Cisco Systems A9014CFD Layer 2 Control Protocol Forwarding, Layer 2 Control Protocol Tunneling

Chapter 35 Layer 2 Control Protocol Peering, Forwarding, and Tunneling

Layer 2 Control Protocol Forwarding

Restrictions

If you want to peer Operation, Administration, and Maintenance (OAM) packets when l2proto-forward tagged command is configured at the interface level, you should also configure the l2protocol peer lacp command.

Layer 2 Control Protocol Forwarding

The ASR 901 forwards Layer 2 Control Protocol (L2CP) packets between customer-edge (CE) devices.

Figure 35-1depicts an end-to-end layer 2 forwarding. The layer 2 traffic is sent through the S-network, and the S-network switches the traffic from end to end. The Cisco ASR 901 router forwards frames from the user network interface (UNI) to the network-to-network Interface (NNI) after appending S-tag. The third party provider edge (PE) router forwards the S-tagged frames. The PE peers the untagged Link Layer Discovery Protocol (LLDP) and Link Aggregation Control Protocol (LACP) frames. On the reverse path (from NNI to UNI), the S-tag is removed.

Figure 35-1 Layer 2 Forwarding

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ASR901

CE

PE

ASR901

CE

1 2 3 2 1

334051

1	L2CP packets are forwarded between CE	3	Third party PE forwards S-tagged frames and
	devices.		peers untagged frames.
2	Frames are forwarded from UNI to NNI after	4	Untagged LLDP and LACP is peered.
	appending the S-tag. On the reverse path (NNI
	to UNI), S-tag is removed.

Layer 2 Control Protocol Tunneling

Layer 2 Control Protocol Tunneling (L2PT) is a Cisco proprietary protocol for tunneling Ethernet protocol frames across layer 2 switching domains. The following tunnel protocols are supported:

•Cisco Discovery Protocol (CDP)

•Dynamic Trunking Protocol (DTP)

•Link Aggregation Control Protocol (LACP)

•Link Layer Discovery Protocol (LLDP)

	Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
35-2	OL-23826-09