ΔΙΚΤΥΟ ΥΠΟΛΟΓΙΣΤΩΝ ΙΙ.

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Δίκτυα Υπολογιστών II – Το Ανεπίσημο Βοήθημα Μανώλης Κιαγιάς, MSc 07/12/2010
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ΔΙΚΤΥΟ ΥΠΟΛΟΓΙΣΤΩΝ ΙΙ.

Transcript of ΔΙΚΤΥΟ ΥΠΟΛΟΓΙΣΤΩΝ ΙΙ.

II , MSc 07/12/2010

ii :

2 , 07/12/2010 [ Web Edition ] Copyright 2009 2010 :

3.0 : http://creativecommons.org/licenses/by-nc-sa/3.0/gr/

: , ,

: ( ). . , , .

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: . , : , , . , . , : http://creativecommons.org/licenses/by-nc-sa/3.0/gr/

a XELTEX. mercurial repository. : http://diktia.chania-lug.gr mirror site: http://www.freebsdworld.gr/diktia/theBookII.pdf

iv ( )

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, . , Richard Bach

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II . 20102011. , , . , , . Creative Commons .

(2004) , , . . , , . , , . . , , . . , . , Buter , . , .

viii

I 6 6.1 . . . . . . 6.2 6.5 ISDN . . . . . . . . . . . . . . . . 6.8 xDSL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13 3 4 6 11 17 17 17 22 22 25 27 28 29 30 31 36 42 45 48 55 56 57 62 64 67

7 Internet 7.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1.1 . . . . . . . . . . . . . . . . . . . . . . . . 7.2 TCP/IP . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.1 TCP/IP . . . . . . . . . . . . . 7.2.2 OSI TCP/IP . . . . . . . . . . . . . . . . . . . 7.2.2.1 . . . . . . . . . . 7.2.2.2 . . . . . . . . . . . . . . . . . 7.2.2.3 . . . . . . . . . . . . . . . 7.2.2.4 . . . . . . . . . . . . . . . 7.2.3 TCP/IP . . . . . . . . . . . . . . . . . . . . . . . . 7.3 TCP . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 TCP . . . . . . . . . . . . . . . . . . . . . . . 7.4 UDP . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 IP . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.1 (Media Access Control, MAC) . . . . . . . . . . . . . . . . . 7.6.2 IP . . . . . . . . . . . . . . . . . . . . . . . 7.6.3 . . . . . . . . . . . . . 7.6.3.1 . . . . . . . . . . . . . . . 7.7 ARP . . . . . . . . . . . . . . . . . . . . . . . . . .

x 7.8

, Domain Name System (DNS) 7.8.1 DNS . . . . . . . . . . . . . . 7.9 . . . . . . . . . . . . . . . . . . . . . . . . . 7.9.1 TCP/IP . . . . . . . . . . . 7.9.2 . . . . . . . . . . . . . . . . . 7.9.3 . . . . . . . . . . . . . . . . 7.9.4 . . . . . . . . . . . . . . . . 7.11 . . . . . . . . . . . . . . . . . . . 7.11.1 . . . . . . . . . . . . . . . . . . . . . 7.11.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 78 81 85 89 90 92 96 96 98

8 117 8.1 . . . . . . . . . . . . . . . . . . . . . . . . . 118 8.1.1 (Configuration Management) . . . 118 8.1.2 (Performance Management)120 8.1.3 (Fault Management) . . . . . . . . 121 8.1.4 (Accounting Management) . . . . . . 123 8.1.5 (Security Management) . . . . . . . 123 8.3 . . . . . . . . . . . . . . . . . . . . . . . . . 123 8.3.1 . . . . . . . . . . . . . . . . . . 124 8.3.2 . . . . . . . . . . . . . . . . . . . 127 8.3.3 . . . . . . . . . . . . . . . . . . . . 129 8.3.4 . . . . . . . . . . . . . . . . . . . . . 133 8.3.4.1 . . . . . . . . . . . . . . 138 8.3.5 . . . . . . . . . . . . . . . . . . . 140 8.3.6 . . . . . . . . . . . . . . . . . . . 142

II

145147

6.1 6.2 6.3 6.4 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 PSTN . . . . . . . . . . . . . ISDN . . . . . . . . ISDN . . . . . . . . . . . . . . . . . . . . . . . SDSL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 9 10 13 18 19 21 26 26 31 32 33 35 37 38 38 41 42 44 47 47 48 50 54 57 59 59 61

OSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OSI TCP/IP . . . . . . . . . . . . . . . . . . . . . . TCP/IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TCP/IP . . . . . . . . . . . . . . . . . . . SMTP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TCP . . . . . . . . . . . . . . . . (Header) TCP . . . . . . . . . . . . . . . . . . . . . TCP . . . . . . . . . . . . . . . . . . . . . . . TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . TCP . . . . . . . . . . . . . . . . . . . . . . . . . . . . UDP . . . . . . . . . . . . . . . . . . . . . . . . . UDP . . . . . . . . . . . . . . . . . . . . . IP . . . . . . . . . . . . . . . . . . . . . . . Fragments . . . . . . . . . . . . . . . . . . . . . . . Fragments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.23 IP . . . . . . . . . . . . . . . . . . . . . . . . . 7.24 IP . . . . . . . . . . . . . . . . . . . . . . .

xii 7.25 7.26 7.27 7.28 7.29 7.30 7.31 7.32 7.33 7.34 7.35 7.36 7.37 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8

. . . . . . . . . . . . . 63 . . . . . . . . . . . . . . . . . . . . . 65 ARP . . . . . . . . . . . . . . . . . . . . . . 72 TCP/IP . . . . . . . . . . . . . . . 75 . . . . . . . . . . . . . . . . . . . . 77 DNS . . . . . . . . . . . . . . . 79 DNS . . . . . . . . . . . . . 80 TCP/IP . . . . . . . . . . . . . . . . . 89 TCP/IP TCP/IP . . . . . . 91 ,, TCP/IP . . . . . . . . . . 93 ,,, TCP/IP 94 browsers: Google Chrome, Mozilla Firefox, Apple Safari107 Skype . . . . . . . . . . . . . 111 OSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . firewall . . . . . . . . . . . . . . . . 118 119 121 122 134 136 138 141

I

6 ( ) , , . , , . (). , . , ( ) (xDSL).

6.1

. , . , , . Wide Area Networks (WAN). , . ( , modem, ..).

4

( ), , , . . . ( ) . (.. ) . ( WAN) : : ( ) .25 : Frame Relay ISDN ATM xDSL : 2001, . . , ( ) .

6.2 , , .

6.2

5

PSTN, Public Switched Telephone Network, ( ) . , . , . , , . : , . , ( ) . , , modem. modems, , . modem . modem Internet () . modem .

6.1: PSTN

6 M

6.1: . . PSTN 56Kbps. , . , , . Internet on-line , (.. ) , -. , .

6.5 ISDN (), ( , , video), ( ) . , Hellaspac Hellascom . telex ( ), .. , : .

6.5 ISDN

7

, , . , . . Integrated Services Digital Network, ISDN. ISDN , , video . : ( ) ( POTS, Plain Old Telephone System, . ). , ( , 300HZ 3400HZ). , ISDN , (; ). ISDN, , ( ), , , video. , ( ) , ( ) . ISDN : : ISDN . ( ) . (common channel signaling). (.. , ...) : ( ()).

8

, . (Basic Rate Interface, BRI) (2 -B) (1 -D). 64 KBps . ( ) 8000 HZ 8bit. D 16 KBps ( / ). . , , . ISDN . , 128 KBps. D ( ) 144 KBps. (Primary Rate Interface, PRI) 30 ( 64 Kbps) D , 64 Kbps ( BRI 16 Kbps). 30 1 D, 64 Kbps (framing) . B D. framing ( ): , (.. ) . , , . 3064 Kbps ( ) + 1 64 Kbps ( D) + 1 X 64 Kbps ( ) = 2048 Kbps = 2,048 Mbps. 1. , 23B+D. D 64 Kbps ( B D) 8 Kbps

6.5 ISDN

9

6.2: ISDN . 23 64 Kbps ( ) + 1 64 Kbps ( D) + 1 X 8 Kbps ( ) = 1544 Kbps = 1,544 Mbps. ISDN ( ), . NT1. ISDN (.. ) ISDN . ( ) . ( , ). NT1 8 -

10

150 . ISDN ( ), . , FAX 4, . () ( ): , ISDN, . ; ISDN , . TA (ADC, Analog to Digital Converter) , (DAC, Digital to Analog Converter) . NT1 . Netmod .

ISDN . 30 30 . ISDN .

6.3: ISDN . . -

6.8 xDSL

11

30 (23 ). ISDN , , ,

6.2: ISDN . , ( ADSL ). (ADSL), ISDN / , . ISDN , ISDN (Narrow Band ISDN). ( ) ISDN (Broadband ISDN) .

6.8

xDSL

xDSL (Digital Subscriber Line) ISDN . , () (local loop). DSL , x ADSL, R-ADSL, HDSL, SDSL, VDSL. ISDN (B) 64Kbps 16Kbps.

12

DSL , . , modem PSTN 56Kbps () ( video, ) Internet. 56Kbps ( modem V90) email. (Fiber to Home), . ( ): ( ) (loading coils). , (300-3400Hz) . , DSL. DSL. - ( 6 ) , DSL. xDSL Mbps. ( ). , 1 (2,048 Mbps) 1 (1,544 Mbps) . . (baseband modem). modem, . ( ) (). : . DSL , . ,

6.8 xDSL

13

Internet. - 2-3 . , DSL . ( ;) : ( , upstream), ( , downstream) .

6.4: SDSL DSL (SDSL, upstream downstream) DSL (ADSL, upstream / downstream). xDSL . , , downstream ( , ). (upstream) (web server ) . DSL E1 1. : DSL -

14 ADSL ADSL Lite HDSL SDSL VDSL Assymetric DSL 1 1 High-bit-rate DSL Single Line DSL Very-high-bit rate DSL 2 3 1 1

8 Mbps downstream 1,5 Mbps upstream 1 Mbps downstream 384 Kbps upstream 2 Mbps Full Duplex (E1) 1,5 Mbps Full Duplex (T1) 2 Mbps Full Duplex (E1) 1,5 Mbps Full Duplex (T1) 13 52 Mbps downstream 1,5 2,3 Mbps upstream 3 Km 6,6 7,5 Km

3,5 4,5 Km 3 Km

0,3 1,4 Km

6.3: xDSL baseband modems ( ) . , , . 6.4 - - SDSL. 128 Kbps 256 Kbps 384 Kbps 512 Kbps 768 Kbps 1152 Kbps 1536 Kbps 2048 Kbps 2304 Kbps 0.4 mm 6.5 5.5 5.1 4.7 4.4 3.8 3.3 2.5 2.2 0.5 mm 8.9 7.5 7.0 6.4 6.0 5.2 4.5 3.4 3.0 0.6 mm 12.7 10.8 10.0 9.2 8.6 7.4 6.5 4.9 4.3 0.8 mm 16.1 13.6 12.6 11.6 10.9 9.4 8.2 6.2 5.4 1.0 mm 22.5 19.0 17.6 16.3 15.2 13.1 11.4 8.7 7.6 1.2 mm 25.1 21.2 19.7 18.1 17.0 14.7 12.7 9.7 8.5

6.4: ( Km) SDSL modem 6.3 , ADSL ADSL Lite. .. ( ). HDSL SDSL , (

6.8 xDSL 1 1) .

15

DSL . DSL online , , video (video on demand), , , IP telephony .. 6.5 . Internet, intranet, IP (VoIP, Voice Over IP) , 1 1. Video (Video on Demand),

.

6.5: xDSL

16

7 Internet . OSI ( ). OSI . TCP/IP (Transmission Control Protocol / Internet Protocol, ) (Internet). : .

7.17.1.1

. -

18

Internet

, . . 7.1 OSI . .

7.1: OSI . ( ). ( 7.2) OSI,

7.1

19

(. , ). . . ( ) ( OSI).

7.2: . . : ( ) ( ,

20 ).

Internet

: , : (Virtual Circuit, VC) (datagrams) : . . , , . . , . ; , ( ). , ( ). :

7.1

21

7.3: , , . . . , . -

22

Internet

( ) . 7.3 : 3, 2, 3 D V. , . . , () . , , .

7.2 TCP/IP7.2.1 TCP/IP TCP/IP , . : . . , (.. Windows UNIX) ( ). To TCP/IP Transmission Control Protocol / Internet Protocol . , TCP IP ( , ).

7.2 TCP/IP

23

TCP/IP . : : FTP (File Transfer Protocol, ), SMTP (Simple Mail Transfer Protocol, ) . . TCP/IP . / . TCP/IP , () . TCP/IP : TCP/IP , . TCP/IP, ( , (hardware) ). : TCP/IP TCP IP. TCP/IP TCP/IP TCP/IP (Internet). TCP/IP, TCP/IP (TCP/IP internets). TCP/IP (Internet). Internet I TCP/IP, internet .

24

Internet

TCP/IP TCP/IP. (Internet) . TCP/IP ( ). () Internet. .. (World Wide Web, WWW). Internet, TCP intranet. . : 1960 (ARPA, Advanced Research Projects Agency). DARPA (Defense Advanced Research Projects Agency). 1960, , : . . ( ) . , , . () . ARPANET . ARPANET 1971, (: FTP telnet). . ARPANET , 1974 TCP/IP -

7.2 TCP/IP

25

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

7.2.2

OSI TCP/IP

TCP/IP OSI . , . OSI . TCP/IP . OSI TCP/IP . . 7.4, . , OSI TCP/IP, . TCP/IP , TCP/IP . , OSI () .

26

Internet

7.4: OSI TCP/IP 7.5 TCP/IP OSI . TCP/IP, . TCP , User Datagram Protocol, UDP . , IP , Internet Control Message Protocol, ICMP. () .

7.5: TCP/IP

7.5: TCP . UDP . ,

7.2 TCP/IP

27

IP ICMP. : Telnet: Telecommunications Network (: Teletype Network) ( ) . SSH (Secure Shell). FTP: File Transfer Protocol . FTP. SMTP: Simple Mail Transfer Protocol . ( email) Internet . TFTP: (Trivial FTP) FTP ( ) FTP.

.

7.2.2.1

. : , , . TCP/IP ( OSI), , . TCP/IP . TCP/IP (Ethernet, Token ring ).

28 7.2.2.2

Internet

TCP UDP (). IP . IP ( IP) ( . ). (IP) . : ; IP (.. ) , MAC . Ethernet, . ( ) - MAC (Media Access Control) OSI. IP . ARP (Address Resolution Protocol) RARP (Reverse Address Resolution Protocol). ARP: RARP: ICMP, Internet Control Message Protocol . IP. . TCP/IP . (.. ) -

7.2 TCP/IP . $ ping 10.14.28.11 Pinging 10.14.28.11 with 32 bytes of data: Destination host unreachable. Destination host unreachable. Destination host unreachable. Destination host unreachable. Ping statistics for 10.14.28.11: Packets: Sent = 4, Received = 0, Lost = 4 (100% loss)

29

, :$ ping www.freebsdgr.org PING www.freebsdgr.org (94.71.112.109): 64 bytes from 94.71.112.109: icmp_seq=0 64 bytes from 94.71.112.109: icmp_seq=1 64 bytes from 94.71.112.109: icmp_seq=2 56 data bytes ttl=62 time=21.849 ms ttl=62 time=21.325 ms ttl=62 time=20.689 ms

7.2.2.3

. TCP ( ) UDP ( ). TCP . TCP (.. ). TCP (). , TCP. TCP . .

30

Internet

UDP . , TCP. UDP: Internet UDP. . . UDP ( ). , .

7.2.2.4 () . ( , , ). TCP/IP. 7.6 TCP/IP . () ( server) . , . ( ) . . , , (: ). : Firefox , .

7.2 TCP/IP

31

7.6: (Web Server) . : : Linux: netstat -npl |more FreeBSD: sockstat -4l |more . FTP (.. ftp://ftp.otenet.gr) : Linux: lsof -Pnl +M -i4 | more FreeBSD: sockstat -4L | more . Windows, !

7.2.3

TCP/IP

TCP/IP, 7.7. , () TCP/IP ,

32

Internet

7.7: TCP/IP . , . ( SMTP ). . SMTP: . SMTP SMTP ( 7.8 SMTP). TCP UDP . SMTP TCP. IP -

7.2 TCP/IP .

33

, (Ethernet, ADSL, token ring ) (.. ) .

7.8: SMTP , . ( ) , SMTP. SMTP ( TCP, ). (.. ) TCP. : TCP/IP : : .. SMTP, FTP, HTTP. (TCP UDP). : TCP UDP. . . : To IP .

34

Internet ( ): (.. Ethernet).

TCP/IP . , . . : (.. Internet) . ( ). . , IP . , IP ( DNS ). , IP . TCP/IP . , . : 15000 bytes (). , . 30 500 bytes. 15000 bytes. , ( . ).

7.2 TCP/IP

35

, . .. 14 13. : . . TCP. . Internet 7.9. OSI , OSI ( 7.1). ;

7.9:

36

Internet

. . IP . IP , . , : : , . , . Internet ( . , ADSL ). ( ) . , . , IP . , . . , .

7.3 TCP , Transmission Control Protocol TCP TCP/IP ( UDP -

7.3 TCP

37

). TCP , , ( 7.10).

7.10: TCP (). SMTP . TCP . , ( 7.11). TCP segments. TCP. (Header) (Data).

38

Internet

TCP . .

7.11: TCP , : Sequence Number Acknowledgment number Window Size (ports) TCP TCP 7.12 (: Wikipedia). -

7.12: (Header) TCP . . . ,

7.3 TCP

39

. , 3, . , . . (bytes) . , 1500 1500. , . TCP . (Window size). , . ( ). . , . , . : 1000, 1000 . 12000, 12000 12000+1000=13000. . 12000. : 1 byte . . byte . , 12000 11999 bytes 12000 . CP (TCP ports). TCP ports

40

Internet

. TCP ( ) TCP . , TCP . (.. Internet , ), . . , Firefox , TCP , . ( ). , , Firefox. Firefox (.. tabs), TCP , . 7.13. 7-10 ;

: , (/) . IP . , /. (/, IP) , / ( ). , TCP

7.3 TCP

41

7.13: TCP . , (.. ) TCP, (: - (non-privileged) 1024). , , , ( , privileged) 1024. , 80. Firefox, TCP 80 . . .. FTP 21, SMTP 25 ... (: , listening ports).

42

Internet

7.3.1 TCP , TCP . TCP . -

7.14: TCP TCP TCP . ( 7.14) . : . . . , IP , ( ) . TCP ( ) .

7.3 TCP

43

TCP , : : FTP (File Transfer Protocol) . FTP ( ) TCP. FTP : FTP . . FTP . FTP . () () FTP ( ) . : O FTP . ( ) FTP . TCP FTP . FTP (port), .. 1234. , (-) , ( ). TCP FTP 21. To 21 ( ) FTP. , ( server ). , 1234 21

44

Internet , TCP .

TCP (1234) (21). : .. 21 FTP, 80 HTTP . . TCP , IP : IP IP . : IP .. 62.103.240.22. . . 1234. IP .. 61.74.29.32. , 21.

7.15: TCP

7.4 UDP

45

, TCP (: ;). . ; . ( 7.15): (FTP) . (.. Firefox) site ( ) . . (: , UNIX . ). : . : , IP . , IP . , . , .

7.4

UDP

TCP . TCP . . . TCP: FTP TCP , TCP FTP .

46

Internet

TCP : (, , ) TCP . . , . , TCP . . : . TCP. , : , . . . , , UDP, User Datagram Protocol . UDP : TCP: , UDP UDP. : . . . . . UDP , . .

7.4 UDP .

47

TCP, UDP (ports), UDP ports. TCP ( . ) 16 bits ( . 0 65535). UDP .

7.16: UDP

7.17: UDP UDP : UDP ports . , DNS ( www.sch.gr IP .. 194.63.238.40) UDP 53 . SNMP ( ) 161. , ( TCP) . UDP , ( 7.17, 7.16 - : Wikipedia).

48

Internet

IP TCP UDP . UDP IP UDP.

7.5 IP TCP/IP, IP, Internet Protocol. IP datagram, ( ). , TCP. TCP UDP ( TCP UDP segments), IP. IP ( ) . IP. IP ( ) . .

7.18: IP , IP ( 7.18) -

7.5 IP

49

, IP . 64 Kbytes. , IP . , ( TCP/IP OSI .. Ethernet , ). 64 Kbyte IP. : MTU, Maximum Transfer Unit. ( , ). Ethernet MTU 1500 bytes. MTU IP , IP . , IP fragments. IP IP . fragments ( 7.19). . IP. . IP IP IP fragment . , . IP -

50

Internet

7.19: Fragments IP fragment IP . blocks 8 bytes ( , wikipedia). IP (fragment) . More Fragments (MF) . 1, fragment . 0 fragment . , MF=1 . (: 0 1 flags ) . , Dont Fragment, (DF), 1. IP . , . :

7.5 IP

51

: . (: IPv4 IPv6. IPv6). : 32 bits. 5. 5*32=160 bits, 8, 160/8=20 bytes. : . IP : , . ; TOS, Type of Service : , : IP , . 64 Kbytes = 64*1024 = 65536 bytes. 20 bytes. 65536-20=65516 bytes. : 1 . , ( ). . : IP . , 6, TCP. ( , IP)

52

Internet : IP () . , . : IP . . : IP . ( ) . IP : . : 32 bits. ( IP )

: 1400 bytes 20 bytes, 620 bytes. Dont Fragment (DF) 0, . , MF ; : . . 1420 bytes. DF=0, ! ! , MF fragments 1 0. 8 ( fragment ).

7.5 IP :

53

fragment 620 bytes. : fragment. , 600 bytes 20 bytes . MF 1. . 0. . : 620 bytes. 600 bytes 20 bytes . H MF 1. . ( ) 600 bytes . 600/8=75. : 200 bytes . 200 bytes + 20 bytes = 220 bytes. H MF 0. . 600+600=1200 bytes . 1200/8=150 : 20 bytes 20*8=160 bit. 5 (532=160). . IP . , . 1 . IP , . .

54

Internet 20 bytes, IP . . . ( ) ( MF=0).

7.20: Fragments : , . , . : , . 100 ( 7.20). . IP MF . MF 1, , . 0 75, . . . IP , MF=1 o .

7.6

55

IP (100) IP . . . IP , MF 0. IP . IP . (.. TCP, UDP) . IP .

7.6

IP , IP . , . , . ( ). , (DNS). IP . , IP . .

56

Internet

7.6.1 (Media Access Control, MAC) : IP (hardware address). , . ( ) . OSI, - Media Access Control, MAC. - , MAC . MAC , . , . OSI ( IP ). MAC ( ). ( Ethernet) 48 bits. . , , IEEE, Institute of Electrical and Electronic Engineers. 24 bits MAC . 24 bits ( 7.21). 24 bits , OUI, Organization Unique Identifier. bit ( ) . 0 (Individual) (Group). , .

7.6

57

7.21: OUI 1, : . bit . 0, IEEE, 1 . . . bit ( ). 22 bit IEEE . 24 bit . (OUI), (.. Ethernet) . 24 bit ( 24 OUI ). , IEEE OUI.

7.6.2

IP

TCP/IP IP 32 bit. IP :

58

Internet

IP () . , . ( DNS ). IP . () ( ). . : , Internet : 10.14.28.10 Ethernet 81.186.52.182 Internet . IP , . ( 7.23). , IP . 7.22 : 22. , 35, 45 55. (1,2,3,4) . , (octets) . : octets 8 . byte. 0 255. ( )

7.6

59

7.22: IP: bytes = 3 * 8 = 24 bits. byte = 8 bits 32 bits. , ( , 254 ) .

7.23: IP

60

Internet

( ) Internet, . Internet . . , , Network Information Center, NIC InterNIC. , NIC . : ; ADSL, IP Internet ( ). NIC , . , . . 24 bits, . , 24 bits . IP 24 + 24 = 48 bits. 32 bits. , ( ) . , A, B, C D ( 7.24). , . : 0. octet 00000000 01111111 . 0 127.

7.6

61

7.24: IP 7 bits 24 . : 128 16 . : B 10. 16 bits ( octets) 14 bits. , octet 10000000 10111111 . 128 191. octets 0 255. . 16384 65536 . C: C 110. 21 bits, 8 bits. 2 256 . octet 11000000 11011111 . 192 223. octets 0 255. D: D : (multicast). . D octet 1110. , IP 8 bits (octets ) . .. : 10.14.28.32

62

Internet

. , . , : ... C, : ... , C 192.168.2.34. 192.168.2 , 34 . .

7.6.3 , (subnets) bits. , IP. , . . : : , 128.6... , . , Ethernet. 128.6.5. 128.6.4.. (). . (.. 7.25) , 128.6.. (

7.6

63

7.25: ) . , : 128.6.4 128.6.5, . 128.6... , B C. B, . C , . NIC Class B, , Class B Class C. Class B NIC, Class C; . . , , . Class C , . -

64

Internet

128.6 , 128.6.4 128.6.5. . , ( ) . 7.6.3.1 (subnet mask) bit, IP . 32 bit IP. . IP: 10.14.28.10 , : 00001010.00001110.00011100.00001010 : 255.255.255.0 : 11111111.11111111.111111111.00000000 , AND . AND 1 1: 00001010.00001110.00011100.00001010 11111111.11111111.11111111.00000000 AND 00001010.00001110.00011100.00000000 , 10.14.28.0 . : 1, IP . -

7.6

65

7.26: 0, IP . 7.26. (MAC) , IP bits 1 ( 255.255.255.255 ) . 1 . : 10.14.28.. : 10.14.28.0 , 0 . 1, 11111111=255. : 10.14.28.255 IP 176.44.25.19 255.255.0.0 ; (Internet). , 32 bit -

66

Internet

( ). , . . 70000 , B , . 300 . C , 65000 ! , - (Classless InterDomain Routing) CIDR. , . . (/) IP . IP ( ) . , : 10.14.28.10/24 24 . 24 bit (. 3 bytes, ) 8 bit . 255.255.255.0. 8. : 10.14.28.10/27 27 , 5 . 32 . CIDR ( ISP, Internet Service Providers).

7.7 ARP

67

. ISP. , () ISP. : IP Windows . TCP/IP . , : ipconfig /all |more UNIX : ifconfig

7.7

ARP

: (MAC) (.. ). , IEEE. IP TCP/IP . Internet, NIC, . . ( Ethernet) ARP, Address Resolution Protocol, . ARP ( ) TCP/IP. ARP; Ethernet, , ( Ethernet

68

Internet

). . ARP, IP . ARP, . ARP IP . (IP , ). , , ( ). . ARP IP . IP MAC ( ). ARP (IP , ). . . ARP : IP 223.1.2.1 223.1.2.3 223.1.2.4 Ethernet 08-00-39-00-2F-C3 08-00-5A-21-A7-22 08-00-10-99-AC-54

ARP IP, ARP : ARP, . , ARP. . IP . IP , .

7.7 ARP

69

, ARP, IP . , ARP. , , ARP , . , . ARP , ( ). . , . , IP . ARP IP. . RARP, Reverse Address Resolution Protocol, ARP. . IP . ( ARP) , RARP. ; IP ; / NIC IP ! : , Internet (.. ADSL ). Internet. . : . . - , .

70

Internet , IP. ARP . , IP.

RARP. IP , RARP (: IP !). ARP IP . , RARP . BOOTP DHCP , ( IP) .

: IP 128.6.4.194 128.6.4.7: 128.6.4.194 128.6.4.7 (Ethernet). ( ). ARP 128.6.4.7. . 128.6.4.7 ARP, . ARP Ethernet 128.6.4.7. 128.6.4.7 08:00:20:01:56:34 ( Ethernet 48 bit, . 6 ). , 128.6.4.194 128.6.4.7.

7.7 ARP

71

ARP , . ARP , IP ( . IP NIC, IEEE). (.. , Telnet) . TCP ( telnet TCP). TCP IP IP . , (Ethernet) . ARP, IP ARP ( 7.27). Ethernet . . , ARP . . ARP IP ARP, . IP , IP (Ethernet) ARP , Ethernet . , : ARP . IP . ARP ARP. , IP Ethernet.

72

Internet

7.27: ARP IP , Ethernet . ARP, ARP IP IP .

7.8 , Domain Name System (DNS) , IP . IP 32 bit ( octets) . IP : 94.69.78.90

7.8 , Domain Name System (DNS)

73

.. . , . : : 10.14.28.10 , : aquarius64.lab1.local PC1, PC2, PC3 , IP . DNS . , IP . . , . IP . IP . IP ( ), , IP. () . , . , , , ( ).

74

Internet

: , .: accounting-pc01 : (accounting, ) (pc, ) (01) . pc , () , . : accounting-lpr01 (To lpr line printer, ) , . , IP . ( ), IP . IP . , , . , IP . 7.28. , , , ( ). :

7.8 , Domain Name System (DNS)

75

7.28: TCP/IP 192.168.0.1 192.168.0.2 192.168.0.3 192.168.0.4 A

, . , 192.168.0.3. : IP . : hosts. , hosts : 127.0.0.1 10.14.28.10 10.14.28.11 10.14.28.12 10.14.28.13 10.14.28.14 localhost localhost.lab1.local aquarius64.lab1.local aquarius64 PC1.lab1.local PC1 PC2.lab1.local PC2 PC3.lab1.local PC3 PC4.lab1.local PC4

IP . hosts . , Windows : C:\Windows\System32\Drivers\etc\hosts UNIX : \etc\hosts

76 .

Internet

. : . . , . . , (ASCII) . . . , . DNS, Domain Name System. DNS . DNS . , . DNS Internet, : . Internet. DNS . , , : joshua.freebsdgr.org joshua freebsdgr.org. DNS

7.8 , Domain Name System (DNS)

77

freebsdgr.org. joshua .

7.29:

DNS, . . ( ). , DNS , ( 7.29). DNS . . (.. ). DNS DNS . DNS ( ). ( ) .

78

Internet

: joshua.freebsdgr.org : DNS .org. DNS joshua DNS freebsdgr.org org. joshua. joshua.freebsdgr.org = 94.71.69.206 . . : DNS .org joshua.freebsdgr.org freebsdgr.org DNS 204.13.248.75. . . DNS, : nslookup dig .

7.8.1 DNS DNS . . 7.30. . ,

7.8 , Domain Name System (DNS)

79

7.30: DNS . : - .arpa: - .com: - .edu: - .gov: - .mil: - .net: - .org: ( - ) ( .. .com ) . ( ) . , .gr, .de .uk. domain. , ( ). . (domain names) . domain names . , ntua.gr . domain ntua

80

Internet

.gr (NTUA=National Technical University of Athens). , freebsdgr.org domain freebsdgr .org. . domain name . , () . subdomain. , domain name . : telecom.ntua.gr telecom subdomain domain ntua .gr (). ( ) ( 7.31).

7.31: DNS

. , subdomain: telecom.ntua.gr pc01 , :

7.9 pc01.telecom.ntua.gr

81

, . . subdomain . : www.freebsdgr.org www domain freebsdgr.org. . () . , : : pc01.telecom.ntua.gr - gr: ( , ) - ntua: . .gr - telecom: . ntua. - pc01: . : ( ) domain, whois UNIX. : whois freebsdgr.org freebsdgr.org ( ). .gr.

7.9

.

82

Internet

. , ( Internet) . . ( ), . . . , ( ). , , . , . , , , . , : : - . : . : - .. . : . .

7.9 .

83

: . . OSI TCP/IP (.. ). , . : . . . . : (. ) ( . ) , . . . , . . , . () . . , . . .

84

Internet

, . : . . (CPU, Central Processing Unit) . . , (.. , ). . . . . , , . , ( ). : : :

7.9 ( )

85

. : , , .

7.9.1

TCP/IP

TCP/IP IP ( ), . TCP/IP . : - hosts: . , . - routers: . : . (routers). , ( ). , . . IP

86

Internet

. , . IP, . , . , . : . ... . IP : (direct routing): . , . . (indirect routing): . . . IP , . , 192.168.0.42 192.168.0.31, , 192.168.0. . , . (Internet) , . .

7.9

87

. ( , rack ). . , , . , . : default gateway. . ( Windows / Linux / FreeBSD): netstat -rn :Routing tables Internet: Destination default 127.0.0.1

Gateway 192.168.0.250 127.0.0.1

Flags UGS UH

Refs Use Netif Expire 0 325353 rl0 0 13404 lo0

192.168.0.250. , , Flags G. . . , : . ICMP. .

88

Internet

: 128.6.4 , 128.6.4.59 128.6.4.1. 128.6.4.59 , 128.6.4.1 . 128.6.4.59 . ; 1. , , 128.6.4.59. . 2. , 128.6.4.1 . . ICMP : , 128.6.4.1. 3. ICMP, . , , 128.6.4.1. (: ). IP: = . 128.6.3.2, = .. 128.6.3

7.9

89

7.9.2

, 7.32. Ethernet. , , . Ethernet ( MAC Address). IP .

7.32: TCP/IP

90

Internet

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

, IP Ethernet. , , IP. Ethernet ( ), Ethernet . IP . IP B IP , IP ( , Ethernet ). , . .

7.9.3 7.33 TCP/IP (). . Ethernet . () IP , . IP ( , ) Ethernet.

7.9

91

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

92 E .

Internet

, Ethernet . , Ethernet . IP Ethernet ()

IP () IP IP , . E, Ethernet . , , : IP Ethernet

7.9.4 , . IP , . IP . () . : IP - IP . .. IP 223.1.2.3 255.255.255.0, 223.1.2 / - (. ) ( ) IP - IP - , .

7.9

93

- , . , . , . , .. 1 : . . , IP . , ( ) .

7.34: ,, TCP/IP 7.34. IP , . 223.1.2.2.

94

Internet

223.1.2 (: , ). . : 1

(223.1.2)

, . , . ( ) . Ethernet, Ethernet ARP 1. 7.35

7.35: ,,, TCP/IP . , ( ) .

7.9

95

. IP : 1 1 1

(223.1.2) (223.1.3) (223.1.4)

( ): 1. IP IP . 2. ( ) . 3. . 4. ARP Ethernet ( , IP - . Ethernet , ) 5. To 1 ( ) . . , IP . 6. O . . .

96

Internet 1 3 2

(223.1.2) (223.1.3) (223.1.4)

1. IP , IP . 223.1.3 2. , . 3. IP 3. IP Ethernet . E , IP . .

7.11 7.11.1 TCP/IP. : , . TCP, IP , (). .

7.11

97

. . : . , . ( ) TCP/IP, . : , . get, put, send. ( ) . . . . (.. ), . . . , . :

98

Internet . ASCII EBCDIC. / . . . .. Windows UNIX.

( ) . TCP IP .

7.11.2 TCP/IP:

email () . . e-mail . email . , , e-mail . , . , , , , ...

7.11

99

, . . . , . (.. ) . e-mail ( Fax ). . . . . : email email . : . , .. ( ). email. spam. (phishing) / ( ).

100

Internet

() , . TCP/IP - Simple Mail Transfer Protocol (: - ). SMTP : SMTP (DNS). . , email [email protected], SMTP otenet.gr , . SMTP , TCP 25. 25 . SMTP . , SMTP . (.. ). , (DATA) . , .

(FTP, File Transfer Protocol) , FTP TCP/IP. -. ( ). . FTP TCP . TCP ,

7.11

101

. FTP . FTP - . .. , . , . . FTP . FTP , , ( , FTP / UNIX - ). , . FTP () (). ( , ). : To FTP , , . . FTP ( ). . FTP SMTP . FTP . ( ) FTP . ,

102

Internet

. , . - :

[13:56:31][pulstar]$ ftp www.freebsdworld.gr Connected to freebsdworld.gr. 220---------- Welcome to Pure-FTPd [privsep] [TLS] ---------220-You are user number 2 of 50 allowed. 220-Local time is now 05:56. Server port: 21. 220 You will be disconnected after 15 minutes of inactivity. Name (www.freebsdworld.gr:user1): user1 331 User user1 OK. Password required Password: 230-User user1 has group access to: user1 230 OK. Current restricted directory is / Remote system type is UNIX. Using binary mode to transfer files. ftp> ls drwxr-x--- 12 user1 user1 4096 Nov 9 16:01 . drwx--x--x 12 user1 user1 4096 Feb 12 15:54 .. drwxr-xr-x 2 user1 user1 4096 Oct 26 08:53 etc drwxr-x--- 8 user1 user1 4096 Dec 17 00:20 mail -rw-r--r-- 1 user1 user1 39228 Oct 27 16:41 php.ini drwxr-x--- 3 user1 user1 4096 Oct 26 08:53 public_ftp drwxr-x--- 12 user1 user1 4096 Nov 9 16:01 public_html 226 7 matches total ftp> cd public_html 250 OK. Current directory is /public_html drwxr-x--- 12 user1 user1 4096 Nov 9 16:01 . drwx--x--x 12 user1 user1 4096 Feb 12 15:54 .. drwxr-xr-x 2 user1 user1 4096 Sep 16 13:40 scripts -rw-r--r-- 1 user1 user1 31877 Oct 26 11:10 site-logo.png 226 4 matches total ftp> get site-logo.png local: site-logo.png remote: site-logo.png 229 Extended Passive mode OK (|||11932|) 150-Accepted data connection 150 31.1 kbytes to download 100% |***********************************| 31877 40.25 KiB/s 226-File successfully transferred

7.11 226 0.004 seconds (measured here), 7.90 Mbytes per second 31877 bytes received in 00:00 (40.23 KiB/s) ftp> bye 221-Goodbye. You uploaded 0 and downloaded 32 kbytes. 221 Logout.

103

, . FTP 150-Accepted data connection. . FTP, ( email ), . , (.. ) () . , TCP port 21 (command channel) TCP port 20 (data channel). : FTP , passive mode. , 229 Extended Passive mode OK. FTP, TFTP, Trivial File Transfer Protocol . FTP . TFTP UDP . - Telnet (Telecommunications Network Teletype Network) Telnet , . telnet

104

Internet

, , . , ( Telnet UNIX). , telnet, Internet. Telnet , ( ) . . : FTP, telnet ( ) . . telnet SSH, Secure Shell . , . : UNIX , . UNIX . , . , -

7.11

105

Telnet. telnet . Telnet TCP/IP. telnet. . .. Telnet . Telnet FTP SMTP . Telnet . , Telnet TCP TCP port 23. , . Telnet. () , . . . Telnet (.. ) ( ) Telnet. telnet:

[15:39:25][[email protected]:~]$ telnet pegasus Trying 62.71.35.221... Connected to pegasus.chania-lug.gr. Escape character is ^]. FreeBSD/amd64 (pegasus.dyndns.org) (pts/3)

106

Internet

login: sonic Password: Last login: Mon Feb 15 15:39:14 from localhost Copyright (c) 1992-2009 The FreeBSD Project. Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994 The Regents of the University of California. All rights reserved. FreeBSD 8.0-RELEASE-p2 (PEGASUS) #1: Sat Jan 30 22:05:14 EET 2010 Welcome to FreeBSD! [15:40:45][[email protected]:~]$ ls -d */ Desktop/ data/ html/ GNUstep/ diktia-new/ logos/ UNIX/ external/ logs/ bin/ fonts/ multimedia/ books/ freebsd-book/ nethome/ logout Connection closed by foreign host.

notes/ original/ page/ some/ tarballs/

(World Wide Web, WWW) World Wide Web WWW . . - hypermedia . , video . . , . links .

7.11

107

. . , . (links). , / , () . , (highlighted). , , browsers. .

7.36: browsers: Google Chrome, Mozilla Firefox, Apple Safari , , -

108

Internet

, (video). (hypermedia). WWW () FTP, , HTTP, Hypertext Transfer Protocol. . ( Web Servers) . , . , browsers. browsers . browsers Mozilla Firefox, MS Internet Explorer Opera. , . , . (ISPs, Internet Service Providers). . . ( WWW). (web site) (home page) www. , . . Internet . -

7.11

109

. , . Google, Google, Google, Google, Bing, Yahoo . : 1993 130 Web sites, 1994 10000, 1996 100000 1997 650000. 2009 200000000 ( !) sites. , 1994 6% Internet 1995 24%. 5 1996, 22 1996 1.5 . 2009! : Netcraft, http://www.netcraft.com

, WAP, Wireless Application Protocol () , Internet. , : Internet email ( ) () : WAP (3G, GPRS). TCP/IP (Intranets)

110

Internet

. TCP/IP Intranets. , Intranets Web. . (browsers). . , Intranet Internet . . Intranet : , . ( , Internet , ). Intranet : Web ( , ) Intranets ( WWW clients, browsers). .

, . . . , ( ). half-duplex . . . (full-duplex).

7.11

111

( ).

7.37: Skype half full duplex, . ( ) (.. ). ( , ). . , .

112

Internet

: . TCP/IP VoIP, Voice Over IP. , . video (video ). .

, . , video (streaming), . video , , (bitrate) . , video . ( ) video . MPEG1 MPEG2 , H.323. 12-15 , (25-30 ). . . , . , Internet 64Kbps.

7.11

113

, CU SeeMee Cornell University. 8-12 , . , . ( ) . , : , , . , ( ) . : , . , .

, . , . , . () . TCP/IP video. , : . , . . .

114 .

Internet

. UNIX, talk Windows, wintalk. . ( ) IRC, Internet Relay Chat. . IRC XChat, IRCII, miRC .. : MSN messenger, Google Talk, . . , , ! , , Internet. , . , EDI, Electronic Data Interchange . email. : (web site) , . , . email , , Shopping Basket. , .

7.11

115

, . , browser () . . , ( .. ) . ( , , , ), , , , . , , .

116

Internet

8 , . WAN VLAN. . , . , . / . , . . . , . , . .

118

8.1 (ISO, International Standards Organization) (framework) OSI. : (Configuration Management) (Performance Management) (Fault Management) (Accounting Management) (Security Management)

8.1: OSI .

8.1.1 (Configuration Management) . ,

8.1

119

. , ( OSI) . (, ) , . , . , (documentation). . , . switch . , firewall ( ), (TCP ports) . , .

8.2:

120

(inventory database) . (.. , , switches ). ( ethernet, token ring ) WAN ( PPP, dial-up / isdn, X.25, Frame Relay ). , , . ( ) .

8.1.2 (Performance Management) , . . , : WAN . .. TCP/IP, IPX, Netbios . . . . ( ). , (alarms). . . . ,

8.1

121

8.3: . , . ( 8.3).

8.1.3

(Fault Management)

. , . , ( . ) . ,

122

, . , .

8.4:

( ). . . (alarms) (log files). , . , .

8.3

123

8.1.4

(Accounting Management)

. . .

8.1.5

(Security Management)

, - ( ). . . , , . , . : - . . . ( , ). .

8.3

Internet ( ),

124

. . , , .

8.3.1 , . . , . ( ). . () , . , . , , () . , , . , . , , . , . : . : UNIX (daemons). , Windows (services). , .

8.3 .

125

() , . , (web server) (. html ). . , . () / . . . , : (authentication): . / (username/password). (integrity): . (confidentiality): . (non-repudiation): () . , . : (validity): . .

126

(Information Availability): . , . .

: (security): , . (information security): , . (security violation): , , . . . (threats) . (, ) ( ). (vulnerabilities) ( ) . . , . . . , , . , .

8.3

127

. , .

8.3.2

, . , . : (Encryption): ( plaintext) () . , . . (Decryption): . () ( ) . . (Key): , ( bits) . . (Public Key): , , . , . () . , .

128

. , . ( , ) (Private Key): . : - . ( ) . . (Secret Key): / . () (Hash Function): ( ) . , , (digests). (Message Digest): () . ( ) , . (.. bit) ( ). .. Internet. downloads, CHECKSUM ( ) . , : . (Digital Signature): bit ( ) ( ) .

8.3

129

8.3.3

. , ( ) (RAM) . . , , Internet ( ). . (Password Attacks) . : passwords: . . passwords , OTP (One Time Password): passwords , . , UNIX Windows, . ( UNIX OTP, ). ( ) ( ) . (brute force attack). (key stroke monitoring) (keylogger) , . . , ( , .. ). social engineering

130

. , Internet (ISP) . . ISP ; ! (shoulder surfing) ( ). . : . , . , ( ) passwords crack . . , (digest). , : digest . , . , , ( ). crack : digests ( hashes) , , digest. . brute force attack. ( ) . , . crack () . UNIX Jack the Ripper,

8.3 .

131

UNIX (root) (login passwd ). ,

(Network Monitoring Network Packet Sniffing) , . ( telnet ftp ), , (clear text). , , , . (packet sniffing) promiscuous. promiscuous mode , . packet sniffing , . . passwords Man-in-the-Middle. . (Masquerade) , . TCP/IP, IP Spoofing IP ( . IP ).

132

firewall ( Internet (trusted)). , IP spoofing client server (point to point). ( ), , . . , . emails , social engineering .

(Denial of Service) , , . ( ) , . (.. , ). sites Internet (Yahoo, CNN, twitter ). , zombies botnet. : (malware) . zombie. , botnet. O botnet zombies , Denial Of Service. , -

8.3

133

IP ( botnet ), (Distributed Denial of Service Attack, DDOS) Denial of Service. , Denial of Service . .

(Application-Layer Attacks) HTTP, ActiveX, Telnet, FTP . , ( , holes). .

8.3.4

, . .

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

134

, ( ). .

, Caesar Cipher 8.5. ,

8.5: . , , , ... . ( ) . , : , . ( , 24) . . , ( ) ( !) .

8.3

135

. , . , , .

: , . . . : CSS ( DVD), A5/1 ( GSM), Blue-Ray .

: DES, Data Encryption Standard, 3DES, Triple DES IDEA, International Data Encryption Algorithm, . 64 bits. 64 bits, 64 bits. , . , . , . , - (.. ) . : , Diffie Hellman , .

136

. , . : , ( Bob Alice!)

8.6: Bob Alice, , . , . , (, , keyservers ). . , , . Alice Bob : Bob.

8.3

137

Bob . , Bob : Alice. . , , ( ) . , . : : . , . , , . , (fingerprint), . , , ( , .. ) . , , , , . Bob Alice. . Bob, Bob . email , . Alice Bob Bob Alice . , : Alice .

138

8.7: Bob Alice ( ). Alice ( ) . . : , . . , , . : . , . . .

8.3.4.1 , . () . (hash). (digest) . MD4, Message Digest 4, MD5, Message Digest 5 SHA, Secure Hash Algorithm (.. SHA1, SHA256).

8.3

139

, : (.. Bob Alice) ( , .. PGP, Digital Signature Standard ) (.. MD5). . . Alice Bob . (digest). , . Bob . O Bob Alice. , . , , Alice. . , ( ) ( ) . - .

: GPG Linux/FreeBSD ( Windows) . .

140

8.3.5 , . . : passwords passwords (One Time Passwords, OTP): . SSL / SSH / SOCKS: . Radius / Tacacs: dial-up . PAP / CHAP: point to point ( , ). Single Sign On: passwords. Single Sign On , . : . IPSec (IP Security): Internet Protocol Security . , OSI. IPSec : IP : . ESP, Encapsulation Security Payload: . IPSec VPN ( , Virtual Private Networks) (dial up). Firewall : .

8.3 Firewall

141

(gateways, - , .. Internet ). firewall, . 8.8 . - ( Internet) . , firewall. (.. ports ).

8.8: firewall , , . .. web server () .

142

, , firewall. port . , . firewall (.. ), . IP () ports (.. HTTP), (.. telnet, rlogin ). (TCP UDP port) . ports. firewall, () . firewall. ( ), .

8.3.6 . , . . , : ( , , , ), (, racks ). (bugs).

8.3 .

143

(.. (corrupted) ). (, ). (crackers, hackers ). , , , . . ( ) . : (recovery): . (Continuity Plan): . (Information Backup): . , . . . , ( ). . , ( ) . .

144

. , (client server). , (servers), main site. , main sites, . sites (.. , ). site . site (, switches ). , ( ) . (LANs). , ( ). , (.. backup. , main site ). . , , . , , .

II

148

2009 1. , () . . 1. (ISDN) 2. (xDSL) 3. 4. (xDSL) . . . . 8 B. , . 1. (xDSL) . 2. OSI , TCP/IP . 3. IP . 4. (DNS) IP . 8 . . 1. TCP/IP; . To (SMTP). . (UDP). . To (IP).

149 . (ICMP). 2. , . . . . . 9

2. TCP/IP; 15 . IP : 150.23.05.0/22 1. ; 5 2. ; 5

3. . IP . , . 1. IP Ethernet ARP . 2. ARP ARP . 3. IP , Ethernet .

150 4. ARP .

5. IP . 10 . , , (5) OSI. 5 . : IP : 11010001.10101010.01010101.00001111 : 11111111.11111111.11110000.00000000 1. bits ; 4 2. . 6

4. IP 2000 bytes 20 bytes 820 bytes (800 bytes 20 bytes ). . 1o DF MF (), , 20 bytes. 16 2o 3o

151 . digital signature standard MD5. B . , B. 9

152

2010 1. , , . . xDSL . . TCP/IP . . (Transmission Control Protocol, TCP) TCP/IP. . . 8 2. . : . To TCP port 20. . TCP port 21. . To TCP port 23. . TCP port 25. 5 A3. . 1. (BRI) 2. (PRI) 3. 4. TCP/IP . 32bits . 32bits . 64 Kbps . 30 64 Kbps 8 A4 ; 4

153

B1. ; 5 2. ; 5 3. ; 8 4. ; 7

1. TCP; 4 2. TCP; 5 3. IP . Class A Class B Class C Class D 16

1. TCP 2.000 10.000 . ; 10

154

2. IP 2.400 bytes 20 bytes 620 bytes. , IP . 1o DF MF (), IP , 20 bytes. 15