Preserve 802.1Q Tagging with 802.1P Marking over ATM PVCs for xDSL Uplinks

Overview

The Preserve 802.1Q Tagging with 802.1P Marking over ATM PVCs for xDSL Uplinks feature enables the transport of 802.1Q VLAN tags over ATM permanent virtual circuits (PVC) specifically for ADSL2+ uplinks. This functionality allows service providers to implement VLAN-based service differentiation, supporting both real-time applications like VoIP and best-effort internet traffic.

Benefits and Requirements

This feature allows Customer Premises Equipment (CPE) to carry traffic with provider-specific 802.1Q tags. By using 802.1P marking, traffic can be prioritized to ensure quality of service (QoS) across the network. Before configuration, users must have a foundational understanding of ATM, bridging, DHCP, and VLANs. The feature is restricted to a single bridged 802.1Q VLAN and must be configured on a point-to-point ATM subinterface using AAL5SNAP encapsulation.

Configuration

Configuration involves defining class maps and policy maps to classify traffic and set CoS values. Key steps include:

• Defining egress and ingress class maps to match traffic based on QoS groups or interfaces.
• Creating policy maps to set CoS values and inner VLAN IDs.
• Applying these policies to the ATM PVC interface.
• Using the bridge-dot1q encap command to specify the provider-assigned VLAN ID.
• Configuring PPPoE clients if dynamic IP addressing is required.

Troubleshooting

To troubleshoot PPP session establishment, administrators can use debug commands such as debug ppp authentication and debug ppp negotiation. Additionally, for RADIUS or TACACS authentication issues, debug aaa authentication and debug aaa authorization are available. Caution is advised when using debug commands as they are CPU-intensive and may impact network performance.