Tisati tatanga dzidziso yevhidhiyo yanhasi, ndinoda kutenda munhu wese akaita kuti kosi yangu izivikanwe paYouTube. Pandakaitanga inenge mwedzi misere yapfuura, ndakanga ndisingatarisiri kubudirira kwakadaro - nhasi zvidzidzo zvangu zvakaonekwa nevanhu 8, ndine 312724 vanyoresa. Handina kumbofunga kuti kutanga kwakaderera uku kungasvika pakakwirira kudaro. Asi ngatisatambise nguva tonanga kuchidzidzo chanhasi. Nhasi tichazadza mapeji akaitika muzvidzidzo zvinomwe zvevhidhiyo. Kunyangwe nhasi ingori zuva rechitanhatu, zuva rechitatu rakaputswa kuita 11208 vhidhiyo zvidzidzo, saka nhasi iwe unonyatso tarisa yechisere vhidhiyo chidzidzo.
Nhasi tichave tichivhara misoro mitatu yakakosha: DHCP, TCP transport, uye nhamba dzechiteshi chengarava. Takatotaura nezve IP kero, uye chimwe chezvinhu zvakakosha muIP kero kumisikidzwa iDHCP.
DHCP inomirira Dynamic Host Configuration Protocol uye iprotocol inobatsira zvine simba kugadzirisa kero dzeIP dzevagamuchiri. Saka tese takaona hwindo iri. Paunodzvanya pane "Tora IP kero otomatiki" sarudzo, komputa inotsvaga sevha yeDHCP inogadziriswa pane imwechete subnet uye inotumira akasiyana mapaketi uye zvikumbiro zvekero yeIP. Iyo DHCP protocol ine 6 mameseji, ayo mana akakosha pakugovera IP kero.
Meseji yekutanga ndeye DHCP DISCOVERY meseji. Meseji yekuwana DHCP yakafanana neshoko rekukwazisa. Kana mudziyo mutsva ukapinda kunetiweki, inobvunza kana paine sevha yeDHCP panetiweki.
Zvaunoona musiraidhi zvinotaridzika sechikumbiro chekutepfenyura uko mudziyo unobata zvishandiso zvese panetiweki uchitsvaga sevha yeDHCP. Sezvandakataura, ichi chikumbiro chekutepfenyura, saka zvese zvishandiso zviri panetwork zvinozvinzwa.
Kana paine sevha yeDHCP pane network, inotumira pakiti - iyo DHCP OFFER inopa. Chikumbiro chinoreva kuti sevha yeDHCP, mukupindura kuchikumbiro chekuwanikwa, inotumira gadziriso kumutengi, ichikumbira mutengi kuti agamuchire chaiyo IP kero.
Sevha yeDHCP inochengetedza IP kero, munyaya iyi 192.168.1.2, haipe, asi inochengetedza kero iyi yemudziyo. Panguva imwecheteyo, iyo yekupa package ine yayo IP kero yeDHCP server.
Kana pane inodarika sevha yeDHCP panetiweki iyi, imwe sevha yeDHCP, payakagamuchira chikumbiro chekutepfenyura chemutengi, inozopawo kero yayo yeIP, semuenzaniso, 192.168.1.50. Hazvina kujairika kuve nemasevha maviri akasiyana eDHCP akagadzirirwa pane imwecheteyo network, asi dzimwe nguva zvinoitika. Saka kana chinopihwa cheDHCP chikatumirwa kumutengi, chinogashira 2 DHCP chinopihwa uye chinofanirwa kusarudza kuti ndechipi chinopihwa neDHCP chainoda kugamuchira.
Ngatifungei kuti mutengi anogamuchira yekutanga application. Izvi zvinoreva kuti mutengi anotumira chikumbiro cheDHCP REQUEST chinoti "Ndinobvuma IP kero 192.168.1.2 inopiwa neDHCP server 192.168.1.1."
Pakugamuchira chikumbiro, 192.168.1.1 DHCP server inopindura "zvakanaka, ndinobvuma," ndiko kuti, inobvuma chikumbiro uye inotumira iyi DHCP ACK kumutengi. Asi isu tinorangarira kuti imwe sevha yeDHCP yakachengeta IP kero ye1.50 yemutengi. Kana yangotambira chikumbiro chekutepfenyura chemutengi, inoziva nezve kutadza uye ichadzosera iyo IP kero mudziva kuitira kuti igoigovera kune mumwe mutengi kana ikagamuchira chimwe chikumbiro.
Aya ndiwo mameseji mana akakosha ayo DHCP inotsinhana painopa IP kero. Zvadaro, DHCP ine 4 mamwe mashoko emashoko. Mharidzo yeruzivo inopihwa nemutengi kana ichida ruzivo rwakawanda kupfuura yayakagamuchira muDHCP OFFER clause mudanho rechipiri. Kana sevha isina kupa ruzivo rwakakwana muchirongwa cheDHCP, kana kana mutengi achida ruzivo rwakanyanya kupfuura zvaive mupacket yekupa, inokumbira rumwe ruzivo rweDHCP. Pane imwezve meseji iyo mutengi anotumira kune server - iyi ndiyo DHCP RELEASE. Iyo inokuzivisa iwe kuti mutengi anoda kuburitsa iyo iripo IP kero.
Nekudaro, zvinowanzoitika ndezvekuti mushandisi anobvisa kubva kune network mutengi asati awana nguva yekutumira DHCP RELEASE kune server. Izvi zvinoitika kana iwe ukadzima komputa, izvo zvatinoita. Muchiitiko ichi, network client, kana kombiyuta, haina nguva yekuzivisa sevha kuti isunungure kero yakashandiswa, saka DHCP RELEASE haisi danho rinodiwa. Matanho anodiwa kuti uwane IP kero ndeaya: kuwanikwa kweDHCP, kupihwa kweDHCP, chikumbiro cheDHCP, uye kubata maoko kweDHCP.
Mune chimwe chezvidzidzo zvinotevera ini ndichakuudza kuti tinogadzirisa sei sevha yeDHCP kana tichigadzira dziva reDNCP. Nekubatanidza tinoreva kuti iwe unoudza sevha kuti ipe kero dzeIP mumhando 192.168.1.1 kusvika 192.168.1.254. Saka, sevha yeDHCP ichagadzira dziva, isa 254 IP kero mairi, uye ichakwanisa kupa kero kune vatengi pane network chete kubva padziva iri. Saka ichi chinhu senge manejimendi ekutonga anogona kuitwa nemushandisi.
Zvino ngatitarisei kuTCP kutapurirana. Handizivi kuti “nharembozha” iri pamufananidzo munoiziva here, asi tichiri vana taimboshandisa zvigaba izvi zvakabatanidzwa netambo kuti titaurirane.
Sezvineiwo, chizvarwa chanhasi hachikwanisi kuwana “umbozha” hwakadaro. Ndinoreva kuti nhasi vana vari pamberi peTV kubva pazera rekutanga, vanotamba PSP uye pamwe izvi zvine nharo asi ndinofunga takanga tine hudiki hwakanakisa, takabuda panze tikatamba mitambo uye Vana vanhasi havabviswe pasofa. .
Mwana wangu ane gore chete uye ndiri kutoona kuti akapindwa muropa neIpad, ndinoreva kuti achiri mudiki asi ndinofunga kuti vana vemazuva ano vakatozvarwa vachiziva kubata magetsi emagetsi. Saka ndaida kuti isu vana kana tichitamba taiita maburi mumarata, toasunga netambo totaura mugaba rimwe chete, rimwe divi munhu wacho anonzwa zviri kutaurwa. kwaari, nokungoisa gaba panzeve yake . Saka zvakafanana chaizvo netiweki yekubatanidza.
Nhasi, kunyangwe kutamiswa kweTCP kunofanirwa kuve nekubatana kunofanirwa kusimbiswa kusati kwatanga kuendesa data chaiko. Sezvatakakurukura muzvidzidzo zvakapfuura, TCP inotapurirana-yakatarisana nekutapurirana nepo UDP iri yekubatanidza-yakatarisana kutapurirana. Ungati UDP ndiko kwandinokanda bhora uye zviri kwauri kuti uone kuti unoribata here. Whether you are ready to do it or not harisi dambudziko rangu, ndichamusiya hangu.
TCP yakafanana iwe uchitaura nemukomana uye uchimunyevera kare kuti iwe uchakanda bhora, saka iwe unoumba chisungo, uye iwe unokanda bhora kuitira kuti mumwe wako angangodaro akagadzirira kuibata. Saka TCP inovaka iyo yekubatanidza uye yobva yatanga kuita iyo chaiyo kutapurirana.
Ngatitarisei kuti inogadzira sei kubatana kwakadaro. Iyi protocol inoshandisa 3-nzira kubata ruoko kugadzira chinongedzo. Iri harisi izwi rehunyanzvi, asi rakagara richishandiswa kutsanangura kubatana kweTCP. Kubata maoko kwe3-nzira kunotangwa nemudziyo wekutumira, nemutengi achitumira pakiti ine SYN mureza kune server.
Ngatitii musikana ari kumberi, uyo watinoona chiso chake, ndiye mudziyo A, uye musikana ari kumashure, ane chiso chisingaoneki, ndiye mudziyo B. Musikana A anotumira SYN packet kumusikana B, uye anoti: "Horaiti, ndiani anozoda kutaura neni. Saka, ndinofanira kupindura kuti ndakagadzirira kukurukura!” Kuzviita sei? Mumwe anogona kungotumira imwe SYN pakiti uyezve ACK inoratidza risiti yepakutanga SYN packet. Asi panzvimbo yekutumira ACKs zvakasiyana, sevha inoumba yakajairika pakiti ine SYN uye ACK uye inoitumira pamusoro petiweki.
Saka panguva ino, mudziyo A watumira SYN packet uye wakagamuchira SYN/ACK packet. Iye zvino mudziyo A unofanirwa kutumira mudziyo B packet yeACK, kureva kuti, simbisa kuti wagamuchira mvumo kubva kumudziyo B kuti utange kutaurirana. Nokudaro, zvose zvigadziri zvakagamuchira SYN uye ACK packets, uye zvino tinogona kutaura kuti kubatana kwave kwakasimbiswa, kureva, 3-nhanho yekubata maoko yakapedzwa uchishandisa TCP protocol.
Tevere tichatarisa TCP Windowing tekinoroji. Zvichitaurwa zviri nyore, inzira inoshandiswa muTCP/IP kutaurirana kugona kweanotumira uye anogamuchira.
Ngatitii muWindows tiri kuyedza kuendesa faira hombe, toti 2 GB muhukuru, kubva kune imwe drive kuenda kune imwe. Pakutanga kwekutamisa, sisitimu inotizivisa kuti kuendesa faira kunotora rinenge 1 gore. Asi masekonzi mashoma gare gare sisitimu inozvigadzirisa yoti: "o, imbomira zvishoma, ndinofunga zvichatora inenge mwedzi mitanhatu, kwete gore." Imwe nguva ichapfuura uye Windows ichati: "Ndinofunga ndingangokwanisa kuendesa faira mumwedzi mumwe." Izvi zvichateverwa neshoko rekuti "6 zuva", "1 maawa", "1 maawa", "6 awa", "3 maminitsi", "1 maminitsi", "20 maminitsi". Muchokwadi, iyo yese faira yekufambisa maitiro inongotora maminetsi matatu. Izvi zvakaitika sei? Pakutanga, kana mudziyo wako uchiedza kutaurirana nemumwe mudziyo, unotumira pakiti imwe uye inomirira kusimbiswa. Kana mudziyo ukamirira kwenguva yakareba kuti usimbiswe, unofunga: "kana ndichifanira kuendesa 10 GB yedata nekumhanya uku, zvinotora makore maviri." Mushure menguva yakati, mudziyo wako unogamuchira ACK uye unofunga, "zvakanaka, ndakatumira pakiti imwe uye ndagamuchira ACK, saka anogamuchira anogona kugamuchira 3 packet. Iye zvino ndichaedza kumutumira mapaketi gumi pane rimwe chete.” Iye anotumira anotumira 3 mapaketi uye mushure meimwe nguva anogamuchira ACK kusimbiswa kubva kune yekugamuchira mudziyo, izvo zvinoreva kuti mugamuchiri ari kumirira inotevera, 2th packet. Anotumira anofunga kuti: “Zvakanaka, sezvo mugamuchiri akabata mapaketi gumi panguva imwe chete, zvino ndichaedza kumutumira mapeji 2 panzvimbo pegumi.” Anotumira mapeji 1, uye mugamuchiri anopindura kuti akaagamuchira uye iye zvino akamirira 10 mapaketi. Nokudaro, nekufamba kwenguva, nhamba yemapakiti anoparadzirwa anowedzera.
Ichi ndicho chikonzero iwe uchiona kukurumidza kuderera kwefaira kopi nguva zvichienzaniswa nezvakataurwa pakutanga - izvi zvinokonzerwa nekuwedzera kugona kuendesa huwandu hukuru hwe data. Nekudaro, panouya poindi apo kumwe kuwedzera kwehuwandu hwekutapurirana kusingaite. Ngatitii makatumira 10000 mapaketi, asi chigadziriso chemudziyo chemugamuchiri chinogona kungogamuchira 9000 9000. Muchiitiko ichi, mugamuchiri anotumira ACK nemashoko: "Ndagamuchira 9001 packets uye ndagadzirira kugamuchira 9000." Kubva pane izvi, mutumi anopedzisa kuti buffer yemuchina wekugamuchira ine huwandu hwe9000 chete, izvo zvinoreva kuti kubva zvino zvichienda mberi ini ndichatumira zvisingapfuure 9000 mapaketi panguva. Muchiitiko ichi, mutumwa anokurumidza kuverenga nguva iyo ichamutora kuti aendese huwandu hwasara hwe data muzvikamu zve3 mapaketi, uye anopa maminitsi matatu. Aya maminetsi matatu inguva chaiyo yekutapurirana. Ndizvo zvinoita TCP Windowing.
Iyi ndiyo imwe yeaya matraffic throttling masisitimu uko mudziyo wekutumira unozonzwisisa kuti chii chaicho network network. Iwe unogona kunge uchinetseka kuti sei vasingagone kubvumirana pachine nguva pane izvo simba rekugamuchira mudziyo? Icho chokwadi ndechekuti izvi hazvigoneke nehunyanzvi nekuti kune akasiyana marudzi emidziyo pane network. Ngatitii une iPad uye ine data rakasiyana rekufambisa / receiver kumhanya pane iPhone, unogona kunge uine marudzi akasiyana emafoni, kana pamwe une komputa yekare. Naizvozvo, munhu wese ane akasiyana network bandwidth.
Ndicho chikonzero teknolojia yeTCP Windowing yakagadziridzwa, apo kutumirwa kwemashoko kunotanga nekumhanya kwakadzika kana nekufambisa kwehuwandu hwemapakiti, zvishoma nezvishoma kuwedzera traffic "hwindo". Iwe unotumira pakiti imwe, mapaketi mashanu, mapaketi gumi, 5 mapaketi, zviuru gumi uye zvishoma nezvishoma kuvhura iro hwindo zvakanyanya uye zvakanyanya kudzamara "kuvhurwa" kwasvika pahuwandu hwehuwandu hwemotokari inotumirwa munguva yakatarwa. Saka, iyo pfungwa yeWindowing chikamu chekushanda kweTCP protocol.
Tevere tichatarisa nhamba dzinozivikanwa dzechiteshi. Mamiriro emhando yepamusoro ndeye kana iwe uine 1 main server, pamwe nzvimbo yedata. Inosanganisira sevha yefaira, web server, mail server uye DHCP server. Zvino, kana imwe yemakomputa emutengi ichibata data data, iyo iri pakati pemufananidzo, ichatanga kutumira faira server traffic kune vatengi zvishandiso. Iyi traffic inoratidzwa mutsvuku uye inofambiswa pane yakatarwa chiteshi kune chaiyo application kubva kune chaiyo server.
Sevha yakaziva sei kwainofanira kuenda imwe traffic? Anodzidza izvi kubva kunhamba yechiteshi chengarava. Kana iwe ukatarisa pafuremu, iwe uchaona kuti mune yega yega kuendesa data pane kutaurwa kweiyo nzvimbo yechiteshi nhamba uye kwainotangira nhamba yechiteshi. Iwe unogona kuona kuti yebhuruu uye tsvuku traffic, uye yebhuruu traffic is web server traffic, ese ari maviri anoenda kune imwechete sevha yemuviri, iyo ine maseva akasiyana akaiswa. Kana iyi iri data data, saka inoshandisa sevhavhavha. Saka vakaziva sei kuti traffic tsvuku yaifanirwa kudzokera kune iyo yakasara laptop neiyo IP kero? Vanoziva izvi nekuda kwenhamba dzechiteshi. Kana iwe ukatarisa kuchinyorwa cheWikipedia "Rondedzero yeTCP uye UDP Ports", uchaona kuti inonyora ese akajairwa manhamba echiteshi.
Kana iwe ukapenengura pasi peji rino unogona kuona kukura kwakaita runyorwa urwu. Iine nhamba dzinosvika 61. Nhamba dzePort kubva pa000 kusvika 1 dzinozivikanwa senhamba dzechiteshi. Semuenzaniso, port 1024/TCP ndeyekutumira ftp mirairo, port 21 ndeye ssh, port 22 ndeyeTelnet, kureva kutumira mameseji asina kunyorwa. Iyo inonyanya kufarirwa port 23 inotakura data pamusoro peHTTP, nepo port 80 inotakura encrypted data pamusoro peHTTPS, iyo yakafanana neyakachengeteka vhezheni yeHTTP.
Mamwe madoko akatsaurirwa kune ese TCP neUDP, uye mamwe anoita mabasa akasiyana zvichienderana nekuti kubatana kuri TCP kana UDP. Saka, zviri pamutemo TCP port 80 inoshandiswa paHTTP, uye zvisiri pamutemo UDP port 80 inoshandiswa paHTTP, asi pasi peimwe HTTP protocol - QUIC.
Naizvozvo, nhamba dzechiteshi muTCP hadzisi nguva dzose dzakagadzirirwa kuita chinhu chimwe chete muUDP. Iwe haufanire kudzidza iyi runyorwa nemoyo, hazvibviri kuyeuka, asi iwe unofanirwa kuziva dzimwe dzakakurumbira uye dzinozivikanwa nhamba dzechiteshi. Sezvandakataura, mamwe ezvikepe izvi ane chinangwa chepamutemo, chinotsanangurwa mumazinga, uye mamwe ane chinangwa chisiri chepamutemo, sezvakaita Chromium.
Saka, iyi tafura inonyora ese akajairika manhamba echiteshi, uye nhamba idzi dzinoshandiswa kutumira uye kugamuchira traffic kana uchishandisa chaiwo maapplication.
Zvino ngatitarisei kuti data inofamba sei kune network zvichienderana neruzivo rudiki rwatinoziva. Ngatitii komputa 10.1.1.10 inoda kubata komputa iyi, kana sevha iyi, ine kero 30.1.1.10. Pazasi peiyo IP kero yechishandiso chimwe nechimwe pane kero yayo yeMAC. Ndiri kupa muenzaniso wekero yeMAC ine mavara mana ekupedzisira, asi mukuita i4-bit hexadecimal nhamba ine mavara gumi nemaviri. Sezvo imwe neimwe yenhamba idzi iine 48 bits, gumi nemaviri hexadecimal manhamba anomiririra 12-bit nhamba.
Sezvatinoziva, kana chishandiso ichi chichida kubata sevha iyi, nhanho yekutanga ye3-nzira yekubata maoko inofanira kutanga yaitwa, ndiko kuti, kutumira SYN packet. Kana chikumbiro ichi chaitwa, komputa 10.1.1.10 inotsanangura nhamba yechiteshi, iyo Windows inogadzira zvine simba. Windows inosarudza nhamba yechiteshi pakati pe1 ne65,000. Asi sezvo nhamba dzekutanga muchikamu 1 kusvika 1024 dzichizivikanwa zvakanyanya, mune iyi nyaya system ichafunga nhamba huru kupfuura 25000 uye kugadzira isina kurongeka sosi port, semuenzaniso, nhamba 25113.
Tevere, iyo sisitimu ichawedzera nzvimbo yekuenda kune packet, mune iyi kesi iri port 21, nekuti application iri kuyedza kubatana neiyo FTP server inoziva kuti inofanirwa kutumira FTP traffic.
Zvadaro, komputa yedu inoti, "Zvakanaka, IP address yangu ndeye 10.1.1.10, uye ndinoda kubata IP kero 30.1.1.10." Makero ese aya anosanganisirwa mupaketi kugadzira chikumbiro cheSYN, uye iyi packet haizochinji kusvika pakupera kwekubatanidza.
Ini ndinoda kuti iwe unzwisise kubva pane iyi vhidhiyo kuti data inofamba sei pane network. Kana komputa yedu ichitumira chikumbiro ichiona kwainobva IP kero uye kero yeIP, inonzwisisa kuti kero yekuenda haisi panetiweki yemuno. Ndakanganwa kutaura kuti aya ese ese / 24 IP kero. Saka kana ukatarisa pa/24 IP kero, uchaona kuti makomputa 10.1.1.10 uye 30.1.1.10 haasi pane imwechete network. Nokudaro, kombiyuta inotumira chikumbiro inonzwisisa kuti kuitira kuti ibve mumbure uyu, inofanira kubata 10.1.1.1 gedhi, iyo inogadziriswa pane imwe yerouter interfaces. Inoziva kuti inofanira kuenda ku10.1.1.1 uye inoziva kero yayo yeMAC ye1111, asi haizivi kero yeMAC yegedhi 10.1.1.1. Arikuitei? Inotumira chikumbiro cheARP chekutepfenyura kuti zvigadziriso zvose zviri pamambure zvichagamuchira, asi chete router ine IP kero 10.1.1.1 ichaipindura.
Iyo router inopindura neayo AAAA MAC kero, uye zvese kwainoenda uye kwekuenda MAC kero ichaiswawo mune iyi furemu. Kana iyo furemu yagadzirira, CRC data kutendeseka cheki, iri algorithm yekutsvaga cheki yekuona zvikanganiso, ichaitwa usati wasiya network.
Cyclic Redundancy CRC zvinoreva kuti furemu iyi yese, kubva kuSYN kusvika kukero yekupedzisira yeMAC, inofambiswa kuburikidza nehashing algorithm, toti MD5, zvichikonzera kukosha kwehashi. Iyo hashi kukosha, kana MD5 checksum, inozoiswa pakutanga kwefuremu.
Ndakainyora kuti FCS/CRC nekuti FCS iFrame Check Sequence, kukosha kwechina-byte CRC. Vamwe vanhu vanoshandisa zita rekuti FCS uye vamwe vanoshandisa zita rekuti CRC, saka ini ndangobatanidza mazita ese. Asi zvakanyanya ingori kukosha kwehashi. Inodiwa kuve nechokwadi chekuti data rese rakatambirwa pane network harina zvikanganiso. Naizvozvo, kana furemu iyi yasvika kune router, chinhu chekutanga icho router ichaita kuverenga iyo checksum pachayo uye kuienzanisa neFCS kana CRC kukosha iyo yakagamuchirwa furemu. Nenzira iyi anogona kutarisa kuti data yakagamuchirwa pamusoro petiweki haina zvikanganiso, mushure mezvo achabvisa checksum kubva paforamu.
Tevere, router inotarisa kukero yeMAC uye yoti, "Zvakanaka, MAC kero AAAA inoreva kuti furemu yakanyorerwa kwandiri," uye bvisa chikamu chefuremu ine MAC kero.
Kutarisa kunzvimbo yekuenda IP kero 30.1.1.10, iye achanzwisisa kuti iyi pakiti haina kutaurirwa kwaari uye inofanira kuenda mberi kuburikidza ne router.
Iye zvino router "inofunga" kuti inoda kuona kuti network ine kero 30.1.1.10 iripo. Hatisati tavhara pfungwa yakazara yekufambisa parizvino, asi isu tinoziva kuti ma routers ane tafura yekufambisa. Tafura iyi ine yekupinda kune network ine kero 30.1.1.0. Sezvaunorangarira, iyi haisi iyo IP kero, asi network identifier. Iyo router icha "funga" kuti inogona kusvika kukero 30.1.1.0/24 nekuenda kuburikidza ne router 20.1.1.2.
Ungabvunza kuti, anozviziva sei izvi? Ingo ramba uchifunga kuti ichaziva izvi kubva kumaprotocol ekufambisa kana kubva kune zvigadziriso zvako kana iwe semaneja wagadzira nzira yakamira. Asi chero zvipi zvazvo, tafura ye router iyi ine nzira yakarurama, saka inoziva kuti inofanira kutumira pakiti iyi ku 20.1.1.2. Tichifunga kuti router inotoziva kwainoenda MAC kero, isu tichangoenderera mberi nekutumira packet. Kana asingazivi kero iyi, achatanga ARP zvakare, agamuchire kero yeMAC ye router 20.1.1.2, uye nzira yekutumira chimiro ichaenderera mberi zvakare.
Saka isu tinofungidzira kuti inotoziva kero yeMAC, tobva tave neBBB sosi yeMAC kero uye neCCC kwainoenda MAC kero. Iyo router inoverenga zvakare FCS / CRC uye inoiisa pakutanga kwefuremu.
Iyo inobva yatumira iyi furemu pamusoro pemambure, iyo furemu inosvika router 20.1.12, inotarisa checksum, inoita kuti data haina kusvibiswa, uye inobvisa FCS / CRC. Inobva yaita "truncates" kero dzeMAC, inotarisa kwainoenda uye inoona kuti iri 30.1.1.10. Anoziva kuti kero iyi yakabatana nechitarisiko chake. Iyo yakafanana furemu yekugadzira maitiro inodzokororwa, iyo router inowedzera kwainobva uye kwainoenda MAC kero kukosha, inoita hashing, inosungirira hashi kune furemu uye inoitumira kune network.
Sevha yedu, yatozogamuchira chikumbiro cheSYN chakataurirwa kwairi, inotarisa hash checksum, uye kana packet isina zvikanganiso, inodzima hashi. Anobva abvisa kero dzeMAC, otarisa IP address obva aona kuti packet iyi yakanyorerwa kwaari.
Mushure meizvozvo, inodimburira kero dzeIP dzine chekuita nechikamu chechitatu cheOSI modhi uye inotarisa nhamba dzechiteshi.
Anoona port 21, zvinoreva kuti FTP traffic, anoona SYN uye saka anonzwisisa kuti mumwe munhu ari kuedza kutaura naye.
Iye zvino, zvichibva pane zvatakadzidza pamusoro pekubata maoko, sevha 30.1.1.10 ichagadzira SYN / ACK packet uye kuitumira zvakare kukombiyuta 10.1.1.10. Paunenge uchigamuchira iyi pakiti, chigadzirwa 10.1.1.10 chichagadzira ACK, ipfuure kuburikidza nemambure nenzira imwecheteyo seSYN packet, uye mushure mokunge sevha inogamuchira ACK, kubatana kuchasimbiswa.
Chinhu chimwe chaunofanira kuziva ndechekuti izvi zvese zvinoitika mukati mesekondi isingasviki. Iyi inzira inokurumidza, yandakaedza kudzikisira kuitira kuti zvese zvive pachena kwauri.
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