VRFs

VRF stands for Virtual Routing and Forwarding. It is a technology that allows multiple separate routing tables to coexist within a single network device, such as a router or switch. Each VRF instance represents an independent routing domain with its own forwarding table and routing processes, enabling multiple networks to share the same physical infrastructure while preventing routes from one VRF from being learned or forwarded in another.

In a VRF-enabled device, interfaces or subinterfaces can be assigned to a specific VRF. Traffic entering or leaving on those interfaces is associated with that VRF, and routing protocols configured within the VRF populate its routing table. A VRF can run independent instances of routing protocols such as OSPF, BGP, or static routes, allowing separate networks to use identical address spaces without conflict.

In service provider and enterprise networks, VRFs are commonly used to isolate customer or departmental traffic. In provider deployments, VRFs are often used with MPLS to deliver VPN-like isolation, using route distinguishers and route targets to keep each customer’s routes separate while sharing the same backbone. In non-MPLS environments, VRF-lite provides similar isolation using per-VRF routing tables and interfaces without MPLS.

Inter-VRF communication, when required, is achieved through explicit mechanisms such as a central gateway or controlled route leaking to prevent unintended leakage of routes between VRFs. Management considerations include planning the number of VRFs, memory and CPU use, consistent policies for import and export of routes, and careful troubleshooting to distinguish issues within a VRF from problems in the shared network.

See also: MPLS, VPN, VLAN, route leaking, route distinguishers.