(ISP). It is important that the ATM interface status is up, the line protocol is up, and that the IP address provided by the ISP is being pinged. If there is no output for 60 seconds, debugging the VPI/VCI values is probably incorrect and you should contact ISP support. Finally, verify the VPI/VCI values and make the necessary changes to the configuration. When you are finished with this troubleshooting task, turn off debugging by using the undebug all command.
Content 2.7 Troubleshooting Broadband ADSL Configurations 2.7.6 Layer 2: Is Data Being Received from the ISP? If the VPI/VCI values are correct and the PVC is active, then the next step is to verify that data is being sent and received on the ATM interface. The show interfaces atm command shows the interface status and counters for incoming and outgoing packets. If the incoming and outgoing packet counters are incrementing, the router is receiving and sending packets from the ISP; therefore, data is received from the ISP and is sent to the ISP.
Content 2.7 Troubleshooting Broadband ADSL Configurations 2.7.7 Proper PPP Negotiation With Layer 1 set up properly, correct VPI/VCI in use, PVC active, and data being received and sent, the next step is to ensure that a PPP session is established properly between the Cisco CPE router and the aggregation router of the service provider. You can observe the PPP negotiation process by issuing the debug ppp negotiation and debug ppp authentication commands. PPP session setup occurs in three stages:
  1. Link control protocol (LCP): A mandatory phase in which parameters to establish, configure, and test the data-link connection are negotiated.
  2. Authentication: In this optional phase, authentication is performed with the authentication protocol (CHAP or PAP) agreed upon in LCP negotiation.
  3. Network Control Protocol (NCP): This mandatory phase establishes and configures different network-layer protocols. The most common Layer 3 protocol negotiated is IP. The routers exchange IPCP messages to negotiate options specific to the IP protocol.
The debug output in Figure shows the successful PPP session establishment. In case the PPP session does not come up successfully, there are four main points of failure in a PPP negotiation:
Content 2.8 PPPoE Simulation Practice 2.8.1 PPPoE Simulation Practice e-Lab Activity e-Lab Activity: PPPoE Simulation This task will provide practice configuring a Cisco ADSL router for connectivity to an ISP using PPPoE. In addition, it will be necessary to configure Dynamic Host Configuration Protocol (DHCP) services for IP addressing of local PCs at the teleworker’s location; also, basic Port Address Translation (PAT) will need to be configured.