Panasonic NN46240-710 - Manual (Page 113)

Nortel Secure Router 8000 Series
Troubleshooting - VPN___________ 4 MPLS L2VPN troubleshooting
The MPLS Layer 2 VPN also uses a label stack to implement transparent transmission of
packets across the MPLS network.
• The outer label, called the tunnel label, is used to transport packets from one PE to another
PE.
• The inner label, called the VC label, is used to distinguish connections in different VPNs.
According to the VC label, the receiving PE determines the CE where the packet is
forwarded.
Figure 4-2 shows the change of label stack in the process of forwarding packets across the
MPLS Layer 2 VPN.
Figure 4-2 MPLS Layer 2 VPN label stack processing
CE1 PE 1 P PE 2 CE 2
L2PDU T V L2PDU T' V L2PDU L2PDU
In Figure 4-2, L2PDU represents the link layer packet; T represents the tunnel label; V
represents the VC label; and, T' represents a modified outer label.
Implementation of MPLS Layer 2 VPN
The Provider-Provisioned Virtual Private Network (PPVPN) workshop of the Internet
Engineering Task Force (IETF) creates multiple MPLS Layer 2 VPN framework drafts.
Martini and Kompella are the major drafts.
• draft-martini-l2circuit-trans-mpls: uses the Label Distribution Protocol (LDP) as the
signaling protocol to transfer Layer 2 information and VC labels.
• draft-kompella-ppvpn-Layer 2 VPN: uses the Border Gateway Protocol (BGP) as the
signaling protocol to transport Layer 2 information and VC labels.
You can also use static VC label configuration, such as Circuit Cross Connect (CCC) and Static
Virtual Circuit (SVC) to implement MPLS Layer 2 VPN.
The process of implementation is described as follows.
4.1.2 CCC MPLS Layer 2 VPN
CCC implements MPLS Layer 2 VPN by means of static configuration.
Unlike common MPLS Layer 2 VPNs, CCC uses a one-level label to transport user data and it
occupies a static LSP exclusively.
There are two types of CCC connection.
• Local connection: refers to the connection between two local CEs. The two CEs connect
to the same PE. The PE functions as a Layer 2 switch that can carry out switching without
a static LSP.
• Remote connection: refers to the connection between a local CE and a remote CE. The two
CEs connect to di^erent PEs, and a static LSP is required to transmit packets from one PE
to another PE. Static LSPs and CCC connections can be associated by using a CLI
command on the PE.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 4-3