2010

1

.

()

(2009-10) :

. & 20/2/2010

2

. &

,

3

4

. &

: . - . 2 . . 2 . . 4 . . 1 . . 1 . . 1 . . 1 . . 1 . . 1 . . 1 .

5

6

. &

7

8

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, .

9

10

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6 . 2161. . . . ( . 196 6.1, 1 ). .. ( . 197, 6.2, 2 ). modem : . . . . . ( . 197, 6.2 1). Internet WAN . , , / . ( ) 1 .. . ( ) , -

2. 3.

4.

5.

6. 7. 8.

. ( ) .25, . ( ) .25 ; ( ) . . ISDN , -

9.

10. ISDN; ISDN : . ' ' , . , (common channel signaling). (, , ).

1

modem . 198, 6.3, 2 . , .11

. . ( . 203)

11. ISDN , . . . . ( . 205, 2 ). 12. Frame Relay ( ) .

13. Frame Relay ; . ( ) 14. CIR; ( ) 15. , ; ( ) 16. : . . . 43 byte. . . ( ) 17. : . . ( ) 18. CD 622 Mbps; ( ) 19. xDSL; xDSL . (loading coils) , . 3 8 KHz (voice band). ( . 210, ). 20. ADSL SDSL; ADSL (downstream, upstream). SDSL .. , . ( . 211, 212).12 . &

21. . ( )

WAN .

,

22. 4 . ( ) 23. , , 64 Kbps. , . 24. , Internet Web, . ISDN , ; ( )

7 INTERNET . 2901. : . . . . . . ( 7.1.1, 2 , . 220). 2. : ( . 222 . 224) 3. : TCP/IP internet Internet Intranet , TCP/IP TCP/IP , Internet WWW

13

TCP/IP internet Internet Intranet

, TCP/IP TCP/IP , Internet WWW

4.

OSI TCP/IP .

, M. TCP/IP ) ) OSI TCP/IP ) ) ) OSI. 5. , , : . . . . . , . . . . , . TCP port ; TCP , 16 bit TCP . TCP TCP (TCP port) . , TCP port , . TCP port . TCP port . 14 . &

6.

TCP port : TCP port . , , (File Transfer Protocol, FTP) TCP port 21. , , TCP port 21. O FTP , TCP port 21 . 7. TCP; TCP, . , TCP. . , . . , . . , 12001 1000, 12001Byte 13000 Byte. , TCP port. , :

8.

( , , ) TCP port . TCP port TCP , 15

. , TCP port , . 9. TCP TCP , :

10. TCP ; O TCP , TCP . , . , , , . , ( , IP ) , . TCP , . TCP : . TCP port . 11. UDP port ; UDP (UDP port) UDP . UDP port 16 bit, UDP . UDP, UDP port. UDP port . UDP port UDP , TCP port. 12. : . To UDP . To UDP TCP . To UDP TCP . To UDP , TCP . ( 7.4 . 240, , 2 ). . ( 7.4 . 240, ). . ( 7.4 . 240, , , ).16 . &

. ( 7.4 . 240, ). 13. , UDP, TCP; . , (7.4 . 240, 1 ), (7.4 . 240, 2 ). 14. , IP: . 64 byte . 64 Kbyte . 64 Mbyte . 128 Kbyte . ( 7.5 . 242, 2 ). 15. P . :

, . 243, 244. 16. , , DF, MF 5.000 byte 20 byte, 820 byte. , , . 5000 byte , 820 byte. 820 byte. T , , 20 byte. 800 byte. 5000 800 , 5000/800=6 7 5000 byte 6X800 byte = 200 byte. DF 0 . MF 1, , 7 220 byte (200 + 20 ), MF 0.

17

, : 1 =0. 2 =800/8=100. 3 =1600/8=200. 4 =2400/8=300. 5 =3200/8=400. 6 =4000/8=500. 7 =4800/8=600. : ( (byte) byte) (byte) 1 5 800 (20) 2 5 800 (20) 3

DF

MF

820

0

1

0

820

0

1

100

5 800 (20) 5 800 (20) 5 800 (20) 5 800 (20) 5 200 (20) 220 0 0 600 820 0 1 500 820 0 1 400 820 0 1 300 820 0 1 200

4

5

6

7

17. IP DF 1 , ; , . DF , , 1. .

18

. &

, . , . 18. DF MF ; , MF 0. , DF 1 DF 0. 19. IP 0 MF 1. ; MF=1 . 0, . . 20. IP 200 MF 1. ; MF=1 . 200, . . 21. IP 1.500 DF 1 1.500 . 2.000 4.470 . ; DF 1. 2000 4470 1500 , . [ 1500 , ]. 22. IP 1.500 100 DF 0 1.500 . 2.000 . 1.500 . ; , , : , MF, DF . 1500 , . DF 0, 1500 . , 2000 1500 . 23. IP 1.500 100 DF 0 1.500 . 628 2 . 1.500 . ; , , 2

625. 5 (=20 byte) .19

: , MF, DF . 1500 628 , . , 5 = 5 32 bit = 160 bit = 20 byte. 1480 byte. H 608 byte (+20 byte , 628 byte). : 608 byte 1480 608 608 = 264 byte. DF 0 (fragment). MF 1 0. : 1 : 0. 2 : 608/8 = 76. 3 1216/8=152. 100. : 32 bit

(fragment)

(byte)

(byte) (byte)

DF

MF

1

5608 820 100 0 1 0

(20)

5608 820 100 0 1 76

2

(20)

5264 284 100 0 0 152

3

(20)

24. MAC . 48 bit. 24 bit OUI (Organization Unique Identifier). bit (/G) (0, 1 ). 1, , . bit OUI 1, , ). bit (U/L) . 0, IEEE, 1, . O , , , , IEEE, . 20 . &

, , , , IEEE. 22 bits , IEEE . 24 bits , . , (OUI) IEEE, , Ethernet, , , (24 bits ) . , , (OUI). 25. IP . , 187.164.72.38. 8bit. , 48=32, 32 bit. : , :

, . 26. IP , ; () , , B, C, D , . . , ( ) , (.. ). 27. . . . (.250,251 ), ( ) 0. , 7 bit ( ), 27=128 . , 00000000 01111111. 00000000 , , 00000001 01111111. 1 127. , 1.0.0.0 127.255.255.255

21

. . 255.0.0.0. , (.250,251 ) . , 255.255.254 3 111111111111111111111110=16.777.214 host. , . , . host. 1: 1bit , : 11111111.10000000.00000000.00000000, ( 255.128.0.0). , .0 .1 , 0 1. 23 bit 8.388.606 host . 2: 21 bit ( 29 ), 2 21 =2.097.152 . 3 ( 001 110) 6 host. , , , host . 255.0.0.0 255.128.0.0 255.192.0.0 255.224.0.0 255.240.0.0 255.248.0.0 255.252.0.0 255.254.0.0 255.255.0.0 255.255.128.0 255.255.192.0 255.255.224.0 255.255.240.03

(host)/8 /9 /10 /11 /12 /13 /14 /15 /16 /17 /18 /19 /20 1 2 4 8 16 32 64 128 256 512 1.024 2.048 4.096 16.777.214 8.338.606 4.194.302 2.097.150 1.048.574 524.286 262.142 131.070 65.534 32.766 16.384 8.190 4.094

255.255.254 255.255.255.255 broadcast , , . 0 . , 182.158.1.0 182.158.1.x, x 1 254.22 . &

255.255.248.0 255.255.252.0 255.255.254.0 255.255.255.0 255.255.255.128 255.255.255.192 255.255.255.224 255.255.255.240 255.255.255.248 255.255.255.252

/21 /22 /23 /24 /25 /26 /27 /28 /29 /30

8.192 16.384 32.768 65.536 131.072 262.144 524.288 1.048.576 2.097.152 4.194.304

2.046 1.022 510 254 126 62 30 14 6 2

28. , , IP . . . 32 bit , AND. : / 11000000.10101000.01111011.10000100 : 11111111.11111111.11111111.00000000 AND ------------------------------------------------------11000000.10101000.01111011.00000000 / : 192.168.123.0 : 00000000.00000000.00000000.10000100 0.0.0.132 29. 255.255.255.255 124.56.255.255. 255.255.255.255 , . , . 124.56.255.255 124.56. 30. IP - (CIDR); CIDR , . , ( ) . O . , 207.13.01.48/25 /25 , 25 bits 7 . CIDR (Internet Service Providers - ISPs), ,23

. , , ISP. , / , ISP. 31. ARP: . IP . IP MAC . , ). 32. ARP RARP. ARP MAC. RARP MAC . 33. ARP; , , . ARP . 34. IP : . . . ). 35. , IP MAC IP . . , . 36. DNS . DNS , , . , :

24

. &

. , , , : .arpa: .com: .edu: .gov: .mil: .net: .org: , , , ( ). , , . .gr .ca. , , . domains . , (domain names), , , . domain names . , ntua.gr domain name ntua , ... (National Technical University of Athens - NTUA). , domain name, . . , subdomain. , domain names . , telecom.ntua.gr ( .gr), domain name ... (ntua.gr), subdomain. To telecom.ntua.gr , ..., , . ektor telecom, , ntua ... . gr . ektor.telecom.ntua.gr.

37. DNS ; (DNS server) (.. www.in.gr) . () , . . , (). ( ) . , .

25

DNS . ( ) . 38. , . , , , , . , . , , . , . 39. , . , : (), , ( ), . , . . , : , , . 40. : ( )

( )

41. ; , , , . . , , . , , , , . , . , , (), . , 26 . &

, , : - . ICMP. , . 42. , IP. () () () , , . () , () , () , :

27

28

. &

43. , (,,,) , . , IP Ethernet (), , .

4 , 223.1.2.4, 2 223.1.3.2. 2 , . 4 Ethernet 4, 2 Ethernet , Ethernet . , (4) (4) Ethernet 4, . 223.1.2.4 223.1.3.2 Ethernet 00-B0-D0-86-BB-F7 1A-2B-3C-4D-5E-6F mac Ethernet 1 ,

Ethernet , .29

4

2. Ethernet , Ethernet 2. 223.1.2.4 223.1.3.2 Ethernet 3A-4B-5C-6D-7E-8F mac Ethernet 2 00-0-C9-14-C8-29 44. . ( ). 45. , . ( ). 46. RIP ( ); ( ). 47. EGP. ( ). 48. ; . , , FAX . , , , . . , ( ) . , . . 49. FTP Telnet SMTP; FTP TCP , 21 ftp 20 . Telnet , , . Telnet TCP 23 . SMTP SMTP . TCP , 25. FTP Telnet, SMTP FTP , ( 21,20), Telnet, SMTP. 50. . (World Wide Web, WWW Web) , 30 . &

. . (hypermedia), , , , , (video) . (links), , . 51. ; , , . , . (links). , . . (hypermedia) , , : , , , . 52. intranet ; TCP/IP (intranet) . intranet . , , . intranet , , , , , . 53. Internet; , , ( ), . , , , , , . 54. , ; video , . , video , , , . 55. , .

31

. , , . , , , . , , , . , , . 56. ; (Web Site) , . , (e-mail), ( ) . , , . , , . , .

8 . 3291. , . OSI, : (configuration management), (performance management), (fault management), (accountig management) , (security management). : o 8.1.1. o 8.1.2. o 8.1.3. o 8.1.4. o 8.1.5. 2. SNMP agent . ( ). 3. cmmunities SNMP;

32

. &

( ). 4. agents agents cmmunity name, managers; ( ). 5. 6. RMON OSI; ( ) : , , . (authentication): . (integrity): . (confidentiality): . (validity) . . , , ; . . ( , , ). ( . 316, ). passwords, . , : , . (keystroke mnitring), o , , o ( ). scial engineering, . . passwrd, . , password crack, . : ) ) . . .

7.

8.

9.

33

10. 5; ( ) . tunneling, , TCP/IP . . 11. firewall ; firewall / , ( ) , . Internet / , . / Firewall, . firewall, , , , . 12. - . , , client - server. , (main site) . site, . site , site. , site switches, routers LAN. , (.. back up).

5

. VPN . 325, . , 6.9 .34 . &

6

. ! .35

6

36

. &

6 6.1 1. WAN LAN ; WAN; (LAN) . , (Wide Area Network, WAN). WAN , modem, , , .. 2. WAN; WAN (, ), , , , . 3. WAN , LAN, ; . 4. WAN; WAN, , . 5. ) ) ( WAN). , ( WAN) , : X.25 : Frame Relay ISDN ATM xDSL

6.2 1. (PSTN); WAN; (Public Switched Telephone Network, PSTN)

37

. . , PSTN, , WAN. 2. modem ; PSTN . , modem. modem . , modem , . - , . .

3.

; ; , . 56 Kbps 7. ; : . on-line . . . , . , , .

4.

5.

7

, .38 . &

6.5 ISDN1. , , ; , : . , , . . ISDN; ISDN , , . ISDN; Integrated Services Digital Network - . POTS ; POTS Plain Old Telephone System. , . ISDN ( ); (), , ( ). ISDN ( , , video, ). , ISDN; . ' ' , . , (common channel signaling). (, , ). . . ISDN; ISDN , .

2.

3. 4.

5.

6.

7.

39

8.

. (Basic Rate Interface, BRI), (2 -B) (1 -D). -B 64 Kbps . -D 16 Kbps . - -B, , 144 Kbps (2B + D).

9.

. (Primary Rate Interface, PRI) 30 64 Kbps (30 B-) 64 Kbps (1 D-). 64 Kbps (framing) . , , 2,048 Mbps, 1. B. 23B+1D ( 64 Kbps) 8 Kbps , , 1,544 Mbps ( 1).

10. 1; ; To ISDN , NT1. - ISDN , , , . , ( , ..). NT1 8 150 . ISDN, , Fax 4, , , , , .. , , (Terminal Adaptor, TA).

40

. &

11. B D ; . 12. ; . , - 30 - (23 ). 13. ISDN; ISDN , . , ' . 14. ISDN ; . 15. , ISDN.

41

6.8 xDSL1. xDSL; xDigital Suscriber Line . x ADSL, R-ADSL, HDSL, SDSL VDSL. xDSL ; xDSL , . xDSL ISDN BRI 2 ( BRI2 2 64 Kbps 16 Kbps). , xDSL , : , (upstream - ) (downstream ). xDSL ; modem (V.90) 56 Kbps , e-mail ( , , ). (Fiber to the Home) , 8. xDSL Mbps 9 . 1 (2,048 Mbps) T1 (1,544 Mbps) , . . modem, , ( baseband modem).

2.

3.

8

(, ) . 9 = . .42 . &

4.

xDSL; (loading coils) , . xDSL , 3 8 kHz (voice band). xDSL (upstream downstream); xDSL . , (downstream upstream). , , (.. ) (.. 1, ).

5.

6.

7.

baseband modem ; baseband modem, xDSL, . , DSL; xDSL , ADSL ADSL Lite. , Internet , VDSL. , E1/T1, HDSL, SDSL.

43

6. , xDSL.

7 INTERNET 7.1 7.1.1 1. ; . 2. OSI ;

44

. &

OSI . . 3. ; . . 4. , ; ; , . , . . 5. ; . ( ). 6. ; : ) ) . 7. ; (VC virtual circuits) (datagrams). 8. . . . , . , . . : , , . , , . . , , . 45

. , . 9. ; : . . . . 10. . . 11. ; , , . ( . 7-3 . 223). 12. ; . ( . 7-3). .. VC 3 VC . 13. (datagram). , , . . , () .

7.2 TCP/IP7.2.1 TCP/IP1. TCP/IP; TCP/IP . (TCP - Transmission Control Protocol) ( IP Internet Protocol) . TCP/IP; TCP/IP : .46 . &

2.

3.

. TCP/IP .

TCP/IP; TCP/IP , , . , . TCP/IP internet (TCP/IP ), (Internet), TCP/IP (intranet). TCP/IP internet TCP/IP. () (Internet) , TCP/IP. TCP/IP (intranet) TCP/IP , (WWW) . TCP/IP; 1960 .. (Advanced Research Projects Agency ARPA 10). ARPA , , . . , . , , . , , ( ), , , . , ARPANET , . To ARPANET 1971 , ,

4.

5.

10

Defense Advanced Research Projects Agency - DARPA.47

. .

ARPANET, 1974 TCP/IP . , . , , , , . 1982 TCP/IP , . TCP/IP ARPANET . ARPANET , . , MILNET , ARPANET . ARPANET , , (Internet).

7.2.2 OSI TCP/IP1. OSI TCP/IP. ; OSI TCP/IP.

48

. &

OSI 7 TCP/IP 4. 2. TCP/IP; TCP/IP , , , , . 3. SI TCP/IP ; . 4. SI TCP/IP; TCP/IP ) ) OSI. 5. SI TCP/IP; TCP/IP ) ) ) OSI. 6. TCP/IP , .

7. , TCP/IP. (IP) M E (Internet Control Message Protocol - ICMP). 8. , TCP/IP. (Transfer Control Protocol - TCP) (User Datagram Protocol UDP). 9. TCP/IP. ; , TCP/IP, (Telnet), (File Transfer, FTP), (Simple Mail Transfer Protocol, SMTP), (Trivial File Transfer Protocol TFTP). , Telnet, FTP SMTP TCP, TFTP UDP. 10. . . .

49

(, , , ). .

11. . TCP UDP. (. IP) . IP : o . o , ( MAC (Media Access Control) OSI). : (ARP Address Resolution Protocol) (RARP) (Reverse Address Resolution Protocol). IP, , (ICMP- Internet Control Message Protocol). To (ICMP ) : o . o ( ), TCP/IP . .. , ICMP, : . 12. IP; ; 11. 13. ICMP ; . 11. 14. . . TCP UDP. To TCP , , : o : TCP . TCP,

50

. &

. o : TCP . o : . (UDP-User Datagram-Protocol) o 11. o . o , ( TCP) .

15. ; ; 14, . TCP. 16. TCP; 14, . 17. UDP; 14, . 18. . : , . , . TCP/IP. 19. TCP/IP; . TCP (client server). , , . .

, ( ) . UDP, ICMP, IPX, NetBEUI .51

11

, . , .

7.2.3 TCP/IP 1. - TCP/IP. , . , . . 2. ; . 3. ; , : . / , . : . . . . TCP IP. [ TCP IP ]. 4. TCP/IP; TCP/IP : ( ). ( TCP ). ( IP, ). , ( .. Ethernet).

52

. &

5. ; ; (Internet IP ). . 6. (), ; , IP . 7. TCP/IP ; . 8. TCP/IP; , . 9. TCP; 15.000 byte. . : , .. 30 500 byte. . , . . 14 . 13. , TCP. 10. ) , , ; ) ; ) ) TCP/IP. 11. , .

53

1. , . 2. , . 3. [ ]. 4. , . 5. , . , . 6. , . 7. , . 8. , . 9. .

7.3 TCP1. TCP; (Transmission Control Protocol, TCP) TCP/IP. . . TCP . , . , (segment). TCP , TCP .54 . &

, , TCP . TCP , TCP IP, .

2. (segment) TCP ;

, TCP , (segment). (), TCP . TCP . 3. , (segment) ; To TCP. 4. TCP ; , E TCP . 3, . 5. - , ) ) ; ) TCP. ) . 6. TCP ; . 7. ; , , . , , . 8. ; . : 55

, , , . 12. , 1501 13 1500. , . 9. TCP ; TCP, . , . . , . . , . . 10. 1000 12000. . 12000 1000, 12001 13000 . 11. ; . TCP, , . . () TCP port . . TCP TCP (TCP port) .

, (Acknowledgement Number) 32 bit, TCP. 1 , . 13 . 234 1500. 1501. .. , () , .

12

56

. &

, TCP port 1002 TCP port 1003 . , . 12. CP ; ; TCP , 16 bit TCP . TCP TCP (TCP port) . , TCP port , . TCP port . TCP port, . TCP port : TCP port . , , (File Transfer Protocol, FTP) TCP port 21. , TCP port 21. O FTP , TCP port 21 .

7.3.1 TCP 1. TCP ; . ( 7.3.1 1 ). 2. TCP; O TCP , TCP . , ( ).

57

, , , . , ( , IP ) , . TCP , . 3. TCP (FTP) . FTP. FTP ( ) FTP . , FTP ( ), TCP port (.. 1234) TCP port 21, FTP . : o ) FTP ( ). . o ) , . TCP port 21. 4. TCP , ; ( : TCP ;) TCP : . TCP port . 5. , TCP , . , ; , IP58 . &

. , FTP, ( ) TCP port 21. TCP port ( ), .

7.4 UDP1. UDP; ; UDP = User Datagram Protocol . UDP . 2. UDP; . UDP : . . : . () . 3. TCP UDP.

TCP . UDP

UDP , . TCP 59

. 14

. .

4. UDP; UDP (UDP port) 16 bit, UDP . UDP UDP . UDP, UDP port. UDP port , . UDP port UDP , TCP port. 5. UDP port, ; TCP port, UDP port, . UDP port, , , , , . , (Simple Network Management Protocol, SNMP), , UDP port 161. 6. UDP ; UDP TCP. , 15 .

7. IP , UDP, UDP; ; , UDP 16, UDP. .

TCP .. 3 1. . . 15 UDP port . port 16 bit. 16 7.5.60 . &

14

7.5 IP1. TCP/IP IP; IP TCP/IP. 2. IP; IP (datagrams), , . TCP. 3. (TCP, UDP) IP; . 4. IP ; ; TCP UDP IP . 64Kbyte.

5. (64 Kbyte); , 61

. (fragment). . 6. ; ; , , , , , , . , , , . IP , , IP ( 4). , , . 7. IP, , ; [ : MF IP ;] IP (More Fragments, MF). MF 1, , . , , 17, MF 1. 8. , ; , (Don't Fragment, DF) 1. 1 DF , . , , , , . , . 9. IP , , , , ; . 18. 10. IP;

17 18

0. .62 . &

IP , ( , ). 11. IP; H IP , . , , , . 12. IP; IP , ( TCP UDP). , , IP , . 13. IP; IP . , , , , . 14. IP; , IP, . , 19. 15. IP; 32-bit. , , 5. . 16. IP; 32 bit, , 32 bit. 17. IP; . 18. IP; ( ). 65.536 byte (64 Kbyte = 64 * 1.024 byte = 65.536 byte). , , . 19. IP;19

IPv4 IPv6.63

, , . , , IP, : , . 20. IP; , , . , . , . , , , . 21. -. ) , IP 1.400 byte , 20 byte. , 620 byte. . (fragment) , MF, . - . ) , : 2, 1, 3. . ) DF , , DF , 0. . . IP 1420byte (1400byte + 20byte ) 620byte, : o 1 : 620 byte (600 byte + 20 byte ). o 2 : 620 byte (600 byte + 20 byte ). o 3 : 220 byte (200 byte + 20 byte ).

64

. &

MF, , . MF 1, , 0. .. 100, . ( ) 0 ( ), 75 (600/8=75, 2 75 1) 3 150 (1200/8, 3 150 1 2 ). , DF,MF, , , , : =100 1 DF=0 MF=1 =0 =100 2 DF=0 MF=1 =75 =100 3 DF=0 MF=0 =150

(fragment) ( 32 bit). = 20 byte = 160 bit 32 bit, , , 160/32 = 5 . 20 byte 5 . ( ) 0 . , . . . , 1. ( .. MF).

. . . . . . . .

65

) 2, 1, 3, :

2 . =100. MF = 1 . 20=75 . 2 (buffer) . 1 . =100. . MF = 1 . =0 . 1 (buffer) / /. 3 . =100. . MF = 0 . =150 . .

7.6 1. TCP/IP, ) ) ) ; ) , . ) . ) . , , , .

7.6.1 (Media Access Control, MAC )1. , , ;20

.66 . &

, (hardware address) MAC.2. MAC ; MAC , . MAC ( ) Ethernet 48bit. 3. OSI MAC, ; OSI, MAC 21 . MAC . MAC , , . OSI , , . 4. ; (Institute of Electrical and Electronic Engineers, IEEE). IEEE (Organization Unique Identifier - OUI), 24 bits, 24 bits , . 5. ; . :

48 bit. 24 bit OUI (Organization Unique Identifier). bit ((/G)) (0, 1 ). 1, , . bit OUI 1, , ).

21

.67

bit (U/L) . 0, IEEE, 1, . O , , , , IEEE, . , , , , IEEE. 22 bits , IEEE . 24 bits , . , (OUI) IEEE, , Ethernet, , , (24 bits ) . , , (OUI).

7.6.2 1. 22 bit; () 23 . , , . 32 bit 24. 2. ; ; . IP , ( ). , , . 3. ; . O IP , . . .

22 23

4. , , . 24 12. 32 bit 4 8 bit (=1byte) 4 . : 00010110.00100011.00000010.00000101, 22.35.2.5 , 22.35.2 3 ( 7-17 ).68 . &

, : 22. : 35, 45 55. , (1,2,3 4). , . 4. ; , 32 bit , ; , 187.164.72.38. 8bit. , 48=32, 32 bit. : , :

, . () , 32it , 3 8 =24bit 1 8 = 8 bit . 5. , TCP/IP ; IP (Network Information Center, NIC). TCP/IP , , , NIC . , , , . ,

69

. 6. ; () , , B, C, D 25, . 7. A,B,C,D; bit . , , 0, 10, C 110 D 1110, , 1111 .

8. . . 7 bit , 27 =128 26 24 bit , 16 27. 9. . . 14bit 16.384 (=214) . 16 bit, 65535 (=216) . 10. C. C 21bit , 2 (221 = 2097152). 8 bit 28 = 256 . 11. D. O D (multicast), , . 12. ; . IP 8 bit, . , IP ... ... C ( , 25 26

. 7 2 2 =126 0 128 . 27 24 2 -2= 16.777.214 .70 . &

, ). , IP , 147.10.13.28, , , 147.10 13.28.

7.6.3 1. ; , , bits . 2. ;

128.6.. . , , .. Ethernet, ( , ). . (, 128.6.. , . , , , , 128.6.4. 128.6.5.). , ( ), , 128.6.4, , 128.6.5. , 128.6.4 128.6.5 . , , , 128.6... 3. C , ; ; C, ..., , ( ).71

, , . , . , , . , . . 4. (subnet mask); . 32 bit , AND. 5. 192.168.123.132 255.255.255.0. . : 11000000.10101000.01111011.10000100 : 11111111.11111111.11111111.00000000 AND ------------------------------------------------------11000000.10101000.01111011.00000000 : 192.168.123.0 : 00000000.00000000.00000000.10000100 0.0.0.132 6. 255.255.192.0 208.85.90.172. . AND. :

: 208.85.64.0 7. 208.85.64.. ; , bit 1. byte, 11111111 ( =255 ). : 208.85.64.255. 8. 147.10.0.0. ;72 . &

, : 147.10.255.255. 9. 255.255.255.255; 255.255.255.255 . 10. CIDR ( 28 -). ; CIDR , . , ( ) . O . , 207.13.01.48/25 /25 , 25 bits 7 . CIDR (Internet Service Providers - ISPs), , . , , ISP. , / , ISP.

7.7 ARP1. ARP; , , . ARP 29 . 2. ARP; ARP IP , . ARP , IP , . . .

ARP IP , ARP , , .28 29

, , . .73

, . , , , ARP . o ARP IP . IP IP , ARP . o H . , ARP , ARP , . , IP ARP. 3. ARP , ARP; ARP ARP , , , ARP . . ARP ARP , . , . O ARP , IP (.. Ethernet) , . 4. (Reserve Address Resolution Protocol RARP); (RARP) ARP. , , IP . RARP , , RARP . 5. ARP. , 128.6.4.194 128.6.4.7. , , , 128.6.4.7 128.6.4.194, (.. Ethernet). , ARP , 128.6.4.7, Ethernet . , Ethernet Ethernet . 128.6.4.7 APR , Ethernet 128.6.4.7 . , ARP, ARP . ARP : Ethernet 128.6.4.7. , , ARP .74 . &

IP , . , 128.6.4.7 , IP ARP : 128.6.4.7 8:0:20:1:56:34. (, Ethernet 48 bits, 6 ). , ARP , , ARP , , .

6. ARP. , (TELNET), TCP, TCP IP. IP TCP IP. TCP IP , IP IP , Ethernet, . , Ethernet . Ethernet ARP . , ARP IP . ARP : IP 223.1.2.2. IP , Ethernet . ARP ARP IP . IP , Ethernet . ARP : IP , Ethernet . ARP ARP . , . ARP IP Ethernet ARP . ARP . , IP , , . IP Ethernet ARP , Ethernet .

75

7. ARP, . ARP . IP . ARP ARP . IP Ethernet ARP . IP , Ethernet . ARP , , , ARP IP IP , .

8. ARP ; ARP , ARP , .

7.8 (Domain Name System DNS)1. , ; ( ) . , IP , . , , , , . 2. , ; . , ( ) , . 3. , () ; , . , . , . 4. . ) ) ; . .

76

. &

5. , ; , . , , . 6. ;

, , , . :

7. / / ; . , . ASCII . , . . O , , ( ) , , . 8. (Domain Name System DNS) ; (Domain Name System DNS) . DNS

77

30. , , . , . , , , .

, DNS (name server), , ( ). 9. (DNS server); , . () , . . , (). ( ) . , . DNS . ( ) .

7.8.1 DNS1. DNS; DNS , , . , :

30

.. .. () , .78 . &

. , , , : .arpa: .com: .edu: .gov: .mil: .net: .org: , , , ( ). , , . .gr .ca. , , . domain . , (domain names), , , . domain names . , ntua.gr domain name ntua , ... (National Technical University of Athens - NTUA).

79

, domain name, . . , subdomain. , domain names . , telecom.ntua.gr .gr, domain name ... ntua.gr, subdomain. To telecom.ntua.gr , ..., , . ektor telecom, , ntua ... . gr .

2. ektor.telecom.ntua.gr; ektor, telecom, , ntua ... .gr .

7.9 1. . ; . .80 . &

2. ; ; , , , , . , , , ( ). , . , , . 3. ; : . ( , , , ). . ( , , ). 4. ; , OSI TCP/IP ( ). , . 5. ; ; : 1. . 2. , . . 6. ; . 7. ; ;

81

, , , , . . , , . , , . . , . , . . , , . . , , , . 8. , ) ) . ) ) , . 9. . : . , . . (Central Processing Unit, CPU), . : ( ). , . 10. . , , . . . . , , , , 82 . &

. . 11. . , : (), , ( ), . , . . , : , , .

7.9.1 TCP/IP1. (host) ; (host) , . , , . 2. ; , ( ) . , . . 3. ; . IP , , IP . 4. ; . , , , . , , . , . , , . , . , , . 5. ;83

, , , . () . , , , . . , , . , , , , . , . , , (), . , , , : . ICMP. , . 6. , . () () () , , . () , () , () 7. ; ICMP. 8. , . , 128.6.4, , : 128.6.4.59 128.6.4.1. 128.6.4.59 , . 128.6.4.1 . 128.6.4.59 . . - , 128.6.4.59. 84 . &

-

-

, 128.6.4.1. , , 128.6.4.1 ( ICMP). IP . , , 128.6.4.1.

7.9.2 1. , :

IP , IP , IP . Ethernet , , Ethernet Ethernet . :

85

IP IP , IP , . , . . 2. , ; , IP , Ethernet. , IP , , IP .

7.9.3 1. TCP/IP , Ethernet. .

, TCP/IP Ethernet , . , TCP /IP , . . , ) () () ) Ethernet () ().

86

. &

, , , , Ethernet .

7.9.4 1. IP , , IP . To IP , . IP . . : IP, , IP . IP . , IP , , . 2. ) ) 31:

31

. Ethernet . 3 3 Ethernet , .87

) : IP IP (223.1.2.2). To IP IP , (223.1.2) . , , .

. ARP IP Ethernet , Ethernet .

) . IP (223.1.3.2). To IP IP (223.1.3). , , , .

88

. &

. , 223.1.3 . ARP , IP Ethernet , Ethernet 1 ( ). , IP IP IP . Ethernet 1 ( ) IP . IP IP , , IP , .

To IP IP ( ) , (223.1.3) ( ) , . , . IP IP 3. , , IP , . Ethernet . Ethernet 3, IP . IP IP , , .

7.11 7.11.1 1. , .. , ; ; , : . . . . . 2. TCP, ;89

TCP , . , ( ) . 3. , . , : (ASCII, EBCDIC). . . , .

7.11.2 1. ; (e-mail) , / . , , , . , , . 2. , ; . . , . , , , . 3. . . . , Los Angeles , Los Angeles . , FAX . , , , .

90

. &

. , ( ) . , . . 4. ; , . 5. ; . 6. , (Simple Mail Transfer Protocol SMTP). SMTP TCP/IP( 7 OSI ). ( ) 32 (.. Outlook, Eudora, ) . ( - Send ), e-mail (.. net, Forthnet, Hol, ). (mail server) . , . (DNS Server) . SMTP TCP , TCP port 25. SMTP . TCP , , , . , . , , . , , . . , SMTP 33. User Agent UA. , POP3 / ( ), .33 32

91

:

(File Transfer Protocol, FTP)7. FTP; . To (File Transfer Protocol, FTP) , TCP/IP. , TCP. FTP . , , , . , . . , . FTP , . , FTP . , , . 8. .

92

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FTP: FTP , , FTP . FTP : ) - TCP port 21 - . , , , XX, . ) , . TCP port 20 34. , . , . 9. FTP, ; ; , FTP, (Trivial File Transfer Protocol, TFTP). TFTP: . . . ( ) UDP.

(Telecommunications Network, Telnet)10. Telnet ; Telnet , , . , , . , , -

34

(active) FTP . (passive) , .93

.

. , , . . Telnet ( FTP SMTP) . Telnet , , . Telnet TCP port 23. , .

11. ; , , . , . Telnet , . 12. Telnet; Telnet, , . Telnet ( FTP) , . , . , , , . , . (.. 94 . &

) , .

(World Wide Web)13. (World Wide Web); (World Wide Web, WWW Web) , . . (hypermedia), , , , , (video) . (links), , .

14. ; , , . , , . . , . (link).

95

, . , , , . 35 (highlighted) , . (highlighted) () . 15. / (browser); , - (browser). , , . 16. (hypermedia) (hypertext); , : , , , (hypermedia). , . 17. ; , , (HyperText Transfer Protocol, HTTP), -. 18. ; (Web servers) , , . , . 19. (Web Clients); (Web clients) . . : Mozilla Firefox, Microsoft Internet Explorer, Apple Safari Netscape Navigator, Netscape Communicator, Microsoft Internet Explorer 36. 20. ; (Web site). , . . (Internet Service Providers, ISPs). , .35

, . 36 Mosaic, .96 . &

21. , ; , (WWW) , . (WWW , .. www.ntua.gr ), . (Web site) (Home page) (WWW ). 22. ; ; , . , . Google Yahoo Alta Vista, Lycos, Excite, Infoseek, .. 23. ; . 130 Web sites 1993, 1994 10.000, 1996 100.000 1997 650.000. 1994 6 % , 1995 24 %. 5 1996 22 2000. , 1 700 . .

24. WAP; WAP , , . 25. WAP; : . . (e-mail). . , . .

TCP/IP (Intranet)26. TCP/IP (Intranet); TCP/IP (Intranet) . Intranet . , intranet Internet . , , . intranet , 97

, , , , . 27. Intranet; , intranet : . Web. . 28. intranet. , ( WWW clients, browsers), . .

(VoIP)29. 37; , . 38, : , , , , . , , . : , , ( ), . , , , , , .

30. video ; video , ( ).37

38

. : ) Skype: . messenger / ( usb ) . ) VoIP Buster: Skype PC PC . ) Teamspeak: Voice over IP, . online .

98

. &

, video , , , . 31. / video ; video , , . , , . , , , . MPEG1 MPEG2 MPEG4 H.323. 32. ; , . , , . . 33. ; : : . . . . . . . : .323, CU-SeeMe NetMeeting .

34. ; , . , , . , , . () , . ,

99

TCP/IP , . 35. ; . , , . , , , . , , , . , , . 36. IRC (IRC clients). mIRC. - , ViRC, leafChat, Klient , Win Talk, irk ii .

37. ; ; , . , , , . , , , fax. , . (Electronic Data Interchange - EDI), e-mail. 38. ; (Web Site) , . , (e-mail), ( ) . , , . , , . , . 39. ; , , , , , , CD, , , , , ..100 . &

40. , ; , .

8 8.1 1. OSI ; OSI, : (configuration management), (performance management), (fault management), (accounting management) , (security management).

8.1.1 (Configuration Management)1. ; , , , ,

. 2. OSI; , , OSI .

101

, (, ) . ' , . 3. ; ; , : (. , , ...). . . , o (inventory database) , . 4. ; ; , , (switches), , (hubs), ( ethernet, token ring ..), wan . , , , , . , .

8.1.2 (Performance Management)1. ; , : WAN .. IP, IPX, Netbios .. . (alarm). 2. ; . . . , , , .

8.1.3 (Fault Management)1. ; / , , , . . &

102

( , , ...) , , . , , . O , , , . . 2. ; (alarm) (log) / . ; . , , .

3.

8.1.4 (Accounting Management)1. ; , , , , .

8.1.5 (Security Management)1. ; , , , .

, . , , , . 2. ; : , , , .103

8.3 8.3.1 1. ; , , . 2. ; , , . , . 3. , , , . (authentication): . (integrity): H . (confidentiality): O . (non repudiation): . 4. (validity); (validity) . . 5. ; (information availability): . 6. , . (security): , . (information security): , . (vilatin) , , , . 7. ; . . O . , ( ). O (.. ) , . , . O , (.. ). 8. ;104 . &

. , . o , , , . , , , , . .

8.3.2 1. (encryption); . , (). . 2. (decryption); . , . 3. (key) ; bit, . 4. (public key). , / . . 5. (private key). , / . , . 6. (secret key). , , / . 7. (hash function); , . 8. (message digest); . 9. (digital signature); bit, .

105

8.3.3 1. ; ( , ...), . , .

2. . : o oo

o o

(Passwrd attacks). (Network Monitoring Network Packet Sniffing) (Masquerade) (Denial of Service) (Application-Layer Attacks)

3. password ; ; password : - password, . - password . passwrd . , Unix Windws, passwrd. 4. passwrd, ; . (, ). 5. password . , : , . (keystroke mnitring), o , , o ( ). scial engineering, . . passwrd, . , password crack, .

106

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6. social engineering; scial engineering, . , , (help desk) passwrd , . shulder surfing, passwrd .

7. crack ; crack , password . password , passwords. crack Unix . 8. (packet sniffing); H . (clear text), . , , , . (packet sniffing). packet sniffers , . 9. (packet sniffer); , (packet sniffing), promiscuous mode. , , . 10. ;

107

! . . , , password. password. 11. (masquerade) spoofing ; IP spoofing . . firewall , (trusted). IP Spoofing , client / server . , , , (spoofed IP address). spoofed IP . , passwrd. , , e-mail. 12. (DoS Denial of Service). , , , (.. web server, mail server). , (, , ) . . , , . 13. ; (Application Layer attack); HTTP, ActiveX, Telnet, Ftp, ..., , . , , .

8.3.4 1. . . . .

108

. &

, : . .

/ :

, Caesar Cipher.

, (Caesar Cipher 39) . , , , . . 2. ; , , . , , , , . , . , , , .

39

.109

, , , , , . 3. ; (Data Encryption Standard, DES), 3DES (triple DES) , (International Data Encryption Algorithm, IDEA). 64 bits. , 64 bits. 4. ; . , . , , . , Diffie Hellman. 5. . ( ) , . . : - . - .

110

. &

, , / . , . . ( , ). , , , , , . , . . , . . , . 6. ; . , , , (smartcard). 7. . RSA (Rivest, Shamir, Adelman) ElGamal. 8. ; ; ; () , . . ) (hash algorithm) ) . () ( ) . :

111

. (1) (message digest). (message digest) (2). . (3). , , . , : (1). , (2). , (message digest) (3). , (4). (5).

112

. &

(message digest) , , ( ) , message digest .

9. ; ! , () , ( ). () ( ). 10. . : Message Digest 4(MD4), Message Digest 5(MD5) Secure Hash Algorithm (SHA).

113

8.3.5 1. . : passwords passwords . SSL / SSH / SOCKS - Radius / Tacacs - . PAP / CHAP - Single Sign On - . , password. - . IPSec (IP Security) - Internet Protocol Security . OSI . IPSec VPN . IPSec : - , . - ESP (Encapsulation Security Protocol), . 2. (firewall). Firewall / , ( ) , . Internet / , . / Firewall, .

firewall, 114 . &

, , , . , firewall. 3. , , . , , , , , , . , , . , , . 4. , . .. IP , HTTP. .. telnet, ftp, tftp rtagin .. . TCP/IP . , , TCP IP . 5. ; . , firewall. .

8.3.6 1. ; : ) 40 41 . ) , . 2. ; : (. , ).4041

, , . .. .115

(. bugs) (. , ) (. , ).

3. ; , , , , , . , , . , . 4. (Recovery), (Continuity Plan), (Information back up). (Recovery) . (Continuity Plan) , . oo (Information back up) - , , . , , . , , , . , , , . 5. ; , , . , , . , , client - server. , (main site) . site, . site , site. , site switches, routers LAN. , (.. back up).

116

. &

117

118

. &

1. ( 242 . .7-14), 4 bit / 4 bit. 8 bit: 01000011.. . ; bit , . 4 bit , , 3. 5 (. . .244). . 2. 0101 0000000000110010. byte . 5, , 5 x 4 = 20byte. 50. 50byte 20byte = 30byte . 3. . MF 0. ; , ; MF. , , MF 0. , MF=0. 4. . MF 1. ; , ; MF 1, ) ) MF 1. . . 5. . MF 1 0 ; , ; MF 1 . , MF 0, . 0 . 6. 5140 byte 20 byte , 1500byte. 100 DF, MF 0. , , DF, MF .119

20 byte, 5120 byte. 1500 byte, , 1480 byte. 5120 byte 3 1480 byte 680 byte. 0. 1480 / 8 = 185. 2960 / 8 = 370. 4440 / 8 = 555. . DF MF

1 2 3 4

100 100 100 100

1500 1500 1500 700

0 0 0 0

1 1 1 0

0 185 370 555

1. ( ) ; . . . 2. ( ) ; . ( ) Ethernet, ( ) . 3. (bit); byte; . 0 1. bit. To byte . byte 10010110, 11100011, 00001111 00000000 11111111. 4. ) 1 bit ) bit ) 3 bit ) 4 bit. ; ) 1 bit : 0, 1 21=2 ) 2 bit : 00, 01, 10, 11 22=4 ) 3 bit : 000, 001, 010, 011, 100, 101, 110, 111 23=8 ) 4 bit : 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111 1000, 1001, 1010, 1011, 1100, 1100, 1110, 1111 24=16120 . &

: bit 2 . 5. bit 4; 32 bit. 6. bit, 4, () ; 32 bit, () : 232= 4.294.967.296, 4 . , . 7. ) ) . 32 (byte), 4 byte. , byte . , ) 11001101.10001110.00010011.11100111 ) : 205.142.19.231 8. 10000001.11011011.11111111.00001111 . , . 10000001.11011011.11111111.00001111 129. 219.255.15 9. 193.11.139.155 . . 193.11.139.155

11000001.00001011. 10001011. 10011011 10. : ) 142.013.65.87 ) 156.17.20.5.7 ) 221.14.301.56 )19.178.00001111.9 ) , . ) . ) 255.121

) . 11. , ; , ( ). (. . 250 .251, 7-19). , 0, 10, C 110 D 1110. 12. : ) 10100011.11100011.10111000.11110110 ) 00000011.11110000.10101010.01101111 ) 11100011.11011011.10111000.11100111 )11010000.10101010.11110000.00001111 ) 10 . ) 0 . ) 1110, D. ) 110, C. 13. , , . [: A,B,C,D . 1 ] 42.

. 250, , : ( ).122 . &

42

14. , ; , , 1 byte. , byte : 0 127 ( 00000000 011111111) / . 128 191( 10000000 10111111) / . 192 223 ( 11000000 11011111) / C. 224 239 ( 11100000 11101111) / D. 15. : ) 132.17.87.65 ) 226.13.15.78 )17.28.132.8 )194.18.65.32 : ) ) D ) ) C 1 byte , 13: ) 132 10000100 . ) 226 11100010 D. ) 17 00010001 . )194 11000010 C. 16. , ) ) ) C ) D; , ( 1). : : 01111111.11111111.11111111.11111111 2.147.483.647 : 00000000.00000000.00000000.00000000 0 = 2.147.483.647 0 + 1 = 2.147.483.648 : 10111111.11111111.11111111.11111111 3.221.225.471 : 10000000.00000000.00000000.00000000 2.147.483.648 : 3.221.225.471 - 2.147.483.648 + 1 = 1.073.741.824

123

C : 11011111.11111111.11111111.11111111 3.758.096.383 : 11000000.00000000.00000000.00000000 3.221.225.472 : 3.758.096.383 - 3.221.225.472 + 1 = 536.870.912 D : 11101111.11111111.11111111.11111111 4.026.531.839 : 11100000.00000000.00000000.00000000 3.758.096.384 : 4.026.531.839 - 3.758.096.384 + 1 = 268.435.456 17. 4 , , C D; . 4 : : 11111111.11111111.11111111.11111111 4.294.967.295 : 00000000.00000000.00000000.00000000 0 = 4294967295 0 + 1 = 4.294.967.296 = = C= D= = 12,5% = 6,25%

50% . . 18. 74. ; ; 74 . 74.0.0.0 74.255.255.255. byte . 224=16777216 . 24 3 byte . ( , . = 16777215 0 + 1 = 16777216).

124

. &

. 19. 178.6. ; ; 178.6 . 178.6.0.0 178.6.255.255. 216=65536. , . 20. C. C 192 223. C 192.0.0.0 223.255.255.255. 21. 143.54.78.2. . (143) . 143.54 78.2. 22. 219.54.17.255, C. ;

219.54.17.255 C , 255 (=11111111). bit 1, . 23. . ; ;

125

, 255.255.255.255 (32 ). bit 1, ,,C,D. [ ]. 24. : ) 112.43.8.2 ) 130.65.6.8 ) 208.43.54.12 ) 112 43.8.2 ) 130.65 6.8. ) C 208.43.54 12. 25. 104.17.22.44 . . 104. : : 104.17.22.44 : 104.255.255.255

1. (/n) ) 255.0.0.0 )255.255.0.0 )255.255.255.0 )255.255.240.0 )255.252.0.0 )/8 )/16 )/24 )/20 )/14 2. 196.174.14.0, 4 . ( .251 -254 . ). ) . ) . ) . ) , . ) , 196.174.14.0,

126

. &

. , . bit . 196.174.14.0 C, 255.255.255.0. ( : 11111111.11111111.11111111.00000000), , . 4 (=22) , 2 ( ). , 00, 01, 10, 11. , 24+2=26 8-2=6 . x =2 ( x ).

(y-x) ( y , / = 2).

, 2, 4 y 8 26=64 43.

43

/ . , , 0 ( ) 1 ( ). / 2(y-x)

-2.

127

) C 255.255.255.0 ( 11111111.11111111.11111111.00000000). , bit , . 11111111.11111111.111111111.11000000, 255.255.255.192. ) , byte . byte. , 1 4 byte 00000000 196.174.14.0. 2 4 byte 01000000 196.174.14.64. 3 4 byte 10000000 196.174.14.128. 4 4 byte 11000000 196.174.14.192. ) 1 bit (. . 253, ). : 1 , byte 00111111 63, 196.174.14.63. 2 , byte 01111111 127, 196.174.14.127. 3 , byte 10111111 191, 196.174.14.191.

128

. &

4 , byte 11111111 255, 196.174.14.255. 3. 25.0.0.0. 8 . ) ) / ) 8 ) . ) , 255.0.0.0 ( 11111111.00000000.00000000.00000000). 8 (=23) 3 000, 001,010,011,100,101,110,111 . 11111111.11100000.00000000.00000000 255.224.0.0. ) / , 2(24-3)2=221 2 = 2.097.150. ) : / / 1 00011001.00000000.00000000.00000000 25.0.0.0 2 00011001.00100000.00000000.00000000 25.32.0.0 3 00011001.01000000.00000000.00000000 25.64.0.0 4 00011001.01100000.00000000.00000000 25.96.0.0 5 00011001.10000000.00000000.00000000 25.128.0.0 6 00011001.10100000.00000000.00000000 25.160.0.0 7 00011001.11000000.00000000.00000000 25.192.0.0 8 00011001.11100000.00000000.00000000 25.224.0.0 ) : / 1 00011001.00011111.11111111.11111111 2 00011001.00111111.11111111.11111111 3 00011001.01011111.11111111.11111111 4 00011001.01111111.11111111.11111111 5 00011001.10011111.11111111.11111111 6 00011001.10111111.11111111.11111111 7 00011001.11011111.11111111.11111111 8 00011001.11111111.11111111.11111111

/ 25.31.255.255 25.63. 255.255 25.95. 255.255 25.127. 255.255 25.159. 255.255 25.191. 255.255 25.223. 255.255 25.255. 255.255

4. . 138.112.80.24/20. ( ), 44 . ) 20, 1 . AND ( ) ,

44

.129

AND

(/ ) /

10001010.01110000.01010100.00011000 11111111.11111111.11110000.00000000 10001010.01110000.01010000.00000000 138.112.80.0

, 138.112.80.0. ) 12 , 212= 4096. ) : 10001010.01110000.01011111.11111111 138.112.95.255 5. . 1, . , 0, 0. , 1 0, 1. , : . 1 0. , 20, 2 1, 1 ( 20) 0. 0. 1, byte . , 1 byte , 138 112 . 0, byte 0. , 0, byte 0. , 1 1. , 1 0, ( 0101) 0. byte 01010000 80. , 1, 2, 4 byte 3 byte. 6. ) 2 ) 6 ) 28 )62 ) 120 ; , 2. .. , 21=2 .

130

. &

2, 2 . , 6 , 3 . , 23=8 , 2 , 22=4 . , : ) 2 1 ) 6 >> >> 3 )28 >> >> 5 >> ) 62 >> >> 6 >> )120 >> >> 7 >> 7. , , 32.0.0.0/8. 500 . ) . ) ; ) ; ) ; ) 8 11111111.00000000.00000000.00000000. 500 < 512 (=29), 9 . : 11111111.11111111.10000000.00000000 /17. ) 32-17 = 15 , 215= 32768 . ) 32.0.0.0 17 (32 0), 0 ( 0) 0. : 32.0.0.0. ( : 00100000.00000000.00000000.00000000. ). , 1, 00100000.00000000.01111111.11111111. 32.0.127.255. ) 500 ( 0 499), 499 ( 111110011 ->(! )). 499 00100000.11111001.10000000.00000000 32.249.128.0 00100000.11111001.11111111.11111111 32.249.255.255. 8. C, 6 .131

C, 255.255.255.0 11111111.11111111.11111111.00000000. , : 11111111.11111111.11111111.11111100. , 22=4. , ( 0 1) .

1. , .

132

. &

2. Caesar Cipher 3, : 8-12 . 321 , . , , , . :

133

134

. &

6 7 ( 7.3.1 (.240)) 7.4 7.6.2 (.251) 7.6.3 7.7 (.259) 7.8 7.9.1 (.269) 7.9.2 8.1.5 (.303) 8.3 8.3.6 (. 330)

135

136

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