Understanding Routing Instances For Layer 3 Vpns - Juniper ACX1000 Configuration Manual

Understanding Routing Instances for Layer 3 VPNs

Copyright © 2017, Juniper Networks, Inc.
Figure 53: Using MPLS LSPs to Tunnel Between PE Routers
Figure 54 on page 827 illustrates how the labels are assigned and removed:
When CE Router X forwards a packet to Router PE1 with a destination of CE Router Y,
1.
the PE route identifies the BGP next hop to Router Y and assigns a label that
corresponds to the BGP next hop and identifies the destination CE router. This label
is the inner label.
Router PE1 then identifies the IGP route to the BGP next hop and assigns a second
2.
label that corresponds to the LSP of the BGP next hop. This label is the outer label.
The inner label remains the same as the packet traverses the LSP tunnel. The outer
3.
label is swapped at each hop along the LSP and is then popped by the penultimate
hop router (the third P router).
Router PE2 pops the inner label from the route and forwards the packet to Router Y.
4.
Figure 54: Label Stack
To implement Layer 3 VPNs in the JUNOS Software, you configure one routing instance
for each VPN. You configure the routing instances on PE routers only. Each VPN routing
instance consists of the following components:
VRF table—On each PE router, you configure one VRF table for each VPN.
Set of interfaces that use the VRF table—The logical interface to each directly
connected CE router must be associated with a VRF table. You can associate more
than one interface with the same VRF table if more than one CE router in a VPN is
directly connected to the PE router.
Chapter 26: Configuring Layer 3 VPNs
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