Dynamic Interfaces and Dynamic Subscriber Interfaces Overview

Dynamic interfaces are created automatically and transparently in response to external events. For example, the router creates dynamic interfaces when a lower-layer link such as an ATM or VLAN receives data. The layers of a dynamic interface are created based on the packets received on the link and can be configured using profiles, RADIUS, or a combination of the two. Dynamic interfaces are used to terminate Broadband Residential Access Server (B-RAS) access such as: Point-to-Point Protocol over Ethernet (PPPoE), Point-to-Point Protocol over ATM (PPPoA), and Point-to-Point Protocol over Ethernet over ATM (PPPoEoA). A PPP session acts as logical separation between one subscriber session and the next. Multiple services using policies and QoS can be applied to the IP interface that is associated with the PPP session.

An example of a dynamic interface configuration is a PPPoE session running on top of a Gigabit Ethernet VLAN interface. Figure 1 shows an example of the dynamic interface stack.

Figure 1: Example of a Dynamic Interface Stack

Example of a Dynamic Interface Stack

You can configure the lower layers of the stack (GE physical interface and VLAN major interface) either dynamically or statically, and dynamically configure the upper layers (VLAN subinterface, PPPoE, and IP). An interface is considered dynamic if at least one of the layers in the interface stack is configured dynamically.

The router creates dynamic subscriber interfaces (DSIs) on demand, in response to external events, such as when a Dynamic Host Configuration Protocol (DHCP) event occurs or when the router detects a packet. DSIs function in a manner similar to dynamic interfaces. However, DSIs have a more specific application than dynamic interfaces. You use DSIs when there are no PPPoE, PPPoA, or PPPoEoA sessions to provide separation between layers and when subscriber management is required. For example, on an Ethernet VLAN, multiple subscribers can enter the network from a Wi-Fi hotspot, as shown in Figure 2:

Figure 2: Example of a Dynamic Subscriber Interface

Example of a Dynamic Subscriber Interface

In Figure 2, multiple subscribers share the same broadcast segment. Each subscriber is identified by an individual IP address or a group of subscribers can be identified with an IP network. When each subscriber is identified by an individual IP address, a dynamic subscriber interface is created for each subscriber. You can manage a group of subscribers identified with an IP network, on a single DSI. You can also manage a group of subscribers using a static subscriber interface (SSI). However, you must manually configure the SSI and you cannot use the same dynamic profiles and RADIUS that DSIs use.

Subscribers can be connected to a single broadcast segment without using dynamic or static subscriber interfaces. This configuration is useful when subscriber management is not required. Subscriber management usually refers to (but is not limited to) tailoring IP policies and QoS profiles to a specific address or a very small group of addresses. For detailed information about the uses for Dynamic Subscriber interfaces, see Example: Configuring Dynamic Subscriber Interfaces .

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