Cisco Catalyst 3750 - Default Layer 2 Protocol Tunneling Configuration; Layer 2 Protocol Tunneling Configuration Guidelines

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Catalyst 3750 MetroSwitch Software Configuration Guide
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Chapter 13 Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
Configuring Layer 2 Protocol Tunneling
This section contains this information about configuring Layer 2 protocol tunneling:
• Default Layer 2 Protocol Tunneling Configuration, page 13-13
• Layer 2 Protocol Tunneling Configuration Guidelines, page 13-13
• Configuring Layer 2 Tunneling, page 13-14
Default Layer 2 Protocol Tunneling Configuration
Table 13-1 shows the default Layer 2 protocol tunneling configuration.
Layer 2 Protocol Tunneling Configuration Guidelines
These are some configuration guidelines and operating characteristics of Layer 2 protocol tunneling:
• The switch supports tunneling of CDP, STP, including multiple STP (MSTP), and VTP. Protocol
tunneling is disabled by default but can be enabled for the individual protocols on 802.1Q tunnel
ports, access ports. or trunk ports.
• The switch does not support Layer 2 protocol tunneling on ports with switchport mode dynamic
auto or dynamic desirable.
• Dynamic Trunking Protocol (DTP) is not compatible with Layer 2 protocol tunneling because you
must manually configure asymmetric links with tunnel ports and trunk ports.
• The edge switches on the outbound side restore the proper Layer 2 protocol and MAC address
information and forward the packets to all tunnel ports, access ports and Layer 2 protocol-enabled
trunk ports in the same metro VLAN.
• For interoperability with third-party vendor switches, the switch supports a Layer 2 protocol-tunnel
bypass feature. Bypass mode transparently forwards control PDUs to vendor switches that have
different ways of controlling protocol tunneling.When Layer 2 protocol tunneling is enabled on
ingress ports on a switch, egress trunk ports forward the tunneled packets with a special
encapsulation. If you also enable Layer 2 protocol tunneling on the egress trunk port, this behavior
is bypassed and the switch forwards control PDUs without any processing or modification.
• EtherChannel port groups are compatible with tunnel ports as long as the 802.1Q configuration is
consistent within an EtherChannel port group.
Table 13-1 Default Layer 2 Ethernet Interface VLAN Configuration
Feature Default Setting
Layer 2 protocol tunneling Disabled for CDP, STP, and VTP.
Shutdown threshold No threshold for packets-per-second of Layer 2 PDUs per
port for the port to shut down.
Drop threshold No threshold for packets-per-second of Layer 2 PDUs per
port for the port to drop the PDUs.
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, the default is 5.