Dynamic PPP and PPPoE Interfaces over Static ATM

Dynamic PPP and PPPoE Interfaces over Static ATM Overview

E Series routers support dynamic PPP and PPPoE interfaces. The configuration procedure is very similar for each.

When using the auto-configure command, select only ppp or pppoe. The router automatically builds the necessary interfaces for you. When you indicate pppoe, on receipt of a PPPoE packet, the dynamic interface built is IP over PPP over PPPoE over ATM. Likewise, when you indicate ppp, the dynamic interface built is IP over PPP over ATM.

Figure 1 shows dynamic PPP interface columns on ATM interfaces.

Figure 1: Dynamic PPP Interface Columns

Figure 2 shows dynamic PPPoE interface columns and illustrates how PPPoE supports multiple IP sessions over each ATM 1483 circuit.

Figure 2: Dynamic PPPoE Interface Columns

You can specify either or both ppp and pppoe for the interface by specifying the auto-configure command for each type of interface. The first packet received defines the type of dynamic interface that is created.

Configuring a PPP or PPPoE Dynamic Interface over an ATM 1483 Subinterface

To configure an ATM 1483 subinterface to support a PPP or PPPoE dynamic interface:

1. Configure a physical interface.
   host1(config)#interface atm 5/0
2. Configure an ATM 1483 subinterface.
   host1(config-if)#interface atm 5/0.1
3. Configure a PVC by specifying the virtual circuit descriptor, the virtual path identifier, the virtual channel identifier, and the encapsulation type. For more information, see Creating a PVC on an ATM 1483 Subinterface.
   host1(config-subif)#atm pvc 10 10 22 aal5snap

   If you want the router to autodetect the encapsulation type, use the aal5autoconfig option.

   host1(config-subif)#atm pvc 10 10 22 aal5autoconfig
4. Assign a profile to the PPP or PPPoE encapsulation types.
   host1(config-subif)#profile ppp foo host1(config-subif)#profile pppoe foo
5. Configure the subinterface to detect and accept dynamic PPP or PPPoE. For more information, see Configuring a Dynamic Interface over an ATM 1483 Subinterface.
   host1(config-subif)#auto-configure ppp host1(config-subif)#auto-configure pppoe

   In addition to ppp and pppoe, you can also specify ip or bridgedEthernet.

6. (Optional) Verify your configuration. For more information, see Monitoring Status or Summary Information for ATM Subinterfaces.

   host1#show atm subinterface atm 5/0.1

                                  Circuit                           Interface
   Interface ATM-Prot VCD VPI VCI  Type   Encap MTU      Status       Type
   --------- -------- --- --- --- ------- ----- ---- -------------- ---------
   ATM 5/0.1 RFC-1483  10  10  22 PVC     SNAP  9180 lowerLayerDown Static
   
   Auto configure status         : dynamic
   Auto configure interface(s)   : PPP  PPPoE
   Detected 1483 encapsulation   : none
   Detected dynamic interface    : none
   Interface types in lockout    : none
   
   Lockout state (seconds)       : Min Max Current Elapsed Next
   ------------------------------- --- --- ------- ------- ----
   PPP                               1 300       0       0    1
   PPPoE                             1 300       0       0    1
   
   Assigned profile (IP)         : none assigned
   Assigned profile (BridgedEnet): none assigned
   Assigned profile (PPP)        : foo
   Assigned profile (PPPoE)      : foo
   Assigned profile (any)        : none assigned
   
   SNMP trap link-status: disabled
   Assigned VC Class: none assigned
   
   InPackets:                0
   InBytes:                  0
   OutPackets:               0
   OutBytes:                 0
   InErrors:                 0
   OutErrors:                0
   InPacketDiscards:         0
   InPacketsUnknownProtocol: 0
   OutDiscards:              0
   InPolicedPackets:         0
   OutPolicedPackets:        0
   1 interface(s) found

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 3, 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 3: 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.