L2CP Tunneling
Layer 2 Control Protocol Tunneling (L2PT) is a Cisco proprietary protocol for tunneling Ethernet protocol frames across layer 2 switching domains. The system supports the following tunnel protocols:
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Link Layer Discovery Protocol (LLDP)
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Link Aggregation Control Protocol (LACP)
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Operation, Administration, Management (OAM)
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Ethernet Local Management Interface (ELMI)
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Cisco Discovery Protocol (CDP)
Some of the L2 transport interfaces are:
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VPWS l2 transport main
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VPWS l2 sub interface
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L2 transport main bridge port
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l2 subinterface bridge port
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VPWS l2 Bundle main port
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VPWS l2 bundle sub interface
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L2 bundle main bridge port
On a subinterface, when control packets such as LLDP and LACP are tunneled, the system tunnels the same control packets to the main interface.
The Cisco NCS 540 Series Routers allows to tunnel layer 2 packets between CEs. The Cisco proprietary multicast address (01-00-0c-cd-cd-d0) is used while tunneling the packet over the NNI interfaces. The following figure depicts Layer 2 Protocol Tunneling. The layer 2 traffic is sent through the S-network, and the S-network switches the traffic from end to end. The Cisco multicast address is added to the frames and sent from UNI to NNI. On the reverse path (NNI to UNI), protocol specific multicast address is attached to the frames and sent to the UNI.
Prerequisites for L2CP Tunneling
A Cisco IOS software that supports Layer 2 Control Protocol Tunneling must be installed previously on the Cisco NCS 540 Series Routers.
Restrictions for L2CP Tunneling
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Received L2CP Control Packets (like STP, CDP, and others) are not mirrored to the destination port.
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Forwarding L2CP tunneled packets over local x-connect is not supported.