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Lecture #1
Chapter 5: Addressing (part 1 of 3)
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Dr. Clincy
Lecture
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Physical Addressing Versus Network Addressing
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Dr. Clincy
Lecture
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IP Addresses
• Internetworking Protocol (IP) of the Network Layer is
responsible for uniquely identifying all devices and
connections on the Internet
• The unique identifier is called an IP address
• IP address consist of 32 bits (for version 4)
• Keep in mind that, if a single device had multiple
connections to the Internet, you would need an IP address
for each connection
• Address space is 232 = 4,294,967,296 32-bit addresses
• In theoretical terms, 4,294,967,296 connections can be
made to the Internet (not really true in real life)
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IP Addresses
• The IP Address has 3 notations: Binary, Dotted-decimal and Hexadecimal
• Binary: 4 Octets: 01110101 10010101 00011101 11101010
• Dotted-Decimal (or dot notation):
• For Dotted-Decimal, each number can range from 0 to 255
• Hexadecimal:
0111 0101 1001 0101 0001 1101 1110 1010
75
95
1D
EA
75951DEA
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EXAMPLES
Change the following IP address from binary notation to dotted-decimal
notation: 10000001 00001011 00001011 11101111
Solution 129.11.11.239
Change the following IP address from dotted-decimal notation to binary
notation: 111.56.45.78
Solution
01101111 00111000 00101101 01001110
Find the error, if any, in the following IP address: 111.56.045.78
Solution
There are no leading zeroes in dotted-decimal notation (045).
Change the following IP addresses from binary notation to hexadecimal
notation: 10000001 00001011 00001011 11101111
Solution
Dr. Clincy
Lecture
810B0BEF16
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IP Addresses: Classful Addressing
• When IP addressing was first started, it used a concept
called “classful addressing”. A newer concept called
“classless addressing” is slowly replacing it though.
• Regarding “classful addressing”, the address space is
divided into five classes: A, B, C, D and E.
Dr. Clincy
Class
# of addresses
Percent of the
Space
A
231=2147483648
50%
B
230=1073741824
25%
C
229=536870912
12.5%
D
228=268435456
6.25%
E
228=268435456
6.25%
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Finding the class in binary notation
Finding the class in decimal notation
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EXAMPLES
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Solution
Find the class of the address:
The first bit is 0. This is a
00000001 00001011 00001011 11101111
class A address
.
Solution
Find the class of the address:
11000001 10000011 00011011 11111111
Solution
Find the class of the address:
The first byte is 227
(between 224 and 239);
the class is D.
227.12.14.87
Dr. Clincy
The first 2 bits are 1; the third
bit is 0. This is a class C
address.
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Netid and hostid
• A, B and C class-addresses are divided into network id
and host id
• For Class A, Netid=1 byte, Hostid = 3 bytes
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• For Class B, Netid=2 bytes, Hostid = 2 bytes
• For Class C, Netid=3 bytes, Hostid = 1 byte
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Blocks in class A
• Class A has 128 blocks or network ids
• First byte is the same (netid), the remaining 3 bytes can change (hostids)
• Network id 0 (first), Net id 127 (last) and Net id 10 are reserved – leaving 125
ids to be assigned to organizations/companies
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• Each block contains 16,777,216 addresses – this block should be used by large
organizations. How many Host can be addressed ????
• The first address in the block is called the “network address” – defines the
network of the organization
Example
• Netid 73 is assigned
• Last address is reserved
• Recall: routers have addressees
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Blocks in class B
• Class B is divided into 16,384 blocks (65,536 addresses each)
• 16 blocks are reserved
• First 2 bytes are the same (netid), the remaining 2 bytes can change (hostids)
• For example, Network id 128.0 covers addresses 128.0.0.0 to 128.0.255.255
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• Network id 191.225 is the last netid for this block
Example
• Netid 180.8 is assigned
• Last address is reserved
• Recall: routers have addresses
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Blocks in class C
• Class C is divided into 2,097,152 blocks (256 addresses each)
• 256 blocks are reserved
• First 3 bytes are the same (netid), the remaining 1 byte can change (hostids)
• For example, Network id 192.0.0 covers addresses 192.0.0.0 to 192.0.0.255
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Class D addresses
are used for multicasting;
there is only
one block in this class.
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Class E addresses are reserved
for special purposes;
most of the block is wasted.
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Network Addresses
The network address is the first address.
The network address defines the network to the rest of the Internet.
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Given the network address, we can find the class of the address, the
block, and the range of the addresses in the block
Given the network address 17.0.0.0, find the class, the block, and the range of the
addresses.
Solution
The class is A because the first byte is between 0 and 127. The block has
a netid of 17. The addresses range from 17.0.0.0 to 17.255.255.255.
Given the network address 132.21.0.0, find the class, the block, and the range of
the addresses.
Solution
The class is B because the first byte is between 128 and 191. The block has
a netid of 132.21. The addresses range from 132.21.0.0 to 132.21.255.255.
Given the network address 220.34.76.0, find the class, the block, and the range of the
addresses.
The class is C because the first byte is between 192 and 223. The block
Solution
Dr. Clincy
has a netid of 220.34.76. The addresses range from 220.34.76.0 to
220.34.76.255.
Lecture
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Mask
Given the network address, we can easily determine the block and range of
addresses
• Suppose given the IP address, can we determine the network address (beginning
of the block) ?
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• To route packets to the correct network, a router must extract the network address
from the destination IP address
• For example, given 134.45.78.2, we know this is a class B, therefore 134.45 is the
netid and 134.45.0.0 is the network address (starting address of the block)
• How would we EXTRACT the network address from the IP address? We would
use a MASK.
A mask is a 32-bit binary number that gives the first address in the block
(the network address) when bitwise ANDed with an address in the block.
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AND operation
• If bit is ANDed with 1, it’s preserved
• If bit is ANDed with 0, it’s changed to
a 0.
• There are 3 default masks: one for each class. The default masks
preserve the netid when ANDed with the addresses
• Class A Default Mask: 255.0.0.0
• Class B Default Mask: 255.255.0.0
• Class C Default Mask: 255.255.255.0
• A simple way to determine the netid for un-subnetted cases: (1) if mask byte is 255,
retain corresponding byte of the address, (2) if mask byte is 0, set corresponding
address byte to 0.
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Examples
Given the address 23.56.7.91 and the default class A mask, find the
beginning address (network address).
The default mask is 255.0.0.0, which means that only the first byte is
preserved and the other 3 bytes are set to 0s. The network address is
23.0.0.0.
Given the address 132.6.17.85 and the default class B mask, find the beginning
address (network address).
Solution
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Solution
The default mask is 255.255.0.0, which means that the first 2 bytes are
preserved and the other 2 bytes are set to 0s. The network address is
132.6.0.0.
Given the address 201.180.56.5 and the class C default mask, find the beginning
address (network address).
Solution
Dr. Clincy
The default mask is 255.255.255.0, which means that the first 3
bytes are preserved and the last byte is set to 0. The network
address is 201.180.56.0.
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Recall IP Addresses: Classful Addressing
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Dr. Clincy
Class
# of addresses
Percent of the
Space
A
231=2147483648
50%
B
230=1073741824
25%
C
229=536870912
12.5%
D
228=268435456
6.25%
E
228=268435456
6.25%
Lecture
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5-bit Address Space Illustration
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No Netid case
32 addresses/block
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Number of blocks: 1
Address range per block: 0 to 31
Netids: N/A
Network Addresses : 00000
Broadcast Addresses: 11111
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5-bit Address Space Illustration
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1-bit Netid case
16 addresses/block
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Number of blocks: 2
Address range per block: 0 to 15
Netids: 0, 1
Network Addresses : 00000, 10000
Broadcast Addresses: 01111, 11111
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Lecture
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5-bit Address Space Illustration
2-bit Netid Case
8 addresses/block
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Number of blocks: 4
Address range per block: 0 to 7
Netids: 00, 01, 10, 11
Network Addresses : 00000, 01000, 10000, 11000
Broadcast Addresses: 00111, 01111, 10111, 11111
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Lecture
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5-bit Address Space Illustration
3-bit Netid Case
4 addresses/block
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Number of blocks: 8
Address range per block: 0 to 3
Netids: 000, 001, 010, 011, 100, 101, 110, 111
Network Addresses : 00000, 00100, 01000, 01100
10000, 10100, 11000, 11100
Broadcast Addresses: 00011, 00111, 01011, 01111
10011, 10111, 11011, 11111
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Lecture
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Mixing 3-bit & 2-bit Cases
(think of the 32-bit case)
4 addresses/block and 8 addresses/block
Number of blocks: 6
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Address range per block: 0 to 3 and 0 to 7
Netids: 000, 001, 010, 011, 10, 11
Network Addresses : 00000, 00100, 01000, 01100
10000, 11000
Broadcast Addresses: 00011, 00111, 01011, 01111
10111, 11111
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Lecture
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