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數(shù)據(jù)轉(zhuǎn)發(fā)過程學(xué)習(xí)內(nèi)容數(shù)據(jù)轉(zhuǎn)發(fā)過程概述0102數(shù)據(jù)封裝03數(shù)據(jù)轉(zhuǎn)發(fā)過程04數(shù)據(jù)解封裝05總結(jié)數(shù)據(jù)轉(zhuǎn)發(fā)過程概述1數(shù)據(jù)傳輸過程是一個(gè)非常復(fù)雜的過程，數(shù)據(jù)在轉(zhuǎn)發(fā)的過程中會(huì)進(jìn)行一系列的封裝和解封裝。對(duì)于網(wǎng)絡(luò)工程師來說，只有深入理解了數(shù)據(jù)在各種不同設(shè)備中的轉(zhuǎn)發(fā)過程，才能夠?qū)W(wǎng)絡(luò)數(shù)據(jù)進(jìn)行正確的分析和檢測(cè)。數(shù)據(jù)轉(zhuǎn)發(fā)過程概述1數(shù)據(jù)包在相同網(wǎng)段內(nèi)或不同網(wǎng)段之間轉(zhuǎn)發(fā)所依據(jù)的原理基本一致。Internet主機(jī)A主機(jī)B服務(wù)器A服務(wù)器B/24/24/24/24RTARTB數(shù)據(jù)轉(zhuǎn)發(fā)過程概述1網(wǎng)絡(luò)接口層數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)數(shù)據(jù)網(wǎng)絡(luò)層傳輸層應(yīng)用層SegmentPacketFrameBitPDU數(shù)據(jù)封裝-TCP封裝2主機(jī)建立到達(dá)目的地的TCP連接后，開始對(duì)應(yīng)用層數(shù)據(jù)進(jìn)行封裝。物理層數(shù)據(jù)鏈路層網(wǎng)絡(luò)層傳輸層TCPHeaderData數(shù)據(jù)段主機(jī)ASYNRSTFINDestinationPort:80SequenceNumberWindowChecksumOptionsSourcePort:1027AcknowledgementNumberHeaderLengthResv.UrgentPointerPSHURGACKPadding數(shù)據(jù)封裝-IP封裝2數(shù)據(jù)包主機(jī)AIPHeader物理層數(shù)據(jù)鏈路層網(wǎng)絡(luò)層傳輸層TCPHeaderDataDSFieldTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocol：0X06HeaderChecksumSourceIPAddress：DestinationIPAddress：IPOptionsVersionHeaderLength數(shù)據(jù)封裝-以太網(wǎng)幀封裝2數(shù)據(jù)幀EthernetHeaderDataFCSD.MACS.MACType物理層數(shù)據(jù)鏈路層網(wǎng)絡(luò)層傳輸層IPHeaderTCPHeader主機(jī)A數(shù)據(jù)轉(zhuǎn)發(fā)過程-路由查找3Network/MaskGatewayInterface/054

/24- Internet主機(jī)A主機(jī)B服務(wù)器A服務(wù)器B/24/24/24/24RTARTB54/24E0/0主機(jī)A必須要擁有到達(dá)目的地的路由。數(shù)據(jù)轉(zhuǎn)發(fā)過程-MAC地址查找3通過ARP緩存表找到下一跳的MAC地址。如果表項(xiàng)里沒有下一跳的MAC地址，主機(jī)A會(huì)發(fā)送ARP請(qǐng)求。主機(jī)A主機(jī)B/2400-01-02-03-04-05/2400-01-02-03-04-0654/2400-01-02-03-04-08InternetHostA>arp-aInternetaddressPhysicaladdressType5400-01-02-03-04-08Dynamic00-01-02-03-04-06DynamicRTAE0/0數(shù)據(jù)轉(zhuǎn)發(fā)過程-數(shù)據(jù)幀轉(zhuǎn)發(fā)3主機(jī)工作在半雙工狀態(tài)下，使用CSMA/CD來檢測(cè)鏈路是否空閑。前導(dǎo)碼Preamble用于使接收者進(jìn)入同步狀態(tài)，定界符SFD用于指示幀的開始。主機(jī)A11010101010101010101010101…1…0100D.MAC(48bits)SFD(8bits)Preamble(56bits)1…0100…..S.MAC(48bits)EthernetHeaderDataFCSIPHeaderTCPHeader數(shù)據(jù)轉(zhuǎn)發(fā)過程-數(shù)據(jù)幀轉(zhuǎn)發(fā)3同一個(gè)沖突域里的設(shè)備都會(huì)接收到主機(jī)A發(fā)送的數(shù)據(jù)幀。只有網(wǎng)關(guān)會(huì)處理數(shù)據(jù)幀，并基于轉(zhuǎn)發(fā)。主機(jī)A主機(jī)BSFDPreambleFCSDataRTAE0/054/2400-01-02-03-04-08目的MAC：00-01-02-03-04-08TYPE：0x0800Ethernet_IIHeader數(shù)據(jù)轉(zhuǎn)發(fā)過程-數(shù)據(jù)包轉(zhuǎn)發(fā)3網(wǎng)關(guān)檢查是否具有到達(dá)目的網(wǎng)絡(luò)的路由條目。如果存在轉(zhuǎn)發(fā)路徑，則為數(shù)據(jù)包添加一個(gè)新的二層幀頭和幀尾，并繼續(xù)轉(zhuǎn)發(fā)。DataIP00/24E0/1RTAE0/0Destination/MaskInterface/24E0/1DSFieldTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddress：DestinationIPAddress：

IPOptionsVersionHeaderLengthSFDPreambleEthernet_IIHeaderFCSData數(shù)據(jù)解封裝-以太幀解封裝4服務(wù)器

A服務(wù)器

B/2400-03-04-05-06-AA/2400-03-04-05-06-BBD.MACS.MACType(0x0800)RTBE0/1SFDPreambleEthernet_IIHeaderFCSDataRTB以服務(wù)器A的MAC地址作為目的MAC繼續(xù)轉(zhuǎn)發(fā)。服務(wù)器A接收到該數(shù)據(jù)幀后，發(fā)現(xiàn)目的MAC為自己的MAC，繼續(xù)處理該數(shù)據(jù)幀。數(shù)據(jù)解封裝-數(shù)據(jù)包解封裝4服務(wù)器A檢查數(shù)據(jù)包的目的IP地址，發(fā)現(xiàn)目的IP與自己的IP地址相同。服務(wù)器A剝掉數(shù)據(jù)包的IP頭部后，會(huì)送往上層協(xié)議TCP繼續(xù)進(jìn)行處理。DSFieldTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddress：DestinationIPAddress：

IPOptionsVersionHeaderLengthDataIPHeader服務(wù)器A服務(wù)器B/2400-03-04-05-06-AA/2400-03-04-05-06-BBRTBE0/1數(shù)據(jù)解封裝-數(shù)據(jù)段解封裝4服務(wù)器A檢查數(shù)據(jù)包的目的端口，剝掉TCP頭部后，會(huì)送往上層對(duì)應(yīng)的應(yīng)用程序繼續(xù)進(jìn)行處理。服務(wù)器BDataTCPHeader服務(wù)器A/2400-03-04-05-06-AA/2400-03-04-05-06-BBRTBE0/1SYNRSTFINSequenceNumberWindowChecksumOptionsAcknowledgementNumberHeaderLengthResv.UrgentPointerPSHURGACKPaddingDestinationPort:80SourcePort:1027總結(jié)5主機(jī)在封裝數(shù)據(jù)包之前，必須要知道目的端IP地址。在封裝數(shù)據(jù)幀之前，必須要知道去往目的網(wǎng)絡(luò)的路由以及下一跳的