# 162117_Lecture 09-Logical Addressing.ppt - Network Layer...

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Network Layer: Logical Addressing And Internetworking

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4-1 IPv4 ADDRESSES 4-1 IPv4 ADDRESSES An An IPv4 address IPv4 address is a is a 32-bit 32-bit address that uniquely and address that uniquely and universally defines the connection of a device (for universally defines the connection of a device (for example, a computer or a router) to the Internet. example, a computer or a router) to the Internet. Address Space Notations Classful Addressing Classless Addressing Network Address Translation (NAT) Topics discussed in this section: Topics discussed in this section:
An IPv4 address is 32 bits long. Note The IPv4 addresses are unique and universal. The address space of IPv4 is 2 32 or 4,294,967,296.

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Figure 4.1 Dotted-decimal notation and binary notation for an IPv4 address
Change the following IPv4 addresses from binary notation to dotted-decimal notation. Example 4.1 Solution We replace each group of 8 bits with its equivalent decimal number and add dots for separation.

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Change the following IPv4 addresses from dotted-decimal notation to binary notation. Example 4.2 Solution We replace each decimal number with its binary equivalent (see Appendix B).
In classful addressing, the address space is divided into five classes: A, B, C, D, and E. Note

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Table 4.1 Number of blocks and block size in classful IPv4 addressing In classful addressing, a large part of the available addresses were wasted.

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Figure 4.3 shows a block of addresses, in both binary and dotted-decimal notation, granted to a small business that needs 16 addresses. We can see that the restrictions are applied to this block. The addresses are contiguous. The number of addresses is a power of 2 (16 = 2 4 ), and the first address is divisible by 16. The first address, when converted to a decimal number, is 3,440,387,360, which when divided by 16 results in 215,024,210. Example 4.5
Figure 4.3 A block of 16 addresses granted to a small organization

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In IPv4 addressing, a block of addresses can be defined as x.y.z.t / n in which x.y.z.t defines one of the addresses and the / n defines the mask. The first address in the block can be found by setting the rightmost 32 − n bits to 0s.
A block of addresses is granted to a small organization. We know that one of the addresses is 205.16.37.39/28. What is the first address in the block? Solution The binary representation of the given address is 11001101 00010000 00100101 00100111 If we set 32−28 rightmost bits to 0, we get 11001101 00010000 00100101 0010 0000 or 205.16.37.32 . This is actually the block shown in Figure 4.3.

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