A、IBGP session must be established between routers R1 R2 and R2 R3, and the synchronization must be turned off. B、IBGP speakers within autonomous 100 must be fully meshed, and the synchronization must be turned on. C、IBGP session must be established between routers R1 R2 and R2 R3, and the synchronization must be turned on. D、IBGP session mu st be established between routers R1 and R3, and the synchronization must be turned off. E、IBGP speakers within autonomous 100 must be fully meshed, and the synchronization must be turned off. F、IBGP session must be established between routers R1 and R3, and the synchronization must be turned on.