Cisco Systems 3750E manual Default Layer 2 Protocol Tunneling Configuration, 17-11

Chapter 17 Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling

Configuring Layer 2 Protocol Tunneling

See Figure 17-4, with Customer X and Customer Y in access VLANs 30 and 40, respectively. Asymmetric links connect the customers in Site 1 to edge switches in the service-provider network. The Layer 2 PDUs (for example, BPDUs) coming into Switch 2 from Customer Y in Site 1 are forwarded to the infrastructure as double-tagged packets with the well-known MAC address as the destination MAC address. These double-tagged packets have the metro VLAN tag of 40, as well as an inner VLAN tag (for example, VLAN 100). When the double-tagged packets enter Switch D, the outer VLAN tag 40 is removed, the well-known MAC address is replaced with the respective Layer 2 protocol MAC address, and the packet is sent to Customer Y on Site 2 as a single-tagged frame in VLAN 100.

You can also enable Layer 2 protocol tunneling on access ports on the edge switch connected to access or trunk ports on the customer switch. In this case, the encapsulation and decapsulation process is the same as described in the previous paragraph, except that the packets are not double-tagged in the service-provider network. The single tag is the customer-specific access VLAN tag.

In switch stacks, Layer 2 protocol tunneling configuration is distributed among all stack members. Each stack member that receives an ingress packet on a local port encapsulates or decapsulates the packet and forwards it to the appropriate destination port. On a single switch, ingress Layer 2 protocol-tunneled traffic is sent across all local ports in the same VLAN on which Layer 2 protocol tunneling is enabled. In a stack, packets received by a Layer 2 protocol-tunneled port are distributed to all ports in the stack that are configured for Layer 2 protocol tunneling and are in the same VLAN. All Layer 2 protocol tunneling configuration is handled by the stack master and distributed to all stack members.

These sections contain this configuration information:

•Default Layer 2 Protocol Tunneling Configuration, page 17-11

•Layer 2 Protocol Tunneling Configuration Guidelines, page 17-12

•Configuring Layer 2 Protocol Tunneling, page 17-13

•Configuring Layer 2 Tunneling for EtherChannels, page 17-14

Default Layer 2 Protocol Tunneling Configuration

Table 17-1shows the default Layer 2 protocol tunneling configuration.

Table 17-1 Default Layer 2 Ethernet Interface VLAN Configuration

Feature	Default Setting
Layer 2 protocol tunneling	Disabled.
Shutdown threshold	None set.
Drop threshold	None set.
CoS value	If a CoS value is configured on the interface for data packets, that
	value is the default used for Layer 2 PDUs. If none is configured,
	the default is 5.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02		17-11