RFC4364 defines three approaches to providing multiple AS backbones. Option A is the most simplistic approach which utilises a back to back VRF between to seperate ASs. eBGP is used between the ASs to connect the two backbones together. A seperate VRF is required for each customer and a full routing table is required on the ASBRs within each VRF. This option is not recommended as a scalable solution.