Understanding Layer 3 Vpn Forwarding Through The Core - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

Understanding Layer 3 VPN Forwarding Through the Core

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Figure 52: Distribution of Routes from PE Routers to CE Routers
The PE routers in the provider's core network are the only routers that are configured to
support VPNs and hence are the only routers to have information about the VPNs. From
the point of view of VPN functionality, the provider (P) routers in the core—those P routers
that are not directly connected to CE routers—are merely routers along the tunnel between
the ingress and egress PE routers.
The tunnels can be either LDP or MPLS. Any P routers along the tunnel must support the
protocol used for the tunnel, either LDP or MPLS.
When PE-router-to-PE router forwarding is tunneled over MPLS label-switched paths
(LSPs), the MPLS packets have a two-level label stack (see
Outer label—Label assigned to the address of the BGP next hop by the IGP next hop
Inner label—Label that the BGP next hop assigned for the packet's destination address
Figure 53 on page 827):
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