What is VRF?

mirzaakberali · ‎12-17-2007

Hi ,

Can any body expalin me what is Virtual Routing Forwarding( VRF) and what are its uses and where all we can use it.

Appreciate your help on this.

Jon Marshall · ‎12-18-2007

Hi Mirza

VRF's are primarily used within an MPLS network. Put simply each vrf is a virtual router running on a physical router. So as an example you could have 2 vrf's on a single router

VRFA

VRFB

If you do a "sh ip route" on the router then you will see routes that are in the global routing table. You will not see routes that belong to VRFA or VRFB.

If you type

"sh ip route vrf VRFA" then you will see routes belonging to VRFA but not VRFB nor the global routing table.

"sh ip route vrf VRFB" will show only routes belonging to VRFB.

So how does the router know which routing table to use ?

Well you assign router interfaces into VRF's.

So lets say the router has 4 interfaces

fa0/0

fa0/1

fa1/0

fa1/1

int fa1/0

ip vrf forwarding VRFA

int fa1/1

ip vrf forwarding VRFB

and you leave int fa0/0 and fa0/1 as they are.

Any packets received on fa1/0 will use the VRFA routing table to forward packets.

Any packets received on fa1/1 will use the VRFB routing table to forward packets.

Any packets on fa0/0 or fa0/1 will use the global routing tables.

One of the main uses of VRF's is to allow the creation of VPN's within an MPLS network. VRF's allow a service provider to have multiple customers connecting to the same router each with a totally separate VRF on that router which keeps all customer traffic logically separate.

Hope this has helped

Jon

mirzaakberali · ‎12-18-2007

Hi Jon,

Thanks for the above input!

Can you let me know on which Router we use VRF and configure VRF. for ex on PE/P router or CE/C Router.

Thanks,

Akber.

Nagendra Kumar Nainar · ‎12-18-2007

Hi,

VRF will be configured in PE router.

Regards,

Nagendra

royalblues · ‎12-18-2007

VRFs can be configured on both the PE's as well as the CE's

When the VRF's are configured on the CE's it is callled VRF-lite or MVRF. The only difference between the two is that VRF lite does not require MP-BGP

HTH

Narayan

mirzaakberali · ‎12-18-2007

Thank you all for above inputs!

Can you let me know what are the commands we use on PE and CE router to configure VRF.

Thanks,

Akber.

Jon Marshall · ‎12-18-2007

Hi Akber

Firstly, apologies for getting your name wrong.

Secondly, that is quite a big question. At it's most basic the config would look like

ip vrf VRFA

route-target export 100:20

route-target import 100:20

int fa0/0

ip vrf forwarding VRFA

However there is a lot more to it than this. You need some way to exchange routes between VRF's on different routers - MP-BGP is often used.

It would be a good idea to have a seach on Cisco web site for a good intro to MPLS which you need to then understand VPN's etc on MPLS.

Jon

royalblues · ‎12-18-2007

Have a look at the this for a basic MPLS VPN example. This does not tlak about VRF lite but is a good one to start

http://www.cisco.com/warp/public/105/mpls_vpn_basic.html

HTH

Narayan

Nagendra Kumar Nainar · ‎12-18-2007

Hi,

VRF will be configured in PE router.

Regards,

Nagendra

ranilgamage · ‎12-18-2007

Hi,

Is there any flavor of VRF for IPSec VPN?

Thanks,

ranilgamage · ‎12-18-2007

Do fVRF & iVRF serve the same purpose within the context of IPSec VPNs ?