IPv4 Addresses Data Communication

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INTRODUCTION

 The identifier used in the IP layer of the TCP/IP protocol suite to identify each device connected to the Internet is called the Internet address or IP address.

 An IPv4 address is a 32-bit address that uniquely and universally defines the connection of a host or a router to the Internet;  an IP address is the address of the interface.

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Note

An IPv4 address is 32 bits long.

The IPv4 addresses are unique and universal.

The address space of IPv4 is 2

32

or 4,294,967,296.

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Dotted-decimal notation

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Example

Change the following IPv4 addresses from binary notation to dotted-decimal notation.

a.

10000001 00001011 00001011 11101111 b.

c.

d.

11000001 10000011 00011011 11111111 11100111 11011011 10001011 01101111 11111001 10011011 11111011 00001111 Solution We replace each group of 8 bits with its equivalent decimal number and add dots for separation: a.

129.11.11.239

b.

c.

d.

193.131.27.255

231.219.139.111

249.155.251.15

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Example

Change the following IPv4 addresses from dotted-decimal notation to binary notation.

a.

111.56.45.78

b.

221.34.7.82

c.

d.

241.8.56.12

75.45.34.78

Solution We replace each decimal number with its binary equivalent: a.

01101111 00111000 00101101 01001110 b.

c.

d.

11011101 00100010 00000111 01010010 11110001 00001000 00111000 00001100 01001011 00101101 00100010 01001110 TCP/IP Protocol Suite 6

Example

Find the error, if any, in the following IPv4 addresses: a.

111.56.045.78

b.

c.

d.

221.34.7.8.20

75.45.301.14

11100010.23.14.67

Solution a.

There should be no leading zeroes (045).

b.

c.

We may not have more than 4 bytes in an IPv4 address.

Each byte should be less than or equal to 255.

d.

A mixture of binary notation and dotted-decimal notation.

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Finding the class of address

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Finding the class of an address using continuous checking

Start 1 0 Class: A 0 1 Class: B 0 1 Class: C 1 0 Class: D Class: E TCP/IP Protocol Suite 9

Example

Find the class of each address: a.

00000001 00001011 00001011 11101111 b.

c.

d.

11000001 10000011 00011011 11111111 10100111 11011011 10001011 01101111 11110011 10011011 11111011 00001111 Solution See the procedure in Figure 5.7.

a.

The first bit is 0. This is a class A address.

b.

c.

d.

The first 2 bits are 1; the third bit is 0. This is a class C address.

The first bit is 1; the second bit is 0. This is a class B address.

The first 4 bits are 1s. This is a class E address.

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Example

Find the class of each address: a.

227.12.14.87

b.

193.14.56.22

c.

14.23.120.8

d.

252.5.15.111

Solution a.

b.

c.

d.

The first byte is 227 (between 224 and 239); the class is D.

The first byte is 193 (between 192 and 223); the class is C.

The first byte is 14 (between 0 and 127); the class is A.

The first byte is 252 (between 240 and 255); the class is E.

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Blocks in Class A

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Millions of class A addresses are wasted.

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Blocks in Class B

Many class B addresses are wasted.

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Blocks in Class C

Not so many organizations are so small to have a class C block.

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The single block in Class D

Class D addresses are made of one block, used for multicasting.

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The single block in Class E

The only block of class E addresses was reserved for future purposes.

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Sample Internet

The network address is the identifier of a network.

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Network mask

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Restrictions

 The number of addresses in a block must be a power of 2  The first address must be evenly divisible by the number of addresses.  For example, if a block contains 4 addresses, the first address must be divisible by 4.

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Example 4 - Find first address

What is the first address in the block if one of the addresses is 167.199.170.82/27 ?

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Example 4 - Find first address

What is the first address in the block if one of the addresses is 167.199.170.82/27 ?

Solution The prefix length is 27, which means that we must keep the first 27 bits as is and change the remaining bits (5) to 0s. The following shows the process: Address in binary: 10100111 11000111 10101010 01010010 Keep the left 27 bits: 10100111 11000111 10101010 010 00000 Result in CIDR notation: 167.199.170.64/27 TCP/IP Protocol Suite 21

Example 5 – Find first address Using binary

What is the first address in the block if one of the addresses is 140.120.84.24/20 ?

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Example 5 – Find first address Using binary

What is the first address in the block if one of the addresses is 140.120.84.24/20 ?

Solution Figure 5.3 shows the solution. The first, second, and fourth bytes are easy; for the third byte we keep the bits corresponding to the number of 1s in that group. The first address is 140.120.80.0/20 .

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Figure 5.3

Example 5

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Example 6 – Find first address Another solution method

Find the first address in the block if one of the addresses is 140.120.84.24/20 .

Solution The first, second, and fourth bytes are as defined in the previous example. To find the third byte, we write 84 as the sum of powers of 2 and select only the leftmost 4 (m is 4) as shown in Figure 5.4. The first address is 140.120.80.0/20 .

See Next Slide TCP/IP Protocol Suite 25

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Example 7 - Number of addresses

Find the number of addresses in the block if one of the addresses is 140.120.84.24/20 .

Solution The prefix length is 20. The number of addresses in the block is 2 32−20 or 2 12 or 4096. Note that this is a large block with 4096 addresses.

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Example 8 - Find last address

Find the last address in the block if one of the addresses is 140.120.84.24/20 .

Solution We found in the previous examples that the first address is 140.120.80.0/20 and the number of addresses is 4096. To find the last address, we need to add 4095 (4096 − 1) to the first address.

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Example 8

(Continued)

To keep the format in dotted-decimal notation, we need to represent 4095 in base 256 (see Appendix B) and do the calculation in base 256. We write 4095 as 15.255.

(256 divides into 4095 15 times with a remainder of 255.) We then add the first address to this number (in base 255) to obtain the last address as shown below: 140 . 120 . 80 . 0 15 . 255 ------------------------ 140 . 120 . 95 . 255 The last address is 140.120.95.255/20 . TCP/IP Protocol Suite 29

Alternate Method

 Not crazy about base 256 arithmetic? Do it in binary.

 .80.0 in binary is 01010000.00000000

 4095 in binary is 1111 11111111  Add the two values:  01011111.11111111

 This is .95.255

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Example 9 - find last address Another method

Find the last address in the block if one of the addresses is 140.120.84.24/20.

Solution The mask has twenty 1s and twelve 0s. The complement of the mask has twenty 0s and twelve 1s. In other words, the mask complement is 00000000 00000000 00001111 11111111 or 0.0.15.255. We add the mask complement to the beginning address to find the last address.

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Example 9

(Continued)

We add the mask complement to the beginning address to find the last address.

140 . 120 . 80 . 0 0 . 0 . 15 . 255 --------------------------- 140 . 120 . 95 . 255 The last address is 140.120.95.255/20 .

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Example 10 - find the block

Find the block 190.87.140.202/29.

if one of the addresses is

Solution We follow the procedure in the previous examples to find the first address, the number of addresses, and the last address. To find the first address, we notice that the mask (/29) has five 1s in the last byte. So we write the last byte as powers of 2 and retain only the leftmost five as shown below: TCP/IP Protocol Suite See Next Slide 33

Example 10

(Continued)

202 ➡ 128 + 64 + 0 + 0 + 8 + 0 + 2 + 0 The leftmost 5 numbers are ➡ 128 + 64 + 0 + 0 + 8

The first address is 190.87.140.200/29

The number of addresses is 2 32−29 or 8. To find the last address, we use the complement of the mask. The mask has twenty-nine 1s; the complement has three 1s. The complement is 0.0.0.7. If we add this to the first address, we get 190.87.140.207/29. In other words, the first address is address is 190.87.140.207/20 190.87.140.200/29 , the last . There are only 8 addresses in this block.

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Example 11

Show a network configuration for the block in the previous example.

Solution The organization that is granted the block in the previous example can assign the addresses in the block to the hosts in its network. However, the first address needs to be used as the network address and the last address is kept as a special address (limited broadcast address). Figure 5.5 shows how the block can be used by an organization. Note that the last address ends with 207, which is different from the 255 seen in classful addressing.

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Note: In classless addressing, the last address in the block does not necessarily end in 255.

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