GPON网络宽带用户PPPoE拨号流程

GPON网络宽带用户PPPoE拨号流程一、PPPoE拨号流程分析本文档以个人用户电脑拨号过程抓取的数据报文为例分析PPPoE拨号过程。抓包软件为WireShark。此处Dell_01:3c:e0为拨号电脑，电脑MAC地址为00:12:3f:01:3c:e0。PPPoE拨号的工作流程包含两大部分：PPPOE发现阶段和PPP会话阶段。PPPOE发现阶段是无状态的，目的是获得PPPoE终结端（BRAS）的以太网MAC地址，并建立一个唯一的PPPoESESSION-ID。PPPOE发现阶段包含四个步骤，当此阶段完成后，通信的两端(PC和BRAS)都知道PPPOESESSION_ID和对端的以太网地址，他们一起唯一定义PPPOE会话。PPPOE发现阶段结束后，就进入标准的PPP会话阶段。PPP会话阶段的主要目的是进行链路层和网络层协议的协商，协商后用户即可发送业务数据报文访问互联网。（一）PPPOE拨号发现阶段PPPOE拨号发现阶段主要涉及4个报文，分别是：PADI、PADO、PADR和PADS，其中PADI和PADR报文由电脑发起，PADO和PADS报文由BRAS发起，具体流程参考如图1。BRASHOSTBRASHOSTPADIPADIPADOPADOPADRPADRPADSPADS图图1PPPOE拨号发现阶段1、首先电脑广播一个PADI数据报文"Dell_01:3c:e0","Broadcast","PPPoED","ActiveDiscoveryInitiation(PADI)"2、BRAS在收到这个PADI报文后，回应PADO报文"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为池州的两个BRAS。在用户电脑发出PADI广播包后，两个BRAS都会给出PADO响应报文。电脑会向最先响应的BRAS发送PADR请求报文。3、用户电脑发送PADR报文"Dell_01:3c:e0","Siara_10:29:c9","PPPoED","ActiveDiscoveryRequest(PADR)"4、BRAS在收到这个PADR请求报文后，会响应一个PADS报文进行发现会话确认，并给出本次会话的SessionID。"Siara_10:29:c9","Dell_01:3c:e0","PPPoED","ActiveDiscoverySession-confirmation(PADS)AC-Name='AHCHI-MB-CMNET-BAS02-SE800-2-B2224180702321'"在PADS报文中，包含了本次PPPOE会话的SessionID:0x3695，如图所示：图2PADS报文抓包截图此时PPPOE发现阶段结束，进入PPP会话阶段。（二）PPP会话阶段BRASHOSTBRASHOSTConfigurationAckConfigurationAckAuthenticate-Authenticate-AckPPPIPCPConfigurationRPPPIPCPConfigurationRequestConfigurationAckConfigurationAck图图3PPP会话阶段1、首先拨号电脑和BRAS互相发送PPPLCP（PPPLCP为PPPLinkControlProtocol）协议的ConfigurationRequest，进行链路层的协商。"Dell_01:3c:e0","Siara_10:29:c9","PPPLCP","ConfigurationRequest""Siara_10:29:c9","Dell_01:3c:e0","PPPLCP","ConfigurationRequest"2、电脑在收到BRAS的请求后，响应一个ConfigurationAck。同样，BRAS在收到电脑的请求后，也响应一个“ConfigurationAck“。"Dell_01:3c:e0","Siara_10:29:c9","PPPLCP","ConfigurationAck""Siara_10:29:c9","Dell_01:3c:e0","PPPLCP","ConfigurationAck"此时已完成链路协商后，进入PPPPAP（PPPPasswordAuthenticationProtocol）协商，进行拨号的用户名密码验证。3、用户电脑发出PPPPAP的Authenticate-Request数据报文，里面包含本次拨号的用户名，密码。"Dell_01:3c:e0","Siara_10:29:c9","PPPPAP","Authenticate-Request"如图所示：图4PPPPAP数据报文抓包截图本次拨号使用的是测试账号，该账号在BRAS进行用户名密码验证。4、BRAS验证完用户名密码成功后，会返回一个“Authenticate-Ack”"Siara_10:29:c9","Dell_01:3c:e0","PPPPAP","Authenticate-Ack"。此时已完成用户名密码验证，进入PPPIPCP（PPPIPControlProtocol）协议的协商。5、用户电脑和BRAS互相发送PPPIPCPConfigurationRequest数据报文。"Siara_10:29:c9","Dell_01:3c:e0","PPPIPCP","ConfigurationRequest""Dell_01:3c:e0","Siara_10:29:c9","PPPIPCP","ConfigurationRequest"6、用户电脑和BRAS在收到对方发送的ConfigurationRequest后，响应一个“ConfigurationAck“"Dell_01:3c:e0","Siara_10:29:c9","PPPIPCP","ConfigurationAck""Siara_10:29:c9","Dell_01:3c:e0","PPPIPCP","ConfigurationAck"在BRAS给出的ConfigurationAck数据报文中包含分配给该用户电脑的IP地址，DNSServer的IP地址。如下图所示：本次拨号用户电脑分配的IP地址为111.141.7.39,主用DNSServer的地址为211.238.180.2,备用DNSServer的地址为221.130.162.223。如图所示：图5BRAS发出的ConfigurationAck报文抓包截图此时IPCP协议协商过程结束，PPPOE拨号已完成，即PPPOE拨号的信令流已经建立完成，此时用户可以正常上网传送数据。（三）PPPOE拨号终结BRASHOSTBRASHOSTTerminationRequestTerminationRequestPADT保文，终结PPPOEPADT保文，终结PPPOE图图6PPPOE拨号总结1、用户断开拨号连接，用户电脑首先向BRAS发出一个TerminationRequest，请求释放本次PPPOE的链路。"Dell_01:3c:e0","Siara_10:29:c9","PPPLCP","TerminationRequest"2、BRAS给出"TerminationAck"响应。"Siara_10:29:c9","Dell_01:3c:e0","PPPLCP","TerminationAck"3、电脑收到BRAS发出的TerminationAck数据报文后，向BRAS发送PADT数据报文，终结本次PPPOE会话。"Dell_01:3c:e0","Siara_10:29:c9","PPPoED","Ac