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Discarding PADR Messages to Accommodate Abnormal CPE Behavior

This topic describes how to avoid a situation where certain CPEs respond inappropriately to normal router behavior.

During PPPoE session negotiation, the router returns PADS messages in response to PADR messages when it accepts or rejects the PPPoE session. The router adds an error tag to the PADS message when it detects a problem.

AC-System-Error is one such tag. This tag is inserted when the router imposes automatic throttling in response to excessive CPU consumption, excessive subscriber connections, or physical interfaces cycling up and down.

When the CPE receives a PADS message with this tag, the typical behavior is to retry sending PADR messages to the router or to restart session negotiation by sending PADI messages. However, some CPEs may respond inappropriately with the result that their subscribers are never connected until the CPE is rebooted.

To avoid this situation when such CPEs have access to your network, you can configure the router to silently discard PADR messages in situations where the PADS would include the AC-System-Error tag. The consequence is that the CPE resends PADR messages. When the conditions that result in the AC-System-Error tag are no longer present, the router once again evaluates PADR packets to determine whether to accept or reject the session.

To silently discard PADR packets:

  • Specify that PADS messages with AC-System-Error tags are not sent.