Overview of Terminating Stale PPPoA Subscribers and Restarting LCP Negotiations

In configurations of dynamic IP over dynamic PPP over a static ATM 1483 subinterface, as shown in Figure 1, any of the following conditions might cause the static ATM 1483 subinterface to transition to a dormant state as the result of an ungraceful subscriber logout:

• Rebooting the router
• Rebooting a line module
• Transitioning the physical (for example, SONET) interface, ATM major interface, or ATM AAL5 interface from up to down to up again
• Transitioning the ATM 1483 subinterface or the ATM permanent virtual connection (PVC) from up to down to up again
• Any other lowerLayerDown operational status condition that affects the dynamic PPP interface; a lowerLayerDown status indicates that a lower-layer interface below the dynamic PPP interface is down

Figure 1: Dynamic PPP Interface Columns

When the ATM 1483 subinterface transitions to a dormant state as a result of any of these conditions, the router tears down the dynamic PPP interface column. The dynamic PPP interface is unable to send an Link Control Protocol (LCP) terminate request to its peer because its own lower-layer interface is down. This action causes a loss of connectivity between the router and the Point-to-Point Protocol over ATM (PPPoA) customer premises equipment (CPE). If the CPE supports the PPP keepalive feature, it can detect the loss of connectivity and restart LCP negotiations in order to initiate a new connection. However, if the CPE does not support PPP keepalive, it cannot detect that the connection is down, and continues to send PPP data packets to the router.

On receipt of an IPv4-over-PPP data packet or an IPv6-over-PPP data packet from the CPE when the ATM 1483 subinterface transitions to a dormant state, the router sends an LCP terminate request packet to the CPE. Receipt of the LCP terminate request packet causes the CPE to restart LCP negotiations in order to initiate a new connection. After the CPE restarts LCP negotiations, the router recreates the dynamic PPP and IP upper-layer interfaces above the static ATM 1483 subinterface. This behavior is always in effect on the router and does not require command-line interface (CLI) or SNMP configuration.

Sending an LCP terminate request packet in response to receipt of an IPv4-over-PPP data packet or an IPv6-over-PPP data packet from a PPPoA CPE device offers the following benefits:

• For CPEs that support PPP keepalive, receipt of an LCP terminate request packet from the router restarts the LCP negotiations more quickly.
• For CPEs that do not support PPP keepalive, receipt of an LCP terminate request packet from the router enables the CPE to detect the connection termination and restart LCP negotiations in response.

The router also sends an LCP terminate request packet to a PPPoA CPE device in configurations of dynamic IP over dynamic PPP over a dynamic (bulk-configured) ATM 1483 subinterface. For more information, see Unresolved xref in Unresolved xref.