VRF Lite

I’ve been spending a while trying to get my noddle around VRF’s in prep for my new job.
I’ve been having real trouble getting decent documentation on it as for the most part VRF is synonymous with MPLS VPN technology.
This hasn’t helped me at all as I’m on the learning curve and don’t get MPLS properly yet either, so trying to absorb the concepts on MPLS too was all a little too much. But, to my delight, I’ve found a few snippets which nicely summarise everything I’ve needed to know quite quickly and here’s everything that helped me, broken down as follows, basics first.

VRF, firstly this acronym means one of two things which are kinda doing the same thing, see wikipedia :

1. Virtual Routing and Forwarding

Virtual Routing and Forwarding actually implemented as VRF Lite is likely to be used in a campus. Given my greater comfort with Switching technologies , the following statement made me feel nice and warm as I finally understood WHY you’d use VRF’s .. “VRFs employ essentially the same concept as VLANs and trunking, but at layer three” AHHHHH!!!
Not having had to deal with traffic segregation on a network segment with routers other than Firewalling at the edge, this really really helped my conceptual understanding. I totally get VLANs, and since it’s put like that, I understand why VRFs are now interesting!

2. VPN Routing and Forwarding

This is what I previously knew about VRFs, in as much as I knew the name and knew it was ‘out there’ and used by my ISP to get data to/from other sites for us and it worked fine and dandy. This link to Cisco is part of their MPLS VPN technology document and although I don’t get it properly yet, shows the instance where VRF is used and how interlinked it is with MPLS VPNs.

I was actually asked what VRF stood for in my interview for the job I start on Monday. I answered with VPN routing and forwarding and was told I was wrong and was fed back with the the other answer Virtual Routing and Forwarding. I’m subsequently glad I’ve now discovered I was actually right, AND they were right, but the answer wasn’t the one they were looking for as the technology they use is VRF Lite, rather than VRF which is described in the above linked Cisco technote and is actually likely to be routing private address spaces across the Internet for customers such as my old employer.

Thanks to Stretch on Packetlife.net for the Eureka moment!

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