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Virtual Routing & Forwarding


Virtualization is the method under which diverse computing resources are hidden from the physical nature and thus makes them appear as a single system that is related to all end users, applications, and other systems. This is realized through a particular physical resource presented in a manner that the latter is seen in a capacity for providing the place of multiple logical resources. Consequently, virtualization presents this possibility either by presenting several real physical resources to be one logical one.

Virtual networks represent an umbrella term including many technologies. One example is virtualization, which offers complete abstracting of resources such as storage and network capabilities to the virtualized network. In essence, these virtual networks provide the illusion of numerous operational networks rather than running on the same hardware and physical interconnectivity.

It is crucial to differentiate among the types of virtualization and pinpoint the layer at which this network virtualization takes place: It is crucial to differentiate among the types of virtualization and pinpoint the layer at which this network virtualization takes place:

Physical (Layer 1): In the TDM, a single physical connection is multiplying to multiple physical connections to keep separation organized, and that process is all taking place all at once.

Data link (Layer 2): For example, technologies like Frame Relay, ATM, and Ethernet switches take advantage of a single physical link while also being able to connect multiple logical or virtual channels.

Network (Layer 3): Routers personify why a multitude of sessions can be simultaneously transferred over one connection; IP addresses act as IDs. Write down at least one sentence for each of the given sentences. IP addresses that can route data correctly remain to be the main tool used by routers. Currently, the router uses the route table for making a decision about the intermediate destination to be reached through the packet transmission. Normally, all the packets within a switching router follow the SmartLink route table or the global table.

Virtualization of Networks

There is always a requirement to keep physical routers separate, which do not interconnect in case operational or commercial needs to access multiple IP networks independently to serve individual companies, departments, or organizations. They can still make use of the same Layer 2 or Layer 1. However, at the layer 3 level, they continue to take different directions and cannot be satisfied as a network.

With the help of network virtualization, a single physical router is routing for several routers, simultaneously allocating different route tables to individual virtual routers. The global table over here represents all IP interfaces tied up with the virtual networks, and the same would contain all route tables of each virtual network.

To provide an illustrative example, let us say that the physical setup is such that the IP interface of FastEthernet 0/0 and FastEthernet 0/1 belong to the virtual networks 10 and 20, respectively. Note that Fast Ethernet 0/0 is used to just forward packets to interfaces belonging to network 10 and is not used to send them to 0/1 because it is not a part of network 10. 10 network has no routing awareness of the other networks.

Throughput enhancement can be attained through multichanneling of the virtual switching devices in a physical connection, which we call Layer 2 logical connections. To illustrate, running multiple virtual LANs (VLANs) may serve as a functional attribute of a FastEthernet physical network port, allowing each VLAN to be operated independently within a virtual network.

The method named Virtual Route Forwarding (VRF) announces the arrival into the entity of the network of any multiple virtual networks. A setting of several VRFs within one firewall network component virtually guarantees separation among virtual networks. A setting of several VRFs within one firewall network component virtually guarantees separation among virtual networks.


VRF, which Integrates Digital (IP) network routers, runs the Multi Tree routing tables in different virtual routers at the same time.

The idea of this feature is to extend connectivity through its ability to slice the network using a single device instead of multiple ones. It thereby empowers network segmentation. VRF plays a vital role in keeping traffic separated at each end on either side of the network boundary VRF. This isolation of the network has great security and can even remove the need for encryption and authentication.

Service providers of the Internet typically create VRF to develop separate VPNs as the mentioned type of IP routing, and forwarding is also known as VPN routing and forwarding.

How do you configure a VRF?

Configuration of a VRF as 'Virtual Routing and Forwarding' simply means a virtual router Internet Protocol networking on TCP/IP platforms. Unlike a logical router that might encompass many routing tables, a virtual router utilizes only one table corresponding to the VRF. This is made possible as the next hop and forwarding table is identified for each data packet, the routing rules, rosters of the devices are also provided and the packet is responsible to follow.

Using such tables routing tables do position traffic only inside a route domain and also they filter out traffic that must remain external to the route domain.

Uses of VRF

VRF, for Virtual Routing and Forwarding, is the principle of deploying numerous routing instances on either a router or layer 3 switch being used for this purpose. First, the central task is to put together and segregate customer traffic flow with the routing process by running everything on the same hardware infrastructure.

Customer traffic is otherwise diverted through the external fences that are physically provided or through sub-interfaces where access control lists are used to differentiate traffic. This being the case, VRF is widely adopted in building perimeter security within LANs, data centers, and network operators who employ technologies like MPLS and MP-BGP.

The RD (Route Distinguisher) value in VRF (Virtual Routing and Forwarding) is a most vital part which works as a basis for organizations to use IP address space within the isolated routing domains. On every customer exist its IP VRF - IP Virtual Routing and Forwarding - through which subnets become segregated from each other by this overlap. The principle that every default route has its separate RD values is based on the fact that all default routes are different or individual within VRF.

What is the difference between VRF and VRF Lite?

The difference between VRF and VRF Lite lies in their implementation: The difference between VRF and VRF Lite lies in their implementation:

Traditional VRF adopts the encapsulation method based on MPLS VPN and M-BGP cloud platforms to keep customer traffic separated along the path from the origin network to the target network, which belongs to the service provider's infrastructure. The segregation of overlapping routes is made possible through the use of IP iLD and LSPs route targets.

Meanwhile, VRF Lite, a protocol which doesn't establish MPLS and MP-BGP, alternatively. In VRF Lite implementation, organizations prefer that to the scenario where in the multiple networks have the same IP while in some segments the traversal is necessary through a firewall. In contrast to the conventional VRF, VRF Lite does not prescribe sites the use of route targets. Alternatively, dynamic or static routes may be versed under a VRF instance which is dictated as necessary.

The RD value in the VRF has been a part of many organizations that rotates in VRF routing domains and creates segregated routing paths with different address spaces. Each digital customer is independent and has a own IP VRF to create an isolated orderly IP environment in which each subnet is separated from one another. By considering RD value in VRF configuration, the second default route associated with it is guaranteed to be unique from the rest within VRF.

Advantages of Virtual Routing and Forwarding (VRF)

Here are a few advantages of Virtual Routing & Forwarding:

  • Virtualization of Multiple Routes: VRF allows one to build multiple routing for a single physical device. Aside the fact that it adds on to the network flexibility, it helps increase resource optimization.
  • Management of Multiple Routing Tables: Various users can operate the routing tables concurrently, decreasing many network management processes and problems.
  • Compatibility with MP BGP and MPLS Deployments: VRF with MP BGP and MPLS technologies in which MP BGP assists in effective routing management and forwarding decision making via MPL mechanisms.
  • Support for Multiple VPNs with Overlapping IP Addresses: Virus configurations provide the option to produce several VPNs (Virtual Private Networks) with their very own overlapping IP Addresses, which serves to optimize the usage of only these Addresses without conflict.
  • Segmentation of Network Paths without Multiple Routers: VRF allows easier and efficient subdivision of physical paths without the need for conventional routers, thus simplifying network and resource management.

Key Terms in VRF Context

Key terms used in VRF context are discussed below:

  • VRF vs VPN: To a large extent, VRF configurations will enable multiple VPN environments to be located on just one physical network infrastructure, thereby leading to the scenario where concurrent network services of varied organizations of the same environment will be separated invisibly to each other.
  • VDC vs VRF vs VLANs: VDC's aim at the virtualization of the actual device, and the switch appears as many virtual ones with each one having its' unique VRF and VLANs settings. VLANs work at Layer 2 of the OSI model where network Ethernet service chopped into multiple virtual local thoroughfares, securing traffic and enhancing its performance.
  • Static Routes: VRF or Virtual Routing and Forwarding whether standards(default) or invoked by the user, always comprises a static route. Users can either designate VRF static route as a default or configure a custom route in VRF configuration mode to allow for a powerful routing management.

Implementation Methods

i) Simple Implementation:

The easier VRF interpretation is traditionally called VRF-Lite. In this type of mesh structure, each router in the network operates virtually in the P2P mode in general. This is also true as it is pretty easy to deploy an,d it is the perfect option for small- and medium enterprises as well as for shared data centers, but it doesn't cope well with the needs of large enterprises and network carriers, including global ones. It is so that for each VRF instance to apply, each interface of the every router, even adjacent routers, must hold the same setup. At inception, VRF alongside MPLS was their utilization. The associated value of VRF gave it an impetus to later operate independently of MPLS technology. For this reason, existing networks many times do not need full-featured VRF where MPLS is used. Therefore, the term "VRF Lite" for these networks is a synonym of using VRFs without MPLS.

Example of Global and VRF Routing Table Summary with Different Routes/Routing Protocols: Example of Global and VRF Routing Table Summary with Different Routes/Routing Protocols:

ii) Full Implementation:

In a full implementation scenario, IP VPNs offer a solution to the scalability limitations of VRF Lite. Here, the backbone network serves as a conduit for data transfer across a wide area, facilitating communication among VRF instances on all edge devices. LANs are commonly utilized to establish insulated private networks, enabling carriers to furnish wide-area backhaul networks to multiple customers or facilitate data sharing within large organizational setups.

Typically, in such deployments, CE routers exert routing control at the local level, while PE routers, with increased complexity, manage virtualized routing tables. Decapsulation occurs when the PE router encapsulates marked traffic to identify the VRF instance, transmitting it across the provider backbone network to the destination PE router. Upon arrival, the target PE router decapsulates the traffic and forwards it to the CE router at the destination. Although the backbone network is transparent to customer equipment, different virtual private networks can share it while maintaining end-to-end traffic separation.

Node journeys within the AS (autonomous system) are governed by iBGP, an interior gateway protocol that extensively utilizes extended community attributes to distinguish customer routes, even if they overlap with IP addresses assigned to other customers.

IP VPNs are typically deployed atop MPLS backbones due to MPLS's inherent labeling feature, which allows MPLS VPNs to designate customers' VRFs. However, some IP VPN implementations, such as IP-VPN Lite (e.g., Nortel's), employ IP-in-IP encapsulation over pure IP networks, providing timely support to mitigate the maintenance and support requirements associated with MPLS environments.


In the end, the VRF plays a defining role in modern day networking. It provides segmentation, flexibility, and ease of management of routing instances within one physical infrastructure. VRF functionality that enables separate virtual routers created on the same hardware makes possible efficient traffic separation, resource optimization, and scalability of the network. VRF can be implemented either as a low-complexity VRF Lite implementation for simpler deployments or a high-scale implementation for extensive networks and service providers. By doing this, organizations can fine-tune their routing environments to their unique needs, yet maintain security as well as performance. Implementation of the VRF is a deliberate decision acting as a tool for overcoming the challenges of networking domain nowadays and utilizing the virtues of virtualization technologies.

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