Hi,
This can be done via central service MPLS VPNs, having each site in a VRF and only having site A and B communicating to site C with out being able to communicate with each other.
Example:
ip vrf A
rd 123:1
route-target both 123:121
route-target export 123:123
route-target import 123:124
ip vrf B
rd 123:2
route-target both 123:122
route-target export 123:123
route-target import 123:124
ip vrf c
rd 123:3
route-target both 123:125
route-target export 123:124
route-target import 123:123
NOTE The use of 123:121, 123:122 and 123:123 is to obey the constrain of IOS12.0T that at least one Import RTs should be equal to one of the export RTs.
HTH,
Mohammed Mahmoud
