Chapter 4. IP Addresses: Classful Addressing. PDF created with FinePrint pdffactory Pro trial version

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1 Chapter 4 IP Addresses: Classful Addressing

2 Outlines Intrductin Classfuladdressing Other issues A sample Internet

3 4.1 INTRODUCTION

4 Intrductin IP address, r Internet Address 32-bit binary address Uniquely and universally defines the cnnectin f a hst r a ruter t the Internet Address Space Ttal number f addresses used by the prtcl IPv4 uses 32-bit address and the address space is 2^32

5 An IP address is a 32-bit address. The IP addresses are unique.

6 Address Space.. addr1.. addr15 addr addr41 addr226 addr31....

7 RULE:.. addr1.. addr15 addr addr41 addr226 addr If a prtcl uses N bits t define an address, the address space is 2 N because each bit can have tw different values (0 and 1) and N bits can have 2 N values.

8 The address space f IPv4 is 2 32 r 4,294,967,296.

9 Ntatin Binary ntatin Dtted-decimal ntatin Hexadecimal ntatin

10 Binary Ntatin

11 Figure 4-1 Dtted-Decimal Decimal Ntatin

12 Hexadecimal Ntatin D EA 0x75951DEA

13 Example 1 Change the fllwing IP address frm binary ntatin t dtted-decimal ntatin Slutin

14 Example 2 Change the fllwing IP address frm dtted-decimal ntatin t binary ntatin Slutin

15 Example 3 Find the errr, if any, in the fllwing IP address: Slutin There are n leading zeres in dtted-decimal ntatin (045).

16 Example 3 (cntinued) Find the errr, if any, in the fllwing IP address: Slutin We may nt have mre than fur numbers in an IP address

17 Example 3 (cntinued) Find the errr, if any, in the fllwing IP address: Slutin In dtted-decimal ntatin, each number is less than r equal t 255; 301 is utside this range.

18 Example 3 (cntinued) Find the errr, if any, in the fllwing IP address: Slutin A mixture f binary ntatin and dtteddecimal ntatin is nt allwed.

19 Example 4 Change the fllwing IP addresses frm binary ntatin t hexadecimal ntatin Slutin 0X810B0BEF r 810B0BEF 16

20 4.2 CLASSFUL ADDRESSING

21 Classful Addressing IP address space is divided int five classes: A, B, C, D, E A: 1/2 B: 1/4 C: 1/8 D: 1/16 E: 1/16

22 Figure 4-2 Occupatin f the Address Space

23 Figure 4-3 Finding the Class in Binary Ntatin

24 Figure 4-4 Finding the Address Class

25 Example 5 Hw can we prve that we have 2,147,483,648 addresses in class A? Slutin In class A, nly 1 bit defines the class. The remaining 31 bits are available fr the address. With 31 bits, we can have 2 31 r 2,147,483,648 addresses.

26 Example 6 Find the class f the address: Slutin The first bit is 0. This is a class A address.

27 Example 6 (Cntinued) Find the class f the address: Slutin The first 2 bits are 1; the third bit is 0. This is a class C address.

28 Figure 4-5 Finding the Class in Decimal Ntatin

29 Example 7 Find the class f the address: Slutin The first byte is 227 (between 224 and 239); the class is D.

30 Example 7 (Cntinued) Find the class f the address: Slutin The first byte is 193 (between 192 and 223); the class is C.

31 Example 8 In Example 4 we shwed that class A has ,147,483,648) addresses. Hw can we prve this same fact using dtted-decimal ntatin? Slutin The addresses in class A range frm t We ntice that we are dealing with base 256 numbers here.

32 Slutin (Cntinued) Each byte in the ntatin has a weight. The weights are as fllws: 256 3, 256 2, 256 1, Last address: =2,147,483,647 First address: = 0 If we subtract the first frm the last and add 1, we get 2,147,483,648.

33 Netid and Hstid An IP address in classes A, B, C is divided int Netid Hstid Ntably, classes D and E are nt divided int netid and hstid

34 Figure 4-6 Netidand Hstid

35 Classes and Blcks Each class is divided int a fixed number f blcks with each blck having a fixed size The number f blcks is based n the netid Each blck s size is depends n the hstid

36 Class A Class A: divided int 128 blcks First blck: ~ Last blck: ~ Each blck cntains addresses T large than the needs f almst all rganizatins In each blck, the first address, e.g., , is called the netwrk address Identify the netwrk f the rganizatin, nt individual hsts

37 Figure 4-7 Blcks in Class A

38 Millins f class A addresses are wasted.

39 Class B Class B: divided int 16,384 blcks First blck: ~ Last blck: ~ Each blck cntains 65,535 addresses larger than the needs f mst mid-size rganizatins In each blck, the first address, e.g., , is called the netwrk address Identify the netwrk f the rganizatin, nt individual hsts

40 Figure 4-8 Blcks in Class B

41 Many class B addresses are wasted.

42 Class C Class C: divided int 2.097,152 blcks First blck: ~ Last blck: ~ Each blck cntains 256 addresses Mst rganizatins d nt want such a blck In each blck, the first address, e.g., , is called the netwrk address Identify the netwrk f the rganizatin, nt individual hsts

43 Figure 4-9 Blcks in Class C

44 The number f addresses in a class C blck is smaller than the needs f mst rganizatins.

45 Class D and Class E Class D Just ne blck Designed fr multicasting and each address is used t identify ne multicasting grup Class E Just ne blck Designed fr use as reserved addresses

46 Class D addresses are used fr multicasting; there is nly ne blck in this class.

47 Class E addresses are reserved fr special purpses; mst f the blck is wasted.

48 Netwrk Addresses The netwrk address is the first address. The netwrk address defines the netwrk t the rest f the Internet. Ruters rute a packet based n the netwrk address. Given the netwrk address, we can find the class f the address, the blck, and the range f the addresses in the blck

49 In classful addressing, the netwrk address (the first address in the blck) is the ne that is assigned t the rganizatin.

50 Example 9 Given the netwrk address , find the class, the blck, and the range f the addresses. Slutin The class is A because the first byte is between 0 and 127. The blck has a netid f 17. The addresses range frm t

51 Example 10 Given the netwrk address , find the class, the blck, and the range f the addresses. Slutin The class is B because the first byte is between 128 and 191. The blck has a netid f The addresses range frm t

52 Example 11 Given the netwrk address , find the class, the blck, and the range f the addresses. Slutin The class is C because the first byte is between 192 and 223. The blck has a netid f The addresses range frm t

53 Mask If the netwrk address is given We can btain the blck and blck size Hwever, if an address is given, hw t find ut the netwrk address? First, find the class f the address Secnd, derive the netid and hstid Finally, netwrk address is btained by setting the hstidt zer.

54 Mask A mask is a 32-bit binary number that gives the first address in the blck (the netwrk address) when bitwise ANDed with an address in the blck.

55 Figure 4-10 Masking cncept

56 Figure 4-11 AND peratin

57 Default Masks Class A Mask in binary: Mask in dtted-decimal: Class B Mask in binary: Mask in dtted-decimal: Class C Mask in binary: Mask in dtted-decimal:

58 The netwrk address is the beginning address f each blck. It can be fund by applying the default mask t any f the addresses in the blck (including itself). It retains the netid f the blck and sets the hstid t zer.

59 Example 12 Given the address and the default class A mask, find the beginning address (netwrk address). Slutin The default mask is , which means that nly the first byte is preserved and the ther 3 bytes are set t 0s. The netwrk address is

60 Example 13 Given the address and the default class B mask, find the beginning address (netwrk address). Slutin The default mask is , which means that the first 2 bytes are preserved and the ther 2 bytes are set t 0s. The netwrk address is

61 Example 14 Given the address and the class C default mask, find the beginning address (netwrk address). Slutin The default mask is , which means that the first 3 bytes are preserved and the last byte is set t 0. The netwrk address is

62 We must nt apply the default mask f ne class t an address belnging t anther class.

63 4.13 OTHER ISSUES

64 Multihmed Devices A cmputer that is cnnected t different netwrks is called a multihmed cmputer Have mre than ne address Each pssibly belnging t a different class

65 Figure 4-12 MultihmedDevices

66 Special Addresses Special Address Netid Hstid Surce r Destinatin Netwrk address Specific All 0s Nne Direct bradcast address Specific All 1s Destinatin Limited bradcast address All 1s All 1s Destinatin This hst n this netwrk All 0s All 0s Surce Specific hst n this netwrk All 0s Specifi c Destinatin Lpback address 127 Any Destinatin

67 Figure 4-13 Netwrk Addresses

68 Direct Bradcast Address The hstid is all 1s in classes A, B, and C Used by a ruter t send a packet t all hst in a specific netwrk Can nly be used as a destinatin address

69 Figure 4-14 Example f Direct Bradcast Address

70 Limited Bradcast Address An address with all 1s fr the netid and hstid in classes A, B, and C Used by a hst t send a packet t every ther hst in a netwrk Ruters will blck a packet having this type f address t ther netwrks Limited bradcast address belngs t class E

71 Figure 4-15 Example f Limited Bradcast Address

72 This Hst n This Netwrk An IP address is cmpsed f all 0s Used by a hst at btstrap time when it des nt knw its IP address Surce address: all 0s Destinatin address: limited bradcast address

73 Figure 4-16 Example f This Hst n This Netwrk

74 Specific Hst n This Netwrk An IP address with a netid f all 0s Used by a ruter r hst t send a packet t anther hst n the same netwrk Ruter will blck this packet t ther netwrks Only used fr a destinatin address

75 Figure 4-17 Example f Specific Hst n This Netwrk

76 Lpback Address An IP address with the first byte equal t 127 This packet never leaves the machine Used nly as a destinatin address

77 Figure 4-18 Example f LpbackAddress

78 Private Addresses A number f blcks in each class are assigned fr private use and nt recgnized glbally. Used in Islatin In cnnectin with netwrk address translatin Class A B C Netid t t Blcks

79 Unicast,, Multicast, and Bradcast Addresses Unicast cmmunicatin is ne-t-ne. Multicast cmmunicatin is ne-t-many. Bradcast cmmunicatin is ne-t-all.

80 Multicast delivery will be discussed in depth in Chapter 14.

81 4.4 A SAMPLE INTERNET WITH CLASSFUL ADDRESSES

82 Sample Internet A Tken Ring LAN: : Class C An Ethernet LAN: : Class B An Ethernet LAN: : Class A A pint-t-pint WAN, fr example a T-1 line Just cnnect tw ruters and n hsts T save addresses, n IP address is assigned A switch WAN, e.g., Frame Relay r ATM Cnnect t three netwrk via three ruters

83 Figure 4-19 Sample internet