In previous example a CE-PE routing protocol was BGP, but it’s not only option. We can also use IGP protocols like OSPF. We use this protocol for customers in VRF_A. On PE router OSPF is redistributed to iBGP and vice versa, otherwise vpnv4 routes won’t be propagated through MPLS domain. MPLS VPN area is usually referred as super backbone and PE routers are ASR routers.
Because of redistribution in normal OSPF operation those routes would be treated as external routes (LSA Type 5) when redistributed back to OSPF. PE router is treated as ASBR. When redistributing from MP-BGP back to OSPF those routes are marked as inter-area routes (LSA Type 3), even if the area numbers on both ends does not match. However if customer network has more than one area PE routers must be in area 0 or virtual-link between PE router and nearest ABR must be configured.