Discussion

VPN, and routes announced by a remote PE router that match the VRF import policy
for that VPN. Customer sites can access only the routes in their VPN’s VRF.
Maintaining the VRF separate from the standard inet.0 and inet.3 routing tables
prevents a VPN’s private routes from mixing with public (Internet) routes or with
routes from other VPNs.
Each VPN has a policy that associates the VPN’s VRF target or target community
with each route before advertising the route and that filters which routes to advertise.
A VPN label is distributed with each route, independently of the bgp.l3vpn.0
table. VPN routes are directly advertised to other PE routers; they are not distributed
from the VRF table into the bgp.l3vpn.0 table.
The best routes from each VRF table are placed into a forwarding table in the
router’s Packet Forwarding Engine (PFE). This forwarding table is associated only
with the VPN and is separate from the forwarding tables populated by the inet.0
and inet.3 routing tables.
The PE routers also maintain inet.0 and inet.3 routing tables for use with regular
and VPN routing. inet.0 contains the usual intradomain routes (non-VPN routes
only) and external (Internet) routes, including those learned by the IBGP sessions
between PE routers. The inet.3 table stores the MPLS labels learned from the signaling
protocol (either LDP or RSVP) that is used for VPN traffic.
Each VPN always has two policies associated with it. An import policy is applied to
VPN-IPv4 routes learned from other PE routers to determine whether to add the
route to the local bgp.l3vpn.0 table. Nonmatching routes are discarded. An export
policy is applied to the VPN-IPv4 routes advertised by the local PE router to other PE
routers. Nonmatching routes are not advertised.
15.1 Setting Up a Simple Layer 3 VPN
Problem
You want to set up a Layer 3 VPN for a customer who wants a private network for
internal network communication and transactions.
Solution
Creating a Layer 3 VPN for the customer involves setting up your PE and P routers.
The customer (or you) can set up the customer’s routers (the CE routers). The PE
and P routers must run an IGP, IBGP, MPLS, and a signaling protocol (RSVP or
LDP). You establish an MPLS LSP between the PE routers and configure the VPN
itself on the PE routers.
Setting Up a Simple Layer 3 VPN | 555
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