3com S7906E 설치 설명서

 

1-2 

Figure 1-1 Typical application of MPLS L3VPNs 

Site 1

Site 3

Site 5

Site 2

Site 4

Site 6

P 1

P 2

P 3

PE 1

PE 2

PE 3

CE 1

CE 2

CE 3

CE 4

CE 5

CE 6

 

 

As shown in 

, VPN A comprises Site 1, Site 3 and Site 5, while VPN B comprises Site 2, Site 

4 and Site 6. A VPN involves the following three types of devices:  

z 

Provider (P) device: device in the core of the provider backbone network. A P device does not 

directly interface with CE devices, but it implements MPLS forwarding.  

z 

Provider edge (PE) device: edge device in the provider backbone network. Directly interfacing with 

one or more CE devices, a PE device processes VPN routing as a main MPLS L3VPN 

implementer.  

z 

Customer edge (CE) device: edge device on a customer network. A CE device can be a router, a 

switch, or a host, that implements route distribution on the customer network.  

In an MPLS L3VPN environment, between any two sites that belong to the same VPN, packets are 

transmitted labeled across the public network. The PE device at the entrance to the provider backbone 

attaches two labels to the packets, one inner label and the other outer label:  

z 

Outer label: the label used for switching within the backbone, representing a label switched path 

(LSP) from the local PE to the peer PE. With this label, a packet can arrive to the peer PE along the 

LSP.  

z 

Inner label: The inner label represents an LSP between two CE devices interconnected over the 

backbone network. It identifies the site to which the packet belongs. The PE forwards the packet to 

the target CE based on the inner label.  

As shown in 

, a network carries three independent multicast services – the public instance, 

VPN instance A, and VPN instance B. A PE multicast device at the edge of the public network supports 

multiple instances, equivalent to multiple independent multicast devices. Each instance corresponds to 

a plane, and all these planes are isolated from one another. For example, 

 shows three