Subscriber Interfaces and PPPoE Overview

Benefits of Using Dynamic PPPoE Subscriber Interfaces

Configuring and using dynamic PPPoE subscriber interfaces offers the following benefits:

• On-demand dynamic interface creation

  Dynamic PPPoE subscriber interfaces provides the flexibility of dynamically creating the PPPoE subscriber interface only when needed; that is, when a subscriber logs in on the associated underlying Ethernet interface. By contrast, statically created interfaces allocate and consume system resources when the interface is created. Configuring and using dynamically created interfaces helps you effectively and conveniently manage edge or access networks in which large numbers of subscribers are constantly logging in to and logging out from the network on a transient basis.

• Dynamic removal of PPPoE subscriber interfaces without manual intervention

  When the PPPoE subscriber logs out or the PPPoE session is terminated, the router dynamically deletes the associated PPPoE subscriber interface without your intervention, thereby restoring any consumed resources to the router.

• Use of dynamic profiles to efficiently manage multiple subscriber interfaces

  By using a profile, you reduce the management of a large number of interfaces by applying a set of common characteristics to multiple interfaces. When you configure a dynamic profile for PPPoE, you use predefined dynamic variables in the 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.

• Denial of service (DoS) protection

  You can configure the underlying Ethernet interface with certain PPPoE-specific attributes that can reduce the potential for DoS attacks. Duplicate protection, which is disabled by default, prevents activation of another dynamic PPPoE logical interface on the underlying interface when a PPPoE logical interface for the same client is already active on the underlying interface. You can also specify the maximum number of PPPoE sessions that the router can activate on the underlying interface. By enabling duplicate protection and restricting the maximum number of PPPoE sessions on the underlying interface, you can ensure that a single toxic PPPoE client cannot monopolize allocation of the PPPoE session.

• Support for dynamic PPPoE subscriber interface creation from PPPoE service name tables

  You can assign a previously configured PPPoE dynamic profile to a named, empty, or any service entry in a PPPoE service name table, or to an agent circuit identifier/agent remote identifier (ACI/ARI) pair defined for these services. The router uses the attributes defined in the profile to instantiate a dynamic PPPoE subscriber interface based on the service name, ACI, and ARI information provided by the PPPoE client during PPPoE negotiation. To specify the routing instance in which to instantiate the dynamic PPPoE subscriber interface, you can assign a previously configured routing instance to a named, empty, or any service, or to an ACI/ARI pair defined for these services. The dynamic profile and routing instance configured for the PPPoE service name table overrides the dynamic profile and routing instance assigned to the PPPoE underlying interface on which the dynamic subscriber interface is created.

Supported Platforms for Dynamic PPPoE Subscriber Interfaces

Configuration of dynamic PPPoE subscriber interfaces over static underlying Ethernet interfaces is supported on MPC/MIC interfaces on MX Series 5G Universal Routing Platforms.

Sequence of Operations for PPPoE Subscriber Access

When a PPPoE subscriber logs in the PPPoE protocol defines the sequence of operations by which a connection is established and traffic flow is enabled on the dynamic PPPoE subscriber interface. Similarly, when the PPPoE subscriber logs out from the network, PPPoE defines the sequence that occurs to terminate the connection and remove the dynamic PPPoE subscriber interface from the router.

The router creates a dynamic PPPoE subscriber interface for each new PPPoE session, and removes the dynamic PPPoE subscriber interface when the session is terminated due to subscriber logout, PPP negotiation failure, or down status of the underlying Ethernet interface. Dynamic PPPoE subscriber interfaces are never reused for multiple PPPoE sessions.

• Sequence When a PPPoE Subscriber Logs In
• Sequence When a PPPoE Subscriber Logs Out

Revival of PPPoE Sessions on Backup Routers (MX240, MX304, MX480, MX960, MX10004, MX10008, MX2010, MX2020 Devices)

Starting from Junos release 23.2R1, the enhanced PPPoE sessions creation functionality supports faster switchover of subscriber PPPoE sessions from an active MX router to a standby MX router.

After failover, the newly active standby router starts receiving traffic from subscribers. The standby router requires at least one unknown session ID packet or control packet from a subscriber, to re-establish the connection.

The PPPoE session can switchover without waiting for the keepalive time to expire. When the standby router receives an unknown session ID packet from a PPP session, it responds with PPPoE Active Discovery Termination (PADT) message. This PADT response causes the PPP client to restart immediately, which reduces the time to restart PPP sessions.

Additionally the following features are supported:

• PPPoE subscribers can quickly re-establish PPP sessions on routers.
• Rate limiting of the number of data and control packets with unknown session ID sent to routers.
• Smooth transition to reconnect all PPPoE subscribers during multiple failovers.