Packet Forwarding - H3C S9500 Series Operation Manual

Routing switches

Hide thumbs Also See for S9500 Series:

Table of Contents

Operation Manual – MPLS

H3C S9500 Series Routing Switches

Reliability and privacy of user routes. As no user routing information is imported,

there is no need for MPLS L2VPN to obtain and process the information, ensuring

the privacy of user routes.

Figure 4-2 illustrates the structure of an MPLS L2VPN packet.

Tunnel label

Figure 4-2 Structure of an MPLS L2VPN packet

The fields in an MPLS L2VPN 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 L2VPNs implemented through circuit cross connect (CCC)

do not contain this label.

Data in MPLS L2VPN 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.

4.1.2 Packet Forwarding

In an MPLS L2VPN, 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 L2VPN, 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.

Table 4-3 illustrates changes of the label stack of a packet during the forwarding.

Chapter 4 MPLS L2VPN

Table of Contents

S9505 S9508 S9512