VRF (Virtual Routing and Forwarding) is a technology that virtualizes a single physical routing device into multiple virtual routing devices, each of them being (relatively) independent of each other, allowing for overlapping subnets, separate routing table to make Layer 3 segregated and separate set of Layer 3 VLAN interfaces assigned to each VRF.
Figure 1. Networking diagram of VRF
PICA8 switches support multiple VRF instances: one global or default VRF and multiple user-defined VRFs. By binding a Layer 3 VLAN interface to a VRF, the system segregates the IP routing table, ARP table, hardware forwarding table, and host hardware forwarding table of different VRFs in customer edge devices. When the switch receives the data packets, it looks up the IP routing table corresponding to the VRF, which is determined by the ingress Layer 3 VLAN interface, and then the switch forwards the data packets based on the routing entry of this VRF.
VRF realizes data traffic segregation among different customers while sharing the same physical router device, that is to say, intra-VRF users could communicate with each other but cross-VRF users could not communicate with each other.
NOTE:
- PICOS supports only VRF-Lite, a lighter version of VRF, referring to VRF without MPLS.
- If a Layer 3 VLAN interface or a static route is not associated to a specified VRF, the default VRF will be used.
VRF Characteristics
- Each VRF has an independent routing table to implement independent routing and forwarding functions.
- Each VRF has an independent address space. This allows address overlapping between different VRFs without address conflicts occurring in the same device.
- Users in the same VRF can communicate with each other, but users in different VRFs cannot communicate with each other.
Application Scenario
This document lists several use cases one can use with VRFs as follows,
- User can deploy VRF function to solve the problem of insufficient IP addresses, as different VRFs have different address spaces which allows address overlapping between different VRFs.
- User can deploy VRF function to achieve traffic isolation of different users and increase data communication security, as the communication between different tenants is segregated in different VRFs.
- VRF virtualizes a single physical routing device into multiple virtual routing devices; this can save hardware costs.