GPON網(wǎng)絡(luò)寬帶用戶PPPoE撥號流程

GPON網(wǎng)絡(luò)寬帶用戶PPPoE撥號流程一、PPPoE撥號流程分析本文檔以個人用戶電腦撥號過程抓取的數(shù)據(jù)報文為例分析PPPoE撥號過程。抓包軟件為WireShark。此處Dell_01:3c:e0為撥號電腦，電腦MAC地址為00:12:3f:01:3c:e0。PPPoE撥號的工作流程包含兩大部分：PPPOE發(fā)現(xiàn)階段和PPP會話階段。PPPOE發(fā)現(xiàn)階段是無狀態(tài)的，目的是獲得PPPoE終結(jié)端（BRAS）的以太網(wǎng)MAC地址，并建立一個唯一的PPPoESESSION-ID。PPPOE發(fā)現(xiàn)階段包含四個步驟，當(dāng)此階段完成后，通信的兩端(PC和BRAS)都知道PPPOESESSION_ID和對端的以太網(wǎng)地址，他們一起唯一定義PPPOE會話。PPPOE發(fā)現(xiàn)階段結(jié)束后，就進(jìn)入標(biāo)準(zhǔn)的PPP會話階段。PPP會話階段的主要目的是進(jìn)行鏈路層和網(wǎng)絡(luò)層協(xié)議的協(xié)商，協(xié)商后用戶即可發(fā)送業(yè)務(wù)數(shù)據(jù)報文訪問互聯(lián)網(wǎng)。（一）PPPOE撥號發(fā)現(xiàn)階段PPPOE撥號發(fā)現(xiàn)階段主要涉及4個報文，分別是：PADI、PADO、PADR和PADS，其中PADI和PADR報文由電腦發(fā)起，PADO和PADS報文由BRAS發(fā)起，具體流程參考如圖1。BRASHOSTBRASHOSTPADIPADIPADOPADOPADRPADRPADSPADS圖圖1PPPOE撥號發(fā)現(xiàn)階段1、首先電腦廣播一個PADI數(shù)據(jù)報文"Dell_01:3c:e0","Broadcast","PPPoED","ActiveDiscoveryInitiation(PADI)"2、BRAS在收到這個PADI報文后，回應(yīng)PADO報文"Siara_10:29:c9","Dell_01:3c:e0","PPPoED","ActiveDiscoveryOffer(PADO)AC-Name='AHCHI-MB-CMNET-BAS02-SE800-2-B2224180702321'""Siara_10:29:4d","Dell_01:3c:e0","PPPoED","ActiveDiscoveryOffer(PADO)AC-Name='AHCHI-MB-CMNET-BAS01-SE800-1-B2224180702319'"AHCHI-MB-CMNET-BAS02-SE800-2-B2224180702321和AHCHI-MB-CMNET-BAS01-SE800-1-B2224180702319為池州的兩個BRAS。在用戶電腦發(fā)出PADI廣播包后，兩個BRAS都會給出PADO響應(yīng)報文。電腦會向最先響應(yīng)的BRAS發(fā)送PADR請求報文。3、用戶電腦發(fā)送PADR報文"Dell_01:3c:e0","Siara_10:29:c9","PPPoED","ActiveDiscoveryRequest(PADR)"4、BRAS在收到這個PADR請求報文后，會響應(yīng)一個PADS報文進(jìn)行發(fā)現(xiàn)會話確認(rèn)，并給出本次會話的SessionID。"Siara_10:29:c9","Dell_01:3c:e0","PPPoED","ActiveDiscoverySession-confirmation(PADS)AC-Name='AHCHI-MB-CMNET-BAS02-SE800-2-B2224180702321'"在PADS報文中，包含了本次PPPOE會話的SessionID:0x3695，如圖所示：圖2PADS報文抓包截圖此時PPPOE發(fā)現(xiàn)階段結(jié)束，進(jìn)入PPP會話階段。（二）PPP會話階段BRASHOSTBRASHOSTConfigurationAckConfigurationAckAuthenticate-Authenticate-AckPPPIPCPConfigurationRPPPIPCPConfigurationRequestConfigurationAckConfigurationAck圖圖3PPP會話階段1、首先撥號電腦和BRAS互相發(fā)送PPPLCP（PPPLCP為PPPLinkControlProtocol）協(xié)議的ConfigurationRequest，進(jìn)行鏈路層的協(xié)商。"Dell_01:3c:e0","Siara_10:29:c9","PPPLCP","ConfigurationRequest""Siara_10:29:c9","Dell_01:3c:e0","PPPLCP","ConfigurationRequest"2、電腦在收到BRAS的請求后，響應(yīng)一個ConfigurationAck。同樣，BRAS在收到電腦的請求后，也響應(yīng)一個“ConfigurationAck“。"Dell_01:3c:e0","Siara_10:29:c9","PPPLCP","ConfigurationAck""Siara_10:29:c9","Dell_01:3c:e0","PPPLCP","ConfigurationAck"此時已完成鏈路協(xié)商后，進(jìn)入PPPPAP（PPPPasswordAuthenticationProtocol）協(xié)商，進(jìn)行撥號的用戶名密碼驗證。3、用戶電腦發(fā)出PPPPAP的Authenticate-Request數(shù)據(jù)報文，里面包含本次撥號的用戶名，密碼。"Dell_01:3c:e0","Siara_10:29:c9","PPPPAP","Authenticate-Request"如圖所示：圖4PPPPAP數(shù)據(jù)報文抓包截圖本次撥號使用的是測試賬號，該賬號在BRAS進(jìn)行用戶名密碼驗證。4、BRAS驗證完用戶名密碼成功后，會返回一個“Authenticate-Ack”"Siara_10:29:c9","Dell_01:3c:e0","PPPPAP","Authenticate-Ack"。此時已完成用戶名密碼驗證，進(jìn)入PPPIPCP（PPPIPControlProtocol）協(xié)議的協(xié)商。5、用戶電腦和BRAS互相發(fā)送PPPIPCPConfigurationRequest數(shù)據(jù)報文。"Siara_10:29:c9","Dell_01:3c:e0","PPPIPCP","ConfigurationRequest""Dell_01:3c:e0","Siara_10:29:c9","PPPIPCP","ConfigurationRequest"6、用戶電腦和BRAS在收到對方發(fā)送的ConfigurationRequest后，響應(yīng)一個“ConfigurationAck“"Dell_01:3c:e0","Siara_10:29:c9","PPPIPCP","ConfigurationAck""Siara_10:29:c9","Dell_01:3c:e0","PPPIPCP","ConfigurationAck"在BRAS給出的ConfigurationAck數(shù)據(jù)報文中包含分配給該用戶電腦的IP地址，DNSServer的IP地址。如下圖所示：本次撥號用戶電腦分配的IP地址為111.141.7.39,主用DNSServer的地址為211.238.180.2,備用DNSServer的地址為221.130.162.223。如圖所示：圖5BRAS發(fā)出的ConfigurationAck報文抓包截圖此時IPCP協(xié)議協(xié)商過程結(jié)束，PPPOE撥號已完成，即PPPOE撥號的信令流已經(jīng)建立完成，此時用戶可以正常上網(wǎng)傳送數(shù)據(jù)。（三）PPPOE撥號終結(jié)BRASHOSTBRASHOSTTerminationRequestTerminationRequestPADT保文，終結(jié)PPPOEPADT保文，終結(jié)PPPOE圖圖6PPPOE撥號總結(jié)1、用戶斷開撥號連接，用戶電腦首先向BRAS發(fā)出一個TerminationRequest，請求釋放本次PPPOE的鏈路。"Dell_01:3c:e0","Siara_10:29:c9","PPPLCP","TerminationRequest"2、BRAS給出"TerminationAck"響應(yīng)。"Siara_10:29:c9","Dell_01:3c:e0","PPPLCP","TerminationAck"3、電腦收到BRAS發(fā)出的TerminationAck數(shù)據(jù)報文后，向BRAS發(fā)送PADT數(shù)據(jù)報文，終結(jié)本次PPPOE會話。"Dell_01:3c:e0","Siara_10:29:c9","PPPoED","Ac