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• PVST.
• STP (including STP, RSTP, and MSTP).
• UDLD.
• VTP.
L2PT operating mechanism
As shown in Figure 90, L2PT operates as follows:
• When a port of PE 1 receives a Layer 2 protocol packet from the customer network in a VLAN,
it performs the following operations:
{ Multicasts the packet out of all customer-facing ports in the VLAN except the receiving port.
{ Changes the packet's destination multicast MAC address to a specified multicast address,
and multicasts it out of all ISP-facing ports in the VLAN. The modified packet is called the
tunneled packet.
• When a port of PE 1 in the VLAN receives the tunneled packet from the service provider
network, it performs the following operations:
{ Multicasts the packet out of all ISP-facing ports in the VLAN except the receiving port.
{ Changes the destination multicast MAC address to the original MAC address, and
multicasts the packet out of all customer-facing ports in the VLAN.
Figure 90 L2PT operating mechanism
For example, as shown in Figure 91, PE 1 receives an STP packet (BPDU) from network 1 to
network 2. CEs are the edge devices on the customer network, and PEs are the edge devices on the
service provider network. L2PT processes the packet as follows:
1. PE 1 performs the following operations:
a. Changes the packet's destination multicast MAC address 0180-c200-0000 to a specified
multicast MAC address (010f-e200-0003 by default) for the BPDU.
b. Sends the tunneled packet out of all ISP-facing ports in the packet's VLAN.
2. Upon receiving the tunneled packet, PE 2 decapsulates the packet and sends the BPDU to CE
2.
Through L2PT, both the ISP network and Customer A's network can perform independent spanning
tree calculations.
PE 1
Service provider network
PE 2
Customer
network
Customer
network
Layer 2 protocol packets
from customer networks
Tunneled packets
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