When one PE router receives routes advertised from a directly connected CE router, it checks the received route against the VRF export policy for that VPN. If it matches, the route is converted to VPN-IPv4 format—that is, the route distinguisher (route target) is added to the route. The PE router then announces the route in VPN-IPv4 format to the remote PE routers. The routes are distributed using IBGP sessions, which are configured in the provider’s core network. If the route does not match, it is not exported to other PE routers, but can still be used locally for routing, for example, if two CE routers in the same VPN are directly connected to the same PE router.
The remote PE router places the route into its bgp.l3vpn.0 table if the route passes the import policy on the IBGP session between the PE routers. At the same time, it checks the route against the VRF import policy for the VPN. If it matches, the route distinguisher is removed from the route and it is placed into the VRF table (the routing-instance-name.inet.0 table) in IPv4 format.
Figure 14 illustrates how Router PE1 distributes routes to the other PE routers in the provider’s core network. Router PE2 and Router PE3 each have VRF import policies that they use to determine whether to accept routes received over the IBGP sessions and install them in their VRF tables.
Figure 14: Distribution of Routes Between PE Routers
 | Copyright © 2008, Juniper Networks, Inc. All rights reserved. Trademark Notice. | |