Advanced Topics in Layer 3 BGP/MPLS Virtual Private Networks


The previous chapter laid out the foundations of BGP/MPLS L3VPN. This chapter explores some of the advanced topics that arise in the context of L3VPNs such as scalability, resource planning, convergence and security. All of these require a network-wide view and analysis. Therefore, it is necessary to first discuss two more important components of the VPN solution: PE–CE routing and route reflectors.


A key concept in the MPLS/VPN solution is that customer routes are kept in a VPN Routing and Forwarding (VRF) table. The VRF is populated with routes learned from the local CE and routes learned from remote CEs as VPN routes. In the previous sections we saw how customer routes are propagated as VPN-IPv4 routes across the provider's network from PE to PE and added to the appropriate VRF. In this section we will take a closer look at how routes are learned from the local CE.

There are several options for a PE to find out about routes from the CE attached to it: static routing, RIPv2, OSPF and BGP.1 Regardless of how the PE finds out about the routes, it must install them in the VRF associated with the interface to the CE. Thus, a routing protocol must install routes learned over a CE–PE interface in the VRF associated with that interface. From an implementation point of view, this is accomplished by creating separate contexts for the routing protocols per VRF.

So far we have ...

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