Packet Forwarding - H3C S9500 series Operation Manual

Routing switches

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Operation Manual – MPLS VLL

H3C S9500 Series Routing Switches

Tunnel label

Label Stack

Figure 1-3 Structure of an MPLS VLL packet

The fields in an MPLS VLL packet are described as follows:

Tunnel label (the outer label) is an MPLS label or a GRE label. It is used to transmit a

packet from one PE to anther.

VC label (the inner label) is a lower layer label used to identify the links between PEs

and CEs. Packets of MPLS VLLs implemented through circuit cross connect (CCC) do

not contain this label.

Data in MPLS VLL can be encapsulated as Ethernet or VLAN packets at the data link

layer. At present, data of different nodes in a VPN must be encapsulated as the same

type of packets.

1.1.3 Packet Forwarding

In an MPLS VLL, CE, PE, and P operate in the same way as those in a BGP/MPLS

VPN. That is, they also forward packets in an MPLS network transparently by using

label stacks. To forward packets in an MPLS VLL, tunnels must be established first

between PEs (this can be achieved by either manual configuration or signaling

protocols). When the interfaces connecting PEs and CEs are up, PEs insert VC labels

for packets sent by CE, and then mark them with tunnel labels. On receiving these

packets, the remote PEs strip off the tunnel labels and send the packets to the

corresponding CEs according to their VC labels.

Figure 1-4

Figure 1-4 Label stack processing of MPLS VLL

VC label

L2 PDU

illustrates changes of the label stack of a packet during the forwarding.

1-3

Chapter 1 MPLS VLL

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