How to get information about the current cluster configurations with list of datacenters? Is any way to get information about the current cluster configurations with a list of datacenters?

I have tried to fetch this list from system.local using cqlsh with setting the consistency level equal to ALL, but it shows me only one datacenter. 

Basically I want to check that all datacenters which I have created are constituting the one cluster.
As far as i understand your question, you can run nodetool status which shows all the data center including all their belonging nodes.

$ nodetool status
Datacenter: DC1
===============
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  &lt;IP&gt;   1.7 TB     256     7.2%              &lt;Host ID&gt;  RAC1

Datacenter: DC2
===============
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address        Load       Tokens  Owns (effective)  Host ID                               Rack
UN  &lt;IP&gt;   1.7 TB     256     7.2%              &lt;Host ID&gt;  RAC1