DELL Force10 : Virtual Routing and Forwarding (VRF)

VRF Overview

Virtual Routing and Forwarding (VRF) allows a physical router to partition itself into multiple Virtual Routers (VRs). The control and data plane are isolated in each VR so that traffic does NOT flow across VRs. Virtual Routing and Forwarding (VRF) allows multiple instances of a routing table to co-exist within the same router at the same time.

DELL OS 9.7 supports up 64 VRF instances. Number of instances can be increased in future versions therefore check current documentation for authoritative number of instances.

VRF Use Cases

VRF improves functionality by allowing network paths to be segmented without using multiple devices. Using VRF also increases network security and can eliminate the need for encryption and authentication due to traffic segmentation. 

Internet service providers (ISPs) often take advantage of VRF to create separate virtual private networks (VPNs) for customers; VRF is also referred to as VPN routing and forwarding.

VRF acts like a logical router; while a physical router may include many routing tables, a VRF instance uses only a single routing table. VRF uses a forwarding table that designates the next hop for each data packet, a list of devices that may be called upon to forward the packet, and a set of rules and routing protocols that govern how the packet is forwarded. These VRF forwarding tables prevent traffic from being forwarded outside a specific VRF path and also keep out traffic that should remain outside the VRF path.

VRF uses interfaces to distinguish routes for different VRF instances. Interfaces in a VRF can be either physical (Ethernet port or port channel) or logical (VLANs). You can configure identical or overlapping IP subnets on different interfaces if each interface belongs to a different VRF instance.

VRF Configuration

First of all you have to enable VRF feature.

conf
feature vrf

Next step is to create additional VRF instance

ip vrf  tenant-1 

vrf-id is assigned automatically however if you want to configure vrf-id explicitly you can by additional parameter. In example below we use vrf-id 1

ip vrf  tenant-1 1

We are almost done. The last step is interface assignment in to particular VRF. You can assign following interfaces

• Physical Ethernet interfaces (in L3 mode)
• Port-Channel interfaces (static and dynamic/lacp)
• VLAN interfaces
• Loopback interfaces 

Below is example how to assign LAN 100 in to VRF instance tenant-1.

interface vlan 100
  ip vrf forwarding tenant-1

Configuration is pretty easy, right?

Working in particular VRF instance

When you want to configure, show or troubleshoot in particular VRF instance you have to explicitly specify in what VRF you want to be.

So for example when you want to do ping from tenant-01 VRF instance you have to use following command

ping vrf tenant-01 192.168.1.1

Conclusion

VRF is great technology for L3 multi-tenancy. DELL Network Operating System 9 supports VRF therefore you can design interesting network solutions.