EXAFUSION_ENABLED = 1 (def=0 )

ExaFusion is Direct-to-Wire protocol which allows DATABASE processes send messages directly over the Infiniband network bypassing  the OS kernel. This means database processes make no syscal to OS. Database process directly write data to IB HCA bypassing normal networking software stack. This is the one of reasons why IB improves the response time in Oracle Exadata Database Machine. Data is transferred directly from user space of one process on one node to user space to other process on other node (no context switch to kernel space).

But, ExaFusion is disabled by default !
To enable ExaFusion look to the documentation:

http://docs.oracle.com/database/121/REFRN/GUID-A0612249-0A65-476D-A2B8-FA94DF5EEC7F.htm#REFRN-GUID-A0612249-0A65-476D-A2B8-FA94DF5EEC7F

You should to set EXAFUSION_ENABLED=1 in the database parameter file.