CoS for L2TP LNS Inline Services Overview

Guidelines for Applying CoS to the LNS

In L2TP configurations, IP, UDP, and L2TP headers are added to packets arriving at a PPP subscriber interface on the L2TP access concentrator (LAC) before being tunneled to the LNS.

When a service interface is configured for an L2TP LNS session, it has an inner IP header and an outer IP header. You can configure CoS for an LNS session that corresponds to the inner IP header only. The outer IP header is used for L2TP tunnel processing only.

However, we recommend that you configure classifiers and rewrite-rules to transfer the ToS (type of service) value from the inner IP header to the outer IP header of the L2TP packet.

Figure 1 shows the classifier and rewrite rules that you can configure on an LNS inline service.

Figure 1: Processing of CoS Parameters in an L2TP LNS Inline Service

By default, the shaping calculation on the service interface includes the L2TP encapsulation. If necessary, you can configure additional adjustments for downstream ATM traffic from the LAC or differences in Layer 2 protocols.

Hardware Requirements for Inline Services on the LNS

Hierarchical scheduling for L2TP LNS inline services is supported on MIC and MPC interfaces only. The services that you can configure depend on the hardware combination. Table 1 lists the supported inline services and peer interfaces for each MIC and MPC combination.