Configuring PPP and PPPoE Dynamic Interfaces over Static ATM

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 40 shows dynamic PPP interface columns on ATM interfaces.

Figure 40: Dynamic PPP Interface Columns

Figure 41 shows dynamic PPPoE interface columns and illustrates how PPPoE supports multiple IP sessions over each ATM 1483 circuit.

Figure 41: 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

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 (VCD), the virtual path identifier (VPI), the virtual channel identifier (VCI), and the encapsulation type.

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

   host1(config-subif)#atm pvc 10 100 22 aal5snap

   host1(config-subif)#atm pvc 10 100 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.

   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.

   host1#show atm subinterface atm 5/0.1

atm pvc

• Use to configure a PVC on an ATM interface. Specify one of the following encapsulation types:
  • aal5autoconfig—Enables autodetection of the 1483 encapsulation (LLC/SNAP or VC multiplexed).
  • aal5snap—Specifies a logical link control (LLC) encapsulated circuit; the LLC/Subnetwork Access Protocol (LLC/SNAP) header precedes the protocol datagram.
  • aal5mux ip—Specifies a VC multiplexed circuit. This option is used for IP only.
• Example

  host1(config-subif)#atm pvc 6 0 11 aal5autoconfig

• Use the no version to remove the specified PVC.
• See atm pvc.

auto-configure

• Use to configure a static ATM 1483 subinterface to support a dynamic interface. Specifies the types of dynamic encapsulation that the subinterface detects and accepts.
• This command creates the layers above ATM 1483 dynamically.
• You can enter the command repetitively to support multiple dynamic interface types.
• Select the dynamic next upper-interface type from these options: bridgedEthernet, ip, ppp, or pppoe.
• Encapsulation type lockout is performed on a per-encapsulation-type basis for each subinterface. An encapsulation type not configured for autodetection with the auto-configure command is automatically locked out. The lockout temporarily prevents the static ATM 1483 subinterface from detecting, accepting, and creating the encapsulation type until the lockout time expires.
• Use the lockout-time keyword to set the minimum lockout time and maximum lockout time, each of which can be in the range 1–86400 seconds (24 hours).The default range is 1–300 seconds (5 minutes).
• Use the none keyword to disable lockout for the specified encapsulation type.

  Note: Disabling lockout can result in undesirable CPU loading; we recommend that you not disable lockout for general use. At a minimum, use the default lockout time.

• For information about the rules that apply when you configure the lockout time for dynamic encapsulation type lockout, see Guidelines for Configuring Encapsulation Type Lockout.
• Example 1—Enables autodetection for the PPPoE encapsulation type using the default lockout time range, 1–300 seconds

  host1(config-subif)#auto-configure pppoe

• Example 2—Enables autodetection for the PPP encapsulation type using a nondefault lockout time range, 5–60 seconds

  host1(config-subif)#auto-configure ppp lockout-time 5 60

• Example 3—Disables encapsulation type lockout for the PPPoE encapsulation type

  host1(config-subif)#auto-configure pppoe lockout-time none

• Example 4—Either command reenables encapsulation type lockout for the PPPoE encapsulation type using the default lockout time range

  host1(config-subif)#auto-configure pppoe

  host1(config-subif)#no auto-configure pppoe lockout-time

• Example 5—Permanently locks out the PPP encapsulation type until the auto-configure ppp command is issued

  host1(config-subif)#no auto-configure ppp

• Use the no version to terminate detection of the specified encapsulation type or, if the lockout-time keyword is specified, to restore the lockout time range to its default value, 1–300 seconds.
• See auto-configure.

interface atm

• Use to select an ATM interface or ATM 1483 subinterface.
• To specify an ATM interface for ERX-7xx models, ERX-14xx models, and ERX-310 routers, use the slot/port.[subinterface ] format.
  • slot—Number of the chassis slot
  • port—Port number on the I/O module
  • subinterface—Number of the subinterface in the range 1–2147483647
• To specify an ATM interface for E120 and E320 routers, use the slot/adapter/port[.subinterface ] format.
  • slot—Number of the chassis slot
  • adapter—Identifier for the IOA within the E320 chassis, either 0 or 1, where:
    • 0 indicates that the IOA is installed in the right IOA bay (E120 router) or the upper IOA bay (E320 router).
    • 1 indicates that the IOA is installed in the left IOA bay (E120 router) or the lower IOA bay (E320 router).
  • port—Port number on the IOA
  • subinterface—Number of the subinterface in the range 1–2147483647
• For more information, see Creating a Basic Configuration in Configuring ATM .
• Examples

  host1(config)#interface atm 5/0.1

  host1(config)#interface atm 5/0/0.1

• Use the no version to remove the interface or subinterface.
• See interface atm.

profile

• Use to assign a profile.
• You must specify the encapsulation type to which the profile applies: bridgedEthernet, ip, ppp, pppoe ,or any.
• Specify a profile name with up to 80 alphanumeric characters.
• Example

  host1(config-subif)#profile ppp foo

• Use the no version to remove a profile assignment.
• See profile.

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 40, 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 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

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 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 PPPoA customer premises equipment (CPE). If the CPE supports the PPP keepalive feature, it can detect the loss of connectivity and restart Link Control Protocol (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 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 Terminating Stale PPPoA Subscribers and Restarting LCP Negotiations in Configuring Dynamic Interfaces Using Bulk Configuration.

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