ip addresses: classful addressing ip addresses. introduction 4.1
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IP Addresses:Classful Addressing
IP Addresses
INTRODUCTION
4.14.1
IP addressIP address
address (IP address) is a numerical address (IP address) is a numerical label assigned to each device (e.g., label assigned to each device (e.g., computer, printer) participating in a computer, printer) participating in a computer network that uses the that uses the Internet Protocol for for ..communicationcommunication
An IP address is a An IP address is a 32-bit 32-bit
address.address.
What is an IP Address?
The IP addresses The IP addresses are are
unique.unique.
Address spaceAddress space rulerule
addr15addr1
addr2
addr41addr31
addr226
…………..…………..
………….. …………..
…………..
…………..…………..
The address space in a protocolThat uses N-bits to define an Address is:
2N
The address space of IPv4 is The address space of IPv4 is
223232 or or
4,294,967,296.4,294,967,296.
IPv4 address spaceIPv4 address space
IP addresses consist of four sectionsIP addresses consist of four sections Each section is 8 bits longEach section is 8 bits long Each section can range from 0 to 255Each section can range from 0 to 255 Written, for example, 128.35.0.72Written, for example, 128.35.0.72
Peter Smith 8
Converting to Decimal (Cont.) Now, for double the money, what is its
equivalent decimal value?
27 26 25 24 23 22 21 20
1 1 1 1 1 1 1 1128 64 32 16 8 4 2 1 The binary number 1111 1111 converts into the decimal number:128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255
01110101 10010101 00011101 11101010
Binary NotationBinary Notation
Figure 4-1
Dotted-decimal notation
Example 1Example 1
Change the following IP address from binary notation to dotted-decimal notation.
10000001 00001011 00001011 11101111
SolutionSolution
129.11.11.239129.11.11.239
Example 2Example 2
Change the following IP address from dotted-decimal notation to binary notation:
111.56.45.78
SolutionSolution
01101111 00111000 00101101 0100111001101111 00111000 00101101 01001110
Example 3Example 3
SolutionSolution
Find the error in the following IP Address111.56.045.78
There are no leading zeroes in Dotted-decimal notation (045)
Example 3 (continued)Example 3 (continued)
SolutionSolution
Find the error in the following IP Address75.45.301.14
In decimal notation each number <= 255301 is out of the range
The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network).
Network prefix and host number
host numbernetwork prefix
CLASSFUL ADDRESSING
In classful addressing the address space is divided into 5 classes:
AA, , BB, , CC, , DD, and , and EE..
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Are You the Host or the Network?
The 32 bits of the IP address are divided into Network & Host portions, with the octets assigned as a part of one or the other.
Network & Host RepresentationBy IP Address Class
Class Octet1 Octet2 Octet3 Octet4
Class A Network Host Host Host
Class B Network Network Host Host
Class C Network Network Network Host
Figure 4-3
Finding the class in binary notation
Figure 4-4
Finding the address class
Show that Class AA has 231 = 2,147,483,648 addresses
Example 5Example 5
Example 6Example 6
SolutionSolution
Find the class of the following IP addresses 00000001 00001011 00001011 1110111111000001 00001011 00001011 11101111
•00000001 00001011 00001011 111011111st is 0, hence it is Class A
•11000001 00001011 00001011 111011111st and 2nd bits are 1, and 3rd bit is 0 hence, Class C
Figure 4-5
Finding the class in decimal notation
Example 7Example 7
SolutionSolution
Find the class of the following addresses158.223.1.108227.13.14.88
•158.223.1.1081st byte = 158 (128<158<191) class B
•227.13.14.881st byte = 227 (224<227<239) class D
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Are You the Host or the Network? (Cont.)
Each Network is assigned a network address & every device or interface (such as a router port) on the network is assigned a host address.
There are only 2 specific rules that govern the value of the address.
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Are You the Host or the Network? (Cont.)
A host address cannot be designated by all zeros or all ones.
These are special addresses that are reserved for special purposes.
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Class A Addresses (Cont.)
There are 16,777,214 Host addresses available in a Class A address.
Rather than remembering this number exactly, you can use the following formula to compute the number of hosts available in any of the class addresses, where “n” represents the number of bits in the host portion:
(2n – 2) = Number of available hosts
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Class A Addresses (Cont.)
For a Class A network, there are:224 – 2 or 16,777,214 hosts.
Half of all IP addresses are Class A addresses. You can use the same formula to determine the
number of Networks in an address class. Eg., a Class A address uses 7 bits to designate
the network, so (27 – 2) = 126 or there can be 126 Class A Networks.
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Class B IP Addresses
Class B addresses use the 1st 16 bits (two octets) for the Network address.
The last 2 octets are used for the Host address.
The 1st 2 bit, which are always 10, designate the address as a Class B address & 14 bits are used to designate the Network. This leaves 16 bits (two octets) to designate the Hosts.
Peter Smith 30
Class B IP Addresses (Cont.)
So how many Class B Networks can there be?
Using our formula, (214 – 2), there can be 16,382 Class B Networks & each Network can have (216 – 2) Hosts, or 65,534 Hosts.
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Class C IP Addresses
Class C addresses use the 1st 24 bits (three octets) for the Network address & only the last octet for Host addresses.the 1st 3 bits of all class C addresses are set to 110, leaving 21 bits for the Network address, which means there can be 2,097,150 (221 – 2) Class C Networks, but only 254 (28 – 2) Hosts per Network.
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Special Addresses (Cont.)
Within each address class is a set of addresses that are set aside for use in local networks sitting behind a firewall or NAT (Network Address Translation) device or Networks not connected to the Internet.
Network AddressesNetwork Addresses
The network address is the first address.
The network address defines the network to the rest of the Internet.
Given the network address, we can find the class of the address, the block, and the range of the addresses in the block
In classful addressing, In classful addressing, the network address the network address
(the first address in the block) (the first address in the block) is the one that is assigned is the one that is assigned
to the organization. to the organization.
Example 8Example 8
SolutionSolution
Given the network address 132.21.0.0, find the class, the block, and the range of the addresses
The 1st byte is between 128 and 191. Hence, Class B
The block has a netid of 132.21. The addresses range from
132.21.0.0 to 132.21.255.255.
Default Mak
Class A default mask is 255.0.0.0 Class B default mask is 255.255.0.0 Class C Default mask 255.255.255.0
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A Trial Separation
Subnet masks apply only to Class A, B or C IP addresses.
The subnet mask is like a filter that is applied to a message’s destination IP address.
Its objective is to determine if the local network is the destination network.
Mask Mask
• A mask is a 32-bit binary number.
• The mask is ANDeD with IP address to get• The bloc address (Network address)
• Mask And IP address = Block Address
Figure 4-10
Masking concept
The network address is the The network address is the beginning address of each block.beginning address of each block.
It can be found by applying It can be found by applying the default mask tothe default mask to
any of the addresses in the block any of the addresses in the block (including itself).(including itself).
It retains the It retains the netidnetid of the block of the block and sets the and sets the hostidhostid to zero. to zero.
Example: ellington.cs.virginia.edu
Network address is: 128.143.0.0 (or 128.143)
Host number is: 137.144 Netmask is: 255.255.0.0 (or ffff0000)Prefix or CIDR notation: 128.143.137.144/16
Network prefix is 16 bits long
Example
128.143 137.144
IP address of a network – Host number is set to all zeros, e.g.,
128.143.0.0 Broadcast address
– Host number is all ones, e.g., 128.143.255.255
– Broadcast goes to all hosts on the network
– Often ignored due to security concerns
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