Applications for Subscriber Interfaces

In a cable modem network, service providers can use subscriber interfaces to:

• Direct traffic toward special local content in the network
• Differentiate traffic for virtual private networks (VPNs)

Directing Traffic Toward Special Local Content

Figure 1 shows an example of a cable modem network. Multiple cable modem termination systems (CMTSs) connect to multiple shared media access LANs. Many subscribers connect to each LAN.

In this example, the service provider uses subscriber interfaces to direct traffic toward special local content on the network: a voice over Internet Protocol (VoIP) service on network 10.11.0.0/16, or a local gaming service on network 10.12.0.0/16. Rate limits and policies on the subscriber interface customize the service level for the associated service. In this application, the E Series router is the first-hop router for the subscribers, and the subscriber interfaces demultiplex traffic based on the destination address.

Figure 1: Subscriber Interfaces in a Cable Modem Network

For instructions on configuring the application shown in Figure 1, see Example: Using a Destination Address to Demultiplex Traffic.

Differentiating Traffic for VPNs

Similarly, service providers can use subscriber interfaces to differentiate traffic for VPNs. Figure 2 shows an example of this application.

Customers on subnet A need to connect to VPN A, and customers on subnet B need to connect to VPN B. The E Series router connects to VPN A through virtual router A and to VPN B though virtual router B. Using two subscriber interfaces on the same primary interface (one on virtual router B and one on virtual router A), the E Series router can separate the traffic from subnets A and B. Because the E Series router is forwarding traffic in this application, the shared IP interface should demultiplex the traffic by using a source address.

Figure 2: Associating Subnets with a VPN Using Subscriber Interfaces

For instructions on configuring the application shown in Figure 2, see Example: Using a Destination Address to Demultiplex Traffic.