to binary
and back
• Every OS has a calculator

15. • Using a Calculator for conversion
– Decimal to binary
• Enter value in decimal view
• Switch to binary view to convert value
• Leading zeroes do not display in Calculator
• Leading zeroes important when working with IP
addresses

16. Figure 7.4 Macintosh OS X Calculator in
Programmer mode

17. Figure 7.5 Converting decimal to binary with
Windows Vista’s Calculator

18. • Every MAC address must be unique
• Every IP address must be unique

19. Figure 7.6 Small network with both IP
and MAC addresses

20. • Utilities for displaying IP and MAC addresses
– Every OS has at least one GUI tool
• Mac OS X system’s Network utility
• Windows Local Area Connection Properties
– Every OS has a command-line utility
• Windows has IPCONFIG
• UNIX/Linux/Mac use IFCONFIG

21. Figure 7.7 Macintosh OS X Network utility

22. Figure 7.8 ipconfig/all

23. Figure 7.9 IFCONFIG in Ubuntu

24. • IP Addresses in Action
– IP must do three things
1. Give each LAN its own identifier
2. Allow routers connecting LANs to use network
identifiers to send packets to the right network
3. Give each computer a way to understand when a
packet is intended for a computer on the local LAN or
for a computer on the WAN

25. 1. IP must give each LAN its own identifier
– Network IDs
• All computers on same LAN must have same network ID
• Each computer on same LAN must have a unique host ID
• Example: 192.168.5.x represents addresses in Figure 7.10
– Network address of this network is 192.168.5.0 (assuming a 24-
bit mask)
– Network ID plus Host ID = one IP address.

26. Figure 7.10 IP addresses for a LAN

27. 2. IP must allow routers connecting LANs to use
network identifiers to send packets to the
right network
– Interconnecting
• Requires a router connection
• Router requires a network connection and IP
address on each LAN
– IP address of router’s connection to a LAN is the
default gateway for that LAN
– Network administrators often give lowest host
address in the network to the router

28. Figure 7.11 LAN with router

29. – Interconnecting (cont.)
• Router uses a built-in router table
– Uses this to determine where to send packets
– How router uses routing table:
Everything for 192.168.5.0 Everything else goes out
goes out 192.168.5.1 14.23.54.223

30. Figure 7.12 Router diagram

31. Figure 7.13 LAN, router, and the Internet

32. – Interconnecting (cont.)
• Limitations of using 192.168.5.0 as host ID
– Limited to 192.168.5.1 through 192.168.5.254
(254 addresses)
• Network ID of 170.45.0.0 has a total of 65,534 hosts
• Network ID of 12.0.0.0 has a total of 16.7 million hosts
• Network IDs allow router to connect multiple LANs to a
WAN

33. 3. IP must give each computer a way to
understand when a packet destination
is local or on the WAN
– Subnet Mask
• Sending to host on same network: broadcast for MAC address
• Sending to host on another network: send to default gateway
• Sending computer uses subnet mask to determine where to send
packet
• Example of a subnet mask using dotted-octet binary notation:
11111111.11111111.11111111.00000000
• Example of the same subnet mask using dotted decimal notation:
255.255.255.0

34. Figure 7.14 The three amigos, separated by
walls or miles

35. Figure 7.15 Sending a packet remotely

36. – Subnet Mask (cont.)
• Line up an IP address with a corresponding subnet mask
in binary
– Portion of IP address that aligns with the ones of the
subnet mask is the network ID of the IP address.
– Portion of IP address that aligns with the zeroes of the
subnet mask is the HostID of the IP address

37. Dotted Binary
Decimal
IP address 192.168.5.23 11000000.10101000.00000101.00010111
Subnet mask 255.255.255.0 11111111.11111111.11111111.00000000
Network ID 192.168.5.0 11000000.10101000.00000101.x
Host ID x.x.x.23 x.x.x.00010111

38. – Subnet Mask (cont.)
• Sending computer compares the destination IP address
to its own IP address using the subnet mask
• If the destination IP address matches the computer IP
wherever there’s a 1 in the subnet mask, sending
computer knows the address is local
• If the destination IP address does not match the sending
computer’s IP wherever there’s a 1 in the subnet mask,
sending computer knows the address is remote

39. Figure 7.16 Comparing addresses

40. – Subnet Mask (cont.)
• When the destination address is local, the sending
computer sends out an Address Resolution Protocol
(ARP) broadcast to determine the destination computer’s
MAC address
• The ARP packet contains the sending computer’s IP
address as well as the destination address
• Destination computer responds to the ARP request by
sending an ARP response containing its MAC address
• Sending computer can now send data packets to
destination

41. Figure 7.17 Sending an ARP

42. Figure 7.19 Computer B responds

43. – Subnet Mask (cont.)
• When the sending computer discovers that the
destination address does not have the same network
ID as itself, then it must send the packet beyond the
local network
• The packet must be sent to the default gateway
• Sending computer must ARP for the MAC address of the
default gateway

44. Figure 7.20 Comparing addresses again

45. Figure 7.21 Sending an ARP to the gateway

46. – Subnet Mask (cont.)
• Some valid subnet masks
11111111111111111111111100000000 = 255.255.255.0
11111111111111110000000000000000 = 255.255.0.0
11111111000000000000000000000000 = 255.0.0.0
• Shorthand for subnet mask
11111111111111111111111100000000 = /24 (24 ones)
11111111111111110000000000000000 = /16 (16 ones)
11111111000000000000000000000000 = /8 (8 ones)

47. – Subnet Mask (cont.)
• An IP address followed by the / and a
number describes the IP and the
address in one statement
201.23.45.123/24 = IP address plus subnet mask
IP address = 201.23.45.123
Subnet mask = 255.255.255.0
184.222.4.36/16 = IP address plus subnet mask
IP address = 184.222.4.36
Subnet mask = 255.255.0.0

48. – Subnet Mask (cont.)
• Network administrators must enter correct IP address
and subnet mask when configuring a network card
• The networking software does the rest
• If you want a computer to work in a routed network,
you must configure the computer correctly with an IP
address, subnet mask, and default gateway

49. – Class IDs
• No two devices on the Internet can share the same IP
address
• Internet Assigned Number Authority (IANA) tracks and
disperses IP addresses in chunks called class licenses
– Oversees several Regional Internet Registries (RIRs)
– RIRs in turn pass out IP addresses to large ISPs
– ISPs pass out IP addresses to most end users

50. First Decimal Hosts per
Value (range) Addresses Network ID
Class A 1 – 126 1.0.0.0 – 126.255.255.255 16,277,214
Class B 128 – 191 128.0.0.0 – 191.255.255.255 65,534
Class C 192 – 223 192.0.0.0 – 223.255.255.255 254
Class D 224 – 239 224.0.0.0 – 239.255.255.255 Multicast
Class E 240 – 255 240.0.0.0 – 255.255.255.255 Reserved
IP Address Classes

51. – Class IDs – More about Class D and E
• Three ways to send a packet
– Broadcast to every computer on the LAN
– Unicast from one computer to another computer
– Multicast from one computer to a group
» Uncommon between computers
» Often used by routers

52. – Class IDs – The state of IP address
• IP class licenses were allocated too generously at first
• Unallocated IP addresses became scarce
• IP class licenses concept did not scale well
– If you needed 2000 IP addresses you had to take a single
Class B or eight Class C licenses
• Solution
– New method for generating blocks of IP addresses
– Classless Inter-Domain Routing (CIDR)

53. CIDR and Subnetting

54. • CIDR and Subnetting Overview
– CIDR based on subnetting
– Subnetting chops up a single class of IP addresses
into multiple smaller groups
– CIDR and subnetting are virtually the same thing
– Subnetting done by an organization on a block of
addresses to create multiple subnetworks
– CIDR done by an ISP on a block of addresses to
create multiple subnets to pass out to customers

55. • Subnetting
– More efficient use of IP addresses than class
licenses
– Enables separation of networks for security
– Enables bandwidth control
– Subnet mask is cornerstone of subnetting
• Extend subnet masks of /8, /16, or /24 subnet by
adding more ones (removing equal number of zeroes).

56. • Subnetting the Internet Café
– 50 computers
• 40 public computers
• 10 back office computers
• 10 wireless clients (maximum)
– Network ID 192.168.4/24
– Must prevent people using the public system from
accessing private machines

57. Figure 7.22 Layout of the network

58. • Subnetting the Internet Café (cont.)
– Begin with the given subnet mask and move it to
the right until you have the number of subnets you
need
– Forget the dots
• Don’t be limited to /8, /16, /24 networks
• Network IDs do not need to end on the dots
• Create subnets of /26, /27, /22, etc.

59. • Subnetting the Internet Café (cont.)
– 192.168.4/24
– Change a zero to a one in the subnet mask
– /24 becomes a /25 subnet
11111111111111111111111110000000

60. • Calculating Hosts
– Hosts on a /24 network
– 192.168.4.1 to 192.168.4.254 = 254 hosts
– Calculate in binary
• In a /24 network 8 binary digits are used for the host ID
• 00000001 to 11111110 = 254 hosts
• 2(number of zeroes in the subnet mask) – 2
• 28 – 2 = 254 total hosts
– Memorize the formula

61. • Calculating Hosts (cont.)
– Hosts on a /16 network
• In a /16 network 16 zeroes are part of the host ID
• 0000000000000001 to 1111111111111110 = 65,534
hosts
• 2(number of zeroes in the subnet mask) – 2
• 216 – 2 = 65,534 total hosts

62. • Calculating Hosts (cont.)
– Hosts on a /26 network
• In a /26 network 6 zeroes are part of the host ID
• 000001 to 111110 = 62 hosts
• 2(number of zeroes in the subnet mask) – 2
• 26 – 2 = 62 total hosts

63. • Your First Subnet
– Convert the 192.168.4/24 net ID into three
network IDs
– Write out the subnet mask in binary
– Place a line at the end of the ones

64. Figure 7.23 Step 1 in subnetting

65. • Your First Subnet (cont.)
– Draw a second line one digit to the right
– Three areas (a Mike Trick, not official terms)
• Subnet mask (SM)
• Network ID extension (NE)
• Hosts (H)
– This is now a /25 subnet mask

66. Figure 7.24 Organizing the subnet mask

67. • Your First Subnet (cont.)
– A subnet mask is always 32 binary digits long
– A string of ones followed by a string of zeroes
11111111111111111111111110000000
– Put periods between every eight digits
11111111.11111111.11111111.10000000
– Then convert to dotted decimal
– The resulting subnet mask:
255.255.255.128

68. • Your First Subnet (cont.)
– Get used to the idea of subnet masks that use
more than 255s and 0s (in dotted decimal form)
– Examples of legitimate subnet masks
• 255.255.255.224
11111111.11111111.11111111.11100000
• 255.255.128.0
11111111.11111111.10000000.00000000
• 255.248.0.0
11111111.11111000.00000000.00000000

69. • Rules for Calculating Subnets
1. Starting with a beginning subnet mask, you
extend the subnet extension until you have the
number of subnets you need
2. You cannot have an NE of all zeroes or all ones,
so you calculate the number of subnets using this
formula:
new subnets = 2(number of zeroes in the subnet mask) – 2
3. You cannot have a single-character network ID
extension. You always start by moving the
subnet at least two digits

70. • Calculating Subnets (cont.)
– Rules 2 and 3 explained
• Adding just a single digit to the beginning subnet mask
only gives you two network IDs: a zero and a one
• You cannot have a network ID extension of all zeroes or
all ones
• Therefore, you need rule 3

71. Figure 7.25 Organizing the subnet mask

72. Figure 7.26 Single-digit network ID extensions
are not allowed

73. • Calculating Subnets (cont.)
– Subnet /24 to /26
– Adds two digits, creating four new network IDs
(two of which are not usable)
– Convert the original network ID to binary and
add the four different network ID extension to
the end
– The possible NEs in binary are 00, 01, 10, 11
– Can’t have all zeroes, can’t have all ones
– Therefore, only two new networks (01 and 10)

74. Figure 7.27 Creating the new network IDs

75. Figure 7.28 New network ID address ranges

76. • Calculating Subnets (cont.)
– The new network IDs in decimal
192.168.4.64/26
hosts = 192.168.4.65 – 192.168.4.126
192.168.4.128/26
Hosts = 192.168.4.129 – 192.168.4.191

77. Figure 7.29 Two networks using the two network IDs

78. • Calculating Subnets (cont.)
– The Internet Café needs three subnets
– How large a network ID extension is needed?
– Two NE digits = 22 – 2 = 2 network IDs
– Three NE digits = 23 – 2 = 6 network IDs
– Therefore, you need to extend the NE three
digits to get at least three network IDs
– Three are wasted

79. • Calculating Subnets (cont.)
– Create a /27 subnet by moving the NE over three
digits
– Calculate the host address ranges for each usable
new subnet
– 192.168.4.32/27 (192.168.4.33–192.168.4.62)
– 192.168.4.64/27 (192.168.4.65–192.168.4.94)
– 192.168.4.96/27 (192.168.4.97–192.168.4.126)
– 192.168.4.128/27 (192.168.4.129–192.168.4.158)
– 192.168.4.160/27 (192.168.4.161–192.168.4.190)
– 192.168.4.192/27 (192.168.4.193–192.168.4.222)

80. Figure 7.30 Moving the network ID extension
three digits

81. Figure 7.31 Two of the six network ID address ranges

82. Manual Binary to Dotted Decimal Conversion
•
Write bit values in decimal from left to right
–
Take binary value of one dotted octet portion and place ones and
– zeroes under appropriate positions
128 64 32 16 8 4 2 1
1 0 0 1 0 1 1 0
Add the decimal values that have a 1 underneath
–
128+16+4+2 = 150

83. • Manual Dotted Decimal to Binary Conversion
– Start with bit values beginning with 128
– Place decimal value above the first value on the
left which it exceeds and subtract and place a one
to represent this binary value
221
128 64 32 16 8 4 2 1
93
1

84. • Manual Dotted Decimal to Binary Conversion
– Place the remainder above the next bit value that
it exceeds (Place a zero in positions that are
skipped)
221 93 29 13 5 1
128 64 32 16 8 4 2 1
93 29 13 5 1 0
1 1 0 1 1 1 0 1
– Decimal 221 = binary 11011101

85. • CIDR: Subnetting in the Real World
– Two situations in which subnetting takes place
• ISPs (Large ones)
– Receive class licenses from IANA
– Subnet those class licenses for customers
• Very large customers
– Take subnets from ISPs
(sometimes already subnetted class licenses)
– Make their own subnets

86. • CIDR: Subnetting in the Real World (cont.)
– Why learn subnetting?
• CompTIA Network+ exam requires it
• There’s a good chance you’ll contact an ISP and get
CIDR addresses
– Think of subnets in terms of CIDR values like
/8, /22, /26, and so on
• More advanced IT certifications (Cisco, Microsoft,
etc.) require this knowledge

87. Using IP Addresses

88. • Overview of Using IP Addresses
– Assigning IP addresses to computers
– Specialty IP addresses

89. • Assigning an IP address, subnet mask, and
default gateway
– Static addressing
• Type in all the information
– Dynamic addressing
• Server program automatically passes out the information
to computers on the network

90. • Static IP Addresses
– Manually type in all IP information
• What are you typing in?
• Where do you type it?
– Assuming a Class C license for 197.156.4/24
• You can do whatever you want with your own network ID
• Use legit IP address and mask for network ID
• Every IP address must be unique
• You don’t have to use the numbers in order
• You don’t have to use 197.156.4.1 as default gateway

91. Figure 7.32 A small network

92. • Static IP Addresses (cont.)
– Network techs’ set of principles
• Give the default gateway the first host IP address in the
network ID
• Try to use the IP addresses in some kind of sequential
order
• Try to separate servers from clients
– Servers host addresses: 197.156.4.10 to 197.156.4.19
– Client host addresses: 197.156.4.200 to 197.156.4.254
• Write down whatever you do so person who comes after
you understands what you did

93. • Static IP Addresses (cont.)
– Give each computer an IP address, subnet mask,
and default gateway
• In Windows use the Internet Protocol Version 4 (TCP/IPv4)
Properties dialog box
• In Macintosh OS X, run the Network utility in System
Preferences
• In UNIX/Linux use the command-line IFCONFIG command

94. Figure 7.33 Entering static IP information in
Windows Internet Protocol Version 4 (TCP/IPv4)
Properties

95. Figure 7.34 Entering static IP information in
the OS X Network utility

96. Figure 7.35 IFCONFIG command to set
static IP address

97. Figure 7.36 Ubuntu’s Network Configuration utility

98. • Static IP Addresses (cont.)
– After adding IP information to at least two systems,
verify with the PING command
– Successful PING confirms two systems can
communicate
– If the PING is not successful
• Check your IP settings
• Check connections, driver, etc.
– Static addressing used for most critical systems
– Most systems today use dynamic IP addressing

99. Figure 7.37 Two PINGs (successful PING on top,
unsuccessful PING on bottom)

100. • Dynamic IP Addressing
– Dynamic Host Configuration Protocol (DHCP)
• More popular form of dynamic IP addressing
• Bootstrap Protocol (BOOTP) older version
– Automatically assigns an IP address whenever a
computer connects to the network
– DHCP uses a simple process
• Computer is configured to use DHCP
• Every OS has a method to tell computer to use DHCP
• Windows setting: Obtain an IP address automatically

101. Figure 7.38 Setting up for DHCP

102. • How DHCP Works
– DHCP Server is configured to pass out IP addresses
• Scope = range of IP addresses
• Subnet mask for scope
• Default gateway for scope
• Gives out other information (detailed in later chapters)

103. • How DHCP Works (cont.)
– When DHCP client boots up it broadcasts a
DHCP discovery packet
• Discovery packet asks “Are there any DHCP servers
out there?”
• DHCP server responds with a DHCP offer
• DHCP clients responds with a DHCP request
• DHCP server responds with a DHCP acknowledge
and maintains a database of the MAC addresses
of DHCP clients along with the IP information assigned
to each
• DHCP client accepts with a DHCP lease

104. Figure 7.39 Computer sending out a DHCP
discovery message

105. Figure 7.40 DHCP server sending DHCP offer

106. Figure 7.41 DHCP request and DHCP acknowledge

107. • How DHCP Works (cont.)
– DHCP Lease
• Set for a fixed amount of time
• Usually 5 to 8 days
• At the end of the lease time, DHCP client makes
another DHCP discovery message
• DHCP server looks at the MAC address, comparing
it to its database of leases
• Unless another computer has taken the lease, server
will give the client the same IP information, including
the same IP address

108. • Living with DHCP
– Possible problems
• DHCP client tries to get a DHCP address and fails
• Symptoms
– OS will post an error
– DHCP client will have an address in the 169.254/16
network ID
– Can access local computers, but cannot connect to
Internet

109. Figure 7.42 DHCP error in Ubuntu Linux

110. • Living with DHCP
– Automatic Private IP Addressing (APIPA)
• Addresses in the 169.254/16 network ID that a DHCP
client will assign to itself when it fails to find a DHCP
server
• Allows computers on same LAN to communicate (if
they are using APIPA)
• APIPA does not provide default gateway, so clients
using APIPA cannot access the Internet
• Use available tool to see IP settings
• If you see an APIPA address, you know you have a
DHCP problem

111. • Living with DHCP
– Reestablish the lease manually
– In Windows
• Ipconfig/renew
– On a Macintosh
• Go to System Preferences and use the Network utility
– May need to force computer to release its lease
• Windows command line: ipconfig /release
ipconfig /renew
• Release in Linux: sudo ifconfig eth0 down
• Renew in Linux: sudo ifconfig eth0 up

112. Figure 7.43 Network utility in System Preferences

113. • Special IP Addresses
– Loopback = 127.0.0.1
• Use to send packets from your NIC to itself
• Test NIC’s capability to send and receive packets:
ping 127.0.0.1
– Private IP addresses
• 10.0.0.0 through 10.255.255.255 (1 Class A license)
• 172.16.0.0. through 172.31.255.255 (16 Class B licenses)
• 192.168.0.0 through 192.168.255.255 (256 Class C licenses)
– All other IP addresses are public IP addresses