In the previous blog, we discussed how VLANs can help to effectively manage workstations, security, and bandwidth allocation. Managing VLANs becomes much easier for network admins when network traffic, user access, and data transfers are isolated and routed separately. Sometimes, network admins face a scenario where devices from different VLANs are communicating with each other because their shared routers have multiple IP addresses of devices within each of them. In this scenario, it's important to take advantage of VLAN management techniques that allow you to isolate traffic, increase admin control, and share resources among users. One such technique that can be used to accomplish this type of management is called Virtual Routing and Forwarding (VFR). In this blog we’ll discuss the basics of Virtual Routing and Forwarding, and how we can use this technology to easily manage Layer 3 devices in your network.
Introducing Virtual Routing and Forwarding (VRF)
VRF is a technology that allows multiple instances of a routing table to coexist within the same router at the same time. Without using multiple devices, VRF enables network engineers to increase the functionality of a single router by allowing the network paths to be segmented. This is done with virtualizing routing tables. When a packet enters a router, it is only forwarded using the routing table where the ingress and egress interfaces are associated with the same VRF.
Is it Easy to Manage Layer 3 devices with VRF?
Yes. In a VRF-configured router, each routing table will have a unique set of entries with their own forwarding detail, thus enabling a logical isolation of traffic. VRF requires a forwarding table with information on the next hop to push traffic through a specific device so that packets aren’t transferred outside the VRF path. There’s no need to encrypt or authenticate traffic since it’s automatically segregated. Additionally, independent routing instances allow you to use the same IP addresses for different groups without conflict.
What are the Challenges in Managing a VRF enabled Network?
VRF reduces the number of the devices in your network by allowing you to share the same network resources. Usually, IT infrastructure service providers implement VRF-configured routers/switches in datacenters for multiple cascading routing instances, while supporting users. ISPs use VRF to create separate VPNs for their users, enabling scalable IP MPLS VPN services. But, if the number of VRF enabled routers increase, administrators managing huge network will find it difficult to isolate and manage each of those virtual routers independently. Without a strong framework, VRF support for your network might result in unfair scheduling of network resources and increased virtualization overhead. For service providers, VRF poses significant challenge in monitoring and analyzing user data for ingress and egress traffic that has different markers from each end of a route.
Managing VRF with Advanced Network Monitoring Tools
Typically network admins implement VRF for DNS, DHCP, and Internet services since it allows them to use the same infrastructure for different users. You can dedicate virtual networks to specific applications/users by isolating traffic in Layer 3 devices using VRF. Advanced network monitoring tools help you to manage VRF-configured devices by providing useful information on amount of traffic, next-hop, etc., while simultaneously managing multiple routing tables. Simultaneously monitoring all the routing tables provides great insight into how VRF enabled routers are performing, making network admin’s job easier.
 Fig 1: Courtesy - Cisco®