First its important to know some basic information about PPPoE, PPP over Ethernet (PPPoE) is a link layer protocol that encapsulates Point-to-Point Protocol (PPP) frames into Ethernet frames. PPPoE enables multiple hosts on an Ethernet to connect to a broadband remote access server (BRAS).
The PPPoE dial-up process includes three stages: Discovery, Session, and Terminate.
Working process:Discovery Stage
The Discovery stage consists of the following steps:
- A PPPoE client broadcasts a PPPoE Active Discovery Initial (PADI) packet that contains service type required by the PPPoE client.
- After receiving the PADI packet, all PPPoE servers compare the requested service with the services they can provide. The PPPoE servers that can provide the requested service unicast PPPoE Active Discovery Offer (PADO) packets to the PPPoE client.
- The PPPoE client receives PADO packets from more than one PPPoE server. The PPPoE client selects the PPPoE server from which the first PADO packet is received and unicasts a PPPoE Active Discovery Request (PADR) packet to the selected PPPoE server.
- The PPPoE server generates a unique session ID to identify the PPPoE session with the PPPoE client, and then sends a PPPoE Active Discovery Session-confirmation (PADS) packet containing this session ID to the PPPoE client. When the PPPoE session is established, the PPPoE server and PPPoE client enter the PPPoE Session stage.
Session Stage
The PPPoE Session stage involves PPP negotiation and PPP packet transmission.
PPP negotiation at the PPPoE Session stage is the same as common PPP negotiation, which includes the LCP, authentication, and NCP phases.
- In the LCP phase, the PPPoE server and PPPoE client establish and configure a data link, and verify the data link status.
- When LCP negotiation is complete, authentication starts. The authentication protocol depends on the LCP negotiation result. The authentication protocol can be Challenge Handshake Authentication Protocol (CHAP) or Password Authentication Protocol (PAP).
- When authentication succeeds, PPP enters the Network Control Protocol (NCP) phase. NCP is a protocol suite used to configure network–layer protocols. A commonly used network-layer protocol is IP Control Protocol (IPCP), which is responsible for configuring IP addresses for users and the domain name server (DNS).
At the PPPoE Session Stage, the PPPoE server and PPPoE client unicast all Ethernet data packets.
Terminate Stage
The PPPoE server and client use PPP to terminate the PPPoE session. If PPP cannot be used, the server and client can use PPPoE Active Discovery Terminate (PADT) packets to terminate the PPPoE session.
After a PPPoE session is established, the PPPoE client or the PPPoE server can unicast a PADT packet to terminate the PPPoE session at any time. After transmitting or receiving the PADT packet, the PPPoE server and PPPoE client are not allowed to use this session to send any PPP traffic.
Troubleshooting:
1. check configuration, if everything looks ok go to step 2.debugging
#
sysname Router
#
acl number 3002
rule 5 permit ip source 192.168.10.0 0.0.0.255
#
interface Dialer1
link-protocol ppp
ppp chap user user1
ppp chap password cipher %^%#LHG2'Q8n%8NSLn'4-i'Z18)-%eT"v*||t1Mh;NbH%^%#
ip address ppp-negotiate
dialer user user1
dialer bundle 1
nat outbound 3002
#
interface GigabitEthernet2/0/0
pppoe-client dial-bundle-number 1
nat outbound 3002 interface Dialer 1
#
ip route-static 0.0.0.0 0.0.0.0 Dialer1
#
return
2.debugging,use the below commands to debugg pppoe:
debugg ppp al interface Dialer 1
debugg pppoe-client all
From the debug information we noticed the following packet/event:
The PPPoe server was accepting only pap packets for authentication and as we checked configuration again we found that we were sending request only using chap
The issue was solved by adding the pap user for authentication:
[Huawei-Dialer1] ppp pap local-user user1 password cipher xyz
