Layer 2 Protocol Tunneling Through a Network Overview
Layer 2 protocol tunneling allows Layer 2 protocol data units (PDUs) to be tunneled through a network. This is useful to provide a single spanning-tree protocol domain for subscribers across a service provider network. It is also useful for tunneling Cisco Discovery Protocol (CDP) or VLAN Trunk Protocol (VTP) PDUs across a network.
When a control packet for STP, CDP, or VTP is received on a service provider edge port configured for Layer 2 protocol tunneling, the multicast destination MAC address is rewritten with the predefined multicast tunnel MAC address of 01:00:0c:cd:cd:d0. The packet is transported across the provider network transparently to the other end of the tunnel and the original multicast destination MAC address is restored when the packet is transmitted.
If a packet is received on a tunnel interface that already has a destination multicast MAC address of 01:00:0c:cd:cd:d0, the port enters an error state and is shut down. To clear the error condition, the administrator must enter the clear error mac-rewrite interface interface-name command.
Layer 2 protocol tunneling is supported on MX Series routers with enhanced queueing Dense Port Concentrators (DPCs).
 | Note: When an MX Series router sends a RADIUS access request, the Chargeable-User-Identity parameter is sent with an empty field. For more information about configuring RADIUS, see the Junos Subscriber Access Configuration Guide. |
