PPPoE Configuration and Troubleshooting Considerations
PPPoE Configuration of the client (SM)
SM parameters affecting authentication and connection negotiation
The following ePMP SM configuration parameters are critical to proper PPPoE operation over the wireless link - ensure that these parameters are congruent with the configuration of the PPPoE server:
- Client Wireless IP Assignment: Static or Dynamic (DHCP) – Is the PPPoE server assigning an IP address to the PPPoE client or not?
- Service Name (optional) – Is the Service Name used by the PPPoE server configured correctly at the PPPoE client?
- Access Concentrator name (optional) – Is the AC Name used by the PPPoE server configured correctly at the PPPoE client?
- Username/Password (mandatory) – Has an account for this PPPoE client been provisioned in the PPPoE server?
- Authentication type: PAP, CHAP or ALL (both) – Is the server configured to use PAP, CHAP or both authentication types supported by the PPPoE client?
- Network location of the PPPoE server – PPPoE server and client need to be part of the same broadcast domain
SM parameters affecting PPoE quality of service
In some cases, verifying the configuration of the following parameters may improve the performance of the PPPoE connection:
- MTU Size (1492 bytes max) – A mismatch of MTU size between PPPoE server and client can result is smaller than optimal packets, causing throughput issues and unnecessary fragmentation of packets.
- MSS Clamping – It can potentially help optimizing TCP connections over PPPoE link by manipulating the MSS advertised in the TCP Sync message during TCP 3-way handshaking to a value that the PPPoE link can handle (http://blog.ipspace.net/2013/01/tcp-mss-clamping-what-is-it-and-why-do.html).
SM parameters affecting recovery time of PPPoE connection failures
Adjust the following parameter to control the way PPPoE connection drops are handled:
- Keep Alive Time – This value controls both the number of timeouts and the duration of the timeouts before a PPPoE connection is declared broken. For example, a value of 10 means that the PPPoE client should miss 10 consecutive keep-alive responses from the PPPoE server, each with a timeout value of 10 seconds before declaring the PPPoE link down and initiating recovery of the link.
PPPoE Connection Inspection and Logging
Using Wireshark to capture and analyze network packet activity is a great way to drill-down into PPPoE connectivity/link issues. These captures normally are captured at the PPPoE server side (between the PPPoE server and the AP). By capturing packets, operators can determine if there are issues in PPPoE server/client configuration or if there are networking issues prohibiting proper delivery of PPPoE messaging.