Cisco 15327 - Manual (Page 145)

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Ethernet Card Software Feature and Configuration Guide, R7.2
Chapter 9 Configuring IEEE 802.1Q Tunneling and Layer 2 Protocol Tunneling
Layer 2 Protocol Tunneling Configuration Guidelines
Layer 2 Protocol Tunneling Configuration Guidelines
These are some configuration guidelines and operating characteristics of Layer 2 protocol tunneling:
• The ML-Series card supports Per-VLAN Protocol Tunneling (PVPT), which allows protocol
tunneling to be configured and run on a specific subinterface (VLAN). PVPT configuration is done
at the subinterface level.
• PVPT should be configured on VLANs that carry multi-session transport (MST) BPDUs on the
connected devices.
• The ML-Series card supports tunneling of CDP, STP (including MSTP and VTP protocols). Protocol
tunneling is disabled by default but can be enabled for the individual protocols on IEEE 802.1Q
tunnel ports or on specific VLANs.
• Tunneling is not supported on trunk ports. If you enter the l2protocol-tunnel interface configuration
command on a trunk port, the command is accepted, but Layer 2 tunneling does not take affect unless
you change the port to a tunnel port.
• EtherChannel port groups are compatible with tunnel ports as long as the IEEE 802.1Q
configuration is configured within an EtherChannel port group.
• If an encapsulated PDU (with the proprietary destination MAC address) is received from a tunnel
port or access port with Layer 2 tunneling enabled, the tunnel port is shut down to prevent loops.
• Only decapsulated PDUs are forwarded to the customer network. The spanning tree instance running
on the service-provider network does not forward BPDUs to tunnel ports. No CDP packets are
forwarded from tunnel ports.
• Because tunneled PDUs (especially STP BPDUs) must be delivered to all remote sites for the
customer virtual network to operate properly, you can give PDUs higher priority within the
service-provider network than data packets received from the same tunnel port. By default, the
PDUs use the same CoS value as data packets.
• Protocol tunneling has to be configured symmetrically at both the ingress and egress point. For
example, if you configure the entry point to tunnel STP, CDP, VTP, then you must configure the
egress point in the same way.
Configuring Layer 2 Tunneling on a Port
Beginning in privileged EXEC mode, follow these steps to configure a port as a Layer 2 tunnel port:
Table 9-2 Default Layer 2 Protocol Tunneling Configuration
Feature Default Setting
Layer 2 protocol tunneling Disabled for CDP, STP, and VTP.
Class of service (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, there is no default. This allows existing
CoS values to be maintained, unless the user configures
otherwise.