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