what is VRF?

[teymur azimov]

Dears,

i want to understand vrf? how can help me to understand that?

[Sandeep Choudhary]

Hi,

VRF meaning Virtual Routing and Forwarding , is a technology implemented in the IP network routers that allows

multiple instances of a routing table to exist on the same router in the same time. Since each VRF is independent, the same IP subnet can exist in 2 different VRFs. Basically you can overlap one

IP address in 2 VRFs but without conflicting with each other. Even this is possible, I would not suggest doing so, unless you have a very good reason to do it.

VRF acts like a logical router, but while a logical router may include any routing tables, a VRF instance uses only a single routing table.in addition, VRF requires 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 tables prevent traffic from being forwarded outside a specific VRF path and also keep out traffic

that should remain outside the VRF path.

Regards

[Alessio Andreoli]

Hi Teymur,

a VRF is a quite complex topic but let's say that per say a VRF can be considered like a routing table generally separated from the global routing table (the one we are used to work with). Essentially the requirements for what the VRF (Virtual Routing and Forwarding) technology was implemented was to separate the networks in order to operate with VPN. If you imagine two routing table on the same device which generally cannot talk each other, you realise the potential for different customer to have their own private network working with a sort of "private" routing table.  As you can imagine the concept of VRF has been heavily implemented and developed by the Service Providers for their customers and furtherly applied to MPLS. Keep in mind that even if MPLS and VRF are technologies that very well work together, they remain different and independent technologies.

When infact you will find the "VRF-lite" definition, this will refer to the solely use of VRFwith NO MPLS implementation.And generally it is not a so common choice in the modern SP networks anymore. I do believe that a good start point in uderstanding the VRF could be wikipedia!!!

http://en.wikipedia.org/wiki/Virtual_Routing_and_Forwarding

Just a note to underline how the concept of VRF strictly embraces the concept of routing table.. You can think about the normal routing table you work with as a global VRF. Maybe it is oversimplified but it is not a wrong association

To start implementing VRF i would suggest to study first VRF-lite and then developing your knowledge/configurations over the wider MPLS field.

Alessio