C/C++ :: Tables Initiated With Pointers

In my code I have lots of structures. I try to make tables of structures and then get access to elements of the structures to use them all along my code: here is an example to clarify things

typedef struct {  
Fabric **closfabric;  
}Network;  

Net is part of another structure called Switch and Fabric itself is a composed structure. I have done the following

aSwitch->net.closfabric = (Fabric **)malloc(3* sizeof(Fabric *));  
aSwitch->net.closfabric[0] = (Fabric *)malloc(m * sizeof(Fabric ));
aSwitch->net.closfabric[1] = (Fabric *)malloc(k * sizeof(Fabric ));
aSwitch->net.closfabric[2] = (Fabric *)malloc(m * sizeof(Fabric ));  

The compilation returns a segmentation fault because aSwitch->net.closfabric is NULL (0) .

Surprisingly, in other codes the same analogy of using tables made of double pointers works perfectly with no problems and I have no problem of core dumped and NULL pointers.

Why am I getting this problem. It is the case whenever I try to use large dimension tables (tab *** struct for example)...