A1 and A2 routers do not know they belong to VRF A. The two interfaces of ISP (which are connected to A1 & A2) should be configured like this (we only show the configure of one interface): ISP router: interface g0/0 description ISP->To_CustomerA ip vrf forwarding A ip address 172.31.100.2 255.255.255.0 router ospf 100 vrf A network 172.31.200.2 0.0.0.255 area 0