Samsung Ubigate iBG3026, Руководство по настройке

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CHAPTER 18. MPLS
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Figure 18.2 Martini L2 VPN Configuration
Since MPLS LSP is uni-directional by nature, a VC is composed of two MPLS
LSPs in opposite directions. The LSPs can be established using either LDP or
RSVP signaling protocol. The ingress and egress nodes of the tunnel use
extension to the LDP to exchange VC labels and to create a virtual circuit.
The edge LDP session configures each other as Target Peer for exchanging of
VC labels. The VC label designates the connection at the tunnel endpoint.
Users additionally provision a VC-ID, a 32-bit number, to bind the VC label
with the Virtual Circuit at both ends.
A customer's L2 traffic is either switched or routed by a CE device to a
Provider Edge(PE) router known as an MPLS Label Edge Router(LER).
Once the frame is deemed valid, the packet is mapped to a user-defined
Forwarding Equivalence Class(FEC), which defines how specific packets get
forwarded. In the L2VPN scenario, the key to identify the FEC is the
incoming packet interface(the PW interface). The FEC lookup determines the
outgoing port(the PSN interface) and two labels. The first label at the top of
the stack is the tunnel label and is used to carry the frame across the provider
backbone. The second label at the bottom of the stack is the VC label and is
used by the egress switch to determine how to process the frame. After adding
the two MPLS headers, one for each label, the frame is encapsulated into the
proper format corresponding to the outgoing interface.
LDP1 LDP2
L2 Interface
CE1
VC Lable Exchang
PE1
PW Interface
PSN Interface
Provider
Provider
PE2
Bidirectional
Vitual Circuit
CE2