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Chapter 4

IP Addressing

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IP Addressing

About IP Address

• The identifier that is used in the IP layer of the TCP/IP protocol is called the Internet address or IP address.

• An IP address is a 32-bit address that uniquely defines a host or a router on the Internet.

• The IP address are unique in the sense that two devices can never have the same address. However, a device can have more than one address.

• Each IP address is made of two parts:

– Net id : The net id defines a network

– Host id : The host id identifies a host on that network.

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Figure 4-1 Internet address

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IP Addressing

4.1 DECIMAL NOTATION Internet address are usually written in decimal form with decimal points separating the bytes.

Figure 4-2 Decimal point notation

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IP Addressing

4.2 CLASSES IP address are divided into five different classes: A, B, C, D, and E.

Figure 4-3 Internet address classes

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IP Addressing

CLASS A

• The first octet(8 bits) defines the net id, the leftmost bit must be zero to define the class as A.

• The remaining 7 bits define different network.(27=128 networks), There are actually 126 networks in class A because two of the addresses are reserved for special purposes.

• In a class A network, 24 bits are used to define the host id.

– (224 = 16,777,216 hosts) - (hostid all 0s and hostid all 1s) = 16,777,214 hosts

CLASS B

• Two octets define the net id and two octets define the hostid.

• The two leftmost bit are 10 to define the class as B.

• The next 14 bits define different network.(214=16,384 networks),

• In a class B network, 16 bits are used to define the host id.

– (216 = 65,536 hosts) - (hostid all 0s and hostid all 1s) = 65,534 hosts

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IP Addressing

CLASS C • Three octets define the net id and one octets define the hostid.

• The three leftmost bit are 110 to define the class as C.

• The next 21 bits define different network.(221= 2,097,152 networks),

• In a class C network, 8 bits are used to define the host id.

– (28 = 256 hosts) - (hostid all 0s and hostid all 1s) = 254 hosts.

CLASS D • The class D address is defined for multicasting.

• There is no netid or hostid./ The whole address is used for multicasting.

• The first 4 bits define the class(1110).

• The remaining 28 bits define different multicast addresses.

CLASS E • Class E is rederved by the Internet for special use. There is no netid or hostid.

• The first 4 bits define the class(1111).

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IP Addressing

Determining the Class of an Address

• If the first number is between 0 and 127 (inclusive), the class is A.

• If the first number is between 128 and 191 (inclusive), the class is B.

• If the first number is between 192 and 223 (inclusive), the class is C.

• If the first number is between 224 and 239 (inclusive), the class is D.

• If the first number is between 240 and 255 (inclusive), the class is E.

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Figure 4-4 Classes using decimal notation.

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IP Addressing

Multihomed Device

• A computer that is connected to different networks is called a multihomed computer and will have more than one address, each possibly belong to a different class.

Figure 4-5 Multihomed devices

Router

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IP Addressing

4.3 SPECIAL ADDRESSES

Special Address Netid Hostid Source or Destination

Network address Specific All 0s None

Direct broadcast address Specific All 1s Destination

Limited broadcast address All 1s All 1s Destination

This host on this network All 0s All 0s Source

Specific host on this network

All 0s Specific Destination

Loopback address 127 Any Destination

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Figure 4-6 Examples of network addresses

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Figure 4-7 Examples of direct broadcast addresses

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Figure 4-8 Examples of limited broadcast addresses

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Figure 4-0 Examples of “this” host on “this” network address

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Figure 4-10 Example of specific host on “this” network

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Figure 4-11 Example of loopback address

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Figure 4-12 Sample internet

4.4 A SAMPLE INTERNET