Ni dung n tp (17

MNG MY TNH

Ni dung n tp (17.6.2013)Phn 1: M hnh lin kt h thng m OSI (Open System Interconnection).-Mc tiu thit k: m bo cc h thng khc nhau c th lin lc vi nhau.-Nguyn tc thit k: theo m hnh phn lp, trong lp n+1 s dng dch v ca lp n thc hin chc nng ca mnh.-M hnh OSI gm 7 lp theo th t: 7-Lp Application Lp ng dng: xc nh giao din gia ngi s dng v mi trng OSI6-Lp Presentation- Trnh by: gii quyt cc vn lin quan n c php v ng ngha ca thng tin c truyn5-Lp Session- Phin / giao dch: thit lp, duy tr, hy b v ng b phin truyn thng gia cc my khc nhau4-Lp Transport Vn chuyn: lin quan n cc giao thc trao i d liu gia cc h thng m, kim sot vic truyn d liu t mt ti mt (End-to-End). 3-Lp Network Mng: chn ng (Routing) i cho cc gi tin t ngun ti ch c th trong cng mt mng hoc khc mng nhau. iu khin tc nghn (Congestion Control)2-Lp Data link Lin kt d liu: thit lp cc lin kt, duy tr v hy b cc lin kt, kim sot li v kim sot lu lng1-Lp Physical- Vt l: xc nh cc chc nng, th tc v in. c, quang kch hot, duy tr v gii phng cc kt ni vt l-C ch truyn thng gia cc h thng m: mi lp thm thng tin iu khin vo n v d liu truyn. n v d liu cng vi tiu ring ca lp c gi l PDU (Protocol Data Unit) ca lp.

(hnh 2.9 trang 32)

-Tng quan gia cc lp trong m hnh OSI v m hnh TCP/IP:

-Cc giao thc in hnh ti tng lp ca m hnh TCP/IP:

Lp ng dng: HTTP (Dch v WWW), FTP (dch v truyn file), SMTP (dch v gi th), DNS (truy vn tn min), POP (dch v nhn th), SNMP (dch v qun l mng)Lp Vn chuyn: TCP (truyn d liu tin cy) v UDP (truyn d liu khng tin cy).Lp lin kt mng: IP (chuyn d liu khng kt ni), ARP (phn gii a ch), ICMP (giao thc iu khin)Lp Lin kt: cc giao thc lin kt ph thuc vo cng ngh mng.

Phn 2: Giao thc IPv42.1- a ch IP:-Cu trc a ch IP: l s nh phn 32 bit, c chia thnh 4 nhm, mi nhm 8 bit. Tng nhm c biu din dng s thp phn:A.B.C.D vi A, B, C, D l cc s thp phn c gi tr t 0 n 255-Phn lp a ch: ph hp vi quy m ca cc h thng mng khc nhau, ng thi tit kim ti nguyn a ch IP, khng gian a ch IPv4 c chia thnh 3 lp: Lp A: 8 bit NetID v 24 bit HostID Lp B: 16 bit NetID v 16 bit HostID Lp C: 24 bit NetID v 8 bit HostIDNhn bit lp a ch:Lp A: nhm u tin c gi tr t 1-127Lp B: nhm u tin c gi tr t 128-191Lp C: nhm u tin c gi tr t 192-223-Phn chia mng con (subnet): c ch phn chia khong a ch cho nhiu mng con nh hn nhm mc ch s dng hiu qu ti nguyn a ch IP. Nguyn tc: ly bt mt s bit ca HostID lm NetID.BT1: Phn b dy a ch t 203.162.44.0 n 203.162.44.255 cho 8 mng con. Xc nh Subnet mask, khong a ch IP ca tng mng, NetID v a ch Broadcast ca tng mng con.-Bc 1: Xc nh s a ch trong tng mng conS a ch trong ton b dy a ch: 256S a ch trong tng mng con: 256/8=32-Bc 2: Xc nh s bit dnh cho NetID v HostID:Phn bit 32 a ch => cn 5 bit HostID (25=32) S bit dnh cho NetID = 32 5=27 bit-Bc 3: Xc nh Subnet mask:11111111.11111111.11111111.11100000Subnet mask = 255. 255.255. 224-Bc 4: Xc nh khong a ch IP cho tng mng con:Mng 1:Bt u: 203.162.44.0Kt thc: 203.162.44.31Mng 2:Bt u: 203.162.44.32Kt thc: 203.162.44.63Mng 3:Bt u: 203.162.44.64Kt thc: 203.162.44.95Mng 4:Bt u: 203.162.44.96Kt thc: 203.162.44.127Mng 5:Bt u: 203.162.44.128Kt thc: 203.162.44.159Mng 6: Bt u: 203.162.44.160Kt thc: 203.162.44.191Mng 7: Bt u: 203.162.44.192Kt thc: 203.162.44.223Mng 8:Bt u: 203.162.44.224Kt thc: 203.162.44.255-Mi mng con: a ch bt u l NetID, a ch kt thc l a ch BroadcastBT2: Phn chia dy a ch IP t 192.168.1.0 n 192.168.1.127 cho 8 mng con bng nhau. Xc nh Subnet mask, khong IP ca tng mng, NetID v a ch Broadcast ca tng mngBT3: Phn chia dy a ch 172.16.0.0 n 172.16.1.255 cho 8 mng con bng nhau. Xc nh subnet mask, khong IP ca tng mng, NetID v a ch Broadcast ca tng mng con.2.2-Cu trc tiu gi IP:

-VER (4 bit): phin bn ca giao thc IP-HLEN (4 bit): chiu di tiu gi IP-Service Type (8 bit): Phn loi dch v-Total length (16 bit): Tng chiu di gi IP-Identification (16 bit): S phn bit gi IP-Flags (3 bit): c phc v cho mc ch phn mnh v ti hp-Offset (13 bit): v tr mnh trong gi d liu gc.-Time to live (8 bit): thi gian sng ca gi IP-Protocol (8 bit): giao thc bn trn giao thc IP-Check sum (16 bit): Kim tra li trn tiu gi.-Source IP (32 bit): a ch IP ca my gi-Destinetion IP (32 bit) a ch IP my nhnBT1: Gi IP ln nht (bao gm d liu v tiu ) c kch thc l bao nhiu byte? Gii thch.BT2: Mt gi IP c gi tr trng HLEN = 5, Total length = 2570, cho bit gi ny cha bao nhiu byte d liu?BT3: Mt gi IP c TTL = 1, source IP = 203.162.44.161, Destination IP = 111.130.16.24. Cho bit gi IP ny c c chuyn n ch c khng? Gii thch?

2.3-Phn mnh IP:-C ch:Khi kch thc tng cng ca gi IP ln hn kh nng truyn ca kt ni lp di (MTU) th gi IP c phn thnh cc mn nh hn cho ph hp vi MTU. pha nhp, cc mnh ca cng gi IP s c ti hp trc khi chuyn cho giao thc lp trn.-Nguyn tc phn mnh: cc mnh u tin c tng kch thc bng MTU, phn l cui cng c cha vo mnh ring.-C ch ti hp: Pha nhn c trn cc trng Identification, flags v Offset sp xp cc gi ng th t ban u. ngha ca cc c:-D (Dont fragment): y l gi khng c phn mnh-M (More): phn bit mnh trung gian v mnh cui cngBT1: Chuyn gi IP c kch thc tng cng l 3245 byte qua mt lin kt c MTU=1500 byte. Bit tt c cc gi IP u khng c option. Hy m t qu trnh phn mnh ca gi IP ny.

Gi IP gcMnh 1Mnh 2M 3MTU

-Kch thc gi IP gc = 3245 byte > MTU => c phn mnh-S lng mnh = (3245-20) / (1500-20) = 3 mnh-Qu trnh phn mnh:+Mnh 1: -Total length = 1500 byte -More = 1 -Offset = 0 / 8 = 0+ Mnh 2: -Total = 1500 byte -More = 1 -Offset = 1480 / 8 =185+Mnh 3: -Total length = 285 -More = 0 -Offset = 2960 / 8 = 370BT2: Chuyn gi IP c kch thc phn d liu 2400 byte qua mt lin kt c MTU = 740 byte. M t qu trnh phn mnh bit tt c cc gi IP u c tiu 20 byte.BT3: Mt gi IP c c More = 1, Hlen = 5, Total length = 820 byte, Offset = 300. Cho bit y l gi IP nguyn thy hay l mt mnh ca gi IP? Nu l mt mnh ca gi IP, cho bit y l mnh th my ca gi IP gc? (v hnh

Phn 3: Giao thc TCP3.1-c im k thut, so snh vi giao thc UDP-TCP l giao thc c kt ni, truyn d liu tin cy t u cui n u cui (end-to-end)-UDP l giao thc khng kt ni, truyn d liu khng m bo ni dung v th t, khng thc hin truyn li khi c li xy ra.-TCP s dng th tc bt tay thit lp kt ni trc khi bt u truyn d liu. S dng c ch iu khin dng (flow control) m bo tc truyn ph hp gia hai h thng.-UDP thch hp cho cc dch v c lu lng thp, yu cu p ng tc thi. TCP ph hp vi cc dch v lu lng d liu ln, chp nhn tr.3.2- Cu trc tiu gi TCP:

-Source port (16 bit): port trn my gi-Destination port (16 bit): Port trn my nhn-Sequence number (32 bit): s th t byte gi-Acknowledge number (32 bit): s th t byte nhn.-Header (4 bit): chiu di tiu -Code bits (6 bit): cc bit iu khin-Windows (16 bit): kch thc ca s, dng cho chc nng iu khin dng-Checksum (16 bit): kim tra li trn ton b gi.-Urgent (16 bit): Con tr xc nh v tr d liu khn+Port TCP: port l mt s nguyn 16 bit, c chc nng xc nh loi dch v lp ng dng. C 65535 port khc nhau, c chia thnh 2 nhm:-Cc port < 1024: c gn c nh cho cc dch v chun-Cc port t 1024 tr ln: c s dng t doMt s port in hnh: HTTP (80), HTTPS (443), SMTP (25), POP3(110), FTP (20, 21), Telnet (23), 3.3-C ch thit lp kt ni TCP:

Trc khi bt u truyn d liu, hai h thng u cui phi thit lp kt ni TCP theo th tc bt tay 3 bc nh sau:(1): My A gi gi d liu c c SYN=1 n 1 port xc nh ca my B. Gi ny c cha s th t khi to ca my A.(2): My B tr li bng gi d liu c c SYN v ACK = 1. Gi ny c cha s th t khi to ca my B, v xc nhn s th t trn my A bng cch tng s th t ca my A ln 1.(3): My A tr li bng gi c c ACK=1, v xc nhn s th t ca my B.3.4-C ch truyn d liu n gin ca TCP:

-Mi gi d liu gi i u phi nhn c hi p trong mt khong thi gian cho trc. Qu thi gian ny, gi s c t ng gi li.-Vic hi p c thc hin bng cc gn gi tr ACK number trn gi tr li bng vi s th t ca byte cui cng nhn c + 1-Gi hi p c th c gi ring l hoc kt hp vi gi d liu trn chiu ngc li.BT1: Hai my A v B truyn d liu dng TCP. B nhn 126 byte d liu t A. Gi s A gi tip 2 gi lin tc cho B. Gi th nht c 80 byte, gi th hai 40 byte. S th t trn gi th nht l 227, source port l 1302, dest port l 80. My B hi p ngay khi nhn xong 1 gi d liu.a-Trn gi th 2 gi t A -> B, cho bit s th t, source port, dest port? V hnh minh ha.

Sequence = 227, Sport = 1302, Dport=80Sequence = 267, Sport = 1302, Dport=80

-Thng tin trn gi th 2 gi t A->B: +S th t = 227 + 40 = 267 +Source port = 1302 +Dest port = 80b- Gi s gi th nht n trc gi th 2, cho bit trong gi hi bo ca my B, ACK number, source port v Dest Port?-Thng tin trn gi hi bo: +ACK number = 228 +Source port = 80 +Dest port = 1302c- Gi s gi 2 n trc gi 1, cho bit trong gi hi bo ca my B, gi tr ACK number=?-Do gi th 2 khng c chp nhn nn my B s yu cu gi li k t byte cui cng m my B nhn thnh cng: S th t trn gi trc gi th nht = 227 80 = 147S ACK trn gi hi bo 147 + 1 = 148.d-Gi s hai gi n ng th t, hi bo ca gi 1 b mt. V s truyn gi, cho bit cc gi tr: sequence number, ACK number, kch thc d liu trn tng gi.

Sequence number = 227, data=80 byteACK number = 228Sequence number = 267, data=40 byteACK number = 268

BT2: Qu trnh thit lp kt ni gia my A v my B nh sau:A -> B: SYN=1, seq=200B->A: SYN=1, ACK=1, seq=300, ack=201A->B: ACK=1, ack=301Sau my A gi tip 1 gi cha 120 byte d liu cho my B, hi cc gi tr SYN, ACK, seq, ack trn gi hi p t my B gi n my A, bit rng my B khng c d liu truyn cho my A. V s m t.

Phn 4: Cng ngh mng LAN4.1-phng thc iu khin truy xut CSMA/CD(ti liu Mng MT, chng 4, phn 4.1.1, trang 59-60)4.2-C ch v c im ca mng Ethernet(ti liu Mng MT, chng 4, phn 4.2, trang 62-68)Phn 5: Cng ngh WAN5.1-c im cng ngh ng dy thu bao s DSL(ti liu Mng MT, chng 6, phn 6.1, trang 103)5.2-Cc m hnh kt ni ADSL (ti liu Mng MT, chng 6, phn 6.1.7, trang 108)V hnh PPPoA, PPPoECu 1(2 im): Trnh by th tc thit lp kt ni ca giao thc TCP. Mt kt ni TCP c thit lp t my A n my B vi gi tr sequence number khi to trn my A l 300, trn my B l 200. Sau khi thit lp kt ni, my A gi cho my B mt gi d liu c kch thc 120 byte. Sau khi nhn thnh cng, my B gi li cho my A mt gi d liu c kch thc 64 byte. Hy v s m t qu trnh truyn nhn (bao gm c th tc thit lp kt ni), gi tr cc c SYN, ACK cng vi gi tr sequence number v acknowledge number trn tng gi d liu. 1- Trnh by th tc thit lp kt ni ca giao thc TCP (0,25)2- V hnh 0,253- Hy v s m t qu trnh truyn nhn (bao gm c th tc thit lp kt ni) (0,5)4- gi tr cc c SYN trn tng gi (0,25)5- gi tr cc c ACK trn tng gi(0,25)6- gi tr seq trn tng gi(0,25)7- gi tr ack trn tng gi(0,25)15