When using OSPF as the CE-PE routing protocol and using unique OSPF process IDs and you want the routes at different vpn sites but the same VRF to have IA - Inter Area routes and not E2 - external (redistributed) routes, you can use the same OSPF Domain ID on the PEs for a single VRF. This changes the routes from E2 to IA.
Configs:
PE 1
R4#sh run | b router ospf
router ospf 5 vrf R5-SW1
domain-id 1.1.1.1
log-adjacency-changes
redistribute bgp 1 subnets
network 10.1.0.0 0.0.255.255 area 0
!
router ospf 6 vrf R6-SW2
domain-id 2.2.2.2
log-adjacency-changes
redistribute bgp 1 subnets
network 10.1.0.0 0.0.255.255 area 0
!
PE2
R3#sh run | b router os
router ospf 7 vrf R5-SW1
domain-id 1.1.1.1
log-adjacency-changes
redistribute bgp 1 subnets
network 10.1.0.0 0.0.255.255 area 0
!
router ospf 8 vrf R6-SW2
domain-id 2.2.2.2
log-adjacency-changes
redistribute bgp 1 subnets
network 10.1.0.0 0.0.255.255 area 0
CE - before using domain-id
R5#sr os
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O E2 10.1.7.7/32 [110/2] via 10.1.45.4, 00:00:39, FastEthernet1/0
O E2 10.1.37.0/24 [110/1] via 10.1.45.4, 00:00:39, FastEthernet1/0
R5#
CE - After using domain-id
R5#sr os
10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O IA 10.1.7.7/32 [110/3] via 10.1.45.4, 00:00:17, FastEthernet1/0
O IA 10.1.37.0/24 [110/2] via 10.1.45.4, 00:00:27, FastEthernet1/0
