Troubleshooting guide

Cisco DSL Router Configuration and Troubleshooting
Guide
PPPoE: PC as a PPPoE Client – Troubleshooting
When the PC clients are running a Point−to−Point over Ethernet (PPPoE) client application, the Cisco Digital
Subscriber Line (DSL) Router is configured as a pure bridge and the troubleshooting steps are the same as a
pure bridging scenario. If you troubleshoot the Cisco DSL Router and determine that it is operating correctly,
contact your Internet Service Provider (ISP) or the PPPoE client application vendor for additional assistance.
Determine the Layer to Troubleshoot
There are many reasons why your DSL connection may not be functioning properly. The goal of this section
is to isolate the cause of the failure and repair it. The first troubleshooting step is to determine which layer of
your Asymetric Digital Subscriber Line (ADSL) service is failing. There are three layers in which the failure
can occur.
Layer 1 – DSL physical connectivity to your ISP's Digital Subscriber Line Access Multiplexer
(DSLAM)
•
Layer 2.1 – ATM connectivity•
Layer 2.2 – Point−to−Point Protocol over ATM (PPPoA), PPPoE, RFC1483 Bridging, or RFC1483
Routing
•
Layer 3 – IP•
The easiest way to determine which layer you should begin troubleshooting is to issue the command show ip
interface brief. The output of this command differs slightly depending on your configuration.
827−ESC#show ip interface brief
Interface IP−Address OK? Method Status Protocol
ATM0 unassigned YES manual up up
ATM0.1 unassigned YES unset up up
Ethernet0 10.10.10.1 YES manual up up
If the statuses of ATM0 and ATM0.1 are up and the protocol is up, begin troubleshooting at Layer 2.
If the ATM interfaces are down, or if they keep coming up and then going down (they don't stay up and up),
begin troubleshooting at Layer 1.
Layer 1 Issues
Is the carrier detect (CD) light on the front panel of the Cisco DSL Router
on or off?
If the CD light is on, go to the Layer 2 Issues section of this document.
If the CD light is off, continue with the next question.
Cisco DSL Router Configuration and Troubleshooting Guide