VRF
From Wikipedia, the free encyclopedia
Virtual Routing and Forwarding (VRF) is a technology used in computer networks that allows multiple instances of a routing table to co-exist within the same router at the same time. Because the routing instances are independent, the same or overlapping IP addresses can be used without conflicting with each other.
VRF may be implemented in a network device by having distinct routing tables, also known as Forwarding Information Bases (FIBs), one per VRF. Alternatively, a network device may have the ability to configure different virtual routers, where each one has its own FIB that is not accessible to any other virtual router instance on the same device.
VRF technology is commonly found in the ISP marketplace, notably in MPLS VPN configurations. In an MPLS environment, only the Provider Edge (PE) routing switches have knowledge of these multiple different virtual routing engines. Customer Edge (CE) devices participate in their MPLS VPN routing via route dissemination to and from the PE for the single routing engine instance supporting the applicable customer VPN. Typically this is done via eBGP, OSPF or static routing.
Provider (P) switches in the transport provider backbone have no knowledge of IP routing in the above context. PE traffic traverses the provider's P core via label switching. PEs gain knowledge of the Label Switched Path (LSP) across the P core via a Label Distribution Protocol. PEs gain knowledge of terminating PE for a customer MPLS VPN via some IGP, typically iBGP. PEs are responsible for converting IP routed traffic flow to and from an LSP flow across the P core. PEs distinguish one MPLS VPN set of routes and traffic flow from that of another MPLS VPN by marking iBGP routes with BGP extended community attributes. These markers are termed route distinguishers. Using route distinguishers, it is then a simple matter for an LSP-terminus PE to insert associated MPLS VPN traffic into the applicable virtual routing engine supporting a given customer network.
