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.
Layer 2 protocol tunneling is supported on MX Series routers with Enhanced (Dense Port Concentrators) DPCs and Enhanced Queuing (DPCs), see Table 2 for a list of the DPCs supported. Layer 2 protocol tunneling is supported on all Modular Port Concentrators (MPCs),
 | Note: Layer 2 protocol tunneling is not supported on Rev-A DPCs on MX Series routers because of microcode space limitations. |
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 and MAC rewrite are supported in VPLS, but only certain hardware configurations are supported.
Table 1 shows the MPCs and Enhanced DPCs supported when configuring Layer 2 protocol tunneling and VPLS.
Table 1: MAC Rewrite and VPLS Configurations
CE-Facing Interface | PE-Core Facing Interface | Layer 2 Protocol Tunneling |
|---|---|---|
MPC | MPC | Yes |
MPC | Enhanced DPC | Yes |
Enhanced DPC | MPC | Yes |
Enhanced DPC | Enhanced DPC | No |
Table 2 lists the DPCs that support the Layer 2 tunneling protocol.
Table 2: DPCs Supported for Layer 2 Protocol Tunneling
DPC Name | DPC Model Number |
|---|---|
| Gigabit Ethernet | |
DPCE-R-40GE-SFP | |
DPCE-X-40GE-SFP | |
Gigabit Ethernet Enhanced Queuing Ethernet Services DPC with SFP | DPCE-X-Q-40GE-SFP |
DPCE-R-Q-20GE-SFP | |
DPCE-R-Q-40GE-SFP | |
| 10-Gigabit Ethernet | |
DPCE-R-2XGE-XFP | |
DPCE-R-4XGE-XFP | |
DPCE-X-4XGE-XFP | |
10-Gigabit Ethernet Enhanced Queuing Ethernet Services DPC with XFP | DPCE-X-Q-4XGE-XFP |
10-Gigabit Ethernet Enhanced Queuing IP Services DPC with XFP | DPCE-R-Q-4XGE-XFP |
| Multi-Rate Ethernet | |
DPCE-R-20GE-2XGE | |
Multi-Rate Ethernet Enhanced Ethernet Services DPC with SFP and XFP | DPCE-X-20GE-2XGE |
Multi-Rate Ethernet Enhanced Queuing IP Services DPC with SFP and XFP | DPCE-R-Q-20GE-2XGE |
| Tri-Rate Ethernet | |
DPCE-R-40GE-TX | |
DPCE-X-40GE-TX | |
| 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. |
