Dynamic PPPoE Subscriber Interfaces over Static Underlying Interfaces Overview

Creating a dynamic PPPoE subscriber interface over a static underlying Ethernet interface consists of two basic steps:

1. Configure a dynamic profile to define the attributes of the PPPoE logical interface.
2. Attach the dynamic profile to a statically created underlying Ethernet interface configured with PPPoE encapsulation.

This overview describes the concepts you need to understand to configure a dynamic PPPoE subscriber interface, and covers the following topics:

• PPPoE Dynamic Profile Configuration
• PPPoE Underlying Interface Configuration
• Address Assignment for Dynamic PPPoE Subscriber Interfaces
• Guidelines for Configuring Dynamic PPPoE Subscriber Interfaces

PPPoE Dynamic Profile Configuration

A dynamic profile is a template for configuring a dynamic interface. You use predefined dynamic variables in the PPPoE dynamic profile to represent information that varies from subscriber to subscriber, such as the logical unit number and underlying interface name. These variables are dynamically replaced with the values supplied by the network when the subscriber logs in. On receipt of traffic on an underlying Ethernet interface to which a dynamic profile is attached, the router creates the dynamic PPPoE logical interface, also referred to as a dynamic PPPoE subscriber interface, on the underlying interface and applies the properties configured in the dynamic profile.

To provide basic access for PPPoE subscribers, the dynamic profile must provide a minimal configuration for a pp0 (PPPoE) logical interface that includes at least the following attributes:

• The logical unit number, represented by the $junos-interface-unit predefined dynamic variable
• The name of the underlying Ethernet interface, represented by the $junos-underlying-interface predefined dynamic variable
• Configuration of the router to act as a PPPoE server
• The PPP authentication protocol (PAP or CHAP)
• The unnumbered address for the inet (IPv4) family

You can also optionally configure additional options for PPPoE subscriber access in the dynamic profile, including:

• The keepalive interval, or the option to disable sending keepalive messages
• The IPv4 address of the dynamic PPPoE logical interface
• The service sets and filters, input filters, and output filters to be applied to the dynamic PPPoE logical interface

PPPoE Underlying Interface Configuration

After you configure a dynamic profile to define the attributes of a dynamic PPPoE subscriber interface, you must attach the dynamic profile to the underlying Ethernet interface on which you want the router to dynamically create the PPPoE logical interface. The underlying interface for a dynamic PPPoE logical interface must be statically created and configured with PPPoE (ppp-over-ether) encapsulation. When a PPPoE subscriber logs in on the underlying interface, the router dynamically creates the PPPoE logical interface and applies the attributes defined in the profile to the interface.

In addition to attaching the dynamic profile to the interface, you can also configure the underlying interface with one or more of the following optional PPPoE-specific attributes:

• Prevention of another dynamic PPPoE logical interface from being activated on the underlying interface when a PPPoE logical interface for a client with the same MAC address is already active on that interface
• Maximum number of dynamic PPPoE logical interfaces (sessions) that the router can activate on the underlying interface
• An alternative access concentrator name in the AC-NAME tag in a PPPoE control packet

Address Assignment for Dynamic PPPoE Subscriber Interfaces

If the subscriber address for a dynamic PPPoE interface is not specified by means of the Framed-IP-Address (8) or Framed-Pool (88) RADIUS IETF attributes during authentication, the router allocates an IP address from the first IPv4 local address-assignment pool defined in the routing instance. For this reason, make sure that the local address assigned for the inet (IPv4) address family is in the same subnet as the addresses obtained from the first IPv4 local address-assignment pool.

The router allocates the IP address from the first IPv4 local address-assignment pool under either of the following conditions:

• RADIUS returns no address attributes.
• RADIUS authentication does not take place because only address allocation is requested.

If the first IPv4 local address-assignment pool has no available addresses, or if no IPv4 local address-assignment pools are configured, the router does not allocate an IP address to the dynamic PPPoE subscriber interface, and denies access to the associated subscriber. To avoid depletion of IP addresses, you can configure linked address-assignment pools on the first IPv4 local address-assignment pool to create one or more backup pools.

For more information, see Configuring Address-Assignment Pools.

Guidelines for Configuring Dynamic PPPoE Subscriber Interfaces

Observe the following guidelines when you configure dynamic PPPoE subscriber interfaces:

• You can configure dynamic PPPoE subscriber interfaces only for the inet (IPv4) protocol family in the current release.
• When you configure CHAP or PAP authentication in a PPPoE dynamic profile, you cannot configure additional options for the chap or pap statements. This is because the router supports only unidirectional authentication for dynamic interfaces; that is, the router always functions as the authenticator.
• When you attach the PPPoE dynamic profile to an underlying Ethernet interface, ensure that both of the following conditions are met:
  • The PPPoE dynamic profile has already been configured on the router.
  • The underlying Ethernet interface has already been statically configured on the router with PPPoE (ppp-over-ether) encapsulation.
• You cannot attach a PPPoE dynamic profile to an underlying Ethernet interface that is already associated with static PPPoE logical interfaces. Conversely, you cannot associate static PPPoE logical interfaces with an underlying Ethernet interface that already has a PPPoE dynamic profile attached.

Related Topics

• Subscriber Interfaces and PPPoE Overview
• Configuring Dynamic PPPoE Subscriber Interfaces Using Dynamic Profiles
• For more information about static PPPoE interfaces, see the Junos Network Interfaces Configuration Guide