This parameter is used to enable Layer 2 Protocol Tunneling. The tunneling mechanism is a propritary solution specified by Cisco. The Layer 2 Control Protocol tunneling feature is only available when accessMethod is transparrentLan.

Customers at different sites connected across a SP network need to use various Layer 2 protocols to scale their topologies to include all remote sites, as well as the local sites. STP must run properly, and every VLAN should build a proper spanning tree that includes the local site and all remote sites across the SP network. Cisco Discovery Protocol (CDP) must discover neighboring Cisco devices from local and remote sites. VLAN Trunking Protocol (VTP) must provide consistent VLAN configuration throughout all sites in the customer network.

When protocol tunneling is enabled, DSLAM on the inbound side of the SP network encapsulate Layer 2 protocol packets with a special MAC address and send them across the SP network. Core switches in the network do not process these packets but forward them as normal packets. Layer 2 protocol data units (PDUs) for CDP, STP, or VTP cross the SP network and are delivered to customer switches on the outbound side of the SP network. Identical packets are received by all customer ports on the same VLANs with these results: Users on each of a customer's sites can properly run STP, and every VLAN can build a correct spanning tree, based on parameters from all sites and not just from the local site. CDP discovers and shows information about the other Cisco devices connected through the SP network. VTP provides consistent VLAN configuration throughout the customer network, propagating to all switches through the SP.

When the Layer 2 PDUs that entered the DSLAM on the inbound side, the DSLAM overwrites the customer PDU-destination MAC address with a well-known Cisco proprietary multicast address (01-00-0c-cd-cd-d0). The DSLAM on the outbound side restore the proper Layer 2 protocol and MAC address information and forward the packets to all PVCs in the same VLAN. Therefore, the Layer 2 PDUs remain intact and are delivered across the SP network to the other side of the customer network.

Tunneling of Layer 2 control protocols is enabled using this bit-map.

The various bit positions are: 0 stp When set Layer 2 Control Protocol tunneling is enabled for Spanning Tree Protocol (destination MAC = 01:80:c2:00:00:00) 1 pvstp When set Layer 2 Control Protocol tunneling is enabled for Per VLAN Spanning Tree Protocol, a Cisco specified extension to STP (destination MAC = 01:00:0c:cc:cc:cd). 2 cdp When set Layer 2 Control Protocol tunneling is enabled for Cisco Discovery Protocol (destination MAC = 01:00:0c:cc:cc:cc). 3 vtp When set Layer 2 Control Protocol tunneling is enabled for Virtual Trunking Protocol (destination MAC = 01:00:0c:cc:cc:cc).

Valid from: EDA 2.1 SP2