R2511-HP MSR Router Series MPLS Configuration Guide(V5)

3. Set up ACs and bind the ACs to the VC, so the PEs can forward user packets from ACs through the

VC:

a. Set up an AC: Configure the link layer protocol on a PE and the connected CE to set up a link

layer connection (such as a PPP connection) between the PE and the CE.

b. Bind the AC to the VC: For most link layer protocols, you bind the AC to the VC by binding the

PE's Layer 3 interface connected to the CE to the VC. For Ethernet links, you can bind the Layer

3 interface to the VC or bind a service instance to the VC. After the binding, the PE forwards

packets received from the AC to the bound VC, and forwards packets received from the bound

VC to the AC.

MPLS L2VPN implements transparent transmission of Layer 2 user packets over an MPLS or IP backbone

by encapsulating user packets with a VC label and a tunnel tag .

• The tunnel tag is used to transfer packets from one PE to another. If the public tunnel is an LSP tunnel

or an MPLS TE tunnel, the tunnel tag is an MPLS label. If the public tunnel is a GRE tunnel, the tunnel

tag is the GRE header and the transport protocol packet header.

• The VC label identifies a Layer 2 connection to a CE. When receiving a packet from the backbone,

a PE forwards the packet to a CE identified by the VC label.

Figure 17 Packet forwarding process

L2 PDU: Layer 2 protocol data unit.

T represents a tunnel tag. V represents a VC label.

As shown in Figure 17, MPLS L2VPN forwards packets in the following steps:

4. After PE 1 receives a Layer 2 packet from CE 1, it adds a VC label to the packet according to the

VC bound to the AC, searches for the public tunnel, adds a tunnel tag to the packet, and then

forwards the packet to the P device.

5. The P device forwards the packet to PE 2 according to the tunnel tag.

6. After PE 2 receives the packet from the public tunnel, it identifies the VC to which the packet

belongs according to the VC label of the packet, deletes the tunnel tag and the VC label from the

packet, and then forwards the resulting packet to CE 2 through the AC bound to the VC.

This packet forwarding process is not applicable to the CCC mode of MPLS L2VPN. For more information

about the CCC mode of MPLS L2VPN, see "CCC MPLS L2VPN."

Local connection establishment

To set up a local MPLS L2VPN connection between two CEs:

L2PDU

CE 1

PE 1

CE 2

PE 2

L2PDUVT