Cisco Catalyst 3550 Command Reference Manual page 229

Chapter 2 Catalyst 3550 Switch Cisco IOS Commands
Command Modes Interface configuration
Command History Release
12.1(9)EA1
12.1(13)EA1
12.1(19)EA1
Usage Guidelines You must enter this command, with or without protocol types, to tunnel Layer 2 packets.
Layer 2 protocol tunneling across a service-provider network ensures that Layer 2 information is
propagated across the network to all customer locations. When protocol tunneling is enabled, protocol
packets are encapsulated with a well-known Cisco multicast address for transmission across the
network. When the packets reach their destination, the well-known MAC address is replaced by the
Layer 2 protocol MAC address.
You can enable Layer 2 protocol tunneling for CDP, STP, and VTP individually or for all three
protocols.
In a service-provider network, you can use Layer 2 protocol tunneling to enhance the creation of
EtherChannels by emulating a point-to-point network topology. When protocol tunneling is enabled on
the service-provider switch for PAgP or LACP, remote customer switches receive the protocol data units
(PDUs) and can negotiate automatic creation of EtherChannels.
To enable tunneling of PAgP, LACP, and UDLD packets, you must have a point-to-point network
topology. To decrease the link-down detection time, you should also enable UDLD on the interface when
you enable tunneling of PAgP or LACP packets.
You can enable point-to-point protocol tunneling for PAgP, LACP, and UDLD individually or for all
three protocols.
Caution PAgP, LACP, and UDLD tunneling is only intended to emulate a point-to-point topology. An erroneous
configuration that sends tunneled packets to many ports could lead to a network failure.
Enter the shutdown-threshold keyword to control the number of protocol packets per second that are
received on an interface before it shuts down. When no protocol option is specified with the keyword,
the threshold is applied to each of the tunneled Layer 2 protocol types. If you also set a drop threshold,
the shutdown-threshold value must be greater than or equal to the drop-threshold value.
When the shutdown threshold is reached, the interface is error-disabled. If you enable error recovery by
entering the errdisable recovery cause l2ptguard global configuration command, the interface retries
the operation again when all the causes have timed out. If the error recovery mechanism is not enabled
for l2ptguard, the interface stays in the error-disabled state until you enter the shutdown and no
shutdown interface configuration commands.
Enter the drop-threshold keyword to control the number of protocol packets per second that are
received on an interface before it drops packets. When no protocol option is specified with a keyword,
the threshold is applied to each of the tunneled Layer 2 protocol types. If you also set a shutdown
threshold, the drop-threshold value must be less than or equal to the shutdown-threshold value.
OL-8566-02
Modification
This command was introduced.
The drop-threshold keywords was added.
The point-to-point, pagp, lacp, and udld keywords were added.
Catalyst 3550 Multilayer Switch Command Reference
l2protocol-tunnel
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