accessports in the same metro VLAN. Therefore, the Layer 2 PDUs remain intact and are delivered across
theservice-provider infrastructure to the other side of the customer network.
Seethe Layer 2 ProtocolTunneling figure in Layer 2 Protocol Tunneling Overview, on page 129, with
CustomerX and Customer Y in access VLANs 30 and 40, respectively. Asymmetric links connect the customers
inSite 1 to edge switches in the service-provider network. The Layer 2 PDUs (for example, BPDUs) coming
intoSwitch B from Customer Y in Site 1 are forwarded to the infrastructure as double-tagged packets with
thewell-known MAC address as the destination MAC address. These double-tagged packets have the metro
VLANtag of 40, as well as an inner VLAN tag (for example, VLAN 100). When the double-tagged packets
enterSwitch D, the outerVLAN tag 40 isremoved, the well-known MAC addressis replaced with the
respectiveLayer 2 protocol MAC address, and the packet is sent to Customer Y on Site 2 as a single-tagged
framein VLAN 100.
Youcan also enable Layer 2 protocol tunneling on access ports on the edge switch connected to access or
trunkports on thecustomer switch. In this case, the encapsulation and decapsulation process is the same as
describedin the previous paragraph, except that the packets are not double-tagged in the service-provider
network.The singletag isthe customer-specific access VLANtag.
Inswitch stacks, Layer 2 protocol tunneling configuration is distributed among all stack members. Each stack
memberthat receives an ingress packet on a local port encapsulates or decapsulates the packet and forwards
itto theappropriate destination port. Ona singleswitch, ingress Layer2 protocol-tunneledtraffic is sent
acrossall local ports in thesame VLAN on whichLayer 2 protocoltunneling is enabled. In a stack,packets
receivedby a Layer 2 protocol-tunneledport are distributed to all ports in thestack that are configured for
Layer2 protocol tunneling and are in the same VLAN. All Layer 2 protocol tunneling configuration is handled
bythe stackmaster and distributed to all stack members.
Related Topics
ConfiguringLayer 2 ProtocolTunneling, on page 135
Example:Configuring Layer 2 Protocol Tunneling, on page 144
Default Layer 2 Protocol Tunneling Configuration
Thefollowing table shows thedefault Layer 2 protocoltunneling configuration.
Table 14: Default Layer 2 Ethernet Interface VLAN Configuration
Default SettingFeature
Disabled.Layer2 protocol tunneling
Noneset.Shutdownthreshold
Noneset.Dropthreshold
Ifa CoSvalue isconfigured on theinterface, that
valueis used to set the BPDU CoS value for Layer 2
protocoltunneling. If noCoS valueis configured at
theinterface level, the default value for CoS marking
ofL2 protocoltunneling BPDUs is 5.This doesnot
applyto datatraffic.
CoSValue
Catalyst 2960-XR Switch VLAN Configuration Guide, Cisco IOS Release 15.0(2)EX1
132 OL-29440-01
Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
Default Layer 2 Protocol Tunneling Configuration