PLANET XGS3-24042 - Manual (Page 676)

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Figure 81-3 Forwarding VPN Packets
1. Site1 sends an IP packet with a destination address of 1.1.1.2, which is sent by CE1 to
PE1.
2. PE1 looks up VPN-instance entries according to the interface receiving the packet and the
destination address, then forwards the packet after adding two layers of label (inner and
outer) to it, if there is a match.
3. The MPLS network will send the packet to PE2 according to the outer layer label (removed
when the packet reaching the last-hop of PE2, leaving only the inner layer) of it.
4. PE1 looks up VPN-instance entries according to the inner layer of label and the destination
address, then forwards the packet to CE2 after determining its egress interface.
5. CE2 forwards the packet to its destination according to the regular IP forwarding process.
81.1.4 BGP/MPLS VPN Networking Resolution
In BGP/MPLS VPN networks, the advertisement and receipt of VPN routes between different sites are
controlled by VPN Target Attribute. The configurations of VPN Export Target and Import Target are
independent, both allowing multiple values, and hence can realize flexible VPN access control and various
VPN networking resolutions.
Basic VPN
In the most basic instance, all users of a VPN form a closed user group, allowing the forwarding of traffic
between them. But no user within the VPN can communicate with outside users.
In such networking, each VPN will obtain an exclusive VPN Target as its Export Target and Import Target,
which should not be used by other VPN.
1.1.1.1/24 1.1.1.2/24
PE2
site1
CE1
PE1
P P
CE2
1.1.1.2
Layer2
Layer1
1.1.1.2
Layer2
1.1.1.2
1.1.1.2
site2