Juniper JUNOSE, Configuration Manual

Page: 414 / 738

A customer site is a network that can communicate with other networks in the same
VPN. A customer site can belong to more than one VPN. Two sites can exchange IP
packets with each other only if they have at least one VPN in common.
Each customer site that is connected to a particular PE router is also associated with
a VPN routing and forwarding instance (VRF). As shown in Figure 70 on page 378,
each VRF has its own forwarding table distinct from that of other VRFs and from the
virtual router’s global forwarding table.
Figure 70: BGP/MPLS VPN Components
A given VRF’s forwarding table includes only routes to sites that have at least one
VPN in common with the site that is associated with the VRF. For example, in Figure
70 on page 378, the forwarding table in VRF B stores routes only to sites that are
members of at least one of the VPNs to which Customer Site 3 belongs.
VRFs exist within the context of a virtual router (VR). A given virtual router can have
zero or more VRFs, in addition to its global routing table (which is not associated
with any VPN, CE router, or customer site). A router can support up to 1000
forwarding tables; that is, up to a combined total of 1000 VRs and VRFs.
You assign one or more interfaces or subinterfaces to a given VRF. If multiple
customer sites are members of the same set of VPNs, they can share a VRF—that
is, you do not need to create a specific VRF for each customer site. In Figure 70 on
page 378, Customer Sites 1 and 2 share VRF A; both sites belong to the same set of
VPNs. The router looks up a packet’s destination in the VRF associated with the
interface on which the packet is received. The VRFs are populated by BGP while it
learns routes from the VPN. If a customer site is a member of multiple VPNs, the
routes learned from all those VPNs populate the VRF associated with the site.
378 ■
Overview
JUNOSe 11.0.x BGP and MPLS Configuration Guide