Ngaphambi kokuba siqale isifundo sevidiyo sanamhlanje, ndifuna ukubulela wonke umntu othe wanegalelo ekudumeni kwekhosi yam kuYouTube. Xa ndiqala malunga neenyanga ezi-8 ezedlulileyo, andizange ndilindele impumelelo enjalo - namhlanje izifundo zam zijongwe ngabantu be-312724, ndinababhalisi be-11208. Andizange ndiyiphuphe into yokuba esi siqalo siphantsi sinokufikelela kwinqanaba eliphezulu. Kodwa masingachithi xesha singene ngqo kwisifundo sanamhlanje. Namhlanje siza kugcwalisa izikhewu ezenzekileyo kwizifundo zevidiyo ezisi-7 zokugqibela. Nangona namhlanje lusuku lwe-6 kuphela, usuku lwe-3 lwaphulwa lwaba yizifundo zevidiyo ezi-3, ngoko namhlanje uya kubukela isifundo sesibhozo sevidiyo.
Namhlanje siza kugubungela izihloko ezi-3 ezibalulekileyo: i-DHCP, i-TCP yothutho, kunye neenombolo zezibuko eziqhelekileyo. Sele sithethile malunga needilesi ze-IP, kwaye enye yezona zinto zibalulekileyo kuqwalaselo lwedilesi ye-IP yi-DHCP.
I-DHCP imele i-Dynamic Host Configuration Protocol kwaye yiprothokholi enceda ngokuguqukayo ukuqwalasela iidilesi ze-IP kwiinginginya. Ngoko sonke siyibonile le festile. Xa ucofa kwi-"Fumana idilesi ye-IP ngokuzenzekelayo", ikhompyutha ibheka iseva ye-DHCP elungiselelwe kwi-subnet efanayo kwaye ithumela iipakethi ezahlukeneyo kunye nezicelo zedilesi ye-IP. Iprotocol ye-DHCP inemiyalezo emi-6, apho emi-4 ibalulekile ekwabeleni idilesi ye-IP.
Umyalezo wokuqala ngumyalezo we-DHCP DISCOVERY. Umyalezo wokufunyanwa kwe-DHCP ufana nomyalezo wokubulisa. Xa isixhobo esitsha sijoyina inethiwekhi, sibuza ukuba kukho iseva ye-DHCP kwinethiwekhi.
Into oyibonayo kwisilayidi ibonakala njengesicelo sosasazo apho isixhobo sinxibelelana nazo zonke izixhobo kuthungelwano sikhangela iseva yeDHCP. Njengoko benditshilo, esi sisicelo sosasazo, ngoko ke zonke izixhobo ezikwinethiwekhi ziyakuva.
Ukuba kukho iseva ye-DHCP kwinethiwekhi, ithumela ipakethi - i-DHCP OFFER offer. Isiphakamiso sithetha ukuba iseva ye-DHCP, ekuphenduleni isicelo sokufumanisa, ithumela uqwalaselo kumxhasi, icela umxhasi ukuba amkele idilesi ethile ye-IP.
Umncedisi we-DHCP ugcina idilesi ye-IP, kule meko 192.168.1.2, ayiboneleli, kodwa kunoko igcina le dilesi kwisixhobo. Ngexesha elifanayo, iphakheji yokunikezela iqulethe idilesi yayo ye-IP yeseva ye-DHCP.
Ukuba kukho ngaphezu kweseva enye ye-DHCP kule nethiwekhi, enye iseva ye-DHCP, xa ifumana isicelo sokusasazwa komthengi, iya kunika kwakhona idilesi ye-IP, umzekelo, 192.168.1.50. Akuqhelekanga ukuba neeseva ezimbini ezahlukeneyo ze-DHCP ezilungiselelwe kwinethiwekhi efanayo, kodwa ngamanye amaxesha kuyenzeka. Ngoko xa umnikelo we-DHCP uthunyelwa kumxhasi, ufumana izinto ezi-2 zeDHCP kwaye kufuneka ngoku enze isigqibo sokuba loluphi unikezelo lweDHCP efuna ukusamkela.
Makhe sicinge ukuba umxhasi wamkela isicelo sokuqala. Oku kuthetha ukuba umxhasi uthumela isicelo se-DHCP REQUEST esithi ngokoqobo "Ndiyayamkela idilesi ye-IP 192.168.1.2 enikezelwa ngumncedisi we-DHCP 192.168.1.1."
Emva kokufumana isicelo, iseva ye-192.168.1.1 ye-DHCP iphendula "kulungile, ndiyavuma," oko kukuthi, ivuma isicelo kwaye ithumela le DHCP ACK kumxhasi. Kodwa siyakhumbula ukuba enye iseva yeDHCP igcine idilesi ye-IP ye-1.50 kumxhasi. Nje ukuba ifumane isicelo sokusasazwa komthengi, iya kwazi malunga nokusilela kwaye iya kubeka loo dilesi ye-IP kwakhona echibini ukuze ikwazi ukwabela omnye umxhasi ukuba ufumana esinye isicelo.
Le yimiyalezo emi-4 ebalulekileyo i-DHCP etshintshiselana ngayo xa inika iidilesi ze-IP. Okulandelayo, i-DHCP ineminye imiyalezo emi-2 yolwazi. Umyalezo wolwazi ukhutshwa ngumxhasi ukuba ufuna ulwazi oluninzi kunokuba lufunyenwe kwigatya le-DHCP OFFER kwinqanaba lesibini. Ukuba umncedisi akazange abonelele ngolwazi olwaneleyo kwi-DHCP enikezela, okanye ukuba umxhasi ufuna ulwazi olungakumbi kunokuba luqulethwe kwipakethi yokunikezela, ucela ulwazi olongezelelweyo lweDHCP. Kukho omnye umyalezo othunyelwa ngumxhasi kumncedisi - lo ngu-DHCP RELEASE. Ikwazisa ukuba umxhasi ufuna ukukhulula idilesi ye-IP esele ikhona.
Nangona kunjalo, oko kwenzeka rhoqo kukuba umsebenzisi unqamula kwinethiwekhi ngaphambi kokuba umxhasi abe nexesha lokuthumela i-DHCP RELEASE kumncedisi. Oku kwenzeka xa ucima ikhompyuter, esiyenzayo. Kule meko, umxhasi wenethiwekhi, okanye ikhompyutha, ayinalo ixesha lokwazisa umncedisi ukuba akhulule idilesi esetyenzisiweyo, ngoko ke i-DHCP RELEASE ayilonyathelo elifunekayo. Amanyathelo afunekayo okufumana idilesi ye-IP ngala: ukufunyanwa kwe-DHCP, umnikelo we-DHCP, isicelo se-DHCP, kunye nokuxhawula ngesandla kwe-DHCP.
Kwesinye sezifundo ezilandelayo ndiza kukuxelela indlela esimisa ngayo iseva ye-DHCP xa sidala i-pool ye-DNCP. Ngokudibanisa sithetha ukuba uxelela umncedisi ukuba abele iidilesi ze-IP kuluhlu 192.168.1.1 ukuya 192.168.1.254. Ngaloo ndlela, iseva ye-DHCP iya kudala i-pool, ibeke iidilesi ze-IP ze-254 kuyo, kwaye iya kukwazi ukunika iidilesi kubaxhasi kwinethiwekhi kuphela kule ndawo. Ke le yinto efana nolungiselelo lolawulo olunokwenziwa ngumsebenzisi.
Ngoku makhe sijonge usasazo lwe-TCP. Andazi nokuba uyayazi na le "phone" ikulo mfanekiso, kodwa sisengabantwana besisebenzisa ezi toti zidityaniswe ngomtya ukuze sincokole.
Ngelishwa, isizukulwana sanamhlanje asinakukwazi ukufumana “ubunewunewu” obunjalo. Ndithetha ukuthi namhlanje abantwana baphambi komabonakude bekwiminyaka enye, badlala iPSP kwaye mhlawumbi iyaxoxwa le nto kodwa ndicinga ukuba sasinobuntwana obungcono kakhulu, siye saphuma ngaphandle sadlala imidlalo kwaye abantwana banamhlanje abanakutsalwa kude nesofa. .
Unyana wam unonyaka qha sendimbona ukuba ulikhoboka le-iPad, ndithetha ukuthi usemncinci kakhulu kodwa ndicinga ukuba abantwana banamhlanje sele bezelwe bekwazi ukuphatha izixhobo ze-elektroniki. So bendifuna ukuthi singabantwana xa sidlala senze imingxuma ngamatoti, sithi xa sibotshwa ngomtya sithethe into kwitoti enye, kwelinye icala ayive lento ithethwayo. kuye, ngokubeka inkonkxa nje endlebeni yakhe . Ngoko ifana kakhulu noqhagamshelwano lwenethiwekhi.
Namhlanje, nokudluliselwa kwe-TCP kufuneka kube noqhagamshelo ekufuneka lusekwe phambi kokuba udluliselo lwedatha lwangempela luqale. Njengoko sixoxile kwizifundo zangaphambili, i-TCP i-transmission-oriented-oriented transmission ngelixa i-UDP i-transmission-oriented transmission. Unokuthi iUDP kulapho ndigibisela khona ibhola kwaye kukuwe ukuba ungayibamba. Noba sowuready ukwenza lonto ayiyongxaki yam, ndizomshiya qha.
I-TCP ifana nokuba uthetha nomfana kwaye ulumkise kwangaphambili ukuba uza kuphosa ibhola, ngoko wenze ibhondi, uze uphose ibhola ukuze iqabane lakho lilungele ukuba liyibambe. Ngoko ke i-TCP yakha umdibaniso kwaye emva koko iqalise ukwenza uthumelo lokwenene.
Makhe sijonge indlela eyenza unxibelelwano olunjalo. Le protocol isebenzisa iindlela ezi-3 zokuxhawula izandla ukwenza umdibaniso. Eli akulona igama lobugcisa kakhulu, kodwa sele lisetyenziswe ixesha elide ukuchaza uxhumano lwe-TCP. Ukuxhawulana kweendlela ezi-3 kuqalwa sisixhobo sokuthumela, kunye nomxhasi othumela ipakethe eneflegi yeSYN kumncedisi.
Masithi intombazana engaphambili, esinokubona ubuso bakhe, sisixhobo A, kwaye intombazana ngasemva, ubuso bayo bungabonakali, sisixhobo B. Intombazana A ithumela ipakethi yeSYN kwintombazana B, kwaye ithi: "Kakhulu, ngubani ofuna ukunxibelelana nam. Ngoko ke, kufuneka ndiphendule ukuba ndikulungele ukunxibelelana!” Yenziwa njani? Omnye unokuthumela nje enye ipakethi ye-SYN kwaye emva koko i-ACK ebonisa ukufunyanwa kwepakethi ye-SYN yoqobo. Kodwa endaweni yokuthumela ii-ACKs ngokwahlukileyo, umncedisi wenza ipakethe eqhelekileyo equlethe i-SYN kunye ne-ACK kwaye iyidlulisele kwinethiwekhi.
Ke ngeli xesha, isixhobo A sithumele ipakethi yeSYN kwaye safumana umva iSYN/ACK ipakethe. Ngoku isixhobo A kufuneka sithumele isixhobo B ipakethi ye-ACK, oko kukuthi, siqinisekise ukuba sifumene imvume kwisixhobo B ukuseka unxibelelwano. Ngaloo ndlela, zombini izixhobo zifumene iipakethi ze-SYN kunye ne-ACK, kwaye ngoku sinokuthi uxhulumaniso lusekiwe, oko kukuthi, ukuxhawula kwe-3-stage kugqitywe usebenzisa i-protocol ye-TCP.
Okulandelayo siza kujonga iteknoloji ye-TCP Windowing. Ukubeka ngokulula, yindlela esetyenziswa kwi-TCP/IP ukuxoxisana ngezakhono zomthumeli kunye nomamkeli.
Masithi kwiWindows sizama ukudlulisa ifayile enkulu, yithi i-2 GB ngobukhulu, ukusuka kwenye idrayivu ukuya kwenye. Ekuqaleni kokudluliselwa, inkqubo iya kusazisa ukuba ukuhanjiswa kwefayile kuya kuthatha malunga ne-1 ngonyaka. Kodwa kwimizuzwana embalwa kamva inkqubo iya kuzilungisa ithi: “Owu, yima umzuzu, ndicinga ukuba iyakuthatha malunga neenyanga ezi-6, hayi unyaka.” Kuza kudlula ixesha elincinci kwaye iWindows iya kuthi: "Ndicinga ukuba ndingakwazi ukuhambisa ifayile kwinyanga enye." Oku kuya kulandelwa ngumyalezo othi “1 day”, “1 hours”, “6 hours”, “3 hour”, “1 minutes”, “20 minutes”, “10 minutes”. Enyanisweni, yonke inkqubo yokudlulisa iifayile iya kuthatha imizuzu emi-3 kuphela. Yenzeka njani le nto? Ekuqaleni, xa isixhobo sakho sizama ukunxibelelana nesinye isixhobo, sithumela ipakethi enye kwaye silinde ukuqinisekiswa. Ukuba isixhobo silinda ixesha elide ukuze siqinisekise, sicinga ukuba: "ukuba kufuneka ndidlulisele i-3 GB yedatha kwesi santya, kuya kuthatha iminyaka eyi-2." Emva kwexesha elithile, isixhobo sakho sifumana i-ACK kwaye sicinga, “Kulungile, ndithumele ipakethi enye kwaye ndifumene i-ACK, kungoko umamkeli anokufumana ipakethi enye. Ngoku ndiza kuzama ukumthumelela iipakethi ezili-2 endaweni yenye.” Umthumeli uthumela iipakethi ze-1 kwaye emva kwexesha elithile ufumana ukuqinisekiswa kwe-ACK kwisixhobo esifumanayo, oku kuthetha ukuba ummkeli ulindele ipakethe elandelayo, ye-10. Umthumeli ucinga: “Kulungile, ekubeni umamkeli ebephethe iipakethe ezili-10 ngexesha elinye, ngoku ndiza kuzama ukumthumelela iipakethe ezili-11 endaweni yeshumi.” Uthumela iipakethe ezili-10, yaye lowo uzifumanayo uphendula athi uzifumene yaye ngoku ulindele iipakethe ezili-100. Ngaloo ndlela, ngokuhamba kwexesha, inani leepakethi ezigqithisiweyo landa.
Yingakho ubona ukuhla ngokukhawuleza kwexesha lokukopisha ifayile xa kuthelekiswa nento echazwe ekuqaleni - oku kungenxa yokunyuka kwamandla okudlulisa inani elikhulu ledatha. Nangona kunjalo, kufika ixesha apho ukunyuka okuthe kratya kwivolumu yothumelo kungenakwenzeka. Masithi uthumele iipakethi ezingama-10000, kodwa isithinteli sesixhobo somamkeli sinokwamkela kuphela i-9000. Kule meko, umamkeli uthumela i-ACK nomyalezo: "Ndifumene iipakethi ezingama-9000 kwaye ngoku ndilungele ukufumana i-9001." Ukusuka apha, umthumeli ugqiba ukuba i-buffer yesixhobo esifumanayo inomthamo we-9000 kuphela, oko kuthetha ukuba ukususela ngoku andiyi kuthumela iipakethi ezingaphezu kwe-9000 ngexesha. Kule meko, umthumeli ubala ngokukhawuleza ixesha eliya kumthatha ukuba adlulisele inani eliseleyo ledatha kwiingxenye zeepakethi ze-9000, kwaye unike imizuzu emi-3. Le mizuzu mithathu lelona xesha losulelo. Yiloo nto eyenziwa yi-TCP Windowing.
Le yenye yezo ndlela zokuxinana kwetrafikhi apho isixhobo sokuthumela ekugqibeleni siyaqonda ukuba yintoni na umthamo wenethiwekhi. Usenokuba uyazibuza ukuba kutheni bengenakuvumelana kwangaphambili malunga nokuba yintoni umthamo wesixhobo esifumanayo? Inyaniso kukuba oku akunakwenzeka ngokobuchwepheshe kuba kukho iintlobo ezahlukeneyo zezixhobo kwinethiwekhi. Masithi unayo i-iPad kwaye inesantya esahlukileyo sokudluliselwa kwedatha/umamkeli kune-iPhone, unokuba neentlobo ezahlukeneyo zeefowuni, okanye mhlawumbi unekhompyuter endala kakhulu. Ke ngoko, wonke umntu une-bandwidth yenethiwekhi eyahlukileyo.
Yingakho iteknoloji ye-TCP Windowing yaphuhliswa, xa ukuhanjiswa kwedatha kuqala ngesantya esiphantsi okanye ngokugqithiswa kwenani elincinci leepakethi, ngokukhawuleza ukwandisa i-traffic "window". Uthumela ipakethe enye, iipakethe ezi-5, iipakethe ezili-10, iipakethe ezili-1000, iipakethe ezingama-10000 kwaye uyivule kancinci kancinci loo festile de “ukuvulwa” kufikelele kumthamo omkhulu wetrafikhi othunyelwe ngexesha elithile. Ngaloo ndlela, ingcamango yeWindowing yinxalenye yokusebenza kweprotocol ye-TCP.
Okulandelayo siza kujonga amanani aqhelekileyo ezibuko. Imeko yeklasikhi xa unomncedisi oyintloko we-1, mhlawumbi iziko ledatha. Ibandakanya iseva yefayile, iseva yewebhu, iseva yeposi kunye neseva yeDHCP. Ngoku, ukuba enye yeekhompyuter zabathengi inxibelelana neziko ledatha, eliphakathi komfanekiso, liya kuqala ukuthumela ifayile yefayile yetrafikhi kwizixhobo zabathengi. Le traffic iboniswa ngombala obomvu kwaye iya kuhanjiswa kwizibuko elithile lesicelo esisuka kumncedisi othile.
Umncedisi wazi njani ukuba i-traffic ethile kufuneka iye phi? Ufunda oku kwinombolo yezibuko lendawo. Ukuba ujonga isakhelo, uya kubona ukuba kugqithiso lwedatha nganye kukho ukukhankanywa kwenombolo yezibuko ekuyiwa kuyo kunye nenombolo yezibuko yomthombo. Uyabona ukuba i-traffic eluhlaza okwesibhakabhaka kunye nebomvu, kunye ne-blue traffic yi-traffic server yewebhu, zombini ziya kwi-server efanayo yomzimba, eneeseva ezahlukeneyo ezifakiwe. Ukuba eli liziko ledatha, ngoko isebenzisa iiseva ezibonakalayo. Ngoko bazi njani ukuba i-traffic ebomvu bekufanele ibuyele kwi-laptop ekhohlo kunye nedilesi ye-IP? Bayazi oku kubulela kumanani ezibuko. Ukuba ubhekisela kwinqaku le-Wikipedia elithi "Uluhlu lwe-TCP kunye ne-UDP Ports", uya kubona ukuba idwelisa zonke iinombolo ze-port eziqhelekileyo.
Ukuba uskrolela phantsi kweli phepha unokubona ukuba lukhulu kangakanani olu luhlu. Iqulethe malunga nama-61 amanani. Iinombolo zePort ukusuka kwi-000 ukuya kwi-1 ziyaziwa njengezona nombolo zezibuko eziqhelekileyo. Umzekelo, izibuko 1024/TCP lelokuthumela imiyalelo yeftp, izibuko 21 yeye ssh, izibuko 22 yeye Telnet, oko kukuthi, ukuthumela imiyalezo engafihlwanga. Ichweba elidume kakhulu le-23 lithwala idatha kwi-HTTP, ngelixa i-port 80 ithwala idatha efihliweyo kwi-HTTPS, efana nenguqulo ekhuselekileyo ye-HTTP.
Ezinye izibuko zinikezelwe kuzo zombini i-TCP kunye ne-UDP, kwaye ezinye zenza imisebenzi eyahlukeneyo ngokuxhomekeke ekubeni uxhulumaniso luyi-TCP okanye i-UDP. Ngoko, ngokusemthethweni i-TCP port 80 isetyenziselwa i-HTTP, kwaye ngokungekho mthethweni i-UDP port 80 isetyenziselwa i-HTTP, kodwa phantsi kwe-protocol ye-HTTP eyahlukileyo - i-QUIC.
Ngoko ke, iinombolo ze-port kwi-TCP azisoloko zijoliswe ukwenza into efanayo nakwi-UDP. Awudingi ukufunda olu luhlu ngentliziyo, akunakwenzeka ukuba ukhumbule, kodwa kufuneka ukwazi amanani athile aziwayo kunye nawona aqhelekileyo. Njengoko benditshilo, ezinye zezi zibuko zinenjongo esemthethweni, echazwe kwimigangatho, kwaye ezinye zinenjongo engafanelekanga, njengoko kunjalo ngeChromium.
Ke, le theyibhile idwelisa zonke iinombolo zezibuko eziqhelekileyo, kwaye la manani asetyenziselwa ukuthumela nokufumana i-traffic xa usebenzisa izicelo ezithile.
Ngoku makhe sijonge indlela idatha ehamba ngayo kwinethiwekhi ngokusekwe koluphi ulwazi oluncinci esilwaziyo. Masithi ikhomputha 10.1.1.10 ifuna ukuqhagamshelana nale khompyutha, okanye lo mncedisi, onedilesi 30.1.1.10. Ngaphantsi kwedilesi ye-IP yesixhobo ngasinye idilesi yayo ye-MAC. Ndinika umzekelo wedilesi ye-MAC enamagama ama-4 kuphela okugqibela, kodwa ekusebenzeni yinombolo ye-48-bit ye-hexadecimal enamagama ali-12. Kuba inani ngalinye kula lineebhithi ezi-4, 12 hexadecimal amanani amele inani lamasuntswana angama-48.
Njengoko sisazi, ukuba esi sixhobo sifuna ukuqhagamshelana nalo mncedisi, inyathelo lokuqala lokuxhawula indlela ye-3 kufuneka lenziwe kuqala, oko kukuthi, ukuthumela ipakethi ye-SYN. Xa esi sicelo senziwe, ikhompyutha 10.1.1.10 iya kukhankanya inombolo yezibuko yomthombo, leyo iWindows iyayidala ngamandla. IiWindows zikhetha ngokungakhethi inombolo yezibuko phakathi kwe-1 kunye ne-65,000. Kodwa ekubeni amanani aqalayo kwi-1 ukuya kwi-1024 ayaziwa ngokubanzi, kulo mzekelo inkqubo iya kuqwalasela amanani amakhulu kune-25000 kwaye idale i-port ye-random source, umzekelo, inombolo ye-25113.
Okulandelayo, inkqubo iya kongeza i-port yokuya kwipakethi, kulo mzekelo i-port 21, kuba isicelo esizama ukuxhuma kule seva ye-FTP siyazi ukuba kufuneka ithumele i-FTP traffic.
Emva koko, ikhompuyutha yethu ithi, "Kulungile, idilesi yam ye-IP ngu-10.1.1.10, kwaye kufuneka ndiqhagamshelane nedilesi ye-IP 30.1.1.10." Zombini ezi dilesi zibandakanyiwe kwipakethi ukwenza isicelo se-SYN, kwaye le pakethi ayiyi kutshintsha kude kube sekupheleni koqhagamshelwano.
Ndifuna uqonde kule vidiyo ukuba idatha ihamba njani kwinethiwekhi. Xa ikhomputha yethu ithumela isicelo ibona umthombo wedilesi ye-IP kunye nedilesi ye-IP yendawo ekuyiwa kuyo, iyaqonda ukuba idilesi yendawo ayikho kuloo nethiwekhi yendawo. Ndilibele ukuthi ezi zizo zonke/24 iidilesi ze IP. Ngoko ukuba ujonge idilesi ye-IP / 24, uya kuqonda ukuba iikhomputha 10.1.1.10 kunye ne-30.1.1.10 azikho kwinethiwekhi efanayo. Ngaloo ndlela, ikhompyutha ethumela isicelo iyaqonda ukuba ukuze ihambe kule nethiwekhi, kufuneka iqhagamshelane nesango le-10.1.1.1, elilungiselelwe kwenye ye-interfaces ye-router. Iyazi ukuba kufuneka ihambe kwi-10.1.1.1 kwaye iyazi idilesi ye-MAC ye-1111, kodwa ingayazi idilesi ye-MAC yesango 10.1.1.1. Inga wenzantoni? Ithumela isicelo sosasazo lwe-ARP ukuba zonke izixhobo kwinethiwekhi ziya kufumana, kodwa kuphela i-router enedilesi ye-IP 10.1.1.1 iya kusabela kuyo.
I-router iya kuphendula ngedilesi yayo ye-AAAA ye-MAC, kwaye zombini idilesi ye-MAC yomthombo kunye nendawo yokuya kuyo nayo iya kufakwa kule freyimu. Emva kokuba isakhelo silungile, i-CRC yokuhlola ingqibelelo yedatha, eyi-algorithm yokufumana i-checksum yokubona iimpazamo, iya kwenziwa ngaphambi kokushiya inethiwekhi.
I-Cyclic Redundancy CRC ithetha ukuba esi sikhokelo sonke, ukusuka kwi-SYN ukuya kwidilesi yokugqibela ye-MAC, iqhutywa nge-algorithm ye-hashing, yithi i-MD5, ekhokelela kwixabiso le-hash. Ixabiso le-hash, okanye i-MD5 checksum, ibekwe ekuqaleni kwesakhelo.
Ndiyibhale nge-FCS/CRC kuba i-FCS luLudwe lweSakhelo sokuHlola, ixabiso le-CRC yebhayithi ezine. Abanye abantu basebenzisa igama elithi FCS kwaye abanye basebenzisa igama elithi CRC, ke ndibandakanyile omabini amagama. Kodwa ngokwesiseko lixabiso nje le-hash. Kuyafuneka ukuqinisekisa ukuba yonke idatha efunyenwe kwinethiwekhi ayiqulathanga iimpazamo. Ngoko ke, xa le freyimu ifikelela kwi-router, into yokuqala eya kuyenza i-router ibala i-checksum ngokwayo kwaye iqhathanise nexabiso le-FCS okanye le-CRC eliqulethe isakhelo esifunyenweyo. Ngale ndlela unokukhangela ukuba idatha efunyenwe kwinethiwekhi ayinayo iimpazamo, emva koko uya kususa i-checksum kwisakhelo.
Emva koko, i-router iya kujonga idilesi ye-MAC kwaye ithi, "Kulungile, idilesi ye-MAC AAAA ithetha ukuba isakhelo sibhekiswe kum," kwaye ucime inxalenye yesakhelo esiqulethe iidilesi ze-MAC.
Ukujonga idilesi ye-IP ye-30.1.1.10, uya kuqonda ukuba le pakethi ayibhekiswanga kuye kwaye kufuneka iqhube ngakumbi nge-router.
Ngoku i-router "icinga" kufuneka ibone apho inethiwekhi enedilesi 30.1.1.10 ikhona. Asikayihlanganisi ingqikelelo epheleleyo yomzila okwangoku, kodwa siyazi ukuba iirotha zinetafile yokuqhuba. Le theyibhile inongeno lwenethiwekhi enedilesi 30.1.1.0. Njengoko ukhumbula, le ayisiyiyo idilesi ye-IP yomkhosi, kodwa isichongi somsebenzi womnatha. I-router iya "kucinga" ukuba inokufikelela kwidilesi 30.1.1.0/24 ngokuhamba nge-router 20.1.1.2.
Usenokubuza, ukwazi njani oku? Gcina nje ukhumbula ukuba iyakukwazi oku mhlawumbi kwiiprothokholi zomzila okanye kwizicwangciso zakho ukuba njengomlawuli uqwalasele indlela engatshintshiyo. Kodwa kuyo nayiphi na imeko, le tafile yomzila we-router iqulethe ukungena okuchanekileyo, ngoko iyazi ukuba kufuneka ithumele le pakethi kwi-20.1.1.2. Ukucinga ukuba i-router sele iyazi idilesi ye-MAC yokuya kuyo, siya kuqhubeka nokuthumela ipakethi. Ukuba akayazi le dilesi, uya kuqalisa i-ARP kwakhona, afumane idilesi ye-MAC ye-router 20.1.1.2, kwaye inkqubo yokuthumela isakhelo iya kuqhubeka kwakhona.
Ke sicinga ukuba sele iyazi idilesi ye-MAC, ngoko ke siya kuba nedilesi ye-MAC yomthombo we-BBB kunye nedilesi ye-MAC yeCCC. Umzila kwakhona ubala i-FCS/CRC kwaye uyibeke ekuqaleni kwesakhelo.
Emva koko ithumela le freyimu phezu kwenethiwekhi, isakhelo sifikelela kwi-router 20.1.12, sihlola i-checksum, siqinisekisa ukuba idatha ayibonakalisi, kwaye isusa i-FCS / CRC. Emva koko "inciphisa" iidilesi ze-MAC, ijonge indawo ekuyiyo kwaye ibone ukuba yi-30.1.1.10. Uyazi ukuba le dilesi iqhagamshelwe kujongano lwakhe. Inkqubo yokwakhiwa kwesakhelo efanayo iphinda iphindwe, i-router yongeza umthombo kunye nendawo yokuya kuyo amaxabiso edilesi ye-MAC, yenza i-hashing, ifake i-hash kwisakhelo kwaye iyithumele ngaphaya kwenethiwekhi.
Umncedisi wethu, xa ekugqibeleni efumene isicelo se-SYN esibhekiswa kuyo, ijonga i-hash checksum, kwaye ukuba ipakethi ayinazimpazamo, icima i-hash. Emva koko ususa iidilesi ze-MAC, ujonge idilesi ye-IP kwaye uyaqonda ukuba le pakethi ibhekiswe kuye.
Emva koko, icutha iidilesi ze-IP ezinxulumene nomgangatho wesithathu wemodeli ye-OSI kwaye ijonge amanani ezibuko.
Ubona i-port 21, oku kuthetha ukuba i-FTP traffic, ibona i-SYN kwaye ngoko iyaqonda ukuba umntu uzama ukuthetha naye.
Ngoku, ngokusekelwe kwinto esiyifundileyo malunga nokubamba isandla, umncedisi we-30.1.1.10 uya kudala ipakethe ye-SYN / ACK kwaye uyibuyisele kwikhompyutheni ye-10.1.1.10. Emva kokufumana le pakethi, isixhobo 10.1.1.10 siya kudala i-ACK, sidlule kwinethiwekhi ngendlela efanayo nepakethi ye-SYN, kwaye emva kokuba umncedisi efumana i-ACK, uxhulumaniso luya kusekwa.
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