某局点MSR路由器PPPOE拨号IPCP阶段协商失败处理案例

拓扑如下：

某局点配置了PPPOE拨号后，始终无法获取地址，且接口物理状态属于UP，但是协议层协商为DOWN，LCP协商为 initial。

===============display interface===============

Dialer1

Current state: UP

Line protocol state: DOWN

Description: Dialer1

Interface Bandwidth: 64 kbps

Maximum transmission unit: 1500

Hold timer: 10 seconds, retry times: 5

Internet protocol processing: Disabled

Link layer protocol: PPP

LCP: initial

Physical: Dialer, baudrate: 64000 bps

设备配置如下：

interface Dialer1

mtu 1492

ppp chap password cipher XXXXXX

ppp chap user XXXXXX

ppp ipcp dns admit-any

ppp ipcp remote-address match

ppp pap local-user XXXXX password cipher XXXXX

dialer bundle enable

dialer-group 1

dialer timer idle 0

ip address ppp-negotiate

tcp mss 1024

nat outbound

检查配置没有发现具体问题，现来分析debugging 信息：

首先理解PPPOE拨号的整个交互过程

由于查看当前接口物理层UP，则说明PPP已经开始进入链路建立阶段（Establish）阶段，PPP在Establish阶段主要进行LCP协商，而LCP协商完成后会进行PAP或CHAP的验证。

*Nov 16 18:00:02:789 2018 ZWIE-MSR5620 PPP/7/EXTERNAL_EVENT: -Slot=2;

  PPP External Event:

      Virtual-Access0 deliver packet to user space success

*Nov 16 18:00:02:790 2018 ZWIE-MSR5620 PPP/7/CHAP_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Input CHAP(c223) Pkt, Len 31

      State ListenChallenge, code Challenge(01), id 1, Len 27

      Value_Size:  16  Value:d1 df 25 50 00 3e e2 1b a0 7a 4a 82 58 c7 6e 6f

      Name: Huawei

*Nov 16 18:00:02:790 2018 ZWIE-MSR5620 PPP/7/CHAP_EVENT_0: -Slot=2;

  PPP Event:

      Virtual-Access0 CHAP Receive Challenge Event

      State ListenChallenge

*Nov 16 18:00:02:790 2018 ZWIE-MSR5620 PPP/7/CHAP_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Output CHAP(c223) Pkt, Len 43

      State ListenChallenge, code Response(02), id 1, Len 39

      Value_Size:  16  Value:17 6c 55 4f 3f cc de 9d 96 e1 f0 dc 76 54 f0 08

      Name: xxxx

*Nov 16 18:00:02:790 2018 ZWIE-MSR5620 PPP/7/CHAP_STATE_0: -Slot=2;

  PPP State Change:

      Virtual-Access0 CHAP: ListenChallenge --> SendResponse

%Nov 16 18:00:03:343 2018 ZWIE-MSR5620 IFNET/5/LINK_UPDOWN: Line protocol state on the interface Virtual-Access0 changed to up.

*Nov 16 18:00:02:790 2018 ZWIE-MSR5620 PPP/7/EXTERNAL_EVENT: -Slot=2;

  PPP External Event:

      Virtual-Access0 deliver packet to user space success

*Nov 16 18:00:02:814 2018 ZWIE-MSR5620 PPP/7/CHAP_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Input CHAP(c223) Pkt, Len 39

      State SendResponse, code SUCCESS(03), id 1, Len 35

      Message: Authentication success,Welcome!

*Nov 16 18:00:02:814 2018 ZWIE-MSR5620 PPP/7/CHAP_EVENT_0: -Slot=2;

  PPP Event:

      Virtual-Access0 CHAP Receive Success Event

      State SendResponse

*Nov 16 18:00:02:815 2018 ZWIE-MSR5620 PPP/7/CHAP_STATE_0: -Slot=2;

  PPP State Change:

      Virtual-Access0 CHAP: SendResponse --> ClientSuccess

此时显示CHAP验证成功，LCP上报Success事件。由于PPPOE在认证完成后则会进入网络层配置协商阶段，进行IPCP协商。IPCP协商的主要内容则是IP地址、DNS服务器地址等，只有当IPCP协商通过后，PPP才可以承载IP报文。

*Nov 16 18:00:02:815 2018 ZWIE-MSR5620 PPP/7/FSM_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Input IPCP(8021) Packet, PktLen 14

      Current State null, code ConfReq(01), id 1, len 10

      IP Address(3), len 6, val 64 40 00 01

*Nov 16 18:00:02:815 2018 ZWIE-MSR5620 PPP/7/FSM_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Input IPv6CP(8057) Packet, PktLen 18

      Current State null, code ConfReq(01), id 1, len 14

      IPv6CP InterfaceID(1), len a, val b6 38 06 ff fe be 00 15

*Nov 16 18:00:02:815 2018 ZWIE-MSR5620 PPP/7/FSM_EVENT_0: -Slot=2;

  PPP Event:

      Virtual-Access0 IPCP Open Event

      State initial

*Nov 16 18:00:02:815 2018 ZWIE-MSR5620 PPP/7/FSM_STATE_0: -Slot=2;

  PPP State Change:

      Virtual-Access0 IPCP: initial --> starting          此时从初始状态变为启动状态

*Nov 16 18:00:02:815 2018 ZWIE-MSR5620 PPP/7/FSM_EVENT_0: -Slot=2;

  PPP Event:

      Virtual-Access0 IPCP Lower Up Event

      State starting

*Nov 16 18:00:02:815 2018 ZWIE-MSR5620 PPP/7/FSM_STATE_0: -Slot=2;

  PPP State Change:

      Virtual-Access0 IPCP: starting --> reqsent     从初始状态变为配置请求发送状态

......

*Nov 16 18:00:02:818 2018 ZWIE-MSR5620 PPP/7/FSM_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Input IPCP(8021) Packet, PktLen 14

      Current State reqsent, code ConfAck(02), id 1, len 10

      IP Address(3), len 6, val 64 40 2b 44

*Nov 16 18:00:02:818 2018 ZWIE-MSR5620 PPP/7/FSM_EVENT_0: -Slot=2;

  PPP Event:

      Virtual-Access0 IPCP RCA(Receive Config Ack) Event

      State reqsent

*Nov 16 18:00:02:818 2018 ZWIE-MSR5620 PPP/7/FSM_STATE_0: -Slot=2;

  PPP State Change:

      Virtual-Access0 IPCP: reqsent --> ackrcvd      从配置请求发送状态变为收到对端确认状态

*Nov 16 18:00:02:818 2018 ZWIE-MSR5620 PPP/7/EXTERNAL_EVENT: -Slot=2;

  PPP External Event:

      Virtual-Access0 deliver packet to user space success

*Nov 16 18:00:05:807 2018 ZWIE-MSR5620 PPP/7/FSM_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Input IPCP(8021) Packet, PktLen 14

      Current State ackrcvd, code ConfReq(01), id 2, len 10

      IP Address(3), len 6, val 64 40 00 01

*Nov 16 18:00:05:807 2018 ZWIE-MSR5620 PPP/7/FSM_EVENT_0: -Slot=2;

  PPP Event:

      Virtual-Access0 IPCP RCR+(Receive Config Good Request) Event     此时从对端收到 Config Good Request 报文

      State ackrcvd

*Nov 16 18:00:05:809 2018 ZWIE-MSR5620 PPP/7/FSM_PACKET_0: -Slot=2;

  PPP Packet:

      Virtual-Access0 Input LCP(c021) Packet, PktLen 8

      Current State closing, code TermAck(06), id 1, len 4

*Nov 16 18:00:05:809 2018 ZWIE-MSR5620 PPP/7/FSM_EVENT_0: -Slot=2;

  PPP Event:

      Virtual-Access0 LCP RTA(Receive Terminate Ack) Event     收到确认终止确认答复

      State closing

*Nov 16 18:00:05:809 2018 ZWIE-MSR5620 PPP/7/FSM_STATE_0: -Slot=2;

  PPP State Change:

      Virtual-Access0 LCP: closing --> closed     LCP协商关闭

此时我们怀疑还是在IPCP出现了问题，查询相关命令说明发现配置存在以下一点问题。

在Dialer口下配置了ppp ipcp dns request 和ppp ipcp remote-address match。 ppp ipcp remote-address match用来使能接口的IP网段检查功能，如果不在同一网段时则IPCP协商失败。

在Dialer口下删除 ppp ipcp remote-address match后问题解决。